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.
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.
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.
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?
The cat heard the bit about skinning, and outran the dog on the way out.
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......
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.
Speaking of, where is that damn dog?
That's ok, I still use my meter and scope and listen while I tweak.
Gets rid of that sterile sound.
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.
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 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.
Yes in my world the PI will probably get overdrivem, or at least the following stage which will then drag down the signal of the PI. I did a slightly simpler circuit a while back with Paraphase, Cathodyne and one LTP combination.Somehow I misplaced a connection and ended up a pole short on the 4 pole switch and the LTP did not work. What did work was the Cathodyne and the Paraphase. I did not spend too much time playing with it but I found the Paraphase to sound fuller when mildly overdriven. It impressed me enough that I decided I would work out a way to simply switch between PI types (using two different switches or more poles would have been easier). I wanted to walk the line between simplicity in operation and variability. I also wanted to use circuit parameters that repeated results of classic circuits.
This is only one of a few ideas I will be throwing together in one amp to increase its versatility and yet limit the amount of gain stages. Too easy to just throw in more tubes.
Still chasing the cat............
I remember seeing a few variations of your multi - PI in that thread. I am still tinkering with my amps from that thread, and have a few more, but I haven't posted into that thread since Mister Killjoy had a fit over the cost of knobs. He also got real irritated at my use of sand, so one of my amps now has a mosfet split load PI. It works pretty good too.
In my case the mechanics and the cabinet building are always the hardest part but I just lucked into a good head start in that department.
Some friends and I were at a hamfest where one of my friends bought a Marshall 4 X 12 cabinet for $100. It contained Celestions too. The vendor had a bunch of dead guitar amps and it seemed that nobody was interested in them so he sold them all to me for $5 each. There are two cheap Fenders, a Crate, a Line 6 stereo head, and a no name reverb box from Japan. All solid state. I had planned to gut them and build tube amps in the cases, but the Fender G-DEC JR got my curiosity up, so I fixed it.
No banana jacks, but no soldering required just screw terminals. 80 Watt screen drive amp shown.
Attachments
Reminds me of a Christmas present I got from my parents waayy -- way back. It had just individual electronic components on plug in yellow plastic carriers with spring wire terminals or pins or something. Wish it had had tube input stages, phase inverters and output stages with OTs back then. I might have actually learned something in grade school then. But it was all solid state low voltage stuff to be safe.
Thought about something like that to play around with. But in the end I want all the choices in the amp to be selected by a switch anyway so I think I will go in that direction.
Yeah, but don't they realize it is dinner time?
I had one version that was to use a mosfet as a PI but never got around to trying it. Glad to hear it works, I may just give it a go for an amp I want to build for my nephew.
I can do some rough metalwork at work, the cabinets are my sticking point especially since it is usually below freezing outside and I have yet to replace the motor on my table saw. Come summer I will catch up on that end.
I like the screw terminals but I have not scrounged enough to do what you have. I am trying to keep this hobby in check as I should be learning to play also.
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