JLH Class A headphone amplifier
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 28th October 2010, 06:07 PM #31 ashok diyAudio Member     Join Date: Jun 2002 Location: 3RS .....Im just not shure if I understood right? I should use capacitors like: - 470uF or 1000uF or 680uf or 2200UF. ?????....... Depends on your headphone impedance and what you want your low frequency turnover to be ( -3dB ) . C= 1/( 2*pi*f*Z) F is the -3dB frequency and Z is the headphone impedance in ohms. So for a 60 ohm headphone and a -3dB at 20 Hz , C = 133uF. For a bipolar capacitor you use two capacitors in series and so each capacitor should have twice this capacitance = 266uF. So a 220uF standard value is just about Ok . Or you could use a higher value possibly 470uF which is easily available. F -3dB will now be 11Hz. - 16V or 25V ?????..... Depends on your dc supply to the circuit. Capacitor voltage rating should be equal to or higher than the supply voltage. So +/-12 V dc supply can use 16 V caps. +/-18 V supply will need 25 V caps....and so on ! - integrate capacitors between the outputs on the amplifier and headphone jack (one for L and one for R)? (from amp thru cap to headphone?)........ Yes ! Connect the minus terminals of the caps together, One plus terminal goes to the amp and the other plus terminal goes to the headphone + ve terminal of one channel. - ve terminal of the two channels is usually connected together and is the ground terminal. Separate capacitors for each channel. So you need 4 capacitors totally. __________________ AM Last edited by ashok; 28th October 2010 at 06:11 PM.
heliguy
diyAudio Member

Join Date: Oct 2010
Some pics, its standard so far I wanted to get it working before I start messing with it. Setting the dc offset was quiet fiddly; it sounds excellent but its my first so don't have anything other than nothing to compare it with.
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 17th November 2010, 05:13 AM #33 Bonsai   diyAudio Member     Join Date: Jul 2003 Location: Europe James, what case are you using? Modushop by any chance? __________________ bonsai https://www.ovationhifidelity.com/ and DIY here http://hifisonix.com/ Ground Loops http://hifisonix.com/ground-loops/
 17th November 2010, 08:01 AM #34 ashok diyAudio Member     Join Date: Jun 2002 Location: 3RS Heliguy, That looks excellent. Yes it's a very good headphone amp , you needn't have to compare it with anything else. I recently had an urge to get a headphone which had very good reports by many guys on the Net. Many claimed it was incredibly priced. So I bought it for US\$48 from Amazon. Audio technica ATH-M30. It is VERY good ! I have a Sennheiser HD580 and many other phones from Philips, Audio technica and Sony and other Sennheisers. But this one is worth every penny. Get it before demand goes up and prices escalate. Is this the best headphone ? There never will be such a thing. It's musical, great bass and nice 'taut' bass , wonderful midrange and sweet highs. Not the best fit but good enough for reasonably long listening sessions without discomfort. It light and it's impedance is fairly flat I think. That will make it quite immune to a large headphone output impedance. With the JLH that isn't any problem. Cheers. I never found any fiddly problems setting the offset. Wonder why you had a problem. In any case if you use a bipolar output cap it doesn't matter at all. __________________ AM
 17th November 2010, 09:06 PM #35 heliguy diyAudio Member   Join Date: Oct 2010 Ok I suppose it was to be expected but After more considered listening there an awful background hum; its not there or at least not noticeable at lower volumes but quiet irritating once I start turning it up a bit. Should I tie the output ground to the chassis? Should I ground the zero volts? Would either of these help or should I be looking elsewhere. Would a toroidal transformer help? Would ferrite cores help?
 17th November 2010, 09:25 PM #36 wakibaki   Banned   Join Date: Jan 2008 This thread seems to have drifted away from the OP's amplifier. I wanted to ask jamesfeline, why would a headphone amplifier want a remote volume control? w
heliguy
diyAudio Member

Join Date: Oct 2010
ok the ferrite cores made little or know difference, but grounding the input made all the diff in the world, there is still a slight hiss any suggestions?
Also its input is an iphone; When its connected to the pc (iphone) there is horrible interference. Disconnect from pc and it gone obvious solution is not to sync while connected to the amp but it would be nice to charge it while listening, any idea's
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Last edited by heliguy; 17th November 2010 at 09:53 PM.

 18th November 2010, 02:46 AM #39 ashok diyAudio Member     Join Date: Jun 2002 Location: 3RS Someone else also had the hiss problem. He found that it actually came from his iPod equivalent source. Short the inputs to ground and see if you get hiss. If you don't then thhe hiss is coming from the source. If there is a digital control for volume on the source the output circuit in it is going full blast and chance of audible hiss is very high. If all else is fine and the hiss is always there, you might be having some HF oscillation. You can try a larger compensating capacitor. Try 50% more, then double its value an dthen triple. But doing that could kill the slew rate and affect the quality of the sound. It would b eideal if you get to see the output on a scope. It should tell all. __________________ AM
 18th November 2010, 06:33 PM #40 owenhamburg   diyAudio Member   Join Date: Oct 2009 Location: Hamburg Dear all, With respect to the ebay JLH amp. I had no problems with hum initially as I evaluated it powered by two car lead acid batteries. I then wired up a transformer without testing so it ended up the wrong way and destroyed the power regulation capacitors. 25 V to 15 V is a lower tolerance than I would have done in my own design. I then replaced the power regulation input capacitors and bought a second ebay amp. I then decided to power it from my preamp power supply of +-15V regulated. This solved most of the HUM issue. I then found an old box of biscuits tin and put it in with an earth connection and finally the HUM was gone. With the new amp I still have some high frequency noises, that sound like an old AM radio, so I guess I have some oscillation issues with it. I have to try my fixed version and see if that has the same issue, as I never noticed it before with the batteries powering the amp. I will get back to you all with some scope measurements some time. Regards Owen

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