I forgot important details in the above explanation. To remove my mistakes...

173.234.157.123

Posted by commentary on May 5, 2012 at 02:59:56

In Reply to: RE: another explanation... posted by commentary on May 4, 2012 at 22:02:08:

The fundamental passes with inversion on each stage, -10 being the gain of each stage.

The 2nd harmonic passes with DOUBLE INVERSION on each stage, thereby it is not inverted in effect through the stage generating that distortion. Let me explain. The first inversion is the polarity flip of the circuit stage itself, the next one comes from the polarities of what constitutes "positive 2nd HD" and "negative 2nd HD."

The triode common cathode circuit produces an inversion of a "negative 2nd HD." To illustrate this, a normal expected non-inverted 2nd harmonic distortion product has the positive cosine peaks of the fundamental coinciding with the positive cosine peaks of the 2nd harmonic. An inversion in the triode stage's distortion curve in the transfer function causes the opposite inverted distortion within it: the positive cosine peaks coincide with an inverted 2nd harmonic signal where the peaks of the positive fundamentals coincide with the peaks of the most negative 2nd harmonic signal output.

When you start with the fundamental of the first stage, the fundamental proceeds obviously as: +1 V => -10 V => +100 V.

The harmonic generated from the 2 triodes is thus: 0 => (1)(0.1)(-10)(-10) = +10 and an addditional (10)(0.1)(-10) just generated by the fundamental on the last triode stage alone = -10. Add the two and you get a complete cancellation.

It can be done by graphical calculations to show this to you better. The graph of Vpk vs. Vgk shows negative gain with the flat top of the bending curve for a straight line to appear flattened on the positive signal end and elongated at the negative going end. This one curve is mainly a 2nd order distortion.

Do this again a second time, doing fundamental gain and curvature of distortion from 2nd order, and this time the anode flattens the opposite polarity of the signal on the positive side. This is converting the 2nd to an odd order "square wave" type distortion. It takes away some harmonic richness for people who like it.

The effect can be taken to extreme with a strong signal generator and see it with a scope. Take a look at each stage. The input will be a nice sinewave, we hope. The input to the second stage will be a cut-off on the positive end of the scope (highest voltage) while an elongated sinewave feature will show on the negative going half-cycle. Finally backing off on amplitude, the output of the second stage will show cutoffs at a certain signal level input to have only one cutoff still, the final tube. Small signal distortion is less noticeable in normal use, but it counted to me.

The most problematic amp area with even order cancellation will probably be between driver and final output triodes. The signals start to get large and both these tubes can generate a great deal about the overall tone.

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Follow Ups Full Thread

Topic - Does any one feel vindicated by TAS' editorial? nt - HiFiOd 12:05:44 04/26/12 (41)

RE: Does any one feel vindicated by TAS' editorial? nt - RGA 18:06:29 05/01/12 (0)

Harley should have asked some designers before saying that. - Ralph 13:05:03 04/30/12 (0)

another commentary... - commentary 00:27:58 04/28/12 (28)

RE: another commentary... - dave slagle 23:43:06 04/28/12 (8)

RE: another commentary... - commentary 00:10:35 04/29/12 (7)

RE: another commentary... - Tre' 21:52:36 04/30/12 (6)

RE: another explanation... - commentary 22:02:08 05/04/12 (4)

RE: another explanation... - Tre' 09:53:43 05/05/12 (2)

RE: another explanation... - commentary 19:16:33 05/05/12 (1)

RE: another explanation... Editing all of "NEXT QUESTION" reply - commentary 19:38:21 05/05/12 (0)

I forgot important details in the above explanation. To remove my mistakes... - commentary 02:59:56 05/05/12 (0)

RE: another commentary... - TubeDriver 09:08:12 05/01/12 (0)

RE: another commentary... - Stuben 12:07:28 04/28/12 (18)

Type 50 Monos - vacuumtube1954 16:19:53 04/28/12 (16)

RE: Type 50 Monos - Stuben 04:39:08 04/30/12 (15)

RE: Type 50 Monos - vacuumtube1954 15:20:44 04/30/12 (1)

RE: Type 50 Monos - Stuben 17:14:34 04/30/12 (0)

RE: Type 50 Monos - vacuumtube1954 13:49:01 04/30/12 (3)

RE: Type 50 Monos - Stuben 17:27:23 04/30/12 (2)

RE: Type 50 Monos - vacuumtube1954 14:30:32 05/01/12 (1)

RE: Type 50 Monos - Stuben 15:00:15 05/01/12 (0)

RE: Type 50 Monos - drummerwill 08:53:45 04/30/12 (8)

RE: Type 50 Monos - Stuben 10:07:24 04/30/12 (7)

RE: Type 50 Monos - dave slagle 19:32:48 04/30/12 (0)

Don't Forgret The... - Gerry E. 10:50:53 04/30/12 (5)

RE: Don't Forgret The... - Stuben 11:26:53 04/30/12 (4)

RE: Don't Forgret The... - Sidewinder 17:25:51 04/30/12 (3)

RE: Don't Forgret The... - Stuben 15:07:14 05/01/12 (2)

Thanks. I'll wait for the files NT - Sidewinder 20:46:48 05/01/12 (1)

RE: Thanks. I'll wait for the files NT - Stuben 14:41:06 05/18/12 (0)

RE: another commentary... - SETdude 13:41:17 04/28/12 (0)

I think TAS' comments are now vindicated by the SET amp owners here. (: NT - commentary 00:19:09 04/28/12 (0)

Not really news. - mwhitmore 08:05:01 04/27/12 (1)

Ain'tcha smart! - HiFiOd 08:23:54 04/27/12 (0)

Rant - Frihed89 03:35:23 04/27/12 (0)

What did it say? nt - Salectric 16:15:37 04/26/12 (1)

RE: What did it say? nt - HiFiOd 09:39:21 04/27/12 (0)

RE: Does any one feel vindicated by TAS' editorial? nt - adaug 15:08:39 04/26/12 (3)

of course, Harley wasn't listening to just ANY ol' SET - triode 22:44:20 04/26/12 (2)

The whole M2.2 design is unlike most SET amps. - Timbo in Oz 23:49:14 04/27/12 (1)

no feedback adjustment on my ML2s - triode 10:20:57 04/28/12 (0)

Follow Ups

I forgot important details in the above explanation. To remove my mistakes... - commentary 02:59:56 05/05/12 (0)

I forgot important details in the above explanation. To remove my mistakes...

173.234.157.123

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