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 Headphone Amp
JLH Headphone Amp
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 14th January 2020, 05:06 PM   #841
MilesCampbell is offline MilesCampbell  United Kingdom
diyAudio Member
 
Join Date: Dec 2010
Location: London
Hello all

It's been a while and you have been busy

Now I have to catch up from where I left off, now where are those boards ??

Miles
  Reply With Quote
Old 14th January 2020, 06:22 PM   #842
MilesCampbell is offline MilesCampbell  United Kingdom
diyAudio Member
 
Join Date: Dec 2010
Location: London
Default I forgot all about doing this ...

Quote:
Originally Posted by EUVL View Post
And I have to wonder why no one actually built the complementary version (Circuit 2) :
The Class-A Amplifier Site - JLH Headphone Amplifiers

If anything, it is much simpler (ignore the circuit around Q3,4 which is just for bias stabilisation).
And it has less even harmonics.

Just because of lack of cheap PCBs ??


Patrick

I completely forgot about this version II thank you for reminding me.

Miles
  Reply With Quote
Old 14th January 2020, 06:25 PM   #843
MilesCampbell is offline MilesCampbell  United Kingdom
diyAudio Member
 
Join Date: Dec 2010
Location: London
Right then, I'm now up to date ..

Sadly lots of images are missing from older post's

My step by step build starts at post #114
The JHL Schematic is at post #119

The original schematic can be found here
The Class-A Amplifier Site - JLH Headphone Amplifiers

So outstanding issues - still an issue with DC offset maybe due to the supplied transistors in the kit which may be out of specification.

And oh joy someone is now making a finished PCB, does this still have the ground plan issue?

Or search for JHL Headphone Amplifier Finished Board
JHL Single-ended Class A Dual Channel Headphone AMP Amplifier Finished Board | eBay

How are people getting on with the finished board ?

Miles
  Reply With Quote
Old Yesterday, 02:12 AM   #844
sgrossklass is offline sgrossklass  Germany
diyAudio Member
 
Join Date: Nov 2004
Location: Germany
Quote:
Originally Posted by MilesCampbell View Post
So outstanding issues - still an issue with DC offset maybe due to the supplied transistors in the kit which may be out of specification.
What would that "issue with DC offset" be? You can't dial it in?

The voltage between input transistor base and output is always going to be approx. 3 B-E drops or ~1.9 V, with the DC offset adjustment giving you approx. 0 ... -2.7 V for the input to compensate. The transistors could hardly be that far out of spec unless they're the wrong thing entirely (even if just wrong pinout), misplaced / rotated, or some other component is wrong (like one of the 4k7s R23/24/5/6).

One thing you need to be aware of is that adjustment will have to be fine-tuned once warmed up, B-E voltage drops being quite temperature dependent (negative TC, ca. -2 mV/K). The zener also has a negative TC though (ca -2 mV/K, reduced by 10k adjustment pot to ca. 2/3 of that).

Reports indicate that increasing 1k resistor R21/22 value to e.g. 3k3 actually reduces DC offset drift during warmup, so the original design may have been overcompensating by running the zener too hot entirely. If so desired, you can try determining the best value experimentally (though no doubt tediously) by using a single-turn 10k pot in place of the 1k, minding power dissipation. It will depend on both transistor heatsinking and zener type / wattage. If the one who put together the schematic is not the one who assembled the kit, chances are DC offset thermal stability won't be ideal.

If the problem is more severe, I'd say grab the multimeter and measure:
* +/- supply voltages
* voltages at E, B and C of every transistor on one channel

Do you have a component tester (e.g. AVR-Transistortester and its numerous Chinese offshoots)?

Last edited by sgrossklass; Yesterday at 02:14 AM.
  Reply With Quote
Old Yesterday, 10:14 PM   #845
nenad88 is offline nenad88  Serbia
diyAudio Member
 
nenad88's Avatar
 
Join Date: Nov 2016
Anyone have spare servo pcb?
  Reply With Quote

Reply


JLH Headphone AmpHide 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 headphone amplifier steveh49 Headphone Systems 8 14th May 2014 04:31 PM
JLH Headphone amp aethelbert Headphone Systems 4 14th July 2009 12:14 AM
JLH headphone amp with FET's and servo nelsonvandal Headphone Systems 17 30th August 2008 10:26 PM
PCB for JLH amp FaTTy Solid State 0 27th March 2007 05:40 PM


New To Site? Need Help?

All times are GMT. The time now is 09:48 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki