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Reisong A10: Technical review.

I wonder if hearing those old radios in movies that are based in another time period usually have the tube radio in the scene sounding tinny with everything rolled off, might be what people who are buying these chifi amps are looking for?

Look how some people think those new crosleys sound good.
 
ejman said:
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".
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I think what's going on in many cases is people lack a good basis for comparison. If you listen with a few friends, and try a few amps, the difference becomes apparent very quickly.
Stage your own A/B/C comparison and do it before the free return period expires.
Our club was in agreement only after we put a "real" amp on the same speakers after listening to the Reisong.
Several real, old school push pull amps utterly trounced the Single ended A50 during our test, which is a different model, but the same design philosophy...
The amplifier wouldn't sell in a brick and mortar store, it's a product of the internet age where you have to trust the opinions of strangers instead of simply listening to each one and choosing the best in your budget.
If a reviewer thinks it sounds like a dream, then I'd be highly skeptical of that reviewer.
I am however thankful that StepheK has the time, energy, and resources to thoroughly investigate, fix, and document these little things so that people who want to enjoy them can attain the best performance and probably learn something in the process.
That's the spirit of Audiokarma.
 
kward said:
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…
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I don't think the issues that Stephe has identified with this amp are unique to this particular example. It's more likely poor design rather than a quality control issue.

I'm not saying all the specs claimed by Chinese amps in their advertising are bogus, but I've become increasingly skeptical. I've posted this link from Hi-Fi Haven a few times before. It's also a SE EL34 but an entirely different amp.

Eventually, the seller (manufacturer??) reluctantly acknowledged that the testing proved the amp did not meet advertised specs and gave the buyer a partial refund. If more buyers complained, and demanded refunds, perhaps the designs would improve.

https://hifihaven.org/index.php?thr...t-it-is-about-economics-and-value.4569/page-2
 
TriodeLuvr said:
The most expensive components in high-end tube amps are the output transformers. You get what you pay for.
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This is an entry level amp, not remotely close to "high-end".

Regardless of their general quality, it may also be that their primary impedance is not a good match. Someone on another board seemed to claim (I say "seemed" due to language issues) that the OTs are 5k.

I looked at all the data sheets and, for SE pentode operation, most suggest loads of either 2k and 3k. Mullard also lists an operating point using 3.5k. They all suggest a plate voltage of 250v with Mullard also listing 300v as an option.

I found it interesting that none of them listed UL operating points. Not sure if there's a reason for that, anyone know? Perhaps they're just the same as pentode.
 
An entry level amp should not sound like a hot mess. It should lack power, or features. I might accept shorter than average tube life. I would accept reasonable levels of noise. "Reasonable" noise would mean that I stopped hearing it when the music plays. I know that some people would only be able to hear the noise and would ignore the music, but I can ignore slight noise to experience an entry level amp. This one seems totally hacked up, either inn the design or because it was built wrong. I will admit that I have not heard it.
 
TriodeLuvr said:
Ken should stick to photography. That's his area of expertise (and one of mine).

Jack
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Ken is a hack when it comes to photography related stuff too lol. I will give him that he knows a little about Leica gear.

Back on topic, this isn't a case of a component or two being 10% off spec, I'm pretty sure there are components 200% off what they need to be, and other needed ones are just totally missing. Also this amp has zero feedback, so it's not like it is unstable from a resistor being slightly out of spec. I don't think this is a design that is sensitive to slight manufacturing tolerances that will have one sample sounds amazing and another is a total dog. But I'm probably going to have to disassemble the amp and measure every part to prove that isn't what is going on here.

I'll know more next week but I'm actually thinking this is a 6V6 amp they stuck EL34 tubes in to claim higher power. They are then operating so far outside of any reasonable operating point, this is the result. The cathode resistor is likely 2X what it should be for a EL34 at this low a plate voltage. And I still have to measure the OT...

We really shouldn't be assuming a made in China product is going to list actual specs, that anyone tested them nor are they going to be held accountable for false advertising etc. The Nobsound 6P1 amp is at best a 2W amp, they claim 6.8. The A50 claims 8 and barely makes 3 at 10% distortion. Why are people shocked this one is also way off what they claim?
 
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While "China" seems to get a lot of mention, pretty sure the country doesn't have much to do with these amps. I think your results much more reflect the fact that you are using the bottom of the barrel products. Show me a comparable SE EL34 amp that sells for under $400 with better results, manufactured anywhere. Not surprising to me that bottom of the barrel products don't perform that well.
 
Selmerdave said:
While "China" seems to get a lot of mention, pretty sure the country doesn't have much to do with these amps. I think your results much more reflect the fact that you are using the bottom of the barrel products.
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This is the 3rd made in China tube amp I've worked on that actually performs less than 20% of their claims. One was a $1000 amplifier. For that price, someone could buy a legit decent tube amp. If they listed this as a "2 watt amplifier at 6% distortion", it would be fine too.
 
StepheK said:
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.
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From my relatively limited experience with Chinese amps, the only one that lived close to published specs (but still not exactly matched them) was amplifier from Line Magnetic. But that one is was in premium price range. Thus when you buy Chinese tube gear in budget price range, you are choosing between bad and ugly. Some devices can be significantly improved with little expense, others are hopeless.
 
FlaCharlie said:
This is an entry level amp, not remotely close to "high-end".

Regardless of their general quality, it may also be that their primary impedance is not a good match. Someone on another board seemed to claim (I say "seemed" due to language issues) that the OTs are 5k.

