Compare/Contrast PI types?

[davidwpack]

Ey! I was doing a bit of studying/brushing up on differences in different Phase Inverters and found this simplified comparison someone drew up on a forum. (Gibson I think.) Anyways, is this essentially correct? Also, would this be a standard paraphase? What differs to make it a "floating" type? If it is correct I thought it would be useful for other people here on the forum to have for a reference. Anyways, thanks...dave

[PRR]

http://www.mylespaul.com/threads/help-explain-differences-in-pis.121845/

[John]

That guy explained it so well even I got it!

[66Strat]

Attached is a section from RDH4 that explains the functionality of the Self Balancing Paraphase. This is the phase inverter used in the 5D3 Deluxe.

[jjasilli]

Different take:  the various PI's are clever and, operationally, all work well or well enough for successful use in hi-fi and guitar amps.


The difference to me is overdrive tone if the PI itself is overdriven.  I think the LTPI outputs a more balanced pair of overdriven signals and thus has a smoother overdrive tone; other types of PI's have a more "ratty" overdrive tone to my ear.

[tubeswell]

Philosophical question - does a paraphase inverter need two gain stages? (to give a reference for the 'inverted' phase? - kind of like a tree falling in the woods - does it make a sound whether anyone is there to hear it or not?)


Purely rhetorical question BTW.

[jjasilli]

Not sure I understand your question.  The paraphase is a unity gain creature.  Though it technically is a gain stage, it's input signal is reduced by a voltage divider, so that it's output voltage (in reverse phase), matches the voltage of the main signal which bypasses the paraphase stage.

Whether that voltage is strong enough to drive the power tubes may be your question.  The signal voltage must be brought up to power tube level either by the prior gainstage to the paraphase, and/or two gainstages after the paraphase.  But the latter alternative is so wasteful as to be impractical. 


Another philosophical question:  If a man is alone hunting in the forest, and there's no woman there to hear him, is he still wrong?

[PRR]

You need Gain and 2 Outputs.

The raw inverter gives "gain" of -1, so needs another gain stage. Traditionally this was the existing driver for a 1-6V6 amp. To make a 2-6V6 amp you added the inverter and another 6V6.

The cathodyne has the two outputs at gains of +1 and -1. It needs a gain stage.

The long-tail is two amplifiers and two outputs. Seems sweet but the gain to each side is half of a single gain stage.

[jjasilli]

Yes, but where is the gain stage located?  I'm saying, before the PI.  E.g., some cathodynes are driven by small pentode stage, with the pentode and triode in one small bottle, like a 7199 tube for example.  So the prior stage provides the needed power tube drive voltage, and the unity gain PI provides mere inversion with no boost.

[davidwpack]

Thanks for all the replies! Think I have a basic understanding  of how they function. I'm still trying to figure out what makes a paraphase "float" but otherwise have a grasp. Here's an article I found interesting if anyone wants to read it. http://www.r-type.org/articles/art-097.htm

{edit: fix munged URL -- PRR}

[PRR]

Just read the dang book:

[davidwpack]

Got it! Thanks PRR.