Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Headphone Systems Everything to do with Headphones

JLH Class A headphone amplifier
JLH Class A headphone amplifier
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 28th October 2010, 06:07 PM   #31
ashok is offline ashok
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
JLH Class A headphone amplifier
.....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.
  Reply With Quote
Old 17th November 2010, 03:53 AM   #32
heliguy is offline 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.
Attached Images
File Type: jpg IMG_0199.jpg (621.0 KB, 1393 views)
File Type: jpg IMG_0201.jpg (429.7 KB, 1291 views)
  Reply With Quote
Old 17th November 2010, 05:13 AM   #33
Bonsai is offline Bonsai  Europe
diyAudio Member
 
Bonsai's Avatar
 
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/
  Reply With Quote
Old 17th November 2010, 08:01 AM   #34
ashok is offline ashok
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
JLH Class A headphone amplifier
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
  Reply With Quote
Old 17th November 2010, 09:06 PM   #35
heliguy is offline 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?
  Reply With Quote
Old 17th November 2010, 09:25 PM   #36
wakibaki is offline wakibaki  United Kingdom
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
  Reply With Quote
Old 17th November 2010, 09:48 PM   #37
heliguy is offline 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
Attached Images
File Type: jpg IMG_0202.jpg (534.0 KB, 1187 views)

Last edited by heliguy; 17th November 2010 at 09:53 PM.
  Reply With Quote
Old 18th November 2010, 01:21 AM   #38
Bonsai is offline Bonsai  Europe
diyAudio Member
 
Bonsai's Avatar
 
Join Date: Jul 2003
Location: Europe
Lets try to fix your issues.

The ferrites will not solve your problem. You should remove them because they add no value in your situation - your problems are elsewhere as outlined below.

1. It looks like you are using non screened wiring to connect your volume control to the circuit board. I'd use some screened wire here - so inner two wires would be signal, and the screen the ground side of the pot. Reason: the pot wiper is a high source resistance, and therefore susceptable to a lot of noise pick-up via capacitive coupling.

2. You potentiomenter housing should have a good connection to ground - this should happen in any event because of the way the pot is mounted on the front panel. However, double check that your potentiometer shaft to chassis is open circuit. Highly unlikely, but just check it anyway.The pot housing acts as a screen, and prevents capacitive coupling onto the pot track.

3. Your cabling from the transformer onto the PCB - twist the wires tightly together so you minimize the area between the wires - this will reduce radiated noise (50/60Hz and harmonics). The way it s hooked up now means all this gunk is coupling into the volume pot wires and the PCB tracks.

4. Your headphone socket. Same story, twist the ground and L and R channels wires tightly together. Keep this bunch of cables well away from your pot cables and the transformer cables.

5. Use a meter and check carefull that your headphone socket is NOT electrically connected to the chassis other than via the headphone ground return wire to the PCB. To do this, unsolder the wires to the headphone socket and measure the socket ground to chassis - it should be open circuit. If you have a short, or low Ohms reading, you have a ground loop, and this will give you noise and hum.

6. Check that your input sockets are not connected to the chassis other than via the screen on the socket to PCB wiring.

7. You must have only 1 connection from your circuit board to the chassis. This must run from the junction of the filter capacitors to a secure point on the chassis. The incomming earth from the AC line receptacle must also be connected to the chassis. If there is any other path to the chassis other than via the single wire from the junction of the filter capacitors, it willl create an earth loop, and you will get hum and noise. Further, if you are anywhere near a PC or SMPS adaptor powered devices, the radiated noise from that adaptor wilol couple into your amplifier causing hum, hash and a lot of HF noise. Terrible stuff.

8. Final points: Keep the potentiometer wiring well way from the headphone and transformer wires. Keep the transformer wiring well away from the headphone and potentiomer wiring. Twist the wiring tightly as mentioned above.

Follow these simple rules and its quite easy to build audio stuff that is as quiet as good commercial equipment - so down at -100 to -120dB.

Lets tackle the problem you have when you plug into your PC after you have sorted the above problems out - I suspect however if you do 1-8 above, your problem will be solved.
__________________
bonsai
https://www.ovationhifidelity.com/ and DIY here http://hifisonix.com/
  Reply With Quote
Old 18th November 2010, 02:46 AM   #39
ashok is offline ashok
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
JLH Class A headphone amplifier
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
  Reply With Quote
Old 18th November 2010, 06:33 PM   #40
owenhamburg is offline owenhamburg  Germany
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
  Reply With Quote

Reply


JLH Class A headphone amplifierHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
JLH 10 Watt class A amplifier tschrama Solid State 5307 Yesterday 11:52 PM
JLH headphone amplifier steveh49 Headphone Systems 8 14th May 2014 04:31 PM
JLH 10 Watt class A amplifier #2 DomKo Solid State 8 30th October 2003 12:32 PM
JLH Class-A Amplifier Geoff Solid State 5 26th May 2001 12:55 AM


New To Site? Need Help?

All times are GMT. The time now is 02:45 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki