Audio Test Bench Setup and Dummy Load Build - BG052

[@kenandbarbie-b6c]

Thanks for sharing, even though this is 7 years old. I’m impressed with the quality you got used for the $$$. I’m afraid the appreciation of this is being lost on Gen Z & this skill is gradually being lost over generations. The curse of having most electronics manufacturing overseas.

[@rayhogan785]

Glad to see your "Test Bench". Toooo many of these internet audio test/repair people or the internet tech wannabes don't use any of this stuff. I hope this will show them some things they need to properly test their equipment.

[@thirdroompro]

I wish you were my neighbor. Lifelong pro musician here getting into learning how to work on my own old tube gear. Taking baby steps. I am going to build a load box, much simpler than yours although your multi output idea is killer. Having it all hooked up at once is a great idea. I bought a 5x8 trailer full of electronics gear from an estate of an old time electronics guy. Everything from early 50s dumont oscilloscopes to 60s transistor radios , loads of tubes and old tube radios, heath kit tube multimeters etc. and some what looks like early 80s oscilloscopes etc( Tek DC503A Universal counter/timer,FG507 2Mhz Sweeping function generator,PS503A dual pwr supply) Tek 434 storage Ocilloscope, . I have a TV 2A/u and a TV 7 D/U tube tester as well . So in order to use any of it I am on a massive education cramming venture. I am getting started putting a bench together so I can actually get to the point of trouble shooting my fender champ and eventually being able to tech my 71 Marshall super lead, along with fixing old tube radios, I have a Fisher 500B I wish to restore as well. Again , I am in baby shoes right now. I can discharge caps and some other assorted low level chores . I need an amp repair guy to come over and give me lessons. Thanks for your info, its really enlightening. Some of the stuff I picked up that got me started on this journey kzbin.info/www/bejne/l2qqZ3Vujat9nrs kzbin.info/www/bejne/mnebn6utrsZ7kKM Check me out at kzbin.info/www/bejne/hJ_Jo5J3nKqLl5o reverbnation.com/blakethompsonband www.throughthedoors.com reverbnation.com/katerusso

[@georgethomas9436]

Thank you for the uploads. I am in the process of building my electronic workshop in my garage. Has good concrete floors and drywall throughout. I work on a lot of reel to reels and receivers. I do this as a hobby. You have many tips that are invaluable. Again thanks for sharing.

[@SinnerSince1962]

I love your video intro guitar solo. Very cool!

[@SinnerSince1962]

A frequency counter is nice when calibrating the speed of tape equipment using a test tape.

[@millstap]

Hello, I'm new to your channel. I'm in desperate need to learn more about basic electronics. Building a dummy load and using my Hitachi oscilloscope (that I have no clue how to use except for testing for outer foils of capacitors) is what brought me to your channel. I would really like to start basic electronics training but have no clue on where I can do that. Do you have any suggestions? I'm almost 70 and retired and have been working on my own vintage Fender guitar amps for about 15 years now and figured out how to repair and maintain them even though I really have no electronics background. In my spare retirement time, I figure it's a good time to start learning about oscilloscopes and how they can help me troubleshoot guitar amp issues. In particular now, I would like to see if an oscilloscope can help me determine where some noisy 60 year old carbon comp resistors might be in the circuit so I can pinpoint which ones to replace. I live by the "only change it if is not functioning as designed" rule on vintage amps and prefer to keep everything as original as possible.

[@tubeDude48]

It would have been nice if you had supplied a link to your box, and have moved the camera around so we could see everything!

[@michaelwarren4998]

Good info. Only thing wrong I noticed that when discussing the trimmer capacitor, it is not 460pF. It is an Arco 460 (part number), It is a 3 - 15pF 175V variable trimmer capacitor.

