Tube Amplifier Tone Stacks: Part 2

In this second of a two-part video series featuring the design and function of tube amplifier (passive) tone stacks, the following topics are covered: 1.) A brief review of Part 1 2.) How to determine the cutoff frequency of high and low pass filters 3.) How to change the cutoff frequency of a filter 4.) A side-by-side comparison of Fender and Marshall tone stacks 5.) The audio spectrum of Fender, Marshall, Vox, and James (passive Baxandall) tone stacks (utilizing the Duncan's Amp Tone Stack Calculator) 6.) How to change a Marshall amp's audio spectrum into that of a Fender amplifier (as a demonstration of the Calculator's capability).
All topics are explained in easily-understood language for those who are seeking a basic understanding of tube amplifier design and function. For those who are ready to take a step-up in technical sophistication, the formula for calculation of cutoff frequency is presented, and its application to guide the modification of tone circuits is explained and demonstrated.
In addition, Rusty makes a guest appearance and faces the toughest test of his video career. It's definitely a must-see for all his fans :)
Link to Duncan's Amp Tone Stack Calculator: www.duncanamps....
If you enjoy videos featuring classic vintage guitar amplifiers, jukeboxes, bizarre homemade electronic marvels, and clear, concise technical presentations, then please subscribe to my channel. You will gain immediate access to about 100 videos, and (if you activate the feature) you will be notified each time a new video is posted. Thanks for watching !!!

[@Mauitaoist]

Uncle Doug words cannot express how wonderful your teaching is things that we could never learn otherwise or would take us years of digging through boring books and you and Rusty you make it happen thank you

[@UncleDoug]

You're quite welcome, Cory. It's great to hear that the videos are helpful and appreciated :)

[@williambock1821]

His videos actually make it more possible to comprehend technical books on amps and circuits. They’re great. A library for anyone interested.

[@rolandmengedoth2191]

For calculation of the frequenzy it's better to use the exponential form with a base of 10.

[@JohanSegeborn]

Thanks for all your great videos. I love your channel! Cheers Johan

[@UncleDoug]

You're welcome, Johan :)

[@aaronowens1627]

@@UncleDoug Thank u so much for taking the time to teach us the technical aspects, the formulas, and where to look for further information on a subject I can't get enough of.

[@UncleDoug]

@@aaronowens1627 Go to the Valve Wizard's internet site, Aaron. He is the guru.

[@mem7856]

Прив

[@Fighterjetpinups]

Johan and Doug in the same circle. Nice!

[@johncostigan6160]

I learn more from watching your videos than I have in years of experimentation and study. Rusty is indeed a remarkable wizard of design.

[@UncleDoug]

That's great to hear, John. Thanks :)

[@kevinwilkins9926]

I just recently acquired an old amplifier out of God knows what from I believe the 50's. I have been watching your videos very carefully and have worked up the knowledge to start a project. I have electrical knowledge as I am a maintenance mechanic/electrician so that helps, but your videos are fantastic for truly understanding what happens with value changes. You are an excellent teacher and do excellent work. I can't thank you enough for taking the time to make these videos. They are priceless in my book.

[@UncleDoug]

Thanks so much for your very kind comments, Kevin. Best of luck with your first (of many) amp project.

[@W3KW]

I watched How do Tubes Work part 1 and 2, and now the Tone Stack, part 1 and 2. I can’t believe how much I learned about electronics. I wish I watched these years ago. Epiphany.

[@UncleDoug]

I'm really glad to hear that, Wesley. Please watch our many other videos for similar revelations :)

[@bullthrush]

A great finish for the tone stack series, very easy to understand. Top quality hand acting as well as steady camera work from Rusty.

[@UncleDoug]

Thanks, BT. I thought the hand acting reached it greatest heights during the back-lit computer scenes.....the stark delineation of black and white tones really added to the drama and suspense. I'm thinking Hand Emmy :))

[@roycemathews772]

Uncle Doug explains it all so good! A great teacher!

[@UncleDoug]

Thanks, Royce :)

[@stephanematis]

Superb teaching material, with a clear understanding that a small pause for entertainment (bone dry humor with Rusty), will actually help digesting it all. :) If you can't tell, I genuinely laugh out loud for the Rusty segments and am ready for more information right after. Bravo!

[@UncleDoug]

Thanks so much, Stephane. Glad you enjoyed the video :)

[@GregsGarage]

comedy, tragedy, mystery and documentary... It's all here! Thanks for taking us on the leap forward with this video. I'll take as much high blood pressure inducing tech talk as you can dole out.

[@SeanWeaver]

These videos are the greatest. I learn so much from them. They also make me laugh out loud at times. Such as “sit back, take a Valium.” Thank you Uncle Doug!!

[@UncleDoug]

That's great to hear, Sean. Thanks for watching :)

[@johngeddes7894]

Never thought I would understand these concepts, but you do a great job simplifying them which is what good teachers do. Thanks!

[@UncleDoug]

You're welcome, John :)

[@mdv426]

What a fabulous series! I've learned more in the last two days than in the last 20 years. Thank you Uncle Doug.

[@UncleDoug]

That's great news, Mick. You're welcome.

[@trickyponyamplification9178]

Woke up this morning and found out the second half was out. One word,"Stellar".

[@UncleDoug]

Thanks, Pisola......and our 100th video will be posted today, so you're in for a viewing extravaganza :)))

[@trickyponyamplification9178]

Very cool ! I look forward it and I am sure I will be viewing it more than once.

