Musical Paradise MP301 MKIII: Initial Circuit Revisions and Results

[@cobar5342]

Stephe, this is why we follow you. Honesty, intelligence, vast knowledge and a scientific validation. Great video

[@jackstanley3529]

What fun! Stephe's doing what she does best and I'm enjoying every minute of it.

[@318ishonk]

Impressive what improvements you made in such short time. Thumbs up! Also great and clear to read schematics that you're sharing. Double thumbs up! 👍👍

[@stephendixon8575]

Well Stephe, I’m astonished at how quickly you not only came up with those improvements, taking the performance in the right direction, but that you did that and was also able to put together a brilliant video explaining what you did, and why that worked in such a clear and helpful way. You’re a legend. I’m very impressed and can only thank you for putting yourself out to do this so well and so quickly, especially as not so long back it looked like you would have preferred to just toss it out the window and move onto some of your other more pressing commitments! 🤣 Glad it didn’t involve totally gutting this thing and after all, and it essentially came down to a few bad decisions that had wiped out the bass response and totally distorted what little was left in the bass region. Still makes me question whether all these Musical Paradise units should be marketed as being ‘capable’ of running such a crazy wide range of tubes in them. I don’t know if this amp has the switches in it that the others they make (which it turns out are to change the heater voltages) to broaden the range of tubes each circuits ‘can’ work with) - but as you’ve ably demonstrated, just because tube pin layout and heater voltages MAY make it ‘capable’ of taking a different tube, that is NOT the same as claiming such a broad range of tubes will actually perform WELL as alternatives; that of course depends on individual tube specifications which specifications the circuit was DESIGNED to work around to produce great sound. It’s a nice idea to give wide flexibility (and also let folks learn in the process) but it would be better to have a smaller suggested list of tubes that could perform well, instead of trying to be a jack of all trades and master of none. Learned a lot today. Looking forward to watching and understanding any further refinements. Thanks again 🙌

[@flyingmattyboy]

Wow! Great work Stephe. Skunkie strikes again!

[@hugobloemers4425]

This is a great clean up. I am really enjoying this series.

[@warwickthorn]

I am so happy to see this. I was about to buy the MP-301 and then panicked when I saw your first video, but, what you can do to tube circuitry with provable results is so impressive, I plan to still get the MP-301 and make your mods. Fantastic work.

[@monrosj]

Looking forward to your continued work on this amp.

[@Kirk-wj9gp]

Very informative video. Really looks like it improved the amp quite a bit . Really brings back a lot of memories from when my uncle had a radio repair shop..

[@panheadchopper]

Hi Steph, Great Job as Usual.!! Hey a triode strapped 6SJ7 is essentially a 6J5 tube. With an amplification factor of around 19 and an RP around 7600 ohms. Thanks, Mark

[@SkunkieDesignsElectronics]

Thanks for sharing!!

[@borissecluna5782]

Hi Stephe. Triode curves for 6SJ7, you got 'em. Refer to the flash drive I sent you. PDF Files => Tube Data => 6SJ7 => 6SJ7 GE. Triode curves are included for this pentode. Hope this helps.

[@SkunkieDesignsElectronics]

THANK YOU! GE data sheet was the missing piece of the puzzle. Doesn't look like this is actually the electrical equivalent of a 6EJ7, less gain triode strapped. Might still be enough with the bias set right

[@borissecluna5782]

@@SkunkieDesignsElectronics You're most welcome. Thank you for making your wealth of knowledge available to us hobbyists.

[@kdsellman]

+1 for an assessment of the tube dac. I've had it for a fews years, sounds great to me. Always interested in improvements.

[@SkunkieDesignsElectronics]

Don't hold your breath, that's not likely to happen.

[@kdsellman]

Understood.

[@paulgood2218]

That's a nice upgrade so far

[@eugenepohjola258]

Howdy. Comprehensive evaluation. And Yeah. The input tube should benefit from some neg. feedback. If the sensitivity suffices one might consider omitting the input tube cathode capacitor. That would provide neg. feedback of the input tube. Or one might consider splitting the cathode resistor into two parts and only capacitor bypass one resistor. Someone might consider using a trimmer and connect the slider/viper to the bypass cap. to obtain tunable gain vs. neg. feedback. But Yes. Skunkie does not like trimmers as they are troublemakers. Point taken earlier. High Regards.

