Phase inverter tone : Sweeter clean or sweeter distortion ?

[d l x r e v e r b]

Comments about the phase inverters in amps often say a split load (cathodyne) circuit as "sweeter" and more musical sounding than a long tail circuit.

Are players referring to the clean tone or the distortion tone ?

Is there any difference in the clean tone between these two phase inverter designs , or is the difference mainly when driving the amp to distortion ?

[diagrammatiks]

usually the phase inverter is the last thing to break up if it ever breaks up at all.

[zenitB]

Clean tone or distortion tone? It is kind of both. To my ears a 5C3 with its paraphase inverter is warm, woody, has lower headroom and is lower powered than a blackface with its long tailed pair. The BF has more power, more headroom and those glassy cleans that Blackfaces are known for.

[leofenderbender]

Both.

It is part of the power section in a push-pull configuration; all of the signal goes through it, so it has to impact tone in some way, whether the tone is clean or distorted.

I'd save my money for the best V1 tube I could find and not bother with a particular kind of PI tube or a perfectly balanced one - if that is your question.

[Science Amps]

IME, most phase inverters sound very similar until overdriven, at which point their individual character comes out. Diagrammatiks is right, but if you have a non-master volume amp, or an amp with a post phase inverter master, you're definitely gonna hear the PI when you crank it up.

So I think maybe people are referring to the overdriven qualities, however I wonder how many people have A/B'd PI's in the same circuit back to back and said, "Hey, that's sweeter!" The PI probably has something to do it, but they say in guitar amps 'everything affects everything', and so it's probably just one part of the 'sweet' pie.

[slagg]

I see NFB playing a huge roll in the PI too.

[d l x r e v e r b]

Original poster checkin' in again ,

I play a Gibson 335 through a blackface Deluxe Reverb amp which was the amp recommended to me a long time ago by several experienced guitarists as best for that guitar. I play mainly clean and with only a lightly overdriven tone.

Reading these forums I have seen comments about the cathodyne (split load PI) as being "sweeter and more musical" than amps with the long tail PI.

Deluxe Reverb is long tail, Princeton is cathodyne , implying Princeton is a sweeter more musical sounding amp.

I got to wondering if the forum comments referring to PI tone were about the clean or the crunch, and why the blackface DR rather than the blackface Princeton was so much more widely suggested to me for the Gibson 335.

[slagg]

To me the cathodyne Pi breaks up quicker and gets kinda nasty when driven too hard.Some don't like the "raspy" breakup,but I do.

[schmidlin]

Good discussion.

IMHO, those PIs sound very much the same in non-clipping mode. The gloves come off when sent into clipping: I'm talking about non-MV/standard tube amp distortion here. The PIs breaking up defines what kind of distortion you will hear. It's not the power tubes, it's the PI. Power tubes each have their own EQ, a filter of sorts. But if you show me a PI design and the voltages, I know exactly what it will sound like overdriven.

The cathodyne falls apart more when overdriven and in wonderful ways...some call that musical, some prefer the added chunk of the long-tail. Other PIs add even more chunk.

That said, many great hi-fi amps use cathodyne PIs, the venerable Dynaco ST-70: great amps. Come to think of it, not sure if I have seen a LTP hi-fi amp, hmm...

Anyway, "musical" is subjective. May as well debate over the *best* color. Try 'em all and decide for yourself. Keep us posted.

[smolder]

Doing the 'paulc' mod to my Princeton reverbs gave them a smoother break up. I'm not sure about 'sweet', but I've heard that described as more even order harmonics than odd order. I've just stepped past my compitant knowledge on the topic.

[TweeDLX]

I recently spent several weeks trying to make a (Fender style) circuit with a cathodyne PI (http://i274.photobucket.com/albums/jj257/paintrdude/Dee-zaster-2.png) sound good with dirt pedals. I finally gave up on using that PI because I couldn't make it happen. Just sounded raspy no matter wehat I tried. It sounded absolutely wonderful on its own (no pedals), which made it all the more frustrating...
Someone more capable than I might have resolved this issue.

[phsyconoodler]

The princeton PI doesn't particularly sound that great with 6V6's,but I've built a few 6L6 princeton reverbs that absolutely rock when dimed.Same PI but higher voltages. About 440v,same dropping resistors.They sound awesome with none of the raspy sound from the 6V6's at all.In fact my live rig is a dimed high-powered PR with no pedals,just the volume on the guitar.Heavenly! Because the PI doesn't have the gain,the amps are not too loud.