[@legrompf]

Marshall has more gain because less signal goes to the ground. This is an example of an easy way to explain things so that I can understand. Thank you so much for your videos. Knolwledge is one thing, but beeing able to share it is another one, and you really master this. Bravo

[@UncleDoug]

Thanks, L. I'm glad the video was clear and helpful.

[@basaltnow]

Rusty and Jack have really picked the perfect assistent Professor Doug. Very good and nice pleasent explenations. I wish I would have had an electronics Professor that good......and also such a wonderful assistent Professor.

[@UncleDoug]

Thanks so much, Sarah. We appreciate your kind comments.

[@willthiessen6361]

Another great video, Uncle Doug! I'm a electronics tech and all these videos are really helping me to better understand what's actually going on inside and how simple it is.

[@UncleDoug]

Thanks, Will. We're glad the videos are helpful :)

[@theonlywaytogta6665]

Dear Uncle Doug, I took a valium as you recommended. It worked! I was able to get thru the math w/o my head exploding. Thank you for making this so easy.

[@UncleDoug]

You're welcome, Leo. Glad you survived it :)

[@charlesgwyn2115]

I built an 18-watt British-style amp kit that had a very "woofy" low-bass response. I used your formula to build a high-pass filter to 'tame' the woof. Used a pot to fine-tune the resistance, measured that and replaced with a resistor... and installed the filter between the gain and master volume controls. Your videos are really helping me enjoy this hobby - thanks!

[@UncleDoug]

You're quite welcome, Charles. The best possible result of any instructional presentation occurs when someone actually puts it to practical use. Congratulations on your successful tone modification :)

[@jordanwilkinson7368]

These videos are phenomenal. Instead of making a Marshall sound like a Fender, I'd say you revealed a way to juice more gain out of a Fender!

[@UncleDoug]

Thanks, Jordan. The knowledge can be used in many ways.....all up to you :)

[@JasonVanzant]

Uncle, I got chills at around 13:00 when the tone controls on my amp all-of-a-sudden made sense! That "more or less attenuated" description really illustrated the tone stack.

[@UncleDoug]

That's great to hear, Jason. Best of luck with your continued acquisition of knowledge.

[@billphillipstube]

I could not have asked for a better tutorial on tone stack function. I have an early 2000s Fender Protube Concert that has a gain channel which is way too bright. The middle knob responds like a treble knob on the clean channel, and the treble knob is more like a presence control. I looked at the schematic and the resistor values and caps are quite different from the clean channel. Following your lead, I plugged the schematic values into the Duncan Amps calculator and it shows that the notch is shifted 600 hz to the right (if I'm reading this semi-log graph correctly). I’m scheming now on how I can swap those components out for more conventional values. Very practical help for me. Thanks.

[@UncleDoug]

You're welcome, Bill. It's great to hear that you're putting the info in the video to good, practical use. Best of luck with your experimentation.

[@SpockTown]

I really dig your videos! I'm an electrical engineer with a developing interest in modding and designing my own tube amps. Your videos are really helping me get going with some foundational understanding. Good on ya!

[@UncleDoug]

Thanks so much, ST. I am very flattered that an EE would find my videos helpful :) Rusty and I really appreciate your interest and kind words of support.

[@acikast]

I am very grateful for this knowledge you passed to all of us watching! This is something I've been looking for a long time. Thank you very, very much!

[@UncleDoug]

You're quite welcome, Alek. Rusty and I are glad to hear that the video is helpful. Thanks for watching and commenting :)

[@mixolydian2010]

Brilliant! Thanks Doug and Rusty. I am no stranger to these concepts and remember the filter equations and ohms law etc for over 30 years. You have opened these concepts up again for me. I have seen the program before when i was looking into making a Ibanez Tube-screamer clone and wanted to add in a bass mid and treble control, about 4 years ago..and i had forgotten almost everything. Your explanations are clear and accurate. I love the tone of Vox and Marshall and thought your adjustments where really neat and kind of exciting too. Love the funny interjections about lap dancers and blood pressure pills..Take care, Colin.

[@UncleDoug]

Thanks so much, Colin. It's great to hear that the video was understandable and helpful. I never know when I post a video whether it's going to be effective or not, but nice comments like yours always put Rusty and me back into "video production" mode. We wish you the best.........

[@oldmanofcotati]

You can be so funny. Between "gouging my eyes out" and the rise of my "blood pressure" the laughter has been like a tonic. Of course an excellent lesson. Thank you again and again.

[@UncleDoug]

You're welcome, Larry.....glad you enjoyed it.

[@TravisOnGuitar]

I never thought I would be able to know how a tone circuit works. Uncle Doug’s true genius isn’t his extensive knowledge of amps, it’s that he can get people like me, an electronics philistine, to understand it. Thanks Uncle Doug. Now if I just watch that cathode biasing video another 6 or 7 times I’m sure I can get that too! 😁

[@UncleDoug]

Thanks so much, Travis. It's great to hear that the videos are effective......and appreciated :)

[@murraybennett3594]

I don’t know , i have been trying to teach my dog photography for years and haven’t got much back. I kept watching even though i did want to spoon out my eyes once you showed me some math but you comments kept me learning. Your a great teacher and have secured all my fathers tubes so i can keep this technology alive. Plus solid state can’t replicate tube sound for guitar amps. Modern technology isn’t always better - Murray Bennett

[@UncleDoug]

Thanks so much, Murray. I completely agree with your final statements :)

[@renemikkers6404]

Thans for the very clear explanation. It was much better to understand than the way my teacher tried to do 50 years ago. I'll certainly use the tool

[@UncleDoug]

You're welcome, Rene :)

[@MartinBurtonGuitar]

Thanks so much for these videos. You remind me very much of my Physics teacher back in school, managing to educate while entertaining. It's a rare quality and, for me, that's the most effective way to learn and make things stick.

