Willsenton R300: Resolving the Frequency Response Issue

[@rosedan100]

Your persistance has paid off .. you are one smart cookie! Willsenton needs to send you a BIG check for all you done for that company!

[@arvindgoudar1586]

I am surprised as to who did the quality check before it went out into the market...😳👎

[@solarman30]

This is a classic case of the intertwining capacitance of the OPT, interacting with the circuit. There was some Hammond OPTs that were famous for this in some circuits. Unfortunately, it's not just the frequency response aberrations, the effect on the phase response is much more damaging. Great sleuthing! Dan

[@SkunkieDesignsElectronics]

It almost looks like it's trying to short out the outputs or something! That can't be good for the output tubes.

[@EskWIRED]

These videos provide huge amounts of value. Thanks!

[@brycejeannotte7699]

That was a really great result. You don't give up! I am glad you found the issue. Willsenton should be very grateful to you.

[@neilfisher7999]

Hi Skunkie, your favorite nemesis here. I am glad you figured this out, and I think if it helps Willsenton make this amp better going forward you deserve kudos! I was trying to figure out why this amp sounds so good to me and many others despite this issue. It is really pretty simple I believe. The highest note that can be played on a violin is the A7 which is 3,520 HZ. The lowest note that can be played on the ultra rare Octobass is the A0 or 27.5 HZ. The only thing that appears musically between 10 - 20 KHZ is the upper level harmonics of cymbals. Therefore, we humans don't really hear much of anything in the frequency range where the Willsenton is deficient here. That doesn't mean they shouldn't fix the problem. It just means that most people may not hear a difference. Many frequencies that we can't hear can have an affect on what we do hear. Cymbals tend to be grating on my listening so in my case it might be better that I can't hear their upper level harmonics. Keep doing what you are doing. Although I might disagree with some of your statements, I think you definitely add value by figuring this stuff out from a technical aspect.

[@SkunkieDesignsElectronics]

The problem IMHO is this issue could create issues in other portions of the spectrum. It also appears these harmonics are shorting the output, which is rough on the output tubes. I've never seen anything like this and points to poor quality transformers.

[@neilfisher7999]

I would be interested to hear if Willsenton makes the changes you suggest. Keep us up to date on what they tell you.

[@Mikexception]

@@SkunkieDesignsElectronics Although Your observatins are true we have little konowledge about it's impact on overall sound impressions received by listener. We live in very not ideal and not aligned to our technical standards world specialy when it comes to listening . In actual situation, when we are not able to make all devices perfect ideal, choosen separate device may not fulfil stright lines expectations . Transformer is working together with amplifer on one side and with cables, speakers. room reflections and ears+brain on other. All this is affected by geometry and resonances. Specially tweeters acousticaly, electricaly, due to high frequencies of surfaces which need to be stiff and very efficient are a bunch of mess- - in my opinion the newer constructions the worse, because are designed up to ideal imagination and production tech capabilities . . . Specially in range above say 10- 12 kHz to 20 kHz I would say that I have little confidence in trust to graphic representation It is for me as to wish for comfortable shoe produced up to drawings made with strighlt line and circle. I always guide myself with ears - measurements in my practice never gave me good hint about outcome in listening. I prize Your observations as part of sciettific research but not for ready conclusion for replacement of transformer.

[@SkunkieDesignsElectronics]

I already reported my personal 300B amp using fairly low cost Edcor iron sounds better. And I'm not ready to report replacement transformers will improve this amp either, but I also just heard from someone at Willsenton that their newest version of this R300 has changes to the output transformers...

[@neilfisher7999]

Hopefully any improvements that they make translate to better sound and reliability. So far I've had this amp for a year and I've had no issues other than a bad tube from the beginning. I upgraded all the tubes from stock to higher end PSVane tubes. It runs dead quiet and sounds fantastic paired with Zu DW speakers. So I have no complaints so far. With the right pair of high efficiency speakers to match the correct tonality it sings.

[@turborotorhead]

Wow. Just wow. I deeply appreciate every minute you've spent of these R300s. Another tip just sent your way via your website. I can't wait to get all my issues resolved.

[@SkunkieDesignsElectronics]

Awesome, thank you!

