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

Solid State Talk all about solid state amplification.

JLH 10 Watt class A amplifier
JLH 10 Watt class A 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 31st October 2019, 06:48 AM   #5611
kokoriantz is offline kokoriantz  Lebanon
diyAudio Member
 
Join Date: Dec 2015
Location: south east asia
May be the PS decoupling electrolytic is defective. Try one on Collector of upper to the emitter of the lower on the bottom side .
  Reply With Quote
Old 31st October 2019, 11:57 AM   #5612
Duffo adele is offline Duffo adele
diyAudio Member
 
Join Date: Oct 2019
Hello
Could you tell me Why on a jlh2003 i find the voltage of the power on V out
  Reply With Quote
Old 31st October 2019, 12:03 PM   #5613
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
I removed all the output transistors, and double checked everything, swapped the pairs between the boards, and put it back together. Now both boards are equal, showing a slight oscillation when I touch the input with my finger. I have tested with signal from a sound card up to clipping with 5,6ohm load, and everything is ok.
I have done the 'finger test' with other amplifier board, and never seen a problem, but in this case maybe it was the test method that was the fault.. Anyway, now they behave the same even with the flawed test method

As a side note, I have played around with a FFT scope, watching for traces of switching from a HP laptop brick. I see the same profile on the output as on the 'input' (power to amp), even if it's lower. I guess PSRR is not so great on these amps? Most of it is out of the audio band, but there seem to be some kind of modulation down to the 5-7kHz area which I don't like.
  Reply With Quote
Old 31st October 2019, 12:13 PM   #5614
Duffo adele is offline Duffo adele
diyAudio Member
 
Join Date: Oct 2019
your answers do not match my question thank you
  Reply With Quote
Old 31st October 2019, 01:17 PM   #5615
stevec67 is offline stevec67  United Kingdom
diyAudio Member
 
Join Date: Feb 2008
Quote:
Originally Posted by Duffo adele View Post
your answers do not match my question thank you
Duffo adele, rallyfinnen is not replying to you, he is talking about his own problems with his build of this amp. Have a look back and you wil see what he is talking about. This thread is a bit like a crowded room, there are a number of conversations happening at the same time. Have patience and someone will talk to you about your problem.
  Reply With Quote
Old 31st October 2019, 02:18 PM   #5616
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
Quote:
Originally Posted by Duffo adele View Post
Hello
Could you tell me Why on a jlh2003 i find the voltage of the power on V out
Maybe you can get some indications here:

The Class-A Amplifier Site - DC Voltages

But I'm not sure what the difference is between 1996 and 2003..
  Reply With Quote
Old 31st October 2019, 04:22 PM   #5617
kokoriantz is offline kokoriantz  Lebanon
diyAudio Member
 
Join Date: Dec 2015
Location: south east asia
Apply 10k resistor grounding the input , or a potentiometers . The base of the input needs this to loop the feedback .
  Reply With Quote
Old 6th November 2019, 06:03 PM   #5618
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
I have got the white boards up and running. Ran them straight from the 19V HP laptop brick (rated 7A) yesterday, and they sounded fine in mid/treble, but 'lazy' in the bass. Today I added a 15mF capacitor on the supply and first impression is that it improved the bass a bit, but I would not call it punchy and tight.

Set Iq to 1,4A, which is about what my temporary setup will handle safely. There seems to be bad thermal contact between transistors and the supplied alu-piece using the supplied pads, there is a big diff in temp between the two.