[@UncleDoug]

+Martin Burton You're welcome, Martin. Rusty and I are glad the videos are helpful and enjoyable.

[@ReFretted]

I have the feeling that I have found something to fill the winter hours this first retirement year. Three or four more times through and I should have it. The teaching is fantastic, the student is just slow. Thanks Uncle Doug - you are the demystifier.

[@UncleDoug]

Thanks so much, ReF. Best of luck with your self-education.

[@thehighhnotes]

I am way late to the party, but I boy do I get to party to this tune. This is absolutely brilliant teaching, thank you!!! Its making my head spin, not from knowledge, but from the implications. To think tone can be adjusted like that.. It blows my mind. It suddenly becomes so much more accessible with so many possibilities.

[@UncleDoug]

That's great to hear, Mark. You're quite welcome.

[@fatcatsound]

Uncle Doug, I appreciate all the knowledge you've gracefully bestowed on us. I am finally getting a grasp on how amps work and how to mod them. Most books tend to gloss over most of the basics. I wanted to comment on the James circuit and one thing I wish you had demonstrated was that circuit is theoretically flat at the "5" settings but that you can achieve something in between the Marshall and Fender circuit by turning the bass and treble knobs up and the midrange stays where it is. There are some very great sounding amps from Ampeg in the 60's (Fliptop, et al.) and Orange in the 70's that use this circuit. I know you're aware of this but I write this more for the benefit of your fans.

[@UncleDoug]

Thanks for your very nice comments and your knowledgeable input, FC. We really appreciate them both.

[@DennisMurphey]

I stuck this out and so glad i t did, I skipped the pole dancer and downloaded the Duncan tool and watched your explanation. WOW! As i am building the 5F1 amp now, i can design a tone stack and build it into this amp as a test, then change it in the simulator and retest different values. WOW that is going to be fun. Thanks for putting all this together so we understand it and can use it. Great Great Great! Dennis

[@UncleDoug]

Glad you liked it, Dennis. Thanks !!!

[@williambock1821]

Another great class! I’m finally able to read my way thru most amp schematics that aren’t TOO complex. The tone stacks and phase inverters is where I got lost. NO MORE!! Connecting a layout with the respective schematic for the first time is like reading a new language. These notes REALLY work. Thanks UD!! I still gotta learn reverb and tremolo circuits.

[@UncleDoug]

It sounds like you're making some great progress, William. Keep up the good work :)

[@williambock1821]

@@UncleDoug Definitely,thanx! I write down the notes you show as writing notes seem to cement info in my mind better than just having them on video or audio. I do go back to the tutorials to see how much has consolidated in my memory and what I may need to remediate. I just wish I could implement my new found knowledge more often! After a 5e3 kit (great fun but more of a paint by numbers situation than a conversion,mod,or build) I’m jumping into another organ conversion. Those are REALLY where learning occurs. And fun!

[@kenorefice5313]

Your videos are absolutely incredible. You layout the details in between that most books and videos glaze over.

[@UncleDoug]

Thanks, Ken. I try to teach in a manner that makes sense to me. If it doesn't, then it won't make sense to anyone.

[@danielsauriol]

7:50 rusty definitely has trouble focusing his attention ! too many options! lol! thank you Uncle Doug for your educational and entertainment videos. I simply never get bored watching them! thanks again..... -dan

[@UncleDoug]

Glad you enjoy our little productions, Dan :)

[@JesusIsLordofMybeing]

Absolutely amazing lesson on tone stacks!!! Love the lead on Duncan Tone Calculator! Amazing time saver.... Thanks Doug!!

[@UncleDoug]

You're welcome, JT :)

[@Modwiz125]

I discovered you about 36 hours ago and have watched a least a dozen videos before commenting. Thank you, Doug. I will have to watch many videos twice. Love the detail and math provided. Preparing for my first amp build and your series of topics is helping me with that. Mojotone vibrochamp clone is what my eye is on. I am 65, to give some perspective.

[@UncleDoug]

Thanks, Mod, and welcome aboard. Like you, I got off to a late start on guitar amps, but I really think we become better students as we get older. There are fewer distractions and the information seems to have more value.

[@ChasesWKshop]

I could learn how to do anything by your teachings. Thanks for the great videos and in-depth explanations.

[@UncleDoug]

Wow.....thanks, Chase. You're welcome :)

[@stefanmoller9318]

These videos are truly like a gift from heaven. They make me eager to boost up my self educational program in electronics again. Thank you!. The way you explain in plain english reveals what´s really going on beneath the hood and the engineering language. I´m a musician and when I studied music the music theory seamed very complex and scared me. But when I finally got it. I could hear and see for my inner self how it works and I almost got angry because it´s a whole lot easier than the language used to describe it. And that´s been my goal too when it comes to my studies in electronics, to be able to boil it down to something I can understand and actually use. I do accept that some things are just complex and there´s no way around to grasp it than plunge in to it and tweak my brain for weeks and months. But I also know that often when I come out of this cloud of learning I tend to say: aha it was not more than that...And then almost always come up with the conclusion that at least half of the learning is to learn, to decipher, the language of the topic witch often can´t be done until I actually learned that topic. When that is done I can see clearly (and I really do enjoy that moment) at the same time as I think : This could be explained a lot more easier....And that is what you do in a very successful manner..So again ..thank you! One day I might be able to repair my own equipment and maybe build some too for my studio. What a wonderful thing!