[@michelholm5209]

Hi Skunkie, you have become the great tube amp guru for all the Chinese tube amp factories, they should hire you as the main tube amp designer😂 grat job👏

[@cobar5342]

Well done Stephe. This is a real achievement

[@vespass225]

Beatiful work, done there, just huge value to us DIY:ers. To me this means I can now consider buying a used R300 and fix it thanks to your work and shared info. Great, thanks again! The question is how to get that Edcor transformer being a swede...! As solarman30 commented below, if this problem is due to OPT intertwining capacitance, picking a 3.5k Hammond instead may possibly not be as safe bet as the very Edcor you used. I by the way bought another even more affordable chinese 300B amp, the LaoChen 300B. Sounds nice, but a little weak, and not "open" enough for my taste. Tried a solid state rectifier instead of the stock 5U4G which made a dramatic change, and thus I got the urge to measure 300B plate voltage at idle. I measured ridiculously low 370V with the 5U4G, 430V with solid state rect., and a in between 411V with New production Mullard 5AR4. Will do: 1) Modify power supply to have 430V with 5U4G tube rectifier if possible, otherwise --> 5AR4 2) Follow your recommendation to rebuild driver 6SN7:s to cascode config. 3) Possibly buy Shuguang Treasure 300B:s, which you thought sounded fabulous, i think Thanks again for tremendous site !!

[@SkunkieDesignsElectronics]

Thermionic labs would be another option to try. I will probably be contacting them about a replacement option to try.

[@vespass225]

@@SkunkieDesignsElectronics OK, thanks for tip. I will probably wait til you have tried out the Thermionic alternative in that case.

[@Mikexception]

Did you proof in advance that such incerase of voltage won't damage 300B tubes ?

[@vespass225]

@@Mikexception Yes, the 300B:s are said to have upper plate voltage limit at 450V. What may be more critical is components downstream from power supply, like caps etc, that may be specified a little to close, or on the wrong side of 430V, I think.

[@SkunkieDesignsElectronics]

Update on all this soon!

[@SuperMcgenius]

Great work again 👍

[@SkunkieDesignsElectronics]

Thank you! Cheers!

[@RaviNewfarm]

Very good that you found the issue. A small bet what the issue is with the trannies: I suspect they have used transformers designed for push - pull use. In those the current is going out to two tubes and the static magnetic fields are cancelling each other out. A transformer for single ended use will have to have a much different layout and more powerful core to handle the strong magnetic field set up by the one-way dc current through it. If you use a push pull transformer in a single ended circuit it may easily go into magnetic saturation and what we see in these traces might be just that. Keep up the good work!

[@kenandbarbie-b6c]

Brilliant work!

[@SkunkieDesignsElectronics]

Thank you! Cheers!

[@paulgood2218]

I bet the manufacturer might help you with cans , they seem to appreciate your work . And it would be great public image boost for them to support there community!!

[@dmark2639]

Good detective work, Stephe!! It's now obvious that the cheap Chinese transformers are crap. Glad you caught it and now all these owners have a chance to swap out the transformers to get better sound.

[@shawnsutton6067]

Stephe, Since you used the Thermionic Opt's with your KT120 Monoblocks and liked the results, perhaps some 5K opt's could be applied to the R300 amps? Since you have a rapport with Thermionic, maybe they can offer a good packaging scenario for your followers. I also emailed you a few links for Opt. covers too. The other alternative you mentioned, talking with the ISO / US Tango representative has me intriqued too.

[@SkunkieDesignsElectronics]

Yeah, I sent an email to the ISO folks. I might give him a call tomorrow as well and see if this is something they are interested in.

[@dinodefuria6294]

I think you hit it on the head when you said that the sound can be very dependent on the room and speakers. I recently bought a R300 to use with an original set of Klipsch RP600m's. The first thing I did was change to 5AR4's and re-bias as you recommended. I have been listening to them for about two weeks and you know what? I didn't like the sound. It felt rolled off and it seemed to struggle to reach a good volume without reaching audible distortion. I was giving up on the R300 because I have run the RP600's with other amps and liked them very much. As a last ditch effort before I boxed it back up, I hooked it my living room speakers which are early 60's klipschorns which I've had for about 25 years. The room they are in is about 18 x 22 or so. You know what? The combo of the R300 and the Klipschorns literally blew me away. It is getting the best sound I have ever heard from these speakers. Bass? Yes! Air and sweet treble? Yes! Midrange? Dean Martin is singing in my room! Crazy right? So the R300 is now staying and going to be the permanent amp for the living room!

[@SkunkieDesignsElectronics]

And then try to use those same speakers in a smaller room and it would be a disaster!

