A question about Cathodyne/split load/concertina PI's - diyAudio
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 15th October 2005, 08:01 PM   #1
diyAudio Member
 
aletheian's Avatar
 
Join Date: Apr 2004
Location: Philly
Default A question about Cathodyne/split load/concertina PI's

I am trying to design an output stage with a minimal tube count. I have settled on the concertina splitter since it uses only one tube to so it's dirty work.

My problem is: I am having trouble visualizing I can inject NFB? Preceeding the splitter is a tone network that is fed from a cathode follower, and then a volume control, so I don't want to inject it into that stage since it will alter the foreward gain in the loop as the tone and volume controls are altered.

So I assume that I have to inject it into the concertina itself. I have drawn up a few variations. The .1uF capacitor I suppose is the culprirt in question.
Attached Images
File Type: jpg split1.jpg (70.8 KB, 508 views)
__________________
Heghlu'meH QaQ jajvam!
  Reply With Quote
Old 15th October 2005, 08:03 PM   #2
diyAudio Member
 
aletheian's Avatar
 
Join Date: Apr 2004
Location: Philly
Default Here is the second option

A variation.
Attached Images
File Type: jpg split2.jpg (69.1 KB, 414 views)
__________________
Heghlu'meH QaQ jajvam!
  Reply With Quote
Old 15th October 2005, 08:06 PM   #3
diyAudio Member
 
aletheian's Avatar
 
Join Date: Apr 2004
Location: Philly
Default Another permutation

Here is the third option
Attached Images
File Type: jpg split3.jpg (71.7 KB, 392 views)
__________________
Heghlu'meH QaQ jajvam!
  Reply With Quote
Old 15th October 2005, 08:09 PM   #4
diyAudio Member
 
aletheian's Avatar
 
Join Date: Apr 2004
Location: Philly
Default Last try

Here is the final thought
Attached Images
File Type: jpg split4.jpg (70.5 KB, 395 views)
__________________
Heghlu'meH QaQ jajvam!
  Reply With Quote
Old 15th October 2005, 08:27 PM   #5
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
Be much easier to just use a LTP. The LTP has both inverting and non-inverting inputs, so there's a natural summing node for NFB. Since types like the 12A*7 series, the 6BQ7, etc. are all dual tridoes, the tube count doesn't change.

FWIW: avoid the 12AU7A. That one has horrible linearity and more distortion than you want.
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 15th October 2005, 08:33 PM   #6
diyAudio Member
 
aletheian's Avatar
 
Join Date: Apr 2004
Location: Philly
Unfortunately, I am using the other half of the 12au7 for the preceeding stage cathode follower, that's why I went with concertina instead of LTP. I thought about subbing in a 12ax7 or 12at7 for the 12au7, but I'll deal with that later. It is the NFB that has me stumped.

Thanx
__________________
Heghlu'meH QaQ jajvam!
  Reply With Quote
Old 15th October 2005, 09:43 PM   #7
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Negative feedback works by trading off gain for distortion/bandwidth/impedance. The problem is that your circuit has no gain to start with...

It's difficult-to-impossible to feedback to a split-load; generally, the split-load is driven by a gain stage and the feedback is brought back to that stage.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 15th October 2005, 09:48 PM   #8
diyAudio Member
 
Miles Prower's Avatar
 
Join Date: May 2005
Location: USA
Blog Entries: 6
If you have to go with the cathodyne, then your best bet would probably be something like what I attached. With the cathodyne, you really don't have a second input for the NFB summing node. So try something like the inverting connection that you'd use with an op-amp. In this case: Avcl= Rf/Rs (or close to it).
Attached Images
File Type: jpg split1.jpg (40.3 KB, 434 views)
__________________
There are no foxes in atheistholes
www.dolphin-hsl.com
  Reply With Quote
Old 15th October 2005, 10:03 PM   #9
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
BTW, when you revise the circuit, make sure that the lower output is taken from the top of the load resistor, not from the load plus cathode resistor.
__________________
You might be screaming "No, no, no" and all they hear is "Who wants cake?" Let me tell you something: They all do. They all want cake.- Wilford Brimley
  Reply With Quote
Old 15th October 2005, 10:11 PM   #10
diyAudio Member
 
aletheian's Avatar
 
Join Date: Apr 2004
Location: Philly
Quote:
Originally posted by SY
BTW, when you revise the circuit, make sure that the lower output is taken from the top of the load resistor, not from the load plus cathode resistor.

I have seen them noth ways, with the signal coming off the junction of the loadresistor/cathode resistor, and with the signal coming off the junctuin of the cathode trsistor/cathode.

Is there a benefit in doing it the other way? Possibly an impedance issue that I am missing?
__________________
Heghlu'meH QaQ jajvam!
  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
How to figure gain on split-load with positive feedback? GordonW Tubes / Valves 4 21st May 2008 05:24 PM
Cathodyne Phase Inverter question woody Tubes / Valves 3 23rd July 2007 06:43 AM
Fourier transforms (split from 25W class A into 1 ohm resistive load) Steve Eddy Everything Else 20 20th April 2004 03:12 PM
Differential amp, Long tail, Split load - what difference in sonics? arnoldc Tubes / Valves 3 1st February 2004 11:23 PM


New To Site? Need Help?

All times are GMT. The time now is 02:03 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