[@UncleDoug]

You're welcome, Stefan, and you bring up a good point. Why must so many topics be cloaked in confusing language? This has always been a concern of mine, too, and in any field of interest that I become involved, I try to boil all the jibberish down to easy assimilated facts. This was my SOP for teaching math and science to school students.....and also for our YT channel. Thanks for acknowledging that our efforts have not gone unappreciated.

[@stefanmoller9318]

Thank you, Doug for your most thoughtful reply on my comment. I´m always impressed by guys like you and my dad. My dad he started out in the early fifties with no particular skills in math or foreign languages, yet did he managed to figure out for instans all of the topics in your videos( I recognize all of the parts in the schematics) and when I grew up during the 70´s our home in the south of Sweden was ful of technical magazines from USA, Great Britain and Germany along with a never ending stream of ongoing amplifier and speaker projects. His university was trial and error, technical magazines and listening to the AM radio served as education in foreign languages. I think to my self , If he could do it with that minimum background in education then I could do it too. The differens is he was twelve when he started out and I´m nearly fifty now so I don´t have the same amount of time to conquer these skills (if I ever will). When he died a couple of years ago I took care of his workshop and all of the literature because I thought that this is a whole era of knowledge that is worth preserving and I did n´t want all of the equipment end up in the dumpster. I have always shared this interest of sound and music in both reproduction(hifi) and production (guitar amplifiers for instance) though I´ve mostly been on musician and listening side. I´m crazy about all of the old vintage stuff, (radio- gramophones , all of the early radios to the big radio consoles all the way to early hifi and the invention of stereo ). They are from an era when home entertainment equipment was ment to be part of a beautiful home. And they are built in such quality that make me cry when I see what´s on the market today, affordable for the common man. My goal is to be able to maintain and restore equipment like this and maybe even build some for my own use. But because I don´t have that much time and I don´t want to blow up dads workshop into smoke (I tried to fix a turntable a year ago that just ended up in a lot of hum-so I said to myself- well, maybe I should get a grip about this in reading some electronics) , I´m thinking that the key of a good starting point for me is to get the knowledge first, about how it all works to have better control, and in the meantime practice soldering on things that doesn´t do any harm involving the fire brigade and damaging priceless vintage gear. All of this is again one of the reasons why I find these videos priceless.. stefan

[@NoosaHeads]

I noticed that there were 6 Thumbs Down.. What kind of person would give this great presentation a thumbs down? I'd be very grateful if those who did, could explain in what way this video was deficient. Some people are incapable of decency or gratitude. How very Democratic.

[@UncleDoug]

Thanks so much for your support, Ian. I agree that posting a negative opinion should be accompanied by an explanation. Who knows? They may have a valid criticism that could result in overall improvement of the videos. But, without this, I must consider the naysayers to be a bunch of mentally deficient adolescents who get off desecrating the work of adults.

[@tom1263]

I have to say, I am hooked on these videos. I'm learning things I may never use but I love electronics, and this is fascinating. Wish I could find a legible schematic for my 1977 marshall 50 W JMP MKII. Everything so far, is really hard to read the values. Now on to part 2!

[@UncleDoug]

Thanks, Tom. I'm glad the videos are helpful :)

[@gerrabath]

Love your explanation style Doug. Watched quite a few of your videos and you make what can be a daunting subject to the student accessible and fun. I feel I have learned so much more than any of the stack of books I have on my shelves could teach me. Thank you very much indeed.

[@UncleDoug]

+gerrabath You're welcome, GB, and thanks for the very kind comments. Rusty and I wish you the best :)

[@keiththornton25]

Thank you, Uncle Doug, for your amazing tutorials. You're an amazing mentor!

[@UncleDoug]

You're welcome, Keith. Glad you enjoy the videos.

[@stevenstewart5980]

These two tone stack videos were fabulous! I was especially impressed with how you used the Duncan calculator to modify the Marshall response graph to match the Fender response with only three component value changes! Thanks for another great teaching video!

[@UncleDoug]

You're welcome, Steven......glad you enjoyed it :)

[@frogman6641]

@@UncleDoug Thanks for this very informative video Uncle Doug. Only thing missing is the effect of the imput impedance. When you change the Marshall impedance from 1.3k to the Fender's 38k the difference in gain reduces to around 2dB rather than 6dB. I changed C1 to 400pF, C2 to 200nF, R3 pot to 500k, C3 to 50nF, R4 to 10k and a small boost from the treble pot to match them. 2dB would still be a useful gain though. Thanks again!

[@UncleDoug]

@@frogman6641 Thanks for your analysis, JB.

[@briansilcox5720]

Beside your excellent presentation, I would just like to add that you deadpan with Jack, Rusty, and "Furry Kitty" is an invaluable aid in keeping this on flattened learning curve. Much appreciated!

[@UncleDoug]

Glad you enjoy the videos, Brian.

[@louismuradas966]

Great stuff, Uncle Doug!!! I learned a ton on tone stacks from your two videos on the matter. You're a gifted teacher.

[@UncleDoug]

Thanks so much, Louis :) We're glad to hear that the videos were helpful and informative ^. .^

[@louismuradas966]

Although, your assistant seems to be doggin' the work a bit.

[@UncleDoug]

Rusty is just playing a role, Louis, and only appears to be lazy and indifferent while the video camera is on. Once it's off, he's a real "dynamo"......I swear ;)

[@circleoftreesmusic]

Damn... this is illuminating as can be, wow! I feel like I have a grip on amps that I NEVER understood before. THANK YOU, THANK YOU, THANK YOU!!!!!!

