JLH 10 Watt class A amplifier - Page 169 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 16th July 2008, 02:54 PM   #1681
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
I think my last calculation showed about 50W for the two outputs together, which seems to match the rough 1C/W I calculated the sinks as being.

The voltage was a bit low last night as I was only useing one secondary of the transformer... which is tapped for 0-24-0-24-0-6 VAC. As you can see I was pulling 1.45A at the time of the picture (that is from PSU, you can take off 10mA for the front of the amp to calculate bias setting.

The full size heatsinl is identical, but twice the height (20cm) so I guess in the region of .6C/W.

I plan to first make some prototypes of the later versions too, before I decide which one to build ultimately.

I just wanted to see for myself if the whole PSU and PSSR thing was realy such a big problem or just a case of bad layouts... I see no insurmountable problem or anything expensive needed.
  Reply With Quote
Old 17th July 2008, 01:51 AM   #1682
qwad is offline qwad  Australia
diyAudio Member
 
Join Date: Mar 2003
Location: adelaide city of churches
OOOOOOOOOOOOOOOps! jonathan is right, seems l got a bit beffudled with all the different device numbers and in my slightly delicate condition is it any wonder?, yes l did mean 3055's,
sorry for the confusion this may have caused and nordic congrats in getting the toshiba devices to work so well as it was documented by geoff that others who tried to use them had oscillation problems with them though they are a great device, the secret must be in your layout l think, cheers, TC
__________________
we all have problems only some people have more than most....
long live the Magyar (Hungarians) in the world!
  Reply With Quote
Old 17th July 2008, 09:06 AM   #1683
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Sadly I do not have a scope, so I can not guarntee it does not ring a little...

However there is no AC (that I can measure on my multi meter), nor do I hear any muffling or overbrightness. And the Transistors gets warm nice and gradualy, but obviously due to my too small sinks are unlikely to hit a thermaly safe operational point yet. also no hum, it will even reproduce the ground noise his in music, but goes dead quiet in between tracks...on a pretty efficient 8ohm driver.

Not to be held back I am allready modifying the board to add better regulation for the two front taps to the V+ rail. I want to hear the change in sound for myself.

I expect it to be a change for the better as I do not like traces drawing uA, mA and 2A connected together.

And I guess it will be totaly unsuitable for MP3's afterwards, as it is allready painfull listening to the artifacts in some badly compressed stuff.... (I have showed my wife 100 times, and she still messes it up). Luckily I only use MP3 sources for innitial testing... (one less ground loop to worry about)
  Reply With Quote
Old 17th July 2008, 12:30 PM   #1684
Pingrs is offline Pingrs  United Kingdom
diyAudio Member
 
Join Date: Jul 2005
Location: NW England
No ringing on any square wave with my version I cobbled together a few years ago. Not done much with it, though - a kind of exercise to use up some old BDY 56's I've got (or a shed load of 3055's). So I thought I'd take some measurements last night. THD fine, but it doesn't seem to like 8R//2u2 yet.

Brian.
Attached Images
File Type: jpg jlhpic3.jpg (57.0 KB, 1272 views)
  Reply With Quote
Old 17th July 2008, 01:44 PM   #1685
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Wow, thats what I call a thermal interface...

I have to say, I am getting obsessed with this sound....
I sneak in as much time as the heatsink can handle, whenever I get a chance...

Its been a while since I fell head over heals in love with an amp.

My eye caught a class AB JLH claiming to sound as good /indistinguishable from the class A. A claim I find hard to swallow. Guess I'll try it in the long run ,but the 69 JLH suits my transformers, and that of most old gainclones... I wish DIY designers would start their designs first looking at which transformer voltages are the most common.

This is the ugliest (yes, even my first dead bug GC looked more elegant), yet best sounding prototype I have ever built. Lots of people claim their amps have a valve like sound... this is as close to it as I think one can come.
  Reply With Quote
Old 17th July 2008, 04:22 PM   #1686
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Quote:
Originally posted by Nordic
Sadly I do not have a scope, so I can not guarntee it does not ring a little...
Nordic

To set your mind at rest a little, I have heard from a couple of people who have used 2SC5200 output transistors in the 1969 version (without additional compensation) and they have not been able to detect or measure any instability. Others have been less fortunate, probably due to layout.

Later versions seem to always oscillate when faster output transistors are used. I put the more benign nature of the 1969 version down to the fact that the bootstrap capacitor loses its effectiveness at high frequencies thus changing the load on Q3.

I am pleased that you have joined the many hundreds, or rather thousands, of constructors who have found the JLH to be rather pleasant sounding (deliberate understatement!).

Geoff
  Reply With Quote
Old 17th July 2008, 06:11 PM   #1687
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
What does C5 DO?

I tested with and without... I got 100u in there now...
Better attack with it, but I need to compare with takeing it out again, unless it has some important function. Hard to compare, because in between installing it, the PSU ate some caps... swapped the 10000ufs for 2x 4700uf now, still no hum...

Guess I need to do a soft start, and here I was thinking you only need those with toroidals...

Would it be enough to just delay the speaker connection with one of my speaker protection modules to reduce the power on spike?

I noticed I am no longer hearing what I believed to be background noisefloor with music playing, so that may be an artifact of this cap... looks like a bootstrap.
  Reply With Quote
Old 17th July 2008, 06:59 PM   #1688
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Quote:
Originally posted by Nordic
What does C5 DO?
There isn't a capacitor labeled C5 on the original 1969 schematic.

If you are referring to the 100uF electrolytic adjacent to R5 then this forms a low-pass filter in conjunction with the 39k resistor connected to +V in order to reduce the amount of supply rail noise that is fed into the input of Q4.

A better input biasing arrangement is that shown in:

http://www.tcaas.btinternet.co.uk/jlh2000.pdf
  Reply With Quote
Old 17th July 2008, 07:03 PM   #1689
paulb is offline paulb  Canada
diyAudio Member
 
Join Date: Jun 2001
Location: Calgary
Quote:
Originally posted by Geoff

I am pleased that you have joined the many hundreds, or rather thousands, of constructors who have found the JLH to be rather pleasant sounding (deliberate understatement!).
Rather pleasant sounding indeed. Even very old recordings seem to sound better. Mine hasn't made it out of the basement.

Good to see your name here again, Geoff.

Paul
  Reply With Quote
Old 17th July 2008, 07:12 PM   #1690
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
http://www.tcaas.btinternet.co.uk/jlh2000.pdf

The one connected close to the bias pot going to the output.

I understood this to be a copy of the original concept... I looked at the actual 1969 document now, which calls it C1 and offers some description of it influenceing LF response.
  Reply With Quote

Reply


Hide 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
20 Watt Class A amplifier JOE DIRT® Solid State 8 31st January 2012 11:41 PM
JLH 10 Watt class A amplifier DomKo Solid State 3 18th November 2003 06:32 AM


New To Site? Need Help?

All times are GMT. The time now is 12:47 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2