[Science Amps]

I recently spent several weeks trying to make a (Fender style) circuit with a cathodyne PI (http://i274.photobucket.com/albums/jj257/paintrdude/Dee-zaster-2.png) sound good with dirt pedals. I finally gave up on using that PI because I couldn't make it happen. Just sounded raspy no matter wehat I tried. It sounded absolutely wonderful on its own (no pedals), which made it all the more frustrating...
Someone more capable than I might have resolved this issue.

The 'fix' (that is if you don't like the raspiness), is to add a large grid-stopper to the input of the cathodyne in the order of 470k-1M. It's explained here towards the bottom:

http://www.freewebs.com/valvewizard/cathodyne.html

[VacuumVoodoo]

The 'fix' (that is if you don't like the raspiness), is to add a large grid-stopper to the input of the cathodyne in the order of 470k-1M. It's explained here towards the bottom:

http://www.freewebs.com/valvewizard/cathodyne.html

This is 95% correct except for the last 5%. Bottom of page, lower waveform picture. What the good wizard calls frequency doubling is in fact phase reversal at plate output.
Careful balancing of this phenomenon against grid stopper resistance can produce that swooshy/swirly sound that some seek and others dislike.

[TweeDLX]

The 'fix' (that is if you don't like the raspiness), is to add a large grid-stopper to the input of the cathodyne in the order of 470k-1M. It's explained here towards the bottom:

http://www.freewebs.com/valvewizard/cathodyne.html

If you follow the link (http://i274.photobucket.com/albums/jj257/paintrdude/Dee-zaster-2.png) in my post, you'll see a 470K at the grid of the PI. In fact, I pretty much used Merlin's page as a reference while working on this amp. I subbed several different values into the PI and gridstopper resistors with no luck.

[Timbre Wolf]

Are players referring to the clean tone or the distortion tone ?
In my experience, it is more difficult to get the cathodyne PI amps to stay clean like the LTP-PI amps can. I like cleans that are on the verge of breakup, and that happens at a much lower volume setting on the cathodyne PI amps - and, they don't have the snap of the LTP-PI amps. Of course, there are other contributing factors, such as fixed-bias vs. cathode-bias power.

- Thom

[VacuumVoodoo]

If you follow the link (http://i274.photobucket.com/albums/jj257/paintrdude/Dee-zaster-2.png) in my post, you'll see a 470K at the grid of the PI. In fact, I pretty much used Merlin's page as a reference while working on this amp. I subbed several different values into the PI and gridstopper resistors with no luck.
Since V2a is used as cathode follower and V2b as split load bootstrap biased PI I suggest using a 12AU7 tube instead and 56k resistors in the split load.
There's no need for high-mu triodes in those two functions.

[phsyconoodler]

Hmmm...that might be the ticket.

[TweeDLX]

Thanks Aleksander! If I ever get around to building that amp again, I'll give the 12AU7 a shot.

[slagg]

Remove the bypass cap 50/50v from the bias resistor and the raspy will go away.

[Keyser Soze]

This is 95% correct except for the last 5%. Bottom of page, lower waveform picture. What the good wizard calls frequency doubling is in fact phase reversal at plate output.
Careful balancing of this phenomenon against grid stopper resistance can produce that swooshy/swirly sound that some seek and others dislike.

I think you two are using slightly different terminology to describe the same thing.

He says " [w]hen driven very hard this can cause an inverted copy of the cathode signal to appear at the anode..." Which is essentially the same thing as being 180 degrees out of phase (what you term phase reversal.) And both of you use that 'swirly' descriptor.

Speaking to the OP's question - it is also important, when looking at the PI, to consider what it can do to the power tubes. A cathodyne can certainly color the signal, but if it is feeding a pair of big bottles that's pretty much the end of the story. As compared to an LTP, which can push the power tubes much harder and even allow you to control the relative mix of pre and power amp distortion.

[MstrBones]

Clean tone or distortion tone? It is kind of both. To my ears a 5C3 with its paraphase inverter is warm, woody, has lower headroom and is lower powered than a blackface with its long tailed pair. The BF has more power, more headroom and those glassy cleans that Blackfaces are known for.

The tweed Bassman has a long tailed pair phase inverter, (I think it might have been the first Fender to get it) - point being the circuit predates BF amps. I agree with the earlier statement that the phase inverter does not breakup all that much compared to the preamp section or the output tube section at high volume.

A lot of the "headroom" in a BF comes from the relocation of the tone stack from earlier designs.

[diagrammatiks]

there's significant feedback circuit changes in all of those fender amps too.

sometimes the different between a lot of apparent headroom and no apparent headroom is like 2 db of negative feedback.