I looked at all the data sheets and, for SE pentode operation, most suggest loads of either 2k and 3k. Mullard also lists an operating point using 3.5k. They all suggest a plate voltage of 250v with Mullard also listing 300v as an option.

I found it interesting that none of them listed UL operating points. Not sure if there's a reason for that, anyone know? Perhaps they're just the same as pentode.
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SEP circuit topology should allow 2-3W at 1% distortion even using EL84 tubes (that is what 1950th tabletop radios were capable to do). EL34 tube may allow up to 5W of reasonably undistorted output, and that does not require ultra-expensive output transformers like needed for 845/211 output tubes.
 
StepheK said:
This is the 3rd made in China tube amp I've worked on that actually performs less than 20% of their claims. One was a $1000 amplifier. For that price, someone could buy a legit decent tube amp. If they listed this as a "2 watt amplifier at 6% distortion", it would be fine too.
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How many similar-topology $1000 tube amps made in other countries have you tested? Again, you're finding that cheap products don't always live up to their claims. The China commonality is not relevant.
 
Selmerdave said:
The China commonality is not relevant.
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Yes it is. I've lived in China, and I can tell you that the underlying culture doesn't support the standards of quality and accountability that the West takes for granted. Despite the last three decades of economic and technological progress, it's still a third world country in many respects. The Chinese themselves realize this, and it's reflected in their love of Western goods. No one with the money to do otherwise buys domestic-brand products. Anyway, this is what you're signing up for when you buy most Chinese goods. They might perform, or they might not. It's always a crap shoot, and you won't often beat the house.
 
for_p1 said:
SEP circuit topology should allow 2-3W at 1% distortion even using EL84 tubes (that is what 1950th tabletop radios were capable to do). EL34 tube may allow up to 5W of reasonably undistorted output, and that does not require ultra-expensive output transformers like needed for 845/211 output tubes.
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I was comparing this A12 both technically and sonically to a DIY EL34 amp using a 6SQ7 driver, using fairly budget parts, Edcor OT with Hammond PT and choke. My DIY amp squeaks out 5W reasonably clean, in the 2-3W range is 1-2% distortion and sounds lovely. This one is over 6% at 1W and cruises past 10% at 2W.

I do have an update: I measured the turns ratio of the OT, it has a primary impedance of 3.2K with a 50% screen tap, so should be in the ballpark. I think most of this issue is the output tube is incorrectly biased (more on that later, still doing some testing).

I did disassemble the amp as needed to measure every part and it's all within a few percent of design specs as per the schematic they supplied. At the same time I reflowed all the solder joints to eliminate cold solder joints and made sure everything is wired right. It tested exactly the same as before on both channels, so IMHO that eliminates this sample being a random "defective unit" and if someone else received one of these that performs differently, it wasn't built to the supplied design/schematic. Honestly this is such a simple amp with very few parts, the power supply has maybe 10 parts including the iron and each channel has about 8, it's not difficult to check all this.
 
TriodeLuvr said:
Yes it is. I've lived in China, and I can tell you that the underlying culture doesn't support the standards of quality and accountability that the West takes for granted.
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I ran into this years ago with Soviet era cameras. Before the digital age, the low price of the Kiev medium format cameras was too tempting to ignore but after going down that rabbit hole, I learned I should have just bought a 'Blad or a Mamiya and enjoyed shooting.
 
TriodeLuvr said:
Yes it is. I've lived in China, and I can tell you that the underlying culture doesn't support the standards of quality and accountability that the West takes for granted. Despite the last three decades of economic and technological progress, it's still a third world country in many respects. The Chinese themselves realize this, and it's reflected in their love of Western goods. No one with the money to do otherwise buys domestic-brand products. Anyway, this is what you're signing up for when you buy most Chinese goods. They might perform, or they might not. It's always a crap shoot, and you won't often beat the house.
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These are sold by an American company to Americans that choose these over American-made products. We choose to make the cultural conclusions we want.
 
for_p1 said:
SEP circuit topology should allow 2-3W at 1% distortion even using EL84 tubes (that is what 1950th tabletop radios were capable to do). EL34 tube may allow up to 5W of reasonably undistorted output, and that does not require ultra-expensive output transformers like needed for 845/211 output tubes.
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I agree. Perhaps you missed my point.

Another poster used the term "high-end" and I merely pointed out that the term would not apply to these amps. Many expensive amps, regardless of which output tubes they use, have OTs which cost as much as, or even considerably more than, the entire cost of this amp. And that's the cost of each "high-end" OT, not a pair.

My point was that the OT might not perform well if its primary impedance was not optimal for the EL34. A post on another forum seemed to indicate that the primary measured 5k and the EL34 data sheets say to use somewhere between 2k and 3.5k depending on the operating point.

I now see that @StepheK has measured the OTs and that they are actually 3.2k so that concern has been eliminated. She seems to be on the right track and it may mostly be an operating point issue.

The data sheet operating points that spec either a 3k or 3.5k OT also run the tubes at their maximum plate dissipation, which is 25w. Not a bad idea to start with the data sheet operating points and try making some adjustments from there.

The amp was running the EL34s at much lower dissipation - just over 50% of maximum. Which makes me wonder if there is a reason for that. Perhaps the transformers (either the PT, the OTs or both) can't handle that much current?

And the fact that the "UL tap" is at 50% raises another question - is this actually a SE OT with a proper gap or is it a PP OT that they're trying to use in SE? I'm no expert on UL but I don't recall ever seeing an UL tap that's higher than 43%. Isn't that considered the "standard"?
 
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