I did some quick distortion measurements to verify that they are ok (abt 1W 8ohm), and it looks like similar distortion levels and distortion profile as the JLH pnp from zerozone I have from before, maybe a little more distortion on these. However distortion levels differs between the two boards (almost 10db on 2nd harmonic with 1kHz 1W). I would guess this is because the hfe of the output transistors varied quite a bit (and I guess on the other transistors too), so open loop gain is quite diffrent between them?
I only measured the hfe with a multimeter at assembly, and I think lowest showed 37, and highest 117. I know it's not a good way to measure them, but I think it gives some kind of indication of the mismatch.
  Reply With Quote
Old 9th November 2019, 05:00 PM   #5619
Rallyfinnen is offline Rallyfinnen  Sweden
diyAudio Member
 
Join Date: Jan 2017
Default Some distortion measurements with MJ15003G

So, I decided to try the white Chinese board with MJ15003G output transistors, since they have been reported to work well with this amp.
I'm a little bit exited about the measurements, so I'm posting some screenshots here. Filenames explain the conditions. Supply to the amps is a 19,5V laptop brick. There is some 50hz and more picked up by the setup, so concentrate on the peaks from the harmonics, and look away from some of the odd peaks/grass elsewhere. All graphs have both channels, with one as overlay. No averaging (I was in a hurry), so the grass would be smoother with averaging.

First, after installing them, I saw that both amps were performing equally, and that was not the case with the transistors that came with the boards. I had the Iq set to abt 1,3A, and it all looked as I expected.

I decided to play around a little with it with FFT running, and that's what got me a bit excited. With a relatively cold amp, I slowly turned it up, and first the distortion decreased a little bit, but suddenly there was a instant dive in the distortion around 1,7A. Mainly the second harmonic that jumped down more than 10dB. If I turned up the current more, it jumped back up again. It was even more significant on the IMD. Here I was almost 20dB down on the sweet spot, compared to 1,3A.

So, I tuned the current to give the lowest IMD and left the amp on for some time. After heating up, the current was up to abt 1,9A, but it seems the 'sweet spot' was still correct, if I adjusted the current either way, distortion went up.
First I was not able to get the IMD to the same level on both amps, so I decided to play around a little with the 'offset' adjustment. I had only adjusted this roughly by observing clipping on the scope. With some adjustment on the offset adjustment, I was able to get the IMD to the same level on both boards.

I'm clueless to how/why this works, but I was amazed to see the result. Must be some 'sweet spot' where the amp is more linear. Maybe more a factor of the potentiometer settings than the actual current?

One might think this is only at high output, with more current available to feed to the load, but the distortion decreases over the whole range.

One observation is that the optimal current is possibly a little bit different depending on frequency, but I'm not sure about this. It seemed I had to adjust the screw slightly to get minimal 2nd order distortion when I had 100Hz, 1KHz and 5KHz sine input.

Will give it a listen now and wait what my ears tell me.
Before I had a headache after listening to it for a couple of hours, but I'm listening on new speakers, so that's a factor too. However, no headache with another amp and the same speakers.
I'm a little bit nervous about running such a high current, but at least the transistors are from a trusted source, so at least they should not be over sensitive.
Attached Images
File Type: jpg 1KhZ 8Vpp 8ohm.jpg (202.3 KB, 384 views)
File Type: jpg 1KhZ 12Vpp 8ohm.jpg (202.1 KB, 379 views)
File Type: jpg 13_14KhZ 8Vpp 8ohm.jpg (218.6 KB, 376 views)
  Reply With Quote
Old 10th November 2019, 09:11 AM   #5620
kokoriantz is offline kokoriantz  Lebanon
diyAudio Member
 
Join Date: Dec 2015
Location: south east asia
On the white Chinese board you have a 220 ohms behind the led . It is quarter watt but by Chinese magic it is dissipating half. After you have adjusted the bias by the series adjust , measure the total resistance it becomes with the 220 ohm . You can vary now the tap point all keeping the sum constant , to adjust the second harmonic .
  Reply With Quote

Reply


JLH 10 Watt class A 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
20 Watt Class A amplifier JOE DIRTŪ Solid State 8 1st February 2012 12:41 AM
JLH 10 Watt class A amplifier DomKo Solid State 3 18th November 2003 07:32 AM


New To Site? Need Help?

All times are GMT. The time now is 03:32 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki