TGM amp goes 'tubey' - 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 13th June 2010, 12:43 AM   #1
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
Default TGM amp goes 'tubey'

I know some people don't like this kind of messing around with perfectly good SS amplifiers but it was too tempting to pass-up - and so I'd like to recommend you give it a try too

There has been much chat over the benefits of tubes for their sound. An infamous paper by Russell Hamm was one of the early attempts to explain it in terms of the harmonic profile.

Here's an extract for a 2 stage triode amplifier. Key things to note:

Low Power: the output starts off mostly as H3 at low power with H2 and H4 close behind.

Medium Power: Overall distortion heavily dominated by H2 then a strong H3 followed by H4;H5 and above remain small.

High Power: dominated by H2, some H4 with H3 falling off. H5 and above remain small.
Attached Images
File Type: jpg RHamm_2stageTriode.jpg (31.6 KB, 741 views)
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 13th June 2010, 12:46 AM   #2
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
I wondered how to achieve this with my TGM amplifier. The first version TGM1 used a resistor to feed some of the output to the top of the LTP resulting in some self-modulation of the signal which creates plenty of H2 and some H3 [TGM Amplifier ?]. But the results became muddy at higher power. Too little injected distortion and it wasn't noticeable, too much and it was nasty.

TGM2 uses a CFP for the LTP and doesn't respond to self-modulation [TGM2 amplifier]. So I created some asymmetry in the feedback loop by taking a little feedback from the emitter of an output device instead of at the junction of the two output emitter resistors.

TGM2 was a little less musical than I had hoped so perhaps this change will help.
Attached Images
File Type: jpg TGM2_tubey.jpg (244.7 KB, 759 views)
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

Last edited by Bigun; 13th June 2010 at 12:49 AM.
  Reply With Quote
Old 13th June 2010, 02:22 PM   #3
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
Simulated results that Hamm would appreciate:

I've built this version and it sounds very good indeed. The bass is strong, the highs are clear. The mids are very smooth, if a little darker and overall it's one of the first SS amps that I've heard that has zero traces of fatigue.
Attached Images
File Type: jpg TGMtubeyFFT.jpg (44.5 KB, 693 views)
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 13th June 2010, 07:25 PM   #4
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
Cool. How did you produce that distortion graph? And I'd also like to see this paper if possible...

What about high order even harmonics though? It seems to me that high order harmonics would be produced during switching. Nevermind, this would surely show up in harmonics up to the seventh...

- keantoken

Last edited by keantoken; 13th June 2010 at 07:29 PM.
  Reply With Quote
Old 13th June 2010, 07:59 PM   #5
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
The distortion graph ? - just throw the answers from spice into a spreadsheet

The infamous Hamm paper is here (and it's contested by some people of course so don't take it as gospel):

http://www.amplificadores.com.br/Tex...istors%20I.pdf

Yup there will be higher order harmonics, not just because it's Class AB but because it has gnf. It's a compromise of course, but sounds good and easy to try.
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 13th June 2010, 09:17 PM   #6
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
FFT at 6V p-p into 8R
Attached Images
File Type: jpg TGM2TubeyFFT.jpg (344.7 KB, 583 views)
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 13th June 2010, 10:35 PM   #7
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
Very nice, Bigun! You discovered a cheap modification while I was off in the corner messing the NTP. The NTP has its merits, but I'm swayed. This should serve as a nice modification to many class AB amplifiers existing already.

- keantoken
  Reply With Quote
Old 14th June 2010, 01:46 AM   #8
Bigun is offline Bigun  Canada
diyAudio Member
 
Bigun's Avatar
 
Join Date: Jan 2009
Blog Entries: 2
The TGM tubey approach can only add distortion so it's limited to amps that are low THD to begin with. It helps out with Class AB that rely on a reasonable amount of gnf to keep their output stages under control and it sounds very good.

Your NTP is probably a better approach because it generates a good profile with low distortion to start with.
__________________
"The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.
  Reply With Quote
Old 14th June 2010, 05:13 AM   #9
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
Bigun, I've tried several times to reply to your post but for some reason I simply have not found an appropriate response.

Let's just say your blameless statement has thrown my brain into deep saturation negotiating and cataloging what things would change were we to switch between NTP and LTP. For me at least, it is not a trivial change.

What I can say is that I suspect net THD might decrease and I also think the spectrum would be more benign. I think the only way to know for sure is to simulate or build, since it depends on the implementation...

Could you post simulation files?

- keantoken
  Reply With Quote
Old 14th June 2010, 05:57 AM   #10
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
NTP has more H2 and H3 distortion than an LTP. Overall, the thd of the NTP, I have found, is higher, though more benign.

It is better at high amplitude than the LTP, which because of the S shaped transfer function tends to compress yielding high order odd harmonics.

Anthony, does this resolve your cerebral dilemma?

Hugh
__________________
Aspen Amplifiers P/L (Australia)
www.aksaonline.com
  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
Make it sound tubey !!! darkfenriz Solid State 58 3rd August 2004 09:50 PM


New To Site? Need Help?

All times are GMT. The time now is 08:53 AM.


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