[@UncleDoug]

You're quite welcome, CoT. Glad you enjoyed it :)

[@UncleDoug]

Andris, your comment did not come with a "Reply" capability, so I'll reply here. I am no expert on Orange or Ampeg amps, but from what I have read, the amps that did come with Baxandall stacks had "active" tone circuits and thus were not covered in this video discussion. The amps that had passive controls actually used the James stack design, as included in the video. In both cases, the B or J stacks have a flat response without the mid-range "scoop" and thus would (at neutral settings) produce a much more mid-range-intensive tone, which many Orange and Ampeg enthusiasts like. Also, it's interesting to note that Orange now offers a "Shape" tone control which allows for mid-range scooping, to allow the amps to sound more like Fender, Marshall, Vox, etc. It's a very complex and subjective topic. Thanks for your input :)

[@alvagoldbook2]

I'm not too familiar with older Orange amps, but some of Orange's newer "lunchbox" type amps, like the Tiny Terror series have an interesting tone set up. The Tiny Terror actually has a post-phase inverter tone control. Weird, I know. It's really quite similar to Vox's "tone cut" control. Ampegs, as I understand them, used what I guess is an active middle control prior to a James type circuit.

[@UncleDoug]

Very interesting, Alva. I'll check into the Tiny Terror schematic, as I am not familiar with post-PI tone controls. Thanks for posting !!

[@mosneedly3751]

Thank you Uncle Doug, Your contribution to KZbin is huge. I hope you are doing well, my friend.

[@UncleDoug]

You're welcome, Dave. Thanks for your nice comments :)

[@djordjeblaga7815]

"Scary formulas"... This is why I came here! ;) Unfortunately there are very few explanations of thes formulas on the Internet... and if there are some, they are generally written by a math professor. :) Thanks for the very informative video!

[@UncleDoug]

You're welcome, DT :)

[@Riff1269]

Uncle Doug, you are my hero. I am learning so much from you. Thank you!!!

[@UncleDoug]

That's great to hear, Jeff. You're quite welcome.....thanks for watching !!!

[@bondsongmusic]

I'm a huge fan of your videos. Thanks a lot for doing them.

[@UncleDoug]

You're welcome, BSM :)

[@Ideal1980]

Thanks Uncle Doug, I really enjoyed these tonestack videos.

[@UncleDoug]

You're welcome, Ideal :)

[@ertreri]

All your videos are absolutely perfect. Thanks, as always. It would be really nice if you could make a video where you look at an amplifier circuit for am amplifier that you own, and then you could color different areas of the schematic for different topics: tone cirucitry area, current rectivation and smothing, etc... And then in each of the different colored areas you could refer to the different videos you have done until now that support understanding the area. And then finally, look at the amplifier in real life with the schematic in front to show it all together. The easier the amplifier, probably the better. 😊

[@UncleDoug]

Wow......very complex. I'll keep your suggestion in mind, E. Thanks.

[@codebeat4192]

Very useful stuff here, very clear explanation and your funny too with your dog, thumbs up.

[@gearathon]

Another great video from the most generous uncle on youtube. Thank you very much. I am very impressed by Rusty as well. Talk about modesty and work ethic . He really doesn't want to take any credit at all or all the great camera work. And still he keeps getting better. True genius. ;-)

[@UncleDoug]

You're welcome, Gear, and thanks for the very kind words. You are quite perceptive about Rusty. His screen persona is one of feigned indifference, but in reality, he is the creative force behind all the videos. I am but his humble assistant.....his "Igor", if you will :)

[@gearathon]

: )

[@sinnerG7]

Another great video Uncle Doug! Very enlightening on why Fenders and Marshalls create their own unique tones.I have a friend with a Carvin tube amp and we can't understand why its so overdiven.I think I'm beginning to understand why now..Looking forward to your next videos.Thanks again for sharing your knowledge

[@UncleDoug]

You're welcome, SG. We're glad the video was informative.

[@robweeks3238]

Fabulous video. Many thanks for taking the time and effort to teach in such an effective manner.

[@UncleDoug]

You're quite welcome, Rob. It's great to hear that the video was helpful :)

[@fredbach6039]

This lesson on tone stacks was very helpful. Thx. I liked the Duncanamps graphic utility!

[@bertalazaar5095]

I am not a musician, I could never understand why someone would adjust bias to increase distortion in an amplifier, or put a dip in the frequency response to correct non linear output of the input transducer. Thank you for enlightening me; very interesting.

[@barxis]

Awesome! Very clear explanations. Finally I learned tube theory and filters

[@UncleDoug]

Thanks, ER. I'm glad it was helpful.

[@johnharjung2128]

Thank you so much for this video, it answers so many questions I have long had about tone circuits and how they work and more importantly how to tweak them. I am going to be building a Fender style amp soon and this is a HUGE help ! Your other videos are also very informative, helpful and presented in a easy to understand manner. Thanks again Uncle Doug !

[@UncleDoug]

You're quite welcome, John. It's great to hear that the videos are helpful and appreciated. I think you'll find the Duncan Tone Calculator to be a very useful tool. Thanks for watching :)

[@ogrebadogre3194]

These videos are so helpful. Thank you so much. Keep them coming.

[@UncleDoug]

+Ogre Badogre You're welcome, OB. We will :)

[@bluesharpfiend]

You are an incredible teacher! Thank you so much for sharing your great knowledge in such a clear way. Does anyone ever replace the resistors in the high/low pass filters with a potentiometer, so that the cutoff point can be adjusted at will?

