36W TMB cascade
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Nestori
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36W TMB cascade
My 36Watt is alive and roaring. I did the "JohnnyCrash"-style cascade, just put the normal volume in the other half of the V1 and I had gain enough! I was just wondering when I was searching for cascade schems and didn't found any switchable system for 36W, so will this work in Richies 36W?
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JohnnyCrash
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I think a cascade mod should definitely be in the "Mods" section.
The 2204 preamp used to be, I don't think it is currently... actually I believe it was a AX84.com Hi-Octane preamp (slightly hotter).
In any case, a switch is great and a footswitch schematic would be cool too. Hoffman does something similar (cascade footswitch) with his 18w Stout, but a "channel switching" 36w would be a great mod schematic to post. It would be loud enough to cover most folks uses and be flexible enough for nearly any use (clean, country, dirt, blues, near-metal).
As far as your drawing - you should check out Hoffman's info on the old One-Wire-Mod:
http://www.el34world.com/projects/hotswitch.htm
View a DPDT switch as two switches. The left three lugs are one switch, the right three another. The middle lugs are the input lugs. The top and bottom are the output lugs. When you flip the switch one way, the opposite lug is tied to the center. For example, flipping the switch up makes the bottom lugs go to the middle lug connection. Down makes the top lugs go to middle.
With the two switches in one, you have the ability to change two items... which is important in this case. Below is an example already from an 18watt.com member in an earlier thread/post...
In cascading you'd want to feed the plate to the other grid... like this:
http://i14.photobucket.com/albums/a303/ ... atic-2.jpg
So you'd need to use more of the DPDT switch (both sides) than your drawing shows.
In any case, you may want to swap out cathode bypass caps in cascade mode. Cascading can often get flubby/farty unless the signal is thinned out a bit. The classic JCM800 cascade preamp has the cathodes as follows: one with a 2.7k resistor and 0.68uF and a 10k (with no cap) on the other. Otherwise it can have a flabby, overly resonant (deep/low presence) sound.
The 2204 preamp used to be, I don't think it is currently... actually I believe it was a AX84.com Hi-Octane preamp (slightly hotter).
In any case, a switch is great and a footswitch schematic would be cool too. Hoffman does something similar (cascade footswitch) with his 18w Stout, but a "channel switching" 36w would be a great mod schematic to post. It would be loud enough to cover most folks uses and be flexible enough for nearly any use (clean, country, dirt, blues, near-metal).
As far as your drawing - you should check out Hoffman's info on the old One-Wire-Mod:
http://www.el34world.com/projects/hotswitch.htm
View a DPDT switch as two switches. The left three lugs are one switch, the right three another. The middle lugs are the input lugs. The top and bottom are the output lugs. When you flip the switch one way, the opposite lug is tied to the center. For example, flipping the switch up makes the bottom lugs go to the middle lug connection. Down makes the top lugs go to middle.
With the two switches in one, you have the ability to change two items... which is important in this case. Below is an example already from an 18watt.com member in an earlier thread/post...
In cascading you'd want to feed the plate to the other grid... like this:
http://i14.photobucket.com/albums/a303/ ... atic-2.jpg
So you'd need to use more of the DPDT switch (both sides) than your drawing shows.
In any case, you may want to swap out cathode bypass caps in cascade mode. Cascading can often get flubby/farty unless the signal is thinned out a bit. The classic JCM800 cascade preamp has the cathodes as follows: one with a 2.7k resistor and 0.68uF and a 10k (with no cap) on the other. Otherwise it can have a flabby, overly resonant (deep/low presence) sound.
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JohnnyCrash
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One other thing - for whatever reasons, typical cathode biased 18w derivatives seem to sound a little weird with cascaded preamps - to me at least. I'm thinking it's the cathode biased power section and the PI, but who knows.
In any case, I've had better luck converting the power sections to fixed bias, rectifiers to SS/diodes, and the filtering to really large (actually huge) values... never got around to playing with the PI's once they seemed dialed in with these changes though.
There is a muddy, fatness/resonance to them that I dislike. Of course, the SS rectification helps reduce any possible sag (depending on the rectifier tube, you may not really encounter sag anyway), more importantly it allows for larger filter caps (40uF +, even dual 50uF is noticeable) which tighten the bottom end a ton.
As far as the cathode biasing, I'm not smart enough yet to understand why going to fixed helps remove the tubbiness of cascaded pre's... perhaps someone here who actually knows can add some real technical info on this part.
I pretty much messed with my 36w until I was happy and it ended up spilling into my 6V6 18w build which is now bolted down and sounding great... my 36w is now a Vox AC30 TopBoost clone
I'd like to tweak my other 18w builds, especially in the PI area to see what I can do, but I think a few folks here already tried that on it's own... I think lovedat800 was one dude who tried quite a few things in this regard (the PI)... which is why I never bothered messing with my PI's on my cascaded 18w's.
In any case, I've had better luck converting the power sections to fixed bias, rectifiers to SS/diodes, and the filtering to really large (actually huge) values... never got around to playing with the PI's once they seemed dialed in with these changes though.
There is a muddy, fatness/resonance to them that I dislike. Of course, the SS rectification helps reduce any possible sag (depending on the rectifier tube, you may not really encounter sag anyway), more importantly it allows for larger filter caps (40uF +, even dual 50uF is noticeable) which tighten the bottom end a ton.
As far as the cathode biasing, I'm not smart enough yet to understand why going to fixed helps remove the tubbiness of cascaded pre's... perhaps someone here who actually knows can add some real technical info on this part.
I pretty much messed with my 36w until I was happy and it ended up spilling into my 6V6 18w build which is now bolted down and sounding great... my 36w is now a Vox AC30 TopBoost clone
I'd like to tweak my other 18w builds, especially in the PI area to see what I can do, but I think a few folks here already tried that on it's own... I think lovedat800 was one dude who tried quite a few things in this regard (the PI)... which is why I never bothered messing with my PI's on my cascaded 18w's.
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