Cascade Mod and Jose Master?

[axeman]

I'm thinking about cascading my 68 and adding a Jose master to increase the gain. Has anyone tried the same mod? and how much gain can I get out of it.

Thanks

Art

[Bainzy]

depends which values you use - you can get a LOT of gain out of a simple cascade mod, or you can limit it to a set level of gain. things like plate resistors and mixers for a start will affect gain, then youve also got what cathode settings you use.

[axeman]

Rite, how about 220k on the plates and 270k on the mixers and a 1k cathode. Does that work for more gain?

[jerrydyer]

cascade and PPIMV and youll be rockin.

[axeman]

Thanks Jerry, I tried that with my 45/100 and used shielded cable and all I got was squeal. The rich mod alone was nice, but looking for more gain.

[flemingmras]

Thanks Jerry, I tried that with my 45/100 and used shielded cable and all I got was squeal. The rich mod alone was nice, but looking for more gain.

Just so you understand how things work in a preamp...

Dropping the value of the cathode resistor (i.e. the resistor connected to pin 3 or the ones connected to 6 and 8 on V1) increases gain. You can also increase gain by raising the value of the plate resistor (i.e. the resistor connected to pin 1).

If you have issues with high frequency oscillation, there are a couple of ways of taming that. You can place a 47pF or some other low value cap across pins 1 and 3 (or 6 and 8 depending on which side of the tube it's coming from) on the stage that you're adding gain to. Placing this cap across the plate resistor should do the same thing. Because it's such a low value, it shouldn't have any noticeable affect on your highs.

On the Super Lead circuit, V1's gain stages are mixed together via the mixer resistors (470K...or 270K, depending on which era circuit you have). Instead of mixing them, you can cascade them for more gain.

[axeman]

Thanks. when you mean cascade the mixers, are you referring to the one wire mod?

[flemingmras]

Thanks. when you mean cascade the mixers, are you referring to the one wire mod?

That would be the one

Cascade (not the beer...lol jk) simply means that the output of one stage feeds the input of the next. On a Super Lead, they're "mixed"...i.e. their outputs are joined together into 1 input.

[axeman]

I've tried the one wire mod on my 69 and was not impressed. I tried the same on my JTM 45/100 with the addition of a PPIMV, was not happy to much oscillation I just need a little more gain on my JTM and maybe an extra preamp tube on my 68.

[joey]

I would be very careful. This usually indicates some sort of oscillation provoked by unwanted capacitive coupling/feedback loop somewhere in the layout that exists even in the stock form..... It just becomes audible when you do the mods. Your layout needs to be super clean for high gain to work well, especially if you are having trouble with tried and true mods.

[axeman]

Thanks Joey, I crank my 68 to around 5-6 and it remains quiet. Wouldn't it oscillate when I crank the amp? The trouble comes when I combine two mods. Like you said.

[axeman]

"capacitive coupling/feedback loop". Joey can you elaborate.

[jerrydyer]

what you have been describing in what you want your amp to do, the cascade mod with a PPIMV will be perfect. When you cascade most people run into trouble back at the switching jacks. They are a little confusing. If you conquer this mod you will prob be happy. I do it in a way to where you can still have the stock sound as well. I think from past post you have already tried the minor mods like changing cathode res and cap values right? Once you get it done you might need a cap over the plate res but ive never needed one on three gain stages, only 4 needs the cap there.

[joey]

"capacitive coupling/feedback loop". Joey can you elaborate.

Capacitances between traces, wires, or components can accidentally couple to one another (like a coupling capacitor), or worse to the input of an amplifier stage and form a feedback loop. If the signal fedback is in phase with an input, or surrounding several time constants, it either becomes positive, or more in phase with whatever it couples to and you will get squeel. High gain circuits are prone to this pickup, and most stages in a guitar amp have high amplification factors. Most amplifiers in general have some on an ultrasonic level. Point is that even though you may not here it in your stock build, it doesn't mean it is not there just waiting for the opportunity to be pushed over the edge. so layout is critical

[axeman]

Thanks Jerry, I know you've told me to take my amp to you, but it's a personal thing. Pride "I did it myself".