A2-Pro HA from Ebay

[gradobob]

Hi All

I've just bought one of these kits from an Ebay seller in China and I am intending to build it over the next week or two



Supposedly - "inspired" by the BD A2 Amp

It's been a while since I built something like this - the last one was the famous Panda amp as featured on these forums a while ago

Build instructions are non-existent, the only paperwork was a badly photocopied schematic (which isn't accurate)



If there's any interest I will update with progress and pictures and maybe even loan it out if members are interested in hearing it.

[PinkFloyd]

May 3, 2017 11:38:12 GMT gradobob said:

Hi All

I've just bought one of these kits from an Ebay seller in China and I am intending to build it over the next week or two



Supposedly - "inspired" by the BD A2 Amp

It's been a while since I built something like this - the last one was the famous Panda amp as featured on these forums a while ago

Build instructions are non-existent, the only paperwork was a badly photocopied schematic



If there's any interest I will update with progress and pictures and maybe even loan it out if members are interested in hearing it.

Hi Bob,

The images / links aren't showing up so I can't see the amp you're talking about. Any fresh input here is most welcome, I look forward to your findings.

best regards,

Mike.

[gradobob]

Hi Mike

I've updated the image links, hopefully they're visable now

[PinkFloyd]

May 4, 2017 11:39:58 GMT gradobob said:

Hi Mike

I've updated the image links, hopefully they're visable now

Wow.... I can see the schematic but can't make out any of the values with my old eyes I trust you can actually make the values out on the paper schematic? Let us know how you get on with it Bob, it sure does look nice but putting it together may be a tad annoying if you can't read the schematic

Best regards.

Mike.

[gradobob]

Hi Mike

Nothing wrong with your eyes, its a poor quality photocopy and some components have values and others don't. To make for more confusion, on the board silkscreen, some are values and some are component numbers and there are two pairs of bc546/bc556 in the kit and on the board that aren't on the schematic.

Currently I'm redrawing the schematic and trying to tie everything together. It's a challenge for sure.

[gradobob]

Well the A2 amp is finally complete and first impressions are pretty good


Managed to figure out where everything went and only made one mistake with the positioning of one of the headphone jacks which I will have to live with as I can't seem to desolder it.
The fuse block wouldn't fit as the pcb holes weren't big enough so I had to drill them out, luckly there was just enough solder pad left so I didn't have to hardwire anything. Installed a fuseblock cover to be on the safe side.

I also decided to install a terminal block for the input wiring in case I want to take it apart in future. Fortunate as the cable I've used is too stiff and thick so I will change this as soon as I can find some decent twin screen cable.

I've only had a quick listen so far but it's hum-free (unlike my Panda) and sounds pretty good so far.

[pingu]

Hi Bob,
This may be a candidate for op amp rolling.. Looks like a couple of Mikes Orange amps may fit the bill here
Martin

[pingu]

So have just built one of these amps
Nightmare of a kit parts missing circuit diagram incorrect and silk screen on board mixture of component values and random numbers. All very much like Bobs experience
All up and working now tho with the help of Bob and his pictures. No hum sound OK but not great, so time for chip swapping. It has mc 33078p's in arm.

Any one know where I can get two pairs of AD 825s mounted on ic sockets ?
Or 825 that are pin not smd
I have have double to single adaptors but they are all pin type and I can not find pin 825s only smd

Any advise on other chips will be appreciated

Marin

[PinkFloyd]

Hi Martin,

I'll have a look in my box of opamps tomorrow..... I know, for sure, that I used to have quite a few AD-825 but whether they are still in the box or inside amps god only knows! Will have a look and let you know.

Best regards,

Mike.

[pingu]

Jul 6, 2017 19:26:01 GMT PinkFloyd said:

Hi Martin,

I'll have a look in my box of opamps tomorrow..... I know, for sure, that I used to have quite a few AD-825 but whether they are still in the box or inside amps god only knows! Will have a look and let you know.

Best regards,

Mike.

Thanks Mike I'll wait to hear from you

All the best

Martin

[pingu]

Jul 6, 2017 19:26:01 GMT PinkFloyd said:

Hi Martin,

I'll have a look in my box of opamps tomorrow..... I know, for sure, that I used to have quite a few AD-825 but whether they are still in the box or inside amps god only knows! Will have a look and let you know.

Best regards,

Mike.

