Switchable PI, Paraphase,Cathodyne, LTP.

[Printer2]

While I did draw this up for guitar use it may be of interest for some here who would like to experiment with the differences between the types of PI's and their effect on a hifi amplifier.The circuit would have been simpler if I only stuck with one LTP but I had the switch positions so I went for it, this has not been tested yet but I think it should work. I will list the switch position function more for reference as to why the different values were selected.

Position 1. - Paraphase 5D3 Deluxe, might make the voltage divider adjustable to dial in the amount of imbalance.
Position 2. - Cathodyne 5E3 Deluxe, the top switch parallels up the 100k plate resistor with a 120k to give 56k. NFB switched to get Harvard-Princeton or 5E3 non-NFB operation.
Position 3. - LTP 59 Bassman, changed the presence control with a Blues Deluxe form so no DC is on the pot. NFB may be switched, not sure yet. first stage 100k plate resistor paralled to get 82k.
Position 4. - LTP 18W Marshall, 100k plates, 820 ohm cathode (or there about)47k tail, no NFB.
Position 5. - LTP AC 15 Vox, 100k plates, 1.2k cathode, 47k tail, no NFB.

I doubt this is something which would be a lot of value to the hifi community, more a curiosity I would guess.

[DF96]

The phase splitter is part of the overall design. You can't simply swap it like a boutique component, as there are significant knock-on effects because of things like gain, input impedance, output impedance, balance, frequency response, distortion. If you know enough to take account of all this issues, you know enough to choose the correct circuit in the first place so no need to swap.

[Printer2]

Originally Posted by DF96

... there are significant knock-on effects because of things like gain, input impedance, output impedance, balance, frequency response, distortion.....

Which gives each circuit their own different sound. A pair of 6V6's biased up does not look any different with one PI or the other. Also the stage before a PI is generally a stand alone stage that will work with any of the above circuits unless it is within the feedback loop. And then the NFB cures many ills.

Not saying that amp design is just stringing a couple of stages together, but after looking at many simple amplifier schematics and their similarities and differences, there is only so many ways of skinning a cat. Like I said, may not have as much value in the hifi world, just showing what I came up with for curiosity sake. Now where was that cat?

[artosalo]

Which gives each circuit their own different sound.

Hifi-amplifiers can not be designed like guitar amps., just by listening.
Good hifi amplifier actually does not have any sound. It should amplify the input signal without modifying it by any sense.

[Printer2]

Originally Posted by artosalo

Hifi-amplifiers can not be designed like guitar amps., just by listening.
Good hifi amplifier actually does not have any sound. It should amplify the input signal without modifying it by any sense.

But if tube amps did not have any sound why not just use transistors?

[tubelab.com]

Now where was that cat?

The cat heard the bit about skinning, and outran the dog on the way out.

Hifi-amplifiers can not be designed like guitar amps., just by listening.

There are still a good number of people who believe exactly that. Listening and tweaking is the only true path to audio nirvana. Those of us who use test equipment and theory just don't understand......

Good hifi amplifier actually does not have any sound.

The SE crowd doesn't see it that way. A bit of second harmonic is good for the soul.....and the ears.

I Think the "Dial a PI" is a cool tool and may be useful for a guitar amp. It's pretty far down on my list of things to build though.

[Printer2]

Originally Posted by tubelab.com

The cat heard the bit about skinning, and outran the dog on the way out.

Speaking of, where is that damn dog?

There are still a good number of people who believe exactly that. Listening and tweaking is the only true path to audio nirvana. Those of us who use test equipment and theory just don't understand......

That's ok, I still use my meter and scope and listen while I tweak.

The SE crowd doesn't see it that way. A bit of second harmonic is good for the soul.....and the ears.

Gets rid of that sterile sound.

I Think the "Dial a PI" is a cool tool and may be useful for a guitar amp. It's pretty far down on my list of things to build though.

That's ok, you keep busy enough as it is. This is an offshoot from the $100 build, just doing it for kicks and to answer some questions.

[GloBug]

I think its a cool concept.

I always thought it would be great to have a breadboard control panel that let you switch different blocks in and out of the circuit. Sure you might have to adjust some components here or there, minor detail compared to having that kind of speed and flexibility for testing.

[Printer2]

Originally Posted by GloBug

I think its a cool concept.

I always thought it would be great to have a breadboard control panel that let you switch different blocks in and out of the circuit. Sure you might have to adjust some components here or there, minor detail compared to having that kind of speed and flexibility for testing.

I did that with a pentode preamp, had pots rather than resistors and capacitors that I could switch in and out. It was a lot of fun seeing what made it tick.

[GloBug]

How about switching out preamp, PI and power amp sections with OPTs, in addition to the pots for resistors and capacitors!

Maybe that's going too far, but a "dial-an-amp" would be cool. Better then Spice.