[@rickg8015]

Hi Stephe.. Good to know that you found out that there’s an inadequate Ck value for the output.. I would personally go a tad lower with ~270uF to 330uF in that position just for more subjective ‘weight’ in the presentation.. I hope the lispy sibilants would get resolved with further mods down the road..

[@SkunkieDesignsElectronics]

going 270-330 isn't going to hurt, I'm not sure with these OT it will matter.

[@rickg8015]

@@SkunkieDesignsElectronics I think when you upgrade the OPT, it will.. The 300R || 330uF will give it subjective heft..

[@SkunkieDesignsElectronics]

You have a point. I wasn't planning on upgrading the OT but that may now be on the table.

[@audiononsense1611]

Stephe- 1st I'll say from my many years in this industry that you'll always have the folks who think they know something, and don't and then there are those who just like "shit sound" (let them eat cake)... it doesn't matter!! Keep doing what you do as no one likes to hear, pardon the pun, that their baby's ugly... Price doesn't always equate to performance and measurements will only take you so far. One who is trained to listen would never buy or setup 1/10 of the craziness I've seen and I have a database of hundreds. I will say that my reference system has never had a bad comment and has blow away most (recording engineers, symphony players and conductors, as well as audio manufacturers (all for under 15K, not including treatments)!! No sub/s I don't have a big enough room.

[@sonhouse9636]

HI, I'm admiring, that's great!!

[@Zoneho]

Thanks Skunkie! very interesting and informative. Wait to see more. Do you think that this amp could be more interesting than the Muzishare X7, which you have said a lot of good things about and without it being subject to modification?

[@SkunkieDesignsElectronics]

"interesting?" hmm... Out of the box for HiFi at anything other than very low SPL or SUPER efficient speakers, no comparison

[@RobertKohut]

Nice work.

[@SkunkieDesignsElectronics]

Still have a lot more to do.

[@swift1696]

Hi , good work . I will apply yor changes.

[@SkunkieDesignsElectronics]

PLEASE WAIT!!!!!!! This is just a start of the mod process!!!!!

[@swift1696]

@@SkunkieDesignsElectronics o.k , when finished!

[@swift1696]

Hi Stephe , when it's going on with it?

[@adamfrandsen]

Looks like a confused design mistake with the switching of the voltages on the tube, great find - also worrying about global negative feedback, is that really valid - I mean, did you ever hear anything negative from a well designed negative feedback design? I mean these THX amps sound great to me. Anyhow, very cool as always. About the voltages, could it also be due to wanting the amp to be able to use as many different tubes as possible(which of course isn't ideal...)?

[@SkunkieDesignsElectronics]

Possibly could be, but those whacky voltages happen with the tubes it is supplied with.

[@HiLift2]

Thank You, Thank You, Thank You (😘) for your work Stephe, you've given me hope that I can get decent sound out of my investment! I don't mind if I have to outlay a conservative amount of money for Edcor xformers (four of them for my two units) to gain much better fidelity, I'll do what it takes. Have your experiments lowered the 60hz noise floor (hum that you heard) or is that a product of the PS? One last thing... Can you please supply a BOM for the replacement parts you're using? I live in the middle of nowhere and parts acquisition can be extremely tedious to say the least. With the BOM I can order top tier items from one source and be done with chasing everything down which leads to revisions done in a more timely manner.

[@SkunkieDesignsElectronics]

Patience, this was just an initial "poke" at a design change, mainly to try to single out what was causing the missing low frequency and weird distortion I was hearing.

[@HiLift2]

@@SkunkieDesignsElectronics Of course Stephe. I see what you're doing and why and and have the utmost confidence that you are on the right path. I realize that this is your first jab at this unit and that component values (and maybe OPT xformers) will maybe have to be massaged to get the best performance out of this hot mess. It's exciting to observe a qualified person discovering shortfalls and a path around them unlike the other people who shotgun PCB's and hope for the best outcome.

[@middleearthltd]

A Lampizator Tube DAC clone would be worthwhile It is apex level

[@fearwolfbrewery5014]

Would be interesting if you tested the pre amp and dac from this company.

[@SkunkieDesignsElectronics]

I honestly have no interest.

[@fearwolfbrewery5014]

@@SkunkieDesignsElectronics ok, such a shame. Would have been really interesting but I respect your opinion.

[@SkunkieDesignsElectronics]

If someone send me one of their pre-amps, I have the ability to test that. I don't really have a way to objectively test a DAC.

[@billparkins3064]

Any chance of you trying out the mp tube dac? Ive heard nothing but good things about it.