Hi

Also had some good reports on opa 627's has anyone any experience of these ?
Quite a bit more expensive than the ad825's


Martin

[PinkFloyd]

Jul 7, 2017 9:36:06 GMT pingu said:

Jul 6, 2017 19:26:01 GMT PinkFloyd said:

Hi Martin,

I'll have a look in my box of opamps tomorrow..... I know, for sure, that I used to have quite a few AD-825 but whether they are still in the box or inside amps god only knows! Will have a look and let you know.

Best regards,

Mike.

Hi

Also had some good reports on opa 627's has anyone any experience of these ?
Quite a bit more expensive than the ad825's


Martin

Had a long hard look in my stash and the AD825 have flown the nest Same with OPA627 AD843 / AD743 quite a few remaining but not an AD-825 in sight..... sorry

[pingu]

Thanks Mike looks like I'll have to keep looking. I'll see what you think about the orange amps and maybe if you add me to the list I'll give them a tast run

All the best
Martin

[durdepa]

Does anyone have some clear pics of the ebay beyerdynamic A2 clone headphone amp diy kit showing assembly and parts placement ? As others have said you can figure out most of it by process of elimination but the bc556 and bc 546 and some other stuff is a mystery. It looks like q3-q6 on the board but who is whom? There is a previous post with pics but is says images link broke. Any help would be greatly appreciated.

[pingu]

Apr 8, 2018 12:25:20 GMT durdepa said:

Does anyone have some clear pics of the ebay beyerdynamic A2 clone headphone amp diy kit showing assembly and parts placement ? As others have said you can figure out most of it by process of elimination but the bc556 and bc 546 and some other stuff is a mystery. It looks like q3-q6 on the board but who is whom? There is a previous post with pics but is says images link broke. Any help would be greatly appreciated.

Hi Durdepa
Not sure what the q3-6 are but the bc trannies are from the front (Vol controller head sockets end) BC556 BC546 BC556 BC546 these were marked on my board and if you look at the print on the board it will give you the correct orientation if you keep the shape of the tranny to the shape on the board. The flat on the 556s facing the heatsinks and the flat on the 546 facing away from the sinks
The associated tranies on heat sinks are BD139 BD140 BD139 BD140 again from front to back
If the links are broken here go over to Diyaudio site there’s a thread on there with pix

Don’t expect too much, it’s ok but for a few pounds more a second hand Heed Can will be miles better

Hope that helps
Martin

[durdepa]

Very helpful thanks. My board was not marked so that sorts out the bc546 and bc556 pairs. The only other unknown is VD1 located right behind the relay near the headphone jacks. Cant find a part number for this VD1 but the pics i have seen show it looks like the other three diodes marked d5,d6,d7. Anyone know for sure? Ive never seen a kit with this few clues...sure hope it sounds good after all the hassle.

[pingu]

Hi durdepa

The vd1 is the switch on delay diode directly behind the relay, mine had a small mark on one end which is the end nearest the switch check orientation on the circuit diagram. Try placing all the other diode and the one left is vd1, no part number on mine either but it’s only a diode marked as ds1 in the circuit diagram in this thread.

Hope that helps sorts things out for you

All the best
Martin

[hellkern]

Hi everyone,
Recently i recivied my kit from aliexpress, soildered it and made some testing.
While i was soildering the devise - each part except transformer and opamps was tested by lcr/hfe meter - resistors are pretty good - in 1% tolerance to it's values, and around 0.5% between each other. Capacitors are mostly ok, but some Wima's are 100% not Wima's, and 3 of "Nichicon" caps were out of spec by Vloss value(4% vloss on 150uF/35V). Also transistors, regulators and opams provided in kit are absolute crap - transistors and opamps are fake ST Microelectronics, regulators - one fake ST, another two - noname.
Replaced main transistors with BD139-16 and BD140-16 from ON Semiconducor, hfe-matched somehow... Small transistors replaced with Faitchild's ones.
About opamps - i've tested several opamps(TL072CP, NE5532AP, OPA2134PA, LME49720NA) and for my ear LME49720NA made the best sound.
Headphones connectors are pretty good, i even think it's genue Neutrik, volume potentiometer is also good, never had hands on genue Alps, so no comments there

The biggest design mistake in this device as i think - ground wire on mains input - i strongly recommend to undo the ground terminal from mains connector, as when ground is connected both on signal source(with any digital stuff) and amplifier there a a LOT of digital noize on amlifier output.

