Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: bruno on June 06, 2013, 04:10:10 am
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Hi,
is there any circuit in the forum's library, or that you guys have knowledge of that acts as a volume/gain control/master which decreases gain in the lower half of the pot range and eventually re-routes signal to an extra triode in the second half of the of the pot range.
Something which actively boosts gain/ adds more gain when turned up, rather than just allowing the entire signal from the previous stages to pass through?
thanks
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Bruno,
I am not sure I understand your question? So if I missed understanding, I apologize in advance.
Are you referring to something like the "FAT" control that Geezer came up with.
With respect, Tubenit
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Hi tubenit,
Thanks for the reply. Although I understand the concept behind Geezer's design, it's not what I'm asking for.
It's hard to explain it properly, so I'll try and add a schematic today, so you guys can see whether it makes sense.
Basically the signal coming out of the preamp, would either be routed to directly to the PI input, or to a triode gain stage. The first half of that control should act as a simple voltage divider, cutting the signal down to nothing, into the PI input. The second half of the control should gradually route the signal into an extra triode stage before going into the PI input.
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maybe something like this ?
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Had a very quick look at it, and I think it might be somewhere along those lines, yes.
You're basically making the signal progress to either the pi input, or the gain stage that follow the initial preamp.
Looks to be very close to what I was thinking. Have you tried it in any of your amps tubenit?
thanks
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Never tried it but I think it is somewhat of a clever idea that you have come up with.
Sort of like a dry/wet mix into the LTPI. Interesting! And I think you could possibly be successful in getting the volume somewhat comparable between the clean and "boost" on the pot, given the gain pots on the OD section.
With respect, Tubenit
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Cool, I'm currently ordering some edcor transformers and a chassis. Will try this circuit very soon, I'm going to try both a centurion and a regular TMB fender tone stack with it.
Hopefully will come out with little, yet toneful amp, to play around the house.
thanks for your help!
cheers
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Notice that Tubenit's OD circuit has an even number (2) of gain stages. This will be important when mixing the normal and OD signals together. If you use a single triode (or any odd number of OD stages), the OD signal will be 180º out of phase with the normal signal and will likely not sound very good.
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Understood, thanks for pointing that out, so maybe use an even number and trim the gain of those additional stages down, just to get some extra boost.
thanks
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Here's a variation of Tubenit's circuit that may have some merit. This circuit will actually blend from full normal signal to full OD signal or anywhere in between.
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Nice!
Another side of the spectrum that I have been thinking about is also the opposite of the previous ideas. Ex: to have a volume/gain control that acts as a regular volume on the upper range of the pot, but also gradually re-routes the signal to an additional gain stage when turned down (on the lower half of the pot's range).
This would make for a control that compensates the volume drop by doing a slight boost afterwards, not sure what the results would be, but it might be worth a try.
I'm guessing the only thing I need to make this work like I though is to get your sugestions (tubenit's circuit, or sluckey's block diagram) and add a dual stacked pot, with one half controlling the routing of the signal, and the other acting as a master volume.