[@thelastofthedinosaurs]

I have it and it is awesome

[@SkunkieDesignsElectronics]

Not likely I will be. I do very little digital streaming, don't have the knowledge about how to even accurately test one other that simply listening and just be careful of these "I have heard nothing but good things" as so many reviewers give EVERYTHING a positive review.

[@Luckiestmanalive-bb1mi]

Those square waves are not flash - what components are used to filter the AC power supply?

[@frankgeeraerts6243]

Nice ............; This kind of operation point on the penthode driver input is called a ( Starving mode operation ) ..sometimes seen in vcertain very old amplifiers. Question : Was this design made for driving speakers or headphones because with one secondary winding you have to choose ......and the other oints were you put the finger on problems are designed by ...hmmm.... OPT is probably questionable quality and the UL here does not make any sense for headphone drive of a n EL34 .............;also pure class A of this tyube type is standard 250 plate ...........triode mode should be used ( dedicated for HPhones).....plus the tandem pentode input/driver followed by Triode for coherent harmonic musical spectrum ..... Voltage on the screen of the penthode is better choosen by lower value of about 112 volt ... operation conditions of the plate voltage must also be adapted etc........... there's a lot of work to do and mayber you can get it sing ..... The cap on the screen ( 6SJ7/5693) must be of quality ... It would be interesting also to see the design of the power supply ...... Good luck and you will find ways to improve this thing within the limits of the amp and opt . kind regards. ( Personaly I would mayb consider to use this amp/chassis to build a quality stand alone powersupply for a preamp or a phono stage ...........if the transformer is good enough ) PS....With a single pentode ( per channel )like a c3m, a 717A/6AK5/408A WE ....one can build a VERY good headphone amplifier..........Yamamoto build some very nice headphone amplifiers and preamplifiers with sope of these pentodes...........and they sound realy very good. In this case very interesting to see what you can get out of this design .....

[@debilthomes501]

Kazoo Sound! I’m dying. 😂

[@Gullsz]

Ever had a look at an Elekit?

[@SkunkieDesignsElectronics]

Someone asked me about building one for them, but that never materialized, so no I haven't.

[@iainbowman8979]

cool

[@VyacheslavFuzik]

So KT88 tubes are not recomended for this amp by any means (pwr trans will fry otherwise) , as I understood today from the new video. Will it happen in case of such schematic changes only? Is there a reasonable modification route to keep these tubes or better not in order to have better sound with mods you are deciding to follow?

[@SkunkieDesignsElectronics]

I said KT120 would likely overheat the transformer.

[@VyacheslavFuzik]

It looks like I've misheard: I'm Russian. Now having no anxiety on keeping on the kt88's. 😊

[@frankgeeraerts6243]

The high screen voltage, somewhat higher than the anode voltage ( in the past era was also a standard used operation design ) it is and was used often correctly a ....LITTLE bit.... higher than the plate voltage ( unlike as seen in this amp , this is starving point operation and gives high gain but also HIGH distortion )...that was practice and normal used design with pentodes to expand the curves and the dynamics as well as amplification............. To document this starvation mode oeration .....( MULLARD UK -Tube manufacture -EL34 and other original famous nos tube ) ....They had such a low power and LOW-FI design.......for radio and simple amplification without any HIFI asiration........to be able to do direct coupling without a capacitor between the driver anode ( EF86/6267) and the grid of the output tube.. The result were not up to quality music reproduction but the amp was CHEAP to build !!

[@SkunkieDesignsElectronics]

I think this design was actually based off a guitar amp, same as the Nobsound 6P1 was.

[@frankgeeraerts6243]

@@SkunkieDesignsElectronics i THINK YOU ARE RIGHT ;......made to distort ... Have a nice day XSteph.

[@mddawson1]

I wonder if the earlier versions had the same incorrect components and design or were these issues introduced over time?

[@SkunkieDesignsElectronics]

I have no way of knowing, and honestly can't spend the time testing every possible variation, if they even are variations.

[@mddawson1]

@@SkunkieDesignsElectronics I was hoping some of the audience might have the older models and look for the internal differences.

[@georgeswanson9483]

20% tap is perfect for a 6V6, UL you'll get a really good four watts.

[@SkunkieDesignsElectronics]

But this is an EL34 amp ....

[@georgeswanson9483]

@@SkunkieDesignsElectronics The voltages look fine for a 6V6, if it has a four and eight ohm output taps it just becomes an eight and sixteen ohm. I didn't see if it had more than one or more output connections. If not, I paid to set up a smaller Edcor with an 8K input impedance and 23% UL tap years ago, they don't have it on their website but let me know if you want to know the model number of the transformer, you should be able to order it without any upcharge as it's set up in their system - it has an eight ohm output impedance.