Also i managed to get schematics for Beyerdynamic A2 clone - V1-V4 = BD139/BD140, Q3-Q6 = BC546/BC556

[pingu]

Hi Hellkern,
Just having rummage around the site and as I’ve just ordered the USB DAC board for my amp I thought I’d have a look and see if there’s any interest in resurrecting this thread.
My unit worked ok, and still does with a selection of op amps, (can’t remember which one I’m using atm probably 4562 or the muse 8820) didn’t have any probs with the earth loop you mention. I used all the bits that came with the kit but now I have “Peak” bit I’ll check the caps and trannies when I do a rebuild, resits we’re all good tho.
I was just wondering if anyone on here or does any one know anything about the USB board? It’s cheap enough to have a look at so wondered if anyone has fitted the extra bits
Another thing springs to mind has anyone used different chips in each side, just a thought
Martin

[pingu]

So after a long Google search I think I’ve found the answer to connecting the DAC. So it’s on order and let’s hope it works
Any one want info DM me and I’ll let you know when it’s all up and running
Martin

[PinkFloyd]

you get what you pay for guys...... I'll say no more......


Mike.

[PinkFloyd]

Jan 27, 2020 18:28:12 GMT hellkern said:

Hi everyone,
Recently i recivied my kit from aliexpress, soildered it and made some testing.
While i was soildering the devise - each part except transformer and opamps was tested by lcr/hfe meter - resistors are pretty good - in 1% tolerance to it's values, and around 0.5% between each other. Capacitors are mostly ok, but some Wima's are 100% not Wima's, and 3 of "Nichicon" caps were out of spec by Vloss value(4% vloss on 150uF/35V). Also transistors, regulators and opams provided in kit are absolute crap - transistors and opamps are fake ST Microelectronics, regulators - one fake ST, another two - noname.
Replaced main transistors with BD139-16 and BD140-16 from ON Semiconducor, hfe-matched somehow... Small transistors replaced with Faitchild's ones.
About opamps - i've tested several opamps(TL072CP, NE5532AP, OPA2134PA, LME49720NA) and for my ear LME49720NA made the best sound.
Headphones connectors are pretty good, i even think it's genue Neutrik, volume potentiometer is also good, never had hands on genue Alps, so no comments there

The biggest design mistake in this device as i think - ground wire on mains input - i strongly recommend to undo the ground terminal from mains connector, as when ground is connected both on signal source(with any digital stuff) and amplifier there a a LOT of digital noize on amlifier output.

Also i managed to get schematics for Beyerdynamic A2 clone - V1-V4 = BD139/BD140, Q3-Q6 = BC546/BC556

Yup, a bag of cheap Chinese fake parts..... best place for them is your nearest bin..... sorry but it would be remiss of me to not tell the truth.

Mike.

[PinkFloyd]

Jan 27, 2020 18:28:12 GMT hellkern said:

Recently i recivied my kit from aliexpress

That pretty much sums it up mate..... did you get a free "I am a mug" T-shirt with your order?

[pingu]

Hi Mike,
Well tbh I found the bits not bad at all as Hellkern said, after some puzzling the kit worked well straight out of the box so not bad at the price. Yes it took a bit of figuring out and a few internet searches but after all that’s the fun of DIY isn’t it? the smell of melting flux. Definitely not one for a raw beginner tho.
Changed the ICs and big improvement, as good as if not better than the JLH ha crisp tight treble and solid base. Not quite the bottlehead crack but the that’s valve and 10x more. Miles better than most.
The price of the kit (which came with its nice looking box) was little more the buying a Chinese box on its own, so even if it was a pile of crap I had a nice enclosure. Caught for PO rip off collection fees and customs duty but that’s life.
I’ve now changed some of the caps checked and changed some of the trannies used different ICs so nothing major and very little expense with some minor improvement.The pcb is good quality and thick, the print looks ok but who knows, all I can say it didn’t lift when o change parts. Now I’m adding a USB DAC for £20 (so worth a punt)
All in all a good and very cheap HA and soon with a DAC (if it works) which looks good too. That makes the cost of the unit exceptionally good value.
No not one for the beginner you need to be able to read and interpret a cir. diagram and be able to use a dmm or better a peak jobbie. Very good value if you can do a little work.
IF YOU GET ONE EXPECT TO DO SOME WORK
So yes I’ll take their T any time because you’ll get nothing else of them (don't bother to email them) lol
All the best
Martin

PS been running a few years now too