eBay class A zero feedback amp

[batteryman]

Has anyone any idea whether this amp might be based on a proprietary amplifier? Many are based on JLH, Krell, Naim, Goldmund, etc but I can't find any schematic using an opamp at the input.

I guess the term 'No feedback DC amplifier' does not mean it is a No feedback design, but just has no feedback at DC. ie zero gain at DC.


YJ 40W+40W 4ohm MJ15024，MJ15025 Class A Stereo No feedback DC Amplifier board

one board supply voltage: DC +-25V to +-35V,
Suggestion: transformer 100W double 22V (need to add rectifier board)
Output power: 20W is 8 euro, 4 euro 40W.2 Europe 80W
Horn impedance: 2-8 ohms


YJ 40W+40W 4ohm MJ15024，MJ15025 Class A Stereo No feedback DC Amplifier board | eBay

 

[avtech]

I've seen these boards on Ali previously.

They may be a generic design as they usually proudly display the clone name otherwise..

One thing I noticed was that it mentioned having UPC1237 'advanced speaker protection' blah blah, but the UPC1237 I thought just came in a 'SIP-8' package not a 'DIP-8' package. Makes me wonder what that DIP IC is? Perhaps a NE5532 preamp or something? Who knows.

 

[batteryman]

I've seen these boards on Ali previously.

They may be a generic design as they usually proudly display the clone name otherwise..

One thing I noticed was that it mentioned having UPC1237 'advanced speaker protection' blah blah, but the UPC1237 I thought just came in a 'SIP-8' package not a 'DIP-8' package. Makes me wonder what that DIP IC is? Perhaps a NE5532 preamp or something? Who knows

I don't believe there is any protection as there isn't a relay shown. I do have a standalone speaker protector which does use the UPC1237 sip package.

I expect the 8pdip will be a NE5532 or similar and could be replaced with a newer opamp.

 

[analog_sa]

I guess the term 'No feedback DC amplifier' does not mean it is a No feedback design, but just has no feedback at DC. ie zero gain at DC.

In regular language this would mean "no overall feedback and no coupling caps". In clueless-Chinese-vendor speak it probably means nothing. Of course the opamp may be a servo, but why on Earth would anyone take a chance with this?

 

[29285]

A crappy translation that confuses "europe" with "ohm" cannot be taken seriously.😀

 

[scottjoplin]

First thing to always do is look at the feedback score, anything under 99.7%, move on.....

 

[phase]

It looks a lot like this one that is allegedly an accuphase clone;

YJ E405 Amplifier Board MJ15024G/MJ15025G 2*200W Class A 4ohm 2SA1930/2SC5171 | eBay

Who knows?!!

 

[batteryman]

I found this design which has a DC servo and pairs of complementary power transistors.

http://buildaudioamps.com/project-4/

But, yes, who knows and the translations are laughable.
Maybe I should offer a translation service to Chinese Ebay sellers!

I will find out in a couple of weeks.

 

[EUVL]

Nothing special but an opamp with emitter follower, DC servo, and Zener based cap multipliers.
You should have had no problems find this on Chinese webites, since your command of the language is so good to offer trasnlation services.

🙂


Happy New Year,
Patrick
.

 

[batteryman]

..since your command of the language is so good to offer trasnlation services.
Happy New Year,
Patrick
.

I wish!

新年快乐

Bliadhna Mhath Ùr, deagh fhortan airson 2019 (Scots Gaelic)

Ps at least I can spell translation. LOL

 

[EUVL]

Yes, you can accuse me of my not-so-perfect typing.


Patrick

 

[phase]

I only saw one op amp, but can’t tell if it’s for a servo or not, didn’t see a single cap nearby to suggest that however.

 

[EUVL]

I guess 8 resistors around a DIP8 is a suggestion for dual opamp ??
And I do see enough size-2 film caps around.
1µF MKS2 is enough for servo, not ?


Cheers,
Patrick
.

 

[Mazeppa]

I found this design which has a DC servo and pairs of complementary power transistors.

http://buildaudioamps.com/project-4/

But, yes, who knows and the translations are laughable.
Maybe I should offer a translation service to Chinese Ebay sellers!

I will find out in a couple of weeks.

I've come to think that the poor translations are intentional sometimes.

The less comprehensible the offering is, the greater the opportunity to plead
"misunderstanding" when complaints come back.

 

[EUVL]

And for what it's worth, it is actually not zero feedback.
The opamp has a local negative feedback loop.
It is just without an outside loop round the emitter follower.

For real zero feedback using opamp (namely AD844), see :
XEN ZGF Portable Headphone Amplifier

There is no feedback loop.
But that is because the AD844 is used not as an opamp here, but as a current conveyor.


Patrick

 

[phase]

Given the value of those caps it likely is indeed a servo, pardon my oversight...

Who knows, what if it is indeed the first decent ebay amplifier board?

My experiences with such have all been chocked up to poor judgement, if anyone has had better luck, please share!


That’s a pretty slick headphone amp there btw...

 

[suzyj]

Could be wonderful. Could even have more than a passing resemblance to the amp pictured. Could even be built with genuine parts.

You never know.

Then again there really is no such thing as a free lunch. It’s much more likely to be a crap design populated with counterfeit parts that’ll fill the room with smoke the instant you ask it to actually do anything.

 

[batteryman]

Could be wonderful. Could even have more than a passing resemblance to the amp pictured. Could even be built with genuine parts.

You never know.

Then again there really is no such thing as a free lunch. It’s much more likely to be a crap design populated with counterfeit parts that’ll fill the room with smoke the instant you ask it to actually do anything.

I will find out soon enough and counterfeit parts are a distinct possibility but can be replaced.
I usually buy bare boards so I have control over component quality.
I'll take some measurements and post them in due course.

 

[Bare]

Reads as perpetuating the 'Scottish ' stereotype: Frugal to foolishness .
Chi Fi is typically Crap.. and ebay variety is deservedly so.
Look elsewhere.
The DIY shoppe's Pass 'stuff' is not that much more $ and is a whole world of better quality

 

[dak20]

On taobao, many people bought it and are full of good reviews. It looks simple.