Reisong A10: Technical review.

[StepheK]

To follow up with the work I did on the big sister amp, the Boyuurange/Reison A50, a viewer had a new in the box A12 dropped shipped for me to review and possibly modify it etc.

I'm going to post this spoiler, it's a hot mess.

Massive distortion was visible on an analog scope and running a THD vs power sweep showed me that what I was seeing on the analog scope was reality. It goes into hard stop, square wave producing clipping at 1/2 the rated watts and crosses the 1% THD mark at 0.015W. It is making 6-7%+ distortion at 1W and it goes past 10% before 2W. The cheap little Nobsound 6P1 out of the box performs better than this. With my DIY >$20 mods it destroys the A12 at almost 1/2 the price.

I go into more detail in the review video and I'm hopeful in future videos I can find a resolution to whatever is causing these problems. It's a shame, as I had high hopes for this little amp, and it has what you would think it takes be a decent performer, 12AX7 driver into a SEUL EL34. But it's clearly a swing and a miss out of the box.

TL;DR at this point I would not recommend buying one of these with the expectation of goodness out of the box or just basic tube rolling. I'm sure this will be controversial, but the numbers don't lie.

 

[tonyg88]

Sounds like that amp really is a hot mess haha nice video thanks for the testing!

 

[Lavane]

Well, there's your title for the rebuild thread. "The Hot Mess"

 

[Old Guy8]

Looking forward to your mods videos.
I have both A10 and A50.
The Voshkod rocket input tubes were an improvement over the stock. Or other 12ax7 with adapers.
With fewer parts than A50. Maybe mods to this one, can be a learning experience, for a neophyte.

I'm interested if the A10/A12 is safe to run on 120 volts. Was very helpful, when you found your A50 was. And I could forgo my APC Line R 1200.

Thanks for your efforts to improve these units.

 

[StepheK]

Here are my ideas to try based on easiest to most complicated: The driver stage doesn't seem to be the main problem, (it could use some help but...) so I plan to start with the output section.

The circuit/voltages seem to be made for a much lower watt output tube and they likely tossed an EL34 in to boost sales. It's only being run at slightly over 50%, so I want to just stuff a pair of 6V6G-S JJ tubes in (which will be running at 94%) and see what that does for it. I get that it won't change the power output, but I'm curious to see if running an SE amp "lazy" like this is part of the problem. My experiments have shown EL34 tubes like being run hard in an SE amp, and they are cheap so no big deal IMHO if their life is shortened. If this tube swap cleans up the distortion, and I can get even 2 much cleaner watts just doing a quick tube swap, that would be a win for many people who aren't DIYers. Without more drastic changes, it's not going to put out more power anyway.

Next, change to full SS rectification. The 290V power transformer has no center tap, so they are doing bridge rectification by using SS diodes for the negative/ground and a cheap China tube for the positive side. I see nothing good happening from that (other than slower start up...) and I need more B+ if I'm gonna get the EL34 tubes to actually do something. I think I can probably get up to 40V more B+ adding some SS diodes and just leave that tube there for decoration.

I am very suspect of these "UL tap" output transformers. I plan to measure the winding ratios, but am also thinking to try strapping the EL34 as a triode and look at the results. If the massive distortion goes away, then I know the screen tap configuration is a problem. On my voltage tests, the screens have almost 5V more on them than the plate does. Possibly add some resistance to the screens might be part of the solution? They only have a 100 ohm resistor and I'm used to using more like a 1.2K resistor on UL taps. That might also be an easy thing to try, just swap a 1.2K resistor in one channel and see what happens.

For whatever reason, I really enjoy trying to "fix" these popular models of china amplifiers, at least as much as is possible. I do wanna also thank the viewer who sent me this one to play with

 

[kward]

I know this is probably obvious, but check the wiring of the output tube sockets too. EL34s have an externally wired suppressor, which should be connected externally to the cathode (pin 1 to pin 8) in most cases unless it's triode wired and then (I suppose) the designer has the choice to connect it to either the plate or the cathode. I have no experience with this, so just making an observation that the supressor is free floating in the EL34 and needs to be externally connected to somewhere.

 

[Pondoro]

I am interested in your Nobsound 6P1 mods and any testing, is there a link?

 

[StepheK]

A long thread as I worked through modifying this amp. Post #52 shows the final schematic.

https://audiokarma.org/forums/index.php?threads/nobsound-6p1-amp-flaws-mods.939092/

I probably need to get someone to send me an unmodified one to do a better video series on this little amp.