[@MrPageplayer]

This is a great idea and I have started acquiring parts for this project, but as mentioned below both the schematic and the image of the inside of the unit are seriously cropped, and being a rookie in this hobby, I'd like to see this better so that I don't blow anything up. Maybe a link to a full size schematic, images and parts list would be easier than doing another video? Heck, There seems to be some confusion about the resistor values etc.. I vote for a follow up video! :)

[@victorclausson4039]

I’m at the stage where I’m looking for 8 ohm resistor as dummy loads. Recently I got a lot of amplifiers for repair (like bigger ones for stages and such) and my questions is… Since they can output A LOT of watt, we’re talking 400-600w maybe. Do I need a resistor that can handle more watt than that or can I have a go easy and lower output of the amp when troubleshooting.

[@MD0MDI]

Any chance e you can post a good schematic for the switch, a lot of what you were talking about was slightly out of shot and would really like to have a go at one of these, just have a problem trying to get hold of the resistors here in the UK...

[@Blueglow]

Schematic is up on my website under sketches.

[@Bluelagoonstudios]

I use as power resistors, break resistors for the breaks on lift motors. 4R 1000w per piece, and a circuit to put 2 of them in series for 8R loads, or shorten 1 resistor for 4R loads with a switch, also a fuse is in there on the active site of the output, just in case., Also the small circuit to get 10/1 output to protect my gear. I picked the schematics from another KZbinr, but you have to get 4 of these gigantic power resistors, to get things going for the left and right channel, and it takes some place, so I mounted the with an aluminum rectangle block under the resistors for cooling and then to the wall. And pretty much thick cabling for the inputs. I think 4mm² silicone cables. And all good isolated, because voltages can be high from an output from an amp.

[@fluiddynamicist]

I like this... removes the cable clutter on the bench. I did however use only one dummy load and as switching is needed between the left and right channel for testing purposes, one speaker, one dummy, two DPDT... makes it simpler... well done. Great videos... keep doing what you are doing... we all learnt a lot... 73 de K1VMP

[@spencerklein6921]

fluiddynamicist ...are you also only inputting signal on the channel under test? Otherwise if you're inputting signal on both channels, they'd both need to loaded, even if you're only making measurements on one at a time. Although it requires an extra dummy load, I like blueglow's setup-- it prevents a potential brain fart of leaving one channel unloaded, plus you can check the amp for full function on both channels through the speakers once you're done. Also, I do a bit of stereo radio repair, so it's nice to have a load on both channels when I can't affect the amplifier input. I think I'll be piecing something together like this soon... I might just try adding a few more impedance options.

[@darkagecult]

Nice test bench/gear! Great information on electronics too but, what really made my day? The Stooges riffing intro! We must be related somewhere down the line. Brothers from another mother perhaps. Salute.

[@Blueglow]

Indeed

[@bigm3797]

As I was watching the video of the schematic and the the photo of the interior of the dummy box were seriously cropped. A clear photo of the interior would be very helpful to me as I am going to build a replica for my bench. Could you post a complete photo or email it to me? I love your channel. Thanks for the great videos.

[@markhenry1144]

Maaaate, If you can't get a good idea from what is shown then you're seriously behind the eight ball.....

[@epos79]

Great vid sir. How would I go about it if I am just building a tube amp, which essential equipment do I need besides the soldering station, Audio Signal Generator, Oszi, DMMs? Thank you and very helpful videos You produce

[@montre16]

Resistor values for the divider aren't quite right, but maybe close enough? 100k /(100k+1000k) = 100k/1100k = 1/11 = ~0.091

[@RandallDibble]

Elegant Solution ! I'm going to build it. OD you have any recommendations or suggestions beyond what's presented here ??

[@Blueglow]

Yeah, go to my website, on there is a tab called sketches & info. Full picture is on there, youtube cropped it some. www.blueglow.net

[@pauldavies6037]

The purists would say do those power resistors represent a none inductive load ? I dont think it would make any difference to most measurements.But they used to use a square signal to look at the output of an amp that was reviewed in HI FI mags with capacitors across the load to see the ringing and stability of it to see if they were suitable to drive electrostatic speakers

[@howardostfeld3802]

Does anyone know where to purchase the RCA mono male plug to female stereo converter at 7:43 in the video. I cannot find it. I have found RCA male to 6.35mm mono female and RCA male to 3.5mm mono female. If possible, please put in a link. Thanks!

