Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 9th November 2010, 10:12 PM   #111
AKSA is offline AKSA  Australia
diyAudio Member
 
Join Date: Sep 2001
Location: Melbourne, Australia
Folks,

Has anyone done a cap coupled SE OTL?

Any circuits around?

Now there's a flavour......

Hugh
__________________
Aspen Amplifiers P/L (Australia)
www.aksaonline.com
  Reply With Quote
Old 9th November 2010, 10:15 PM   #112
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Quote:
Originally Posted by sepolansky View Post
1) Is not the feedback dependent on the volume pot setting? The 34k seems to be in series with the shunt portion of the volume pot from the perspective of the series feedback resistor.
Yes, it is. That's why applying the NFB in that manner is not viable unless the input is buffered. You can get away with it when using op-amps since the Zo of an op-amp is quite low. Otherwise, changing the volume changes the gNFB. Not good.

Quote:
2) Why is it necessary to have the 1uF and 34k resistor series connected then paralleled with the 1M resistor in the unused grid circuit? If differential input is never to be used, cannot that grid simply be shorted to ground?
It's not necessary unless you need to float the grids above DC ground.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 9th November 2010, 11:27 PM   #113
banat is offline banat  Serbia
diyAudio Member
 
Join Date: Dec 2009
Location: near Belgrade
Quote:
Originally Posted by AKSA View Post
Folks,

Has anyone done a cap coupled SE OTL?

Any circuits around?

Now there's a flavour......

Hugh
See the post #11 at this thread:6C33C OTL DC schematic needed

Good Luck
  Reply With Quote
Old 10th November 2010, 11:23 AM   #114
diyAudio Member
 
sepolansky's Avatar
 
Join Date: Nov 2007
Location: Maryland
Quote:
Originally Posted by Miles Prower View Post
Yes, it is. That's why applying the NFB in that manner is not viable unless the input is buffered. You can get away with it when using op-amps since the Zo of an op-amp is quite low. Otherwise, changing the volume changes the gNFB. Not good.



It's not necessary unless you need to float the grids above DC ground.
Thanks Miles,

Kind of what I thought.

Stuart
  Reply With Quote
Old 10th November 2010, 12:15 PM   #115
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
Quote:
Originally Posted by sepolansky View Post
Man do I know how to shut down a thread or what?
Hehe. I seem to have the same effect more often than not

There are a few things I don't like in this circuit which stopped me from further consideration to build one (and following this thread)...NFB looping over two gain stages, high ohm resistors in series with signal, cap at input, 12AX7, EF86, and probably some more if Im in the mood.

The unused input probably has the components equal the used input b/c that's wise in SS where leakage will create unessesary offsets if not equal. I recon the designer is primarily an OPAMP guru...Oh now I'm about to step on some toes...gotta stop...

Saying all this neg I must add I appreciate unusual designs, and Tim Mellow deserves kudos for that. But I'll stick to my own OTL design.
  Reply With Quote
Old 10th November 2010, 12:54 PM   #116
diyAudio Member
 
Join Date: Dec 2004
Location: NE USA
Quote:
Originally Posted by SemperFi View Post
Saying all this neg I must add I appreciate unusual designs, and Tim Mellow deserves kudos for that. But I'll stick to my own OTL design.
SemperFi

Can you point the way to you own OTL design. I love glass houses
  Reply With Quote
Old 10th November 2010, 01:50 PM   #117
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
Quote:
Originally Posted by desperateaudio View Post
SemperFi

Can you point the way to you own OTL design. I love glass houses
Sure.

Here is a version...I like the possibilities current mirrors give, and to me the pros outweigh the cons. (No capacitor, wideband response, gain and bias (of the output tubes) in one, load resistors placed at any voltage level, etc)

For simplicity only a single 6AS7 is shown, and for simulations the load is 32ohms. 4 tubes in parallel is fine for 8ohms.
Many think the cathode resistance in the output is too high, but I've tested and believe it both sounds better, and provides better harmony between the parallel tubes.

The mirrors can be modded in all kinds of ways, cascoded, wilson style, base drive with another pnp's emitter to the mirror bases, etc etc.

The load/gain resistors can be varied without any change in distortion, just gain. U can experiment with various values for max symmetry, but I cannot hear distortion if it is slightly off, since it's all benighn second order.

The bias is adjusted with a potentiometer in series with the LTP tail resistor.

Btw, do u know why a CCS in the tail of the PI is actually worse in this circuit?

Cathode followers driving the output helps increase power, obviously, but I prefer the sound of the lesser powered CF-less version.

I don't use NFB, R13 is not there, but if u like, R13 can be up to 2kohms...actually, u decide, it can be any value...
Attached Images
File Type: jpg OTL_2.JPG (46.9 KB, 511 views)

Last edited by SemperFi; 10th November 2010 at 01:53 PM. Reason: Forgot to mention R13....
  Reply With Quote
Old 10th November 2010, 02:23 PM   #118
diyAudio Member
 
Join Date: Jan 2002
Location: nowhere
Thought I'd mention...I have been building this type (totempole) OTL the last 10years, but have finally decided to build a circlotron. I like the symmetry at the output...I will of course mod the Atmasphere circuit and use my mirror and DC couple thru out...Unfortunately time is not abundant as usual, so I don't expect anything finished in a while.
  Reply With Quote
Old 10th November 2010, 03:18 PM   #119
dwhitf is offline dwhitf  United States
diyAudio Member
 
Join Date: May 2008
Send a message via Skype™ to dwhitf
Talking 12ax7 to russian 6n2p-ev

How about tube rolling? maybe a 6n2p-ev instead of the 12ax7.
Darrell
Attached Images
File Type: gif rb6n2pcv.gif (14.4 KB, 492 views)
  Reply With Quote
Old 10th November 2010, 03:28 PM   #120
diyAudio Member
 
Join Date: Dec 2004
Location: NE USA
Quote:
Originally Posted by SemperFi View Post
For simplicity only a single 6AS7 is shown, and for simulations the load is 32ohms. 4 tubes in parallel is fine for 8ohms.

Nice,

I will probably have several questions but for now my main question is how did you deal with your 6AS7 matching since so many of those tubes just do not have matched triodes in the same envelope?
  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
OTL design recommendation? (6C33C maybe?) arteitle Tubes / Valves 14 16th January 2012 03:37 PM
6C33C OTL DC schematic needed neazoi Tubes / Valves 29 25th June 2010 04:25 PM
Custom designed transformer for Andrea Ciuffoli 6c33c OTL AMP.... zxcxz Tubes / Valves 2 10th July 2009 04:14 PM
Transformer for 6C33C OTL WALTER BURKHARD Swap Meet 1 29th June 2003 10:06 AM
Availability of 6C33C tubes? I need some for OTL amps tubetvr Tubes / Valves 39 31st January 2003 08:21 PM


New To Site? Need Help?

All times are GMT. The time now is 04:47 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