[@UncleDoug]

Wow....thanks for the very nice appraisal, BSF. Rusty and I really appreciate it. If you look at the schematics of most tone stacks, the resistors in the filters actually are the potentiometers that you use to adjust the treble, midrange, and bass cutoff points.

[@tubical71]

Are we now in 2nd level lectures by now? Are we?....cool...!! *Great* stuff, as always, thanx so much, Doug!!

[@UncleDoug]

Thanks, TC. Yes, I stepped it up a little. Hopefully I didn't discourage anyone or lose any subscribers. This topic is just so complex that it requires a more technical approach. Maybe the next video should be on soldering iron safety, to compensate :)))

[@nfijef]

I'm in awe. Not just in the fantastic explanations you do, but that I almost get it. The light is getting brighter Uncle Doug! I want to build a dummy guitar with pickups straight out to breadboard to try some tone circuits before the actual amp, but this has been priceless. I.m also curious about why you can't do active tones win tube amps, or is it just another tap on a transformer, etc etc. Thank you so much for the inspiration. And I love Math.

[@UncleDoug]

Thanks, NF. If you're wondering about active tone controls, they are more frequently seen in HiFi amps. Rather than simply shunting some unwanted frequencies to ground, they can actually boost the 'wanted' frequencies. Try some Google searches for details.

[@HitchHiker4Freedom]

Thank you for the awesome videos and series. Learned a lot in plain english. Comes in handy for developing audio circuits in the CB radios I have been working on

[@t1d100]

Excellent. Thank you. This is a true story... Back in the day, when I was still young and pretty, I worked with a sound company out of Tuscaloosa, Alabama, home of the University of Alabama. The Georgia Satellites were needing money to cut their first album, containing the wedding ring song. So, they took a pick up gig at a U of A fraternity. We met with them, before the setup, and they asked if we had ever heard of them. We had not. For mixing purposes, they wanted us to know that ["we are] louder than four hells." They were all using big, Marshall stacks (including the bass man.) True to their word, they all walked on stage and directly turned ever knob, on every amp, fully to the right. No kidding. We saw them do it and knew there was going to be challenges. Now, we were a professional company and had brought plenty of sound gear. But, we struggled to get the vocals up, over their amps. We were inside the house, in a fairly large room. IIRC, maybe 25'x40'. We didn't run a db meter, but I know they were way over the limit. We were concerned that they were actually going to do permanent hearing damage to the students - and us! I was surprised that the fire department didn't show up and shut us down. It was stupid loud - the loudest we ever worked with, but they did fully attain that great, classic Marshall sound.

[@UncleDoug]

Thanks for sharing this great story with us, t1. Based on their one big hit, which I loved, I always hoped for more from this talented bunch. Having attended a few ear-damaging concerts in my day, I now wish that many early bands focused more on their musical skills than their volume knobs.....especially when the singing and lyrics were as good as they were with this group.

[@alexpietrogiovanna6829]

I almost never comment on any videos, perhaps this is my first comment ever, but I have to let you know that you are a fine gentleman for putting out these very informative videos, I am extremely grateful for you being here, I subscribed to your channel and I am really enjoying it; by the way, those brake segments with Rusty really made me laugh out loud, what a riot!! Thank you so very much, you really made my day brighter Uncle Doug.

[@UncleDoug]

You're quite welcome, Alex. Rusty and I are flattered that your first comment would 1.) Be so nice....we really appreciate it ! 2.) Be for one of our videos. It's great to hear that the videos are both informative and helpful. That's our goal, and we truly appreciate your kind approval of our efforts :)

[@sski]

Excellent video! That Duncan's Amp Tone Stack Calculator is going to come in very handy for the conversion of the Hammond AO-50-C1 tube amp I mentioned in another video comment. There is no tone stack to speak of as the organ it was pulled from had a bank of tone modules that were located below and behind the keyboards and rocker selector switches. So I'm going to have to build a tone stack into the chassis. But now I know how and have a tool to figure it out! Thanks Uncle Doug for all you do! EDIT: Hey Rusty!!!

[@UncleDoug]

You're welcome, SS. I'm glad the video will be helpful. I'm sorry to say that Rusty passed away over a year ago. He is greatly missed.

[@sski]

Oh no. I'm so sorry. I lost my best friend, my German Shepherd of 17 years last year. I miss him every day.

[@UncleDoug]

We're crazy to get so attached to our pets......but it's the type of crazy that I embrace.

[@greg4272]

Dear Uncle Doug, Would you please do a series on tube distortion characteristics, and their circuit designs? I mean the different sounding overdrive / distortion tones (the "fabric" of distortion, I do not mean the EQ filtering) that various amp brands offer, and how they were achieved in the circuit and why. For example, high voltage vs. low voltage tube designs, different topographies, various ways of feedback, etc. and their effect on sound. This would be a huge help modding an amp and achieving the tone we desire. Thank you so much for your explanations, I benefit a lot of these lectures, which I need to be able to repair a bunch of preamps, and other guitar rack stuff, sitting uselessly besides me on the shelve!

[@UncleDoug]

See my video on determination of proper bias levels in fixed-bias amps, Greg.

[@marstyn1962]

I finely know how to use The Duncan Calculator! Wonderful video!

[@UncleDoug]

Thanks, Marstyn. Rusty and I are glad to hear that the video was helpful :)

[@JoseBatista-yx9sh]

Your channel is awesome! Extremely valuable stuff here! Thank you very much!

[@UncleDoug]

You're very welcome, Joao. Glad you enjoyed the video.

[@bookwormeffects5919]

Great video! The Baxandall is such an interesting design.