[@Blueglow]

www.amazon.com/Monoprice-107241-Stereo-Adaptor-Plated/dp/B001T1ZZPY/ref=sr_1_25?dchild=1&keywords=rca+mono+3.5&qid=1590282505&sr=8-25

[@howardostfeld3802]

@@Blueglow Thank You!

[@howardostfeld3802]

@@Blueglow www.zoro.com/monoprice-rca-plug-to-35mm-s-jack-adapter-7241/i/G4477094/ 62 cents a piece from Zoro.com instead of $4.99 for 1 piece on Amazon. I am getting 10 pieces for $11.20 because shipping is $5.00.

[@sympathy4devils]

Thanks for the very interesting video. Could you tell me how the amp being tested is powered - with an isolation transformer or maybe through a residual current device? I understand oscilloscope probes are grounded to the mains earth, so if the oscilloscope ground was accidentally connected to a hot wire in the amp it would cause a short which could lead to damage to the test unit or much worse? Thanks, Mike

[@Blueglow]

+Mike All (Mike A) I run my power through an isolation xfmr then into a variac, then into the unit on the bench

[@sympathy4devils]

+Blueglow Electronics Thanks very much for your reply - much appreciated.

[@dennisqwertyuiop]

building a dual channel dummy load, do I need to keep the amp neg black outputs seperate or can they all have a common ground thanks

[@richardweisman6556]

I am trying to duplicate your elegant BCN jack box. From the video shot I am unsure about the 1/10 divider. Is the output at R2 divided to both + and to ground? Is the path at the jack: input goes capacitor, then R1, then R2 where it splits to + and to ground? Thank you for the teaching on the videos.

[@RupertHandford]

Nice setup. Want to get a distortion analyser but they are so expensive.

[@edvaioli7340]

Mark, Thank you for your fun and educational videos. I just looked at your drawing for the test bench and assume the switch marked SPST that feeds the BNC array should actually be labeled SPDT.

[@dennisqwertyuiop]

when injecting a 1 k audio tone for both left and right is there any thing special connection can I just join both R and L together to testing amp thank you

[@steveball4525]

Great video,thanks! I've been wanting to build one of these dummy loads, but since nearly all of my work is done on 50 watt or less output amps, could I use 100 watt 8 ohm resistors? If so, could I still use the same values for the voltage divider? Thank you, I always look forward to all your videos!

[@Blueglow]

+Steve Ball Yes, and yes. However, make sure the resistors you use are "non-inductive", which is not the case with a lot of power resistors as they are wire wound and have some characteristics of an inductor as a result.

[@Blueglow]

+Blueglow Electronics Also, anything between 300 and 500pf for the trimmer cap will work

[@steveball4525]

+Blueglow Electronics Thank you Mark, much appreciated!

[@noonan1587]

Love your videos and thanks for sharing. I just built a dummy load based on this video and one by 'ElPaso TubeAmps'. I could very well be wrong but I believe the trimmer cap you are using is a Series 46 (460) which has a range of 3-15pf.

[@charlieharris8414]

is there any reason that the audio to the patch connectors from the input only has the hot or plus sideds connected

[@Bully000001]

Enjoy your videos. Always clearly explained. For some reason the schematic on this video was cropped on all the edges. Any idea why? I use an apple macbook pro . Cheers

[@silasfatchett5693]

Same on my Windows desktop.