[@SkunkieDesignsElectronics]

The current draw will kill 6V6

[@georgeswanson9483]

@@SkunkieDesignsElectronics Couldn't you change the operating point by changing the value of the cathode resistor? In any case, you're well along turning this pig's ear into a silk purse, I'm sure it'll sound great when you're done.

[@SkunkieDesignsElectronics]

Sure if you want to turn this into a 6V6 4W amp.

[@davidkuo8779]

510k grid leak resistor is too high. It might cause el34 current drift. Any thoughts?

[@SkunkieDesignsElectronics]

The data sheet says 500K, why would it be too high? BTW I've been using that in my amps with no issues.

[@davidkuo8779]

@@SkunkieDesignsElectronics I am just thinking of that 500K is the design max limit. I am working on a KT88 parallel amp, fixed bias (adjustable individually). One particular PSVane tube burned through 4 cathode resistors (100 ohm for Ik measurement). Finally, I changed it from 220K resistor to 100K this morning after it burned another cathode resistor last night. Cathode current drift is a monster for the new tubes. Maybe it is not a concern for EL34. My thought is why to push to the design limit. Will it make the amp sound better? My ear is not good enough to tell the difference these days. Let me know your thoughts. Thanks.

[@hksunchaser1]

😃

[@alaingingras7224]

What I dont get is how did MP get it so wrong .I hope their Preamp is not the same...

[@SkunkieDesignsElectronics]

Doing some research, this looks like it is either a design copied from a VERY old radio that was never intended for hifi use and/or from a guitar amp designed to inject "funky" distortion. I suppose to some people's ears, this funky distortion = "Tube sound"?

[@VyacheslavFuzik]

@@SkunkieDesignsElectronics This is the point ! 👌Very logical inference your wise brains are making. 😉

[@ПолётШмеля-ь7ъ]

The original circuit is a classic circuit, from the time of the advent of pentodes. Works great in the normal power range. Why do you need to add feedback? Add odd harmonics and make your amp sound harsher? Well, the power will decrease a little, but the sound will definitely get worse. We know, we went).

[@SkunkieDesignsElectronics]

No it's not "A classic circuit". Someone posted a totally unrelated circuit schematic on a forum and people (fan boys) took it as gospel. No "classic circuit" runs the screen at 2X the plate voltage. And this type of feedback doesn't add odd order harmonics. Nice fan boying though :)

[@ПолётШмеля-ь7ъ]

@@SkunkieDesignsElectronics Exactly! I didn’t notice this) the second grid works instead of the anode. Maybe this is a feature of the author). Cool). Doesn't matter. Isn't it easier to put a resistor in parallel with the capacitor in the circuit of the second grid of the first triode? Bring the circuit to a classic pentode. In this mode, the 6sj7 has good musical sound without audible distortion.

[@rickg8015]

@@ПолётШмеля-ь7ъ The decoupling values are not right either, 0.22uF is too low for the grid for example in the stock circuit.. Usually 4.7uf PIO or even higher..

[@nevillegoddard4966]

@​@@rickg8015 PIO? What is that?

[@rickg8015]

@@nevillegoddard4966 Paper-In-Oil capacitor (usally aluminim foil), which was the traditionally used type of cap by the early DIY SET builders/experimenters from Japan and Europe almost 50 years ago for a Pentode fromt end’s g2 decoupling.. But you can also use Polypropylene film, subjectively faster sounding though.. This part is critically audible so I would put something like a Claritycap in there if using Film..

[@Mr_J_J]

How is your doggie doing?

[@SkunkieDesignsElectronics]

Much better thank you!!

[@xiretsa9166]

Although I have absolutely nothing to do with tube amplifiers until the first tube-based DSP is finally available, I still like to take a look at your videos now and again out of interest. Your posts on the MP 301 are currently being discussed in the German community of tube enthusiasts. I wanted to form my own opinion and watched your videos. I noticed - regardless of the technical content - that there are hardly any critical comments on your views. Statistically speaking, this is an outlier and particularly noticeable in the context of the debate here that I know of, in which the pros and cons of the MP 301 are almost equally divided. Have there been no critical comments on your videos, or are they all so disrespectful that it would be better to delete them?

[@SkunkieDesignsElectronics]

I don't delete comments about my content.