phase splitter issue - Page 51 - 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 11th December 2011, 10:20 PM   #501
diyAudio Member
 
Join Date: Nov 2011
Well, then, are you going to reveal it to me? I'm not a mind reader (my mother's favorite expression.)

And let's not forget I'm going down your chosen path. When are you going to respond to what the current mirror circuit tells you about your flawed rise time analysis?
__________________
"It is error only, and not truth, that shrinks from inquiry." - Thomas Paine
  Reply With Quote
Old 12th December 2011, 12:54 AM   #502
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
Equal loads. Balance is a consequence of boundary conditions, not a "given."
__________________
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 12th December 2011, 10:36 AM   #503
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Q1: How do you measure output impedance of a balanced cathodyne?
Subsidiary question Q1a: How do you measure output impedance?
A1a: By changing the load impedance and seeing how the voltage varies.
Subsidiary question Q1b: How do you maintain a balanced cathodyne?
A1b: By ensuring the same load at both output ports.
A1: By changing both load impedances at the same time and seeing how the voltage varies.

Q2: What do I mean by the output impedance of a balanced cathodyne?
A2: The impedance I would use as the upper part of a potential divider or RC low pass filter in order to calculate the gain or frequency response of a balanced loaded cathodyne.

Q3: Isn't this just half the differential output impedance of a balanced cathodyne?
A3: You might choose to call it that - if you place twice the load on twice the impedance you get the same gain and frequency response. Balance means that the centre-point of the doubled impedance can be grounded, as it is already at ground potential anyway.
  Reply With Quote
Old 12th December 2011, 12:30 PM   #504
diyAudio Member
 
Join Date: Nov 2011
Your mission, should you accept it Jim, is to apply your boundary conditions without violating Thevenin's theorem. Take me through it, step by step.

When are you going to respond to what the current mirror circuit tells you about your flawed rise time analysis?
__________________
"It is error only, and not truth, that shrinks from inquiry." - Thomas Paine
  Reply With Quote
Old 12th December 2011, 12:35 PM   #505
diyAudio Member
 
Alfred Centauri's Avatar
 
Join Date: Jul 2007
Location: Metro Atlanta, Georgia
DF96:

Q1c: Can the individual output impedances be measured by changing both load impedances at the same time?

A1c: No, unequivocally no. Thevenin's Theorem is clear on this and Chris' LTE circuit unambiguously demonstrates this. There is no rational doubt possible. Whatever it is you measure, it is not the individual output Thevenin impedances.

The outputs of Chris' circuit, by inspection, have vastly different Thevenin impedances and yet, by "ensuring the same load at both output ports", you might incorrectly infer that the outputs have equal Thevenin impedances.

To maintain that it is possible to measure the individual output Thevenin impedances while varying both loads is to dispute one of the most elementary, fundamental results in circuit theory.

Guys, stop trying to fit square pegs into round holes. All the word play in the world isn't going to change reality.
  Reply With Quote
Old 12th December 2011, 12:38 PM   #506
diyAudio Member
 
Join Date: Nov 2011
You can measure the impedance between the p-k by varying a load connected between p&k, the center point of which is ground. This is why the identical grounded loads in a Cathodyne look like a single (differential) load between the p&k.

I believe I agree with what you say, as long as you are talking about the impedance between the p & k (the differential output impedance of the balanced Cathodyne) and not the impedance from p to gnd or k to gnd.

Your treatment is different from what SY says - that the p to gnd and k to gnd impedances are 1/gm.
__________________
"It is error only, and not truth, that shrinks from inquiry." - Thomas Paine
  Reply With Quote
Old 12th December 2011, 12:50 PM   #507
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
I have always been careful to accept that if you measure the output impedances individually then you get different results. That is not in dispute.

