DIY Beyerdynamic A1 Clone

[tim-tom]

Can somebody help me to find out what transformer this assembly needs(better with an ebay link). Tong Beyerdynamic A1 Headphone Amplifier Headphone Protection | eBay
and which one is preferable - toroidal or EI core transformer?
Im also curious of what the difference between clones of Beyerdynamics A1 (the one I linked looks just very close to original by design)
Thanks!

 

[tim-tom]

sorry duplicated

 

[[email protected]]

Hi Audiodoc,

sorry if my English is not 'top notch'.....I'am from the Netherlands and Dutch is my native language.

I have build exactly the same headphone amp as you've done, only mine has a R core transformer.....and a small problem.

7 seconds after powering up, the relay clicks and perfect sound is audible through the headphones.....but then......6 seconds later.....it seems the relay isn't being powered anymore, I can hear a small 'click' and sound is discontinued. Switching the amp off and than on again, the same happens. Do you have an idea what could cause this? Could it be a problem with the TL 801C ?

Greetings from the Netherlands, Roel van der List

 

[[email protected]]

Hello Audiodoc,

I first want to apologise if my English is not 'spot on'. I did build exactly the same amplifier, except for the transformer (R core) and the fact that mine has a little problem.
7 Seconds after switching on, the relay clicks and I hear a perfect sound through the headphones. But then.....6 secondes later, it seems as if the relay doesn't get any current anymore, it clicks, and the sound is discontinued.

Switching the power off and on again, the whole repeats itself.....after 7 seconds: sounds.....6 seconds later.....no sound.

My knowledge of electronics is just basic. I was thinking if it is possible that the TL 081 has something to do with the problem?

Greetings from the Netherlands,

Roel van der List

 

[Chris190]

Hello Audiodoc,

I first want to apologise if my English is not 'spot on'. I did build exactly the same amplifier, except for the transformer (R core) and the fact that mine has a little problem.
7 Seconds after switching on, the relay clicks and I hear a perfect sound through the headphones. But then.....6 secondes later, it seems as if the relay doesn't get any current anymore, it clicks, and the sound is discontinued.

Switching the power off and on again, the whole repeats itself.....after 7 seconds: sounds.....6 seconds later.....no sound.

My knowledge of electronics is just basic. I was thinking if it is possible that the TL 081 has something to do with the problem?

Greetings from the Netherlands,

Roel van der List

A bit older post but I think I know the problem with yours.... It's the R core transformer wired up to the a1 clone circuit board that's wrong. This amp has dual voltage input....so basically you need 2 secondary taps on the r-core each outputting 12-18V...so you have 4 secondary A/C wires ....you take the middle 2 and connect them together and these go on the middle input labeled ground...then the remaining 2 go each on one of the Vs... hope that makes sense and hopefully will help others too

Regards,

Chris

 

[Audiodoc]

Saw the answer today.

The relay is in the headphone protection circuit and will click if there is dc at the output. That may mean some soldering problems down the line or higher dc offset. Measure the offset without connecting the headphone. Since I had purchased the pcb from Hong Kong and procured the components locally except for the polypropylene caps and transistors I found that the bd 139 140 ones should be matched for a low offset.