[@UncleDoug]

Thanks, BE. Yes, it is :)

[@siccohoekstra4882]

Good stuff to compare. I used this tool to design my own tone stacks. However, if you drive the Fender and the Marshall stacks with the same Zsrc impedance and use the same output impedance the output levels are much more close. The low Zsrc impedance of the Marshall must be generated by cathode follower and the high Fender Zsrc impedance is taken directly from the anode resistor. I hope this helps a little. Keep the good work!

[@UncleDoug]

It does, Sicco. Thanks !!

[@profxpedals2009]

Excellent video as usual Uncle Doug! Thank You

[@UncleDoug]

You're welcome, Prof. X :)

[@djfrank59]

Another great video Doug! I never get bored with the math...in fact, I feel it is important to know the math first, then the easy way out afterward. This is what makes the difference between electronics technicians and parts changers, not to mention tube yankers :). I've been teaching vacuum tube electronics part time to a class at a local vocational school on a volunteer basis to give the less fortunate kids the opportunity to keep off the streets and out of trouble while giving them the gift of a future in audio electronics and know vacuum tube theory which is hardly covered in electronics schools today (if at all) Well, 5 of my top students are dying to meet Uncle Doug since I've shown some of your videos in the classroom! And, Rusty is gaining popularity with the ladies in the class :) Keep 'em coming Doug, you're always on to something good :)

[@UncleDoug]

Thanks so much, Frank. It's great that you are teaching at a vocational school and helping youngsters to develop marketable skills. I'd like to offer my encouragement to all of your students, and wish them the best. Also, be sure to tell the girls that, unlike his stepfather (me), Rusty is even more charming in person :)

[@tubical71]

Fank, let´s record it and upload your lessons here...so we can all see you teaching, would be cool...:)

[@djfrank59]

I would have to get permission from some of the parents and the school itself, but it would be cool! I'm very strict with the kids, and they know I'm doing it on a voluntary basis...There's a few class clowns, but all I do is warn them that I will use their index finger as a probe for my VTVM and head them right for pin-3 LOL :)

[@UncleDoug]

I must admit that I am interested to see what type of electronics presentation could hold the attention of a group of inner city youth......so please post a lesson if you can, Frank.

[@djfrank59]

I will look into it early next week...I will check with the administrator of the school. :)

[@miyamotomusashi5184]

I love these videos, you are an excellent teacher. Thank you so much for sharing your knowledge!

[@UncleDoug]

You're welcome, MM. Thanks for the nice comments.

[@Starcrunch72]

Thank you , Thank you, Thank you Uncle Doug---Fantastic...Now I have a direction with the understanding to finish the tone modifications to my '66 Bassman.

[@UncleDoug]

You're welcome, SC.......glad the videos were helpful.

[@marthesemercieca5197]

HI again Doug I dropped the value of the .05 coupling cap to .022 on the first pre amp on the 5D5 fender and that made a great difference bought the treble up. Just like to thank you for your help once again and a big pat to Rusty Cheers Tony

[@UncleDoug]

That makes sense, MM. Coupling caps have a significant effect on tone. We're glad to have been of assistance.

[@timsmith5327]

Thanks Uncle Doug! absolutely priceless lesson, much appreciated.

[@UncleDoug]

You're welcome, Tim :)

[@cello_melow]

You are a legend! Thanks for sharing your knowledge and wisdom with the world.

[@UncleDoug]

You are too kind, Marcelo. Thanks so much :)

[@rredd7777]

Thanks for doing these videos. They're really helpful. I'm looking into building a hi-fi phono preamp, and these tone stack lessons are giving me better insight into how the equalization circuits needed for a phono preamp work. And why the worries about the math? You presented them in a very straight-forward way. Thanks again!!

[@UncleDoug]

You're welcome, Brad. It's good to hear that the videos were helpful. I taught math for many years and just know that some people, probably due to bad experiences (and teachers) in school, have a mental block when it comes to math. I never want to discourage, bore, or alienate my viewers.....so I get a little apprehensive when presenting complex topics and math formulas. Thanks for the reassurance.

[@larryayres4592]

Great video and it helps to explain why I couldn't stand the tone of a Marshall head I bought. I finally managed to tame it with a lower gain NOS Mullard preamp tube. It was so different sounding from my 2 Fenders and my Vox. Now I know why. My Marshall has exactly the same tone stack caps that you showed. So if I wanted to I could change them to the values you came up with at the end. I now like the Marshall though. It has a clarity to it that my 50's designed Fenders lack and it is LOUD when I need it to be.

[@UncleDoug]

Thanks, Larry. Glad the video was helpful :)

[@OscarDad]

Such FANTASTIC Tutorials !!!!! Thank You

[@UncleDoug]

You're welcome, Oscar :)

[@bhosterman]

Now we're cookin"! This is exactly what I've been looking for! Thank you again!

[@UncleDoug]

You're welcome, BH. I'm glad the video was helpful :)

[@burgermeister911]

Neat to see how easily the tone stacks adjust. I think the difference in the amplitude of the Marshall vs Fender tone stack is in large part due to the impedance of the signal source. The Marshall is 1.3K (cathode follower), the Fender is 40-ishK (common cathode gain stage)

[@UncleDoug]

Thanks for your input, BM.

[@zopilotesky3014]

Another outstanding series. Thanks again!

[@UncleDoug]

You're welcome, ZS.

[@BioStuff415]

Thanks again for sharing your knowledge with master pedagogy.

[@UncleDoug]

You're welcome, Bio. It's my pleasure :)

[@dreamlessfull]

Very interesting, Doug, once again excellent material!