[@paulgood2218]

Great video seems like a easy fix now. !!

[@SkunkieDesignsElectronics]

Just have to decide what transformers to use. I want to see how 5K ones perform in this circuit and listen to both.

[@bc5299]

great work. I wonder what willsenton does with the information.

[@SkunkieDesignsElectronics]

Good question!

[@Mikexception]

Just wondering - what is the issue - may be it is the serial resonance of windings - it may be due to mechanical vibrations of coil (some of us remember HV coils in TV sets producing audible 16750 even it was sealed in plastic) but also any combination of electrical values.- I would be interested about load you conneceted to output - was it resistance or speaker? Speaker have own resonances. Up to my experience I often observed such evident dip in range 15 - 17 kHz but I always observed it in acoustic outcome in both channels of class B tube. . I suspected then dome speaker.

[@SkunkieDesignsElectronics]

The same 100W 8 ohm non-inductive load I use for everything.

[@geomorphdog]

I'm impressed and horrified, since OPTs are usually the most expensive parts. Sure makes me wonder what's under that can!

[@SkunkieDesignsElectronics]

We will find out.

[@nevillegoddard4966]

@@geomorphdog. There's possibly a matchbox sized O.P.T. in there! Did they think no one would find out the crap transforners they used would not be discovered? How cheap rubbish must the factory OPT's be if a $75 GUITAR AMP OPT absolutely murders them? $7.50? The MASSIVE garbage can covers over the OPT's are a JOKE! Hey Stephe are these amps light as a feather or what lol? What's Mr. Willsenton's minion on about, keeping the 300B driving circuit a secret? Did this same guy say anything about not mentioning the crap transformer performance too?

[@geomorphdog]

@@SkunkieDesignsElectronics Oo! Then I'm looking forward to that! Wouldn't it be something if those huge cans were all for show and the actual OPTs were smaller than the Edcors?

[@tlpplacement9355]

Looks like Willsenton needs to upgrade the output ransformers. The OEM cost of upgrading 2 output transfomer may cost an extra US$100, and that could add US$100 x 3 = US$300 to the retail price. Of course, if the upgraded output transformers are much bigger, then physical size may pose a bigger problem (bigger transformer covers and chassis). But that's not bad, because you save all the labour cost of modifying the output transformers. Besides, better output transformers could also reduce the distortion and noise. Willsenton could just call the upgraded version a 'SE' or 'Stephy' model! I am so grateful Stephy is doing all this work, because the last time I touched any electronics, I was in high school = nearly 45 years ago.

[@SkunkieDesignsElectronics]

Pretty sure the cans are much larger than the iron inside them.

[@alaingingras7224]

Same with the Hammond SE1628 5K ohms OPT .Cuts of @8-10 k hz...

[@SkunkieDesignsElectronics]

These little Edcors and even the 25W ones work fine.

[@flyingmattyboy]

Those are the massive 5kg Hammonds. I have a set of SEA's in an amp that I hardly ever listen to now. Says it all. As I recall the older SE variant had known response issues. George at Tubelab covered this.

[@CollectingRetro]

Woah! Good sleuthing! Maybe very poor winding technique? Might be blasphemous to put ISO/Tango on that amp...lol. I think you need to do a nice custom build with ISO transformers and see how they compare to your other builds. Skipping coupling caps and going transformer coupled would be pretty sweet. I love how my transformer coupled amp sounds.

[@SkunkieDesignsElectronics]

There are some 30W iso transformers that would fit, $900 for a pair.

[@billpeirce7]

The manufacturer should be sending you consulting fees. Great job.

[@SkunkieDesignsElectronics]

We are talking about it :)

[@alaingingras7224]

I would not be surprised that under all that potting ,you have oxygen laden copper that is GREEN !Can't see it but ...Chinese copper ?!

[@el_arte]

So, basically, they do no QA before they put these in the shipping box. Good to know.

[@SkunkieDesignsElectronics]

They all are like this AFAIK. I have two of them here and both have this weird frequency response issue.

[@el_arte]

As Spock would say: “Fascinating!”

[@frankgeeraerts6243]

Asthonishing performance for the cheap EDCORE ........almost just as good as the old Tango 707....

[@SkunkieDesignsElectronics]

I use these same transformers on my 6SQ7/EL34 amp and they rock.

[@frankgeeraerts6243]

They seem to be free of problems and without nasty resonances as well as gentle sloops ......nice find and quality for the money . @@SkunkieDesignsElectronics