Freyette/VHT amps - Anyone know how gain I&II work?

[JWK]

I have a Sig:X and like how the "GAIN I" and "GAIN II" work together. I was wondering if anyone knows the topology of these stages.

Freyette states the input is a parallel 12ax7, so I can't figure out what's going on here. I'm not trying to get a schematic or specific values, just the outline. The amp in general has way too much gain for me and is not voiced to my liking for a lot of stuff. I would like to see if I could implement the concept of those beginning stages if it's not a big secret or anything.

Anyone know?

[John_P_WI]

You might want to ask the guys over at Sloclone, they may be able to help better. The one thing that I do know about Freyette, he liked to do things a little differently, some of it I am sure was for fun to tease those who like to reverse engineer his designs and some of it "was just because he could".

[Colossal]

JWK,

For a paralleled input tube, this is just running the input triode in parallel with the other half of the tube. This lowers the noise floor, thickens the sound slightly, affords the opportunity for dissimilar cathode biasing (while maintaining the shared, common anode and grids), and lowers the output impedance of the stage (plate resistance value is halved, cathode resistors halved, and bypass cap values doubled). An example of this can be found on the Marshall 1974 and 1974x circuits. The 1974 uses just one R and C however.

As for the SigX, I can't help you there but I know the Deliverance has been discussed at SloClone. Best to just search there on your own as you will likely get a cold reception if you create a user-id, show up, and start asking outright for a schematic. There are tons of schematics posted there (just search) and you should be able to find the Deliverance 60 or 120. I don't know if the SigX and 60 or 120 share the same gain structure in common. Yes, as John mentioned, Fryette does some things differently, perhaps there is some tone in his method or just because he can and it's fun and less boring. An example of this is that on the Deliverance amps, Fryette uses multiple slope resistors and treble caps in series/parallel to get the typical values. Whether this adds some mojo due to inductance, I don't know, but it looks cool

Going on some 20 years ago, I had a friend who had a then hand-wired Egnater preamp (none of this wave-soldered garbage now) mated with a VHT stereo power amp. Killer high gain tone. Super clear grind without fizz (as it should be).

[JWK]

Thanks, I'll go over to sloclone. Never been there before as that's not my type of amp.

I understand about the parallel input tube; used it myself. I just meant I couldn't imagine how he took that and then went two different directions to come back again... Yes, he does things differently but makes great amps.

The general topology of gain I (voicing) and gain two mixed together is the same on many of his amps, including the Deliverance. I'm really not looking for a schematic, just an outline. It might turn out that I really don't want to use it if I think it causes too much hiss. I'm more into tone shaping and harmonic distortion than CRUNCH.

Wish me luck!

[Colossal]

JWK,

PM sent.

[Darkbluemurder]

Gain I is a 1 meg audio pot with a 1000pf bright cap. Gain II is also a 1 meg audio pot but wired as a variable resistor to a 47k and from there to ground. The output of Gain I connects to a 470k resistor and from there to the top of Gain II. Together they form a voltage divider.

This double gain pot arrangement kills a bit of gain so it's best in a preamp design with at least 3 gain stages - as is the case with the Fryette designs.

[roberto]

It seems Gain I and Gain II are like in the Deliverance.

If you are already a sloclone user, PM me (I'm a mod) and open a Sig.X thread with some internal pics. It will be simpler to help you.