Schematic for Ebay Beyerdynamic A1 Amp

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Almeg69

Member
Joined 2009
I have bought and built this headphone amp for testing my various audio projects:

2015 Latest Headphone Amplifier kit reference to Beyer dynamic A amp | eBay

Does anyone have the circuit diagram ? I have done a search but all I can get is a very low res image PNG or something or another which is unreadable. I have even tried the various sellers but they say the bitmap view is all they have.

Thanks Alex.
 
Aatto

Aatto

Member
Joined 2017
hi
funny, got exact same board a few days ago, just finished it today, actually better than i expected, a little bit much mid hi maybe, but i think it would be fine with better caps maybe. how s your experience? lemme know if you change anything on yours to improve.

thanks
 
Stixx

Stixx

Member
Joined 2003
original-ton.net
2 mins. Google found this.


1484519184_circ.jpg
 
K

killingtime

Member
Joined 2008
Hello Stixx,

Thanks for posting this. Your Google skills must be better than mine because all I could find were pictures of the completed amp...

The image posted links back to what appears to be a German electronics DIY forum website. So I searched the forum and located the post containing the schematic:

bitmania.de

The OP on this forum has included a pictorial build log, so if you have this kit and are looking for further guidance then this is a useful resource.

A translation of the German introduction reads:

Headphone Preamp DIY Beyerdynamic A1
Now we come to a class A headphone amplifier.
The circuit is classic and proven. There are no secrets.
They are also available from commercial manufacturers. It works best with Beyerdynamic 250 ohm headphones. I found this kit in an auction house.

The circuit requires a transformer with center tap. Best 18 0 18.

On the board there is a bridge rectification with completely oversized sieving. Then it goes on with LM7815 and LM7915 to supply the output stage of BD 139 and BD 140. The precursor and difference OP are MC33078P.
Drivers are BC 556 and BC 546

A UPC 1237 IC is used as switch-on delay and DC monitoring.

Everything is mercilessly overkill oversized. The individual stages are also consuming decoupled. an Alps RK 27 poti is planned, but there was a cheap one. For Aen start OK.

Circuit diagram and instructions or assembly instructions do not exist.

I have partially documented the construction times and also found a circuit diagram that seems to fit.

---------------------

For anyone considering this kit, my experience is that there are plenty of people selling it on various portals, and they nearly all show an ALPS27 included, but what you receive is an ALPS16. The 'chinglish' description on all the portals I could find was that bad you couldn't work out exactly what was on offer anyway. Just factor this in when making the purchase, or find a seller that offers the upgrade to a 27 for an extra few ££.

Regards,
 
D

DJDestiny

Member
Joined 2011
killingtime said:
Hello Stixx,

Thanks for posting this. Your Google skills must be better than mine because all I could find were pictures of the completed amp...

The image posted links back to what appears to be a German electronics DIY forum website. So I searched the forum and located the post containing the schematic:

bitmania.de

The OP on this forum has included a pictorial build log, so if you have this kit and are looking for further guidance then this is a useful resource.

A translation of the German introduction reads:

Headphone Preamp DIY Beyerdynamic A1
Now we come to a class A headphone amplifier.
The circuit is classic and proven. There are no secrets.
They are also available from commercial manufacturers. It works best with Beyerdynamic 250 ohm headphones. I found this kit in an auction house.

The circuit requires a transformer with center tap. Best 18 0 18.

On the board there is a bridge rectification with completely oversized sieving. Then it goes on with LM7815 and LM7915 to supply the output stage of BD 139 and BD 140. The precursor and difference OP are MC33078P.
Drivers are BC 556 and BC 546

A UPC 1237 IC is used as switch-on delay and DC monitoring.

Everything is mercilessly overkill oversized. The individual stages are also consuming decoupled. an Alps RK 27 poti is planned, but there was a cheap one. For Aen start OK.

Circuit diagram and instructions or assembly instructions do not exist.

I have partially documented the construction times and also found a circuit diagram that seems to fit.

---------------------

For anyone considering this kit, my experience is that there are plenty of people selling it on various portals, and they nearly all show an ALPS27 included, but what you receive is an ALPS16. The 'chinglish' description on all the portals I could find was that bad you couldn't work out exactly what was on offer anyway. Just factor this in when making the purchase, or find a seller that offers the upgrade to a 27 for an extra few ££.

Regards,
Click to expand...

I bought this kit about... uh i don't know, 15 or 16?
Somewhere around there.

I found that it has issues that Beyerdynamic didn't fix.

Beyerdynamic A1 clone gold, opamp rolling

Post 6 lists the mods you should do. Right now my A1 is still in limbo because I bought a billion other amps and never touched it even though I literally have a bespoke chassis for it. (Bespoke meaning nobody else has it in the same format)

I started out with a junky "biggermouth P5" did a lot of mods then got a SMSL sApII then bought the A1 kit... which I built heard and fumbled around deciding what trafo I would give it or would I do external PSU or not and in the end I bought the cutest non sealed toroid in the world :D


I replaced the MC33078 with OPA1652s and believe me when I say beyerdynamic still charges too much for the A20 (basically same thing) using more or less the same cheap opamps that I don't care much for.
In the end I put 2 of those OPA1652 and another two in a MBL6010 preamp

But yeah, I sort of questioning myself why I bought the A1 kit when I bought a fully built HA5000 clone and that is my benchmark basically.
 
DreadPirate

DreadPirate

Member
Joined 2006
There are some assembled units on aliexpress for these for around $100US. I wonder how these would compare with the O2? I just got one on the massdrop for $100 and am pleased. My HD570 needs a boost when using the laptop or portable device due to its low sensitivity (92dB).
 
D

DJDestiny

Member
Joined 2011
DreadPirate said:
There are some assembled units on aliexpress for these for around $100US. I wonder how these would compare with the O2? I just got one on the massdrop for $100 and am pleased. My HD570 needs a boost when using the laptop or portable device due to its low sensitivity (92dB).
Click to expand...

I dare say it's a step up... even if it isn't modified. I heard a A20 in store and was like... Wtf is this? this was sold for 599usd?


Note : I absolutely don't like the O2 either. But if you want to plonk 100USD buy something better. Buy a assembled TPA6120 amp that has proper power supply (it should have 4 heatsinks behind the chip which means it has the full constant current power supply)
 
DreadPirate

DreadPirate

Member
Joined 2006
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