[@UncleDoug]

Thanks, D.

[@lvstofly]

Where's commander qualude when you need him?(RIP)🙏🦅This is my second time thought this video, I almost have it. Thanks Uncle Doug, love your channel.

[@UncleDoug]

I'm glad the video is informative, PT. Thanks so much :)

[@obewankobe9903]

Thanks Doug. The scratchy sounds sre as you described them. I've just about replaced all the resistors and caps in the whole amp and am still stumped. I've changed the resistors on the preamp filter caps as well as the caps themselves. The filter caps are about ten years old so maybe I should change them again.

[@mrbaiser4133]

Great video, I learned a lot! What I still don't understand completely, are the tone stacks of the brown and blonde versions of the Bandmaster amp (6g7 and 6g7-a)... One small correction: It is possible to get a reasonable mid scoop with a James tonestack, if you choose the right values and replace R3 (in the duncan program) with a pot. Carvin does that in their Vintage series.

[@UncleDoug]

Thanks, Immo. I too don't fully grasp some of the nuances of vintage (and modern) amps. Thanks for the update on the James tonestack.

[@jamescarter4175]

Another great lecture series. Thanks again!

[@UncleDoug]

You're welcome, James.

[@GregsGarage]

Oh, and just to put a bug in your ear... I'd love to see you go through a quick analysis of the Dumble ODS design. I've heard it referred to as the amplifier within an amplifier. It has more switches and controls than most players care to deal with, but they sound incredible... Searching craigslist for organs now.

[@UncleDoug]

Here is the best description of the Dumble circuit you will ever see: pdfelectronics.com/dumble-ods-124/ He goes into great detail regarding the tone controls.

[@GregsGarage]

Thanks. That was a great breakdown of the amplifier.

[@johnzook7533]

Doug, I attended school for electronics back in the seventies and this type of circuit was given barely five or ten minutes. I spent a great deal of time looking over schematics for Fender, Marshall and Sunn amps as I owned two Sunn amps in the past. My attempt to modify the tone stack on a Sunn Sentura II to match a Fender tone stack did not fare too well as my understanding of tone stacks was inadequate. If I knew then what I now understand, thanks to you, I'm sure it would have come out fine. By the way I did manage to add a mid boost and presence control to that amp. It's been quite a few years since mu foray into tube amps as I spent most of it dealing with RF circuits (car radios) and other related electronics for automotive functions but my interest has been renewed in these circuits. Additionally, have you ever looked into the type of circuits Carvin uses, especially their tone stacks. I own a Carvin Belair and it does have very nice tone. Too bad Rusty didn't seem to have much interest in video recording ...about the same as my cat Frodo. Cheers and thanks for all the great video lessons from an old tech.

[@UncleDoug]

You're welcome, John. It's great to hear from you. Rusty and I are glad you enjoy the videos and really appreciate your kind words. While I hold Carvin products in high esteem, I have not had the opportunity to own or work upon one of their amplifiers. I looked up the Belair and was quite impressed by its appearance and specifications. Re Rusty, don't be fooled by his screen persona. He's into method acting and simply becomes immersed in his role as scornful, reticent assistant :)

[@Kilgore40]

Once again, crystal clear and very informative. Thanks!

[@UncleDoug]

You're welcome, K40.....we're glad the video was helpful :)

[@FG-pr2ds]

Hey Uncle Doug! Thanks for sharing your knowledge and wisdom. Wondering where to go for the Russian Pole Dancer and Valium 😜. Great job as always!

[@UncleDoug]

It's our pleasure, FG. We'll be glad to share :) Thanks !!

[@SarcastSempervirens]

geez, these videos change everything for me, like finally being in school for amps :D I've read hundreds of sites and pdfs and articles on these subjects, but non are suitable enough for a beginner and they don't exactly bring you up to a decent level like these calculations of frequency cutoffs etc., it's all mostly for educated enginers. thank you once again for sharing your knowledge! are you a teacher? cause you seem to have the ability to present this mass of information in a very linear and organised way, with little summaries at the end, it's very hard to follow complex subjects when people DO know their stuff, but they explain it with "so, yeah.. um, so.. like, yeah, so.." and keep hopping back and forth in the subject. I actually feel confident I could really build something after this. I always felt like I understood the schematics, I could follow the instructions, did have some knowledge on the matter but always with a lot of questions about the key things that affect the outcome of such a project greatly, like the voltages, frequencies and that "why is this res. 100 and that one 82 to the plate" :D and as I live in a small country that has no summer seminars on building guitars and amps and all the parts have to be ordered from the US, it's hard to find a decent local source of information. even if you find someone, they tend to be not so willing to share, so this channel is pretty much invaluable to me

[@UncleDoug]

Thanks so much for these great comments, Sarcast. I was indeed a classroom teacher (math and science) for many years and do my best to present information in a way that I, as a student, would have most appreciated and benefitted from. As a teacher, knowing a subject is only part of the battle (the lesser part)....to succeed, you have to be able to successfully communicate with your audience. I too suffered with many mediocre teachers, some of whom were quite knowledgeable but completely inept at effective communication. You have to wonder how they became so knowledgeable.....probably from teachers who, unlike them, had developed effective communication skills. Sadly, knowledge reached a dead end when it entered their minds. To me, knowledge is intended to be shared, so that others can take what they learn and amplify it with their own personal study, application, and originality. I too am confident you can build something, and would strongly encourage you to apply the basic concepts from these videos to a project of some sort. Through experience, your knowledge and skills will rapidly develop. Best of luck.