As far as I remember, SY's main practical point is that it is incorrect to include a cathode build-out resistor. I think you accept that? If so, we probably are arguing about the meanings of words rather than the design of circuits.
  Reply With Quote
Old 12th December 2011, 12:57 PM   #508
Merlinb is offline Merlinb  United Kingdom
diyAudio Member
 
Merlinb's Avatar
 
Join Date: May 2006
Location: Lancashire
Quote:
Originally Posted by DF96 View Post
we probably are arguing about the meanings of words rather than the design of circuits.
This was my feeling all along...
  Reply With Quote
Old 12th December 2011, 03:37 PM   #509
diyAudio Member
 
Join Date: Nov 2011
Merlinb, DF96, just to be clear, I believe that if I start with an unloaded Cathodyne, with equal plate and cathode resistors, I can measure 3 impedances: P-K, P-Gnd and K-Gnd. Assuming an AC grid voltage is applied, I can measure the impedances of each pair of nodes by dividing the open circuit voltage difference between the two nodes by the current that flows between them when I short the two nodes together (of course I would use a large capacitor as an AC short for this test so as not to unbias the triode from normal operation.)

The results of these tests are that Zp-k is a bit less than 2/gm, Zp-gnd is a little less than the plate resistor and much larger than Zk-gnd, which is a bit more than 1/gm. In our Letters to the Editor in Linear Audio, Mr. Vogel and I give identical exact results for these parameters.

SY disagrees. He says Zp-gnd = Zk-gnd = about 1/gm.

This is more than just a difference about the meanings of words.

Certainly, SY has correctly championed the point that you should not add a build-out resistor to the cathode that you don't add to the plate. He recently pointed out that problems due to grid current drawn during overload conditions can be ameliorated if equal value resistors are added as P & K build-outs, and again I agree. This is particularly helpful for the low impedance cathode to limit the current available to charge the grid coupling capacitor. I'm not sure that SY would agree with that last sentence, but it can be easily confirmed that the overload characteristics of the P & K are different.

With the bove explanation, do you still think this is just about the meaning of words?
__________________
"It is error only, and not truth, that shrinks from inquiry." - Thomas Paine
  Reply With Quote
Old 12th December 2011, 04:12 PM   #510
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Quote:
Originally Posted by CPaul View Post
janneman, I agree that you can use 5K and 10K loads to test impedanaces - you don't have to use open and short circuits.

But look at Thevenin's theorem. Wikipedia actually has a good presentation. The test is about two nodes and two nodes only. There is no room in the theorem for tests involving three nodes. Thevenin doesn't know and doesn't care about SY's "boundary conditions." Thevenin's theorem applies to any two nodes in any linear circuit. No special cases; no special pleading.

Whenever SY does a test with three nodes, he automatically violates Thevenin.
He doesn´t do a test with three nodes. He tests two nodes. But why can't he just test two Thevenin sources at the same time? You short TWO thevenin sources, and you MUST do that because the claim says: 'IF the two loads are the same...' so you need to test the two sources at the same time in the same way, infinite load or short circuit.
So you short the two nodes of one source, and the two nodes of the other source. Then you see that two nodes actually are the same so you end up with several nodes (three) connected all together. Well, that may look curious at first sight but it doesn't change anything, thevenin still holds. Why wouldn't it?

OTOH, Chris´ current source circuit in his last LTE does bother me....

jan
__________________
I won't make the tactical error to try to dislodge with rational arguments a conviction that is beyond reason - Daniel Dennett
Check out Linear Audio Vol 7!

Last edited by jan.didden; 12th December 2011 at 04:16 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
Phase Splitter Help famousmockingbird Tubes / Valves 16 10th May 2011 09:40 PM
Phase splitter Hojvaelde Tubes / Valves 9 6th May 2011 07:32 PM
phase splitter grungeman91 Tubes / Valves 2 5th May 2011 01:58 AM
Need help on phase splitter guwakzhai Power Supplies 7 23rd December 2010 05:51 PM
Phase Splitter Name Gold_xyz Tubes / Valves 17 21st February 2008 09:48 AM


New To Site? Need Help?

All times are GMT. The time now is 02:26 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