Long tail vs cathodyne phase inversion... in non-technical terms.

[Che_Guitarra]

Ah yes... this old chestnut once again.

I've read a good bunch of threads on this. Many do a magnificent job of explaining electronic and circuitry differences. I can find technical definitions, expert opinions, graphs demonstrating points, component value suggestions. On the other hand, very few of these threads do a great of explaining the audible differences between LT and cathodyne PIs... brief and/or limited descriptions, not a single audio example, not a single video example. Bummer.

There's no point trying to compare a Princeton to a SLO100, so let me establish a comparative context.

1. A Deluxe Reverb. Assuming all other components are exactly the same, what would be the audible differences if one were built with a cathodyne PI, compared to a stock DR with a LTPI?
2. A JCM800. Assuming all other components are exactly the same, what would be the audible differences if one were built with a cathodyne PI, compared to a stock 2204 with a LTPI?
3. A Tweed Deluxe... for the sake of an example amp that is inherently cathodyne. Assuming all other components are exactly the same, what would be the audible differences if one were built with a LTPI, compared to a stock cathodyne PI?

If you have the gift of elaboration, and an ability to avoid terms such as B+, zero gain unity, grid stopper, triode oscillation coefficient of even-order harmonic artefacts... please help to turn my 144p picture quality of LT vs cathodyne into something a little closer to HD.

 

[tubejockey]

In every instance the audible difference will be less power tube drive with a cathodyne. However it obviously frees up a triode.

 

[jhundt]

I have a Princeton Reverb that has been modified with a Deluxe Reverb power transformer and an Allen TO26 output transformer. The rest of the circuit is almost completely original. This has a cathodyne PI.

I also have a Princeton Reverb II which I modified by removing much of the excess bells-and-whistles. It is now very similar to a Princeton Reverb, but with a long-tail inverter similar to a Deluxe Rev. This amp also has a TO26 output transformer.

There are still too many variable between the amps to consider them identical. The PRII has lower plate voltage for one thing. But they are close. The PR currently has an old 12" V30 Celestion, while the PRII has a Jensen Neo 100; I have swapped these speakers around sometimes. Here's what I think:

The cathodyne Princeton sounds great, the long-tail PRII just sounds a little bit better. There is a deeper, rounder sound, a very noticeable 3-dimensional quality that the other amp doesn't offer. Next to the PRII, the Princeton sounds more two-dimensional and in-your-face.

I play with no effects or distortion devices. I like chords and open-string voicings, long notes. Maybe like the Shadows from the 60's (though I don't really play that material) I don't play over-drive lead guitar, and I do not want a bunch of amp and/or speaker break-up.

My last regular group was a classic-rock cover band, I played rhythm guitar behind a very busy lead player. The Princeton (with modified transformers) sounded very good there. I think that in most live situations, the difference between the amps would not be significant to the audience. Perhaps the less-developed sound of the Princeton even works better in a group.

But if I was playing in studio for a recording, or in a small intimate setting, I would certainly choose the richer, rounder sound offered by the long-tail PRII amp.

But remember - the difference may be due to other details too. This is just my experience.

 

[robrob]

The clean tone of the two phase inverters will be very similar if their outputs are similarly balanced (more imbalance = more harmonic distortion and a fatter clean tone).

The Long Tail Pair will typically have better overdrive tone (the LTP itself being overdriven). A cathodyne phase inverter can get funky when overdriven too hard.

The LTP will hit the power tubes harder (due to phase inverter gain) so you can get more power tube distortion--this is usually a good thing.

 

[Old Tele man]

EVEN order harmonics (2, 4, etc.) reinforce the fundamental, making it sound fuller...but also muddier.

ODD order harmonics (3, 5, etc.) turn a smooth sinusoidal wave into 'peaky' sawtooth or triangular waves, making it sound harsh and distorted.

 

[FenderLover]

If both circuits are balanced and perfect, there is no difference in sound. Clean is as clean as clean can be. However, the long tail offers gain, the cathodyne does not. It's ultimately a function of what you are after, in terms of gain and overdrive.

In your questions above:
1 - less gain
2 - less gain
3 - you'd have a Brownface Deluxe (more gain)

 

[FenderLover]

EVEN order harmonics (2, 4, etc.) reinforce the fundamental, making it sound fuller...but also muddier.

ODD order harmonics (3, 5, etc.) turn a smooth sinusoidal wave into 'peaky' sawtooth or triangular waves, making it sound harsh and distorted.

Even harmonics are a high frequency thing, 'muddy' is a low frequency thing.

Even harmonics turn a sine wave into an asymmetrical sine wave, odd order turns a sine wave into square waves.

Sawtooth and triangular are characteristic of a violin, which a guitar aspires to be on a good day.

 

[Old Tele man]

Even harmonics are a high frequency thing, 'muddy' is a low frequency thing.

Even harmonics turn a sine wave into an asymmetrical sine wave, odd order turns a sine wave into square waves.

Sawtooth and triangular are characteristic of a violin, which a guitar aspires to be on a good day.

The even harmonics reinforce (add to) the fundamental, fattening it, making it loose brightness, which is muddiness.

• square wave is an infinite summation of ODD harmonics added in-phase.
• triangular wave is an infinite summation of ODD harmonics added out-of-phase.
• sawtooth wave is an infinite summation of BOTH even & odd harmonics.