 

[StepheK]

Well I spend some time listening to it today: I can honestly say, this is the worst sounding HiFi amplifier I have ever hooked up a pair of speakers to. I seriously do not understand how this thing gets such good reviews. I do note all the reviewers are quoting the claimed 6W and > 1% THD claimed by the maker. This is a good example on how even some of these "skilled reviewers" can't hear garbage, and at the same time can hear cable elevators needing to break in and preach how important power conditioners are....

 

[kward]

Something’s not adding up here for me. I can’t believe they would blatantly mis-state the specs that badly. It almost seems like some sort of wiring error or component error that was not caught by their Q/C.
Did they just accidentally put the wrong power transformer on?

Can Steve Guttenberg’s ears be that bad? Dunno just speculating…

 

[StepheK]

Every China amp I have tested is this far off. The 300B A50 couldn't put out 3W either. Steve probably read the specs and believed them, heard some tube lushies and thought it sounded "rich". If you actually listen to his video, he dances around all the problems I am hearing, lack of detail, rumbling bass which is all related to high distortion. Tubes cover up sins that would be painful on a SS amp. I can say just lowering the cathode resistor and getting the amp running at a higher plate dissipation operating point made a huge improvement.

 

[Frank Sol]

@StepheK Thanks for your review , time & effort

 

[mcgjohn]

yes, would agree with @Frank Sol , thank you for your effort. Over the years have bought and tried a dozen and a half of the various chinese made amps. The Single ended versions have been a disappointment.

But a few have been a real surprise, such as the Music Angel EL34 amp. about 30-35 watts per channel using P-P EL34 amps. It is one of those amps you can sit down and listen to all day long. Very musical sounding.

The other item that is/was a nice surprise, (believe there are several posts here AK), is the Zerozone Marantz 7 clone line stage. Just a great sounding piece.

 

[Frank Sol]

This just reinforces my healthy dose of skepticism of YouTube 'Reviewers' especially the younger (<45) ones... Guys trying to live off of youtube hits

 

[trainbuftony]

Something’s not adding up here for me. I can’t believe they would blatantly mis-state the specs that badly. It almost seems like some sort of wiring error or component error that was not caught by their Q/C.
Did they just accidentally put the wrong power transformer on?

Can Steve Guttenberg’s ears be that bad? Dunno just speculating…

Believe it.
He spouts all of this, Blah Blah Blah. But doesn't even take the time to measure the output and see if it even works. He is making a fool of himself and only a few, in the minority are able to see it, because we do test things.
The emperor wears no clothes.

This just reinforces my healthy dose of skepticism of YouTube 'Reviewers' especially the younger (<45) ones... Guys trying to live off of youtube hits

Daily life should reinforce your skepticism.
Something slipped from my mouth the other day and it rhymed and was true and has slipped from my mouth multiple times since.
"I'm a critic, and I'm unapologetic"
Stephe too.
Keep up the good work @StepheK
Credibility and integrity are difficult to find these days...

 

[Saponetto]

As per any aspect of the human condition, subjectivity is the key to metabolize and incorporate the rationality that should be the beacon of our lives.
Audiophiles do not subtract themselves off from this rude law.
My subjectiveness tells me to keep with care what @StepheK reports, being this an easy way to learn and apply the rational approach I need to enhance my listening experience.

 

[Pondoro]

It is very possible that this amp has some good units and some bad units, if the quality is not well managed. So a positive reviewer may have gotten a good one and a negative reviewer may have gotten a bad one. I am not defending the manufacturer nor recommending the amp. I am just explaining that maybe all the reviewers are speaking well informed truth. I see lots of foreign made solid state equipment that has more than 1,000 online reviews, most positive, but ten to twenty percent are negative! Often the negative reviews say, "Junk, broke immediately" and the positive reviews say "It works great!"

 

[Shibatube]

I believe most reviewers on youtube and elsewhere are just shills and don't really pay much attention to them. Including Mr Guttenberg.

 

[ejman]

It would be interesting to see if a second unit, from an owner that thinks it sounds fine in his system would test the same way. I down own this amp so I don't have a dog in this hunt but I'm still very curious to see how this evolves. I mean is it really the case that 5-10% distortion and maximum output at 1-2 watts really doesn't matter or can't be heard by most people? This blows my mind. I do remember reading at one time in an old Stereophile that Fremer went gaga over the sound of a Wavac amplifier that cost mucho $$$$ and that their editor Atkinson that does their technical testing determined that the amp was basically "broken".

 

[opnly bafld]

FWIW
Ken Rockwell testing (listening and measuring) the Elekit TU-8200:
"While rated 8 WPC and delivering only a few watts at a few percent THD with sine waves, I see 30 W RMS come up at the onset of audible distortion with music."