[@amahrielove4853]

Hi. I'm a newbie to electronics so can someone please explain to me the voltage divider at 24:10 of the video? What I don't get is that it's suppose to be a 10:1 divider but with the resistors given in the video if 100 volts in that would be 0.99 volts out? Shouldn't it be 99Kohm and 1Kohm then 100 volts in would be 1 volt out? I'm trying to build a dummy load as well and so I want to understand this concept better if someone could please explain it to me better. Also if I order precision resistors (for voltage dividers) at what wattage should the precision resistors be? Thanks in advance -Mary

[@rzw7447]

Amarie Me You're right, it's Kirchhoff law , voltage should be Uin*100k/(900k+100k) assuming 100k and 900k series, but you can combine 909k and 90.9k because 900k is not an usual resistor value. Also large values resistors are used to because you don't want large power resistors in this divider, tolerance could be worst than low power resistors has...

[@Drforbin941]

Hi...Thank you for producing this video for me! Quick question. What about using a toroid similar to how you sniff rf on ham radios?

[@tubeDude48]

Those 2 Pieces or HP on the far-right cost more then $3K alone.

[@markhenry1144]

Fantastic information. Thank you.

[@georgethomas9436]

thank you. yes I did find them right now for $39.00 each.

[@IlhanNegis]

at last your voice is not coming out of a tin box

[@georgethomas9436]

Wow Mouser sells the Dale 8 ohm resistors. A wopping $312.00 a piece.

[@Blueglow]

I get them off eBay typically used for around $20-25 each. Keep an eye out for them

[@navpers4764]

Thank you so much for this video :) Awesome !

[@tecnisdaimondm.g9321]

Excelente

[@kwapedog]

audio sounds good to me

[@georgethomas9436]

ha...never mind. I found it over at schetches.

[@stephenbobby6715]

sadly nothing is in focus

[@renanjhosf363]

sensaciocinal

[@lesstime1678]

eu nao disse nada but you know

[@Hr.0ldenberg]

Ach ja, das Video ist auch schon sechs Jahre alt, sehr viel Gerede um unnützen Kram. 20 Minuten blablabla

[@EmilioGarcia-fr5po]

Oh jeeezzz stop saying basically cmon

[@basildouglas855]

You want to know something, consider this. You certainly have a very good work shop set up with a great line up of test equipment which would clearly indicate that you are very competent at what you do. So why do you present this sloppy drawing of your test application that is cropped so badly it's laughable. In life, excellence always gets rewarded and mediocre never gets a mention. However, when sloppiness gets a mention, that is bad!

[@Blueglow]

Sorry my videos and work don't meet your expectations. I work a 60 hour day job, travel all the time, and somehow fit these videos in for you guys. Doing the best I can with the time I have, the alternative no videos...

[@basildouglas855]

Blueglow Electronics I believe you are missing the big picture here. Your video is about a dummy load, so the focus is upon that. What you accomplished was informing the viewers about "Your" equipment, " your choice", how "you use it", and then at the tail end, you present the dummy load which is where the focus was supposed to be. But you meticulously focused on yourself by creating an illusion of grandeur. When you get to the real focus, you feel the need to tell us about the software that you have mastered and prefer to use. So we see you junior school drawing, cropped to almost "unrecognisable", and then you draw horrible wiggly lines and circles. No one is interested in your prowess. Go and read your own words ......."my dummy load that I built"....... believe me, your video is all about you. Now, look at your reply to me. " I work a 60 hour day job". That is your problem, no one forced you to post that video. But again, it's all about you, it is just the way you think. Now consider this, you say that you do the best that you can with the time available. This is true and I believe you 100%. And you actually accomplish your best. But your best is about yourself and when you get to the subject of your video, it is poorly and badly presented. So now, in the final analysis, you take the "high road" when you say......" it's that or no videos" shame on you, now you are a cry baby! Get over it. If this video was titled, "A walk around my work shop", it would have scored top marks. What you did was to invite your viewers to a dinner, and then you served them "crumbs". I guarantee you, your next video will be a vast improvement. Regards

[@Blueglow]

Basil Douglas again, I apologize for not meeting your expectations.