 

[robrob]

Harmonics will be present above and below the fundamental frequency so the added lows can add mud.

 

[FenderLover]

Harmonics will be present above and below the fundamental frequency so the added lows can add mud.

Harmonics are above the fundamental, intermodulation products are below the fundamental. Circuit specifics allow or suppress either.

 

[FenderLover]

The even harmonics reinforce (add to) the fundamental, fattening it, making it loose brightness, which is muddiness.

Intermodulation adds muddiness.
Doubling (second order) and quadrupling (fourth order) of a frequency is brightness and ice pick.

Infinite summation doesn't mean much when the components are down 20,40,60 dB.

 

[Old Tele man]

Intermodulation is the sum, the difference and two original frequencies.

The word HARMONIC explicitly defines even/odd ratios.

 

[FenderLover]

Intermodulation is the sum, the difference and two original non-frequencies.

The word HARMONIC explicitly defines even/odd ratios.

Did I disagree? Posting definitions is not what the OP was asking. You are not applying the application of the definitions. Start a new thread.

 

[Old Tele man]

Did I disagree? Posting definitions is not what the OP was asking. You are not applying the application of the definitions. Start a new thread.

Snip from OP's post: "...triode oscillation coefficient of even-order harmonic artifacts..."

 

[FenderLover]

Snip from OP's post: "...triode oscillation coefficient of even-order harmonic artifacts..."

LOL!!

You deliberately excluded, "and an ability to avoid terms such as..." preceding you quote...

 

[Old Tele man]

Simply working backward from "...a picture is worth a thousand words..." to THE words defining extraneous sonic creation/demotion within electronic circuits such as the LTP...ie: what 'comprises' deviation from sine to distorted tones...without using Fourier.

Knowing what comprises something provides insight into what causes & effects it.

 

[Bendyha]

A long tail pair will tend to have a gain of somewhere around 53 using two halves of a 12xx7 tube
A Cathodyne is normaly accompanied by a driver, again using two halves of a 12xx7. It will then have a gain of somewhere around 75. So the cathodyne will be louder, more sensitive to a given input.

That said, the output of the cathodyne triode is doing the whole job with the power supply, whereas the LTP triodes are both doing half the job with the whole power supply.
This means that the LTP will not be as loud with a small imput, but given a large input, it will be able to amplify it, wheras the cathodyne will have reached its limits.

That said, if you are driving 6V6 or EL84 output tubes, the cathodyne (if the power supply is designed to allow) will be able to deliver more than enough output to heavily overdrive them. If you are driving 6L6 or EL34, this may not be the case.

That said, it all depends very much on whats happening around the phase inverter, it is just one part of a circuit that was designed to deliver the small output of the guitar, to be a voltage swing suitable for driving the speaker in the cab. So how the phase inverter will sound will depend upon so many things, that inter-relate, and should be matched up.
You could just do a direct swap, and be very unhappy with the results, but that would not be a wise amp modification, because with just a few additional well planned tweaks, the addition or swapping out of a few resistors and maybe caps, and out of the unsatisfactory swap, you might well end up with a sonic result that you will love.

 

[amp-shark]

I got this thread researching the Marshall SL5, which is a single EL34 output valve fed by a cathodyne phase inverter.

Apparently it is a departure from Marshall’s typical LTP. Its adherents rave about its sensitivity dynamics and ability to let the unique individual character of each individual axe shine through.

Interesting to note lots of tube amp gurus preach simplicity of circuit for maximum tone and response, me wonders what Ken Fischer would say here? Can anyone tell me about Dr. Z - some of his designs must flirt with cathodyne vs LTP??

LOL why is resurrecting an old thread something to apologize for? THANK YOU gifted and kind TDPRI contributors!

God Bless America

HAPPY NEW YEAR!!!

 

[NTC]

That said, if you are driving 6V6 or EL84 output tubes, the cathodyne (if the power supply is designed to allow) will be able to deliver more than enough output to heavily overdrive them. If you are driving 6L6 or EL34, this may not be the cas

It all depends on the circuit design. See the Sunn 2000s Bass amp. https://el34world.com/charts/Schematics/files/Sunn/Sunn_2000s.pdf

A cathodyne drive 4x 6550"s. I have measured 110 watts out of mine before it distorts much. Haven't tried to drive it to distortion while playing - too loud and I don't have enough speakers. Plus, it is a bass amp.

Since we are talking about phase inverters, how does a paraphase inverter's sound compare? It just seems to be teo gain stages where the sugnal to the second is attenuated from the first in an attempt to match the two amplitudes driving the output tubes.

 

[Bendyha]

I got this thread researching the Marshall SL5, which is a single EL34 output valve fed by a cathodyne phase inverter.

The SL5 is a single ended amp, and therefor does not have, or need, a phase inverter. I admit at fist glance at the schematic the driver tube has been drawn-up to look a bit like it is set-up as a cathodyne, but that is only the negative feedback from the output transformer that is injected into the cathode of the driver over the biasing resistor. The cathodyne would always have an equal bias load on the cathode as on the plate, whereas here we have 82k plate and 12,2k on the cathode....but the 10k is parallel to the resistance on the output transformers secondary, which won't be much, making the total not that much different to a normal gain stage.