Schematic Question - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 23rd November 2014, 08:50 PM   #1
diyAudio Member
 
Join Date: Sep 2012
Location: Michigan
Default Schematic Question

I thought it might be more appropriate to create a new thread for this question than to have it hidden away in another thread. Anyway, I'm new to building amps and electronics in general, but I am interested in giving this project a try. I've got some electrical knowledge and am fine with a soldering gun. The De-Lite amp document only shows what one channel of the amp looks like, but as a beginner I am not confident in building it unless I know what the stereo version looks like. I've attached a drawing to see if I got the idea right. Proper star grounding scheme not included....

Click the image to open in full size.

I've see numerous photos of people using two B1's and two R1's, often with several more caps (C1 and C2)....is this necessary to make the most basic stereo version of this amp? I don't believe NP's own unit shown in picture on the first page of the pdf has that....correct?

Last, I read about many attempts at this project having hum at first, but if I understand enough, is that because everyone is using parts bin stuff and different chassis layouts? Meaning if I build the amp EXACTLY as it looks in NP's photo, with the EXACT same parts (same specs anyway), I would not have hum?

Last edited by soundwavesteve; 23rd November 2014 at 11:15 PM.
  Reply With Quote
Old 23rd November 2014, 09:45 PM   #2
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

No. The power supply needs uprating. TBH you'd be much better
off looking at the "Death of Zen" (search) to learn something,

rgds, sreten.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
  Reply With Quote
Old 23rd November 2014, 11:22 PM   #3
diyAudio Member
 
Join Date: Sep 2012
Location: Michigan
I updated my drawing to be the correct version of what I want to build. Nelson's own doc says the number of parts in my drawing is correct:

"...[a transformer], fuse, diode bridge, two big electrolytic capacitors, a one ohm power resistor, two 300 watt light bulbs (with sockets), two RCA connectors, two smaller electrolytic capacitors, two small resistors and two power Mosfet transistors."

If this drawing is not correct, what does the correct stereo schematic look like?

Nelson says that the PS needs to be at least 350VAC per channel, while the transformer in the picture says 50VAC on the secondaries. So, if I bought a 800VAC 50+50 transformer, I would only use one set of the 50s and I would tape off the second set cause it's not used....correct? If not....why?

And I did find Elliott's DoZ page and printed it off for further reading...
  Reply With Quote
Old 24th November 2014, 01:15 AM   #4
diyAudio Member
 
Join Date: Apr 2003
Location: Eastern Pennsylvania
A major problem with that De-Lite circuit is that it has no power supply rejection. Any noise or ripple voltage on the supply rail will appear directly at the amplifier outputs. Which is probably why you've read reports by other builders of hum problems. This also means that because the supply is directly shared by both channels, any modulation of the supply rail by music on one channel will be directly coupled to the opposite channel's output as crosstalk.
__________________
Ken

Last edited by Ken Newton; 24th November 2014 at 01:19 AM.
  Reply With Quote
Old 24th November 2014, 03:54 AM   #5
diyAudio Member
 
Join Date: Sep 2012
Location: Michigan
So, that's why some builders use an extra set of caps, power resistor and another bridge to help isolate the crosstalk?

This project is more for fun, as I build it and its variations, I will learn more and hear the improvements as I go. Eventually I want to build an F5 Turbo, but until this, it's all for fun and learning.

Thanks for the help so far
  Reply With Quote
Old 24th November 2014, 03:15 PM   #6
diyAudio Member
 
Join Date: Apr 2003
Location: Eastern Pennsylvania
There is an circuit modification you could try that would provide very good power supply rejection to both channels, while requiring no additional parts. Simply move the wires connecting the grounded output terminals over to the +65V supply rail. Also, reverse the connection polarity of the electrolytic output coupling caps. So, any supply rail noise or ripple would appear matched between the output terminals, thereby canceling

This would also place 65VDC on the output of the two affected output terminals, which, while low enough that it shouldn't be much of a safety concern, still should have certain precautions taken for it. Such as, inserting a fuse directly in the supply rail common feed should it not already have one, and making certain that the output terminals are insulated from the chassis.
__________________
Ken

Last edited by Ken Newton; 24th November 2014 at 03:19 PM.
  Reply With Quote
Old 24th November 2014, 03:36 PM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Your added channel is correct.
You have a two channel amplifier powered by one PSU.
BUT
I suggest you build one channel and get it working, then decide what you might want to do to make it fit for purpose, presumably to reproduce music.
Kens mod is worth implementing
Quote:
Simply move the wires connecting the grounded output terminals over to the +65V supply rail. Also, reverse the connection polarity of the electrolytic output coupling caps.
hear, and measure what difference it may make.
__________________
regards Andrew T.
  Reply With Quote
Old 28th November 2014, 08:54 PM   #8
diyAudio Member
 
Join Date: Mar 2010
Why no try this variation?

Amplificador Clase A pura 1 etapa Single Ended Light

Click the image to open in full size.

Regards
  Reply With Quote
Old 28th November 2014, 09:52 PM   #9
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Quote:
Originally Posted by AndrewT View Post
Kens mod is worth implementing, and measure what difference it may make.
And be careful not to touch the output terminals.

  Reply With Quote
Old 29th November 2014, 08:10 PM   #10
diyAudio Member
 
Join Date: Apr 2003
Location: Eastern Pennsylvania
Quote:
Originally Posted by Nelson Pass View Post
And be careful not to touch the output terminals.

A safer version of this mod, and which features the same PSRR performance, would be to move the output coupling cap. connection from the MOSFET's drain to the +65V rail, then connect the grounded speaker output terminal to the drain. This would reduce the exposed D.C. voltage to around 25V. I should have thought of doing it this way initially.
__________________
Ken

Last edited by Ken Newton; 29th November 2014 at 08:22 PM.
  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
PL84 schematic question. nonsuchpro Tubes / Valves 15 28th December 2013 12:13 PM
question about this schematic ? RobertE Analog Line Level 21 3rd November 2010 09:04 PM
Schematic Question zobsky Tubes / Valves 2 3rd July 2007 09:29 PM
schematic question impsick Solid State 2 25th April 2007 09:01 AM
a few question on this schematic Ahmad_tbp Solid State 21 7th March 2005 05:38 PM


New To Site? Need Help?

All times are GMT. The time now is 01:49 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2