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Old 10th April 2013, 01:36 PM   #11
Luda is offline Luda  Germany
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Join Date: Jul 2006
00940: I'll look at that more closely in a minute, thanks.
I'm not sure I can replace all the transistors with ones that I already have, since I don't have any big P-channel FETs.
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Old 11th April 2013, 10:45 AM   #12
Luda is offline Luda  Germany
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Join Date: Jul 2006
Bipolar tansistors, not FETs, of course. Sorry.
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Old 11th April 2013, 03:42 PM   #13
00940 is offline 00940  Belgium
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Join Date: Sep 2003
Location: Liège
Well, you could replace the VAS transistors by more sk170, sj74, depending on the idss you've got (do you have complementary matched pairs ?).

You really need to get PNP transistors though to get decent current without an output cap. If you go on, you can easily get 10bd139-bd140 pairs for 5€. That will allow you to build a much better amp.

Here is the general idea (R1-R2 is a 200r trimmer to set the output offset due to mismatch in jfet, r13 a 2K trimmer to set the output current, R5-R6 set the current in the VAS and have to be adjusted according to the idss of your jfet, the more the better, R7-R8 set the gain):

Click the image to open in full size.

If you insist on using your parts... just make a kind of darlington with 1 2SK170 and 1 bd135and stick it on a 100maq ccs made with another bd135. You'll have no gain and you'll need an output cap. No need for input cap if you use a +/-12v supply.

PS: there might be a virtue with output caps in discrete design. No risk to get murdering offset at the output if your parts aren't well matched enough or trimmers go bad.
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Last edited by 00940; 11th April 2013 at 03:45 PM.
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Old 25th April 2013, 02:57 PM   #14
robbo33 is offline robbo33  United Kingdom
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Join Date: Apr 2013
Location: london
Thumbs up robbo33

Hi i have just built a headphone amp & use the same headphones as you. I found a site call William Neo audio & headphone tutorial site DIY Simple Headphone Amp Tutorialcant give it enouge praise. On the site (top right) under most viewed, click on the 4 options & there is all the info you need. I built one of the easier ones, (based on a cmoy) but used 470uf 16v instead of 220uf 16v & used a ic AD712jn i origanally used a TL072 cos that was the only one the shop had, it sounded abit distorted. Perhaps the Blurr Brown that are sugggested would be as good as the AD712 as i used, it give better deth/bass NO distortion. There are also class a mosfet amps dia. & parts list which i may have a go at. I want to build an amp with bass/treble next, i've got diagram but need more detailed parts list & pcb lay out. Hope this site is of help to you or anyone else. Good luck. DIY Simple Headphone Amp Tutorial
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