Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: phsyconoodler on May 13, 2011, 03:49:57 pm
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Has anyone tried adding a deep switch to an AB763 tone stack with treble.mid and bass controls?I've tried doing it the way the AA165 bass does and simply adding another cap in parallel made it trebly,not deep.What am I missing here?
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Yeah, its not that good and I never cared for it. Try a .02 and another .02 in parallel. That should get you what you want. I used two .047's in series in my fender build to get the two different tone stacks. Works great for me. I use the series arrangement because there is hardly any pop that way.
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Not quite sure what you mean by series? Why does the deep work so well in an AB763 and not in another Fender amp?
Edit: I think I know what but correct me if I'm wrong.The AB165 has two .1uf caps in parallel and when you add another cap it cutts the rating down making it like a normal fender.The cap OUT of the circuit is the Deep.
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I thought that the deep 120pf cap was wired to the volume pots wiper and the other lead of the 120pf cap through a carling switch and back to the right volume pot terminal. Taking the cap out of circuit using the switch just lessens the bright function of the tone and thus you have a deeper tone (Deep)
Is this what you are thinking? I have used 250pf caps for a brighter tone. But when switched off or out of circuit it's dull and deep as usual
OK i know what your saying now. There is a different layout i have seen that does something different with the deep cap. Let me go find it/
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IIRC LooseChange reported success with a "girth" control. tubenit may have drawn a schematic or two incorporating the switch.
Don't know if that helps,
Chip
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"Girth"? Maybe we need a contest for the most unusual amp control name. That's got my vote.
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This is not really what you're asking about, but this is an idea I drew up a few yrs ago and posted on the forum. Don't know if anyone ever tried it and I never got around to it either. The layout presumes a terminal strip between the board and the pots for paralleled components.
The idea was to approximate some different Marshallish and Fenderish type tones.
With respect, Tubenit
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Here's the Girth control from LC:
http://www.el34world.com/Forum/index.php?topic=6920.msg60895#msg60895
It lifts the "Mid" pot somewhat but frequencies above a certain point bypass the Girth control.
I've also seen a control somewhere that moved the frequency of the mid-scoop but can't remember where it was right now...
Chip
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Not quite sure what you mean by series? Why does the deep work so well in an AB763 and not in another Fender amp?
Edit: I think I know what but correct me if I'm wrong.The AB165 has two .1uf caps in parallel and when you add another cap it cutts the rating down making it like a normal fender.The cap OUT of the circuit is the Deep.
When putting caps in parallel, just add the values to get total capacitance - They're additive. The two .1 add to .2, which will be a crap load of bass and low mid cut. It's not to far from the .1. To me any ways.
With the AB165, just one .1 alone is the deep. Adding in the other .1 is the cut. The way it is designed sucks in my opinion. The .1 alone is already enough cut in the low mids/lows except the deepest lows in the 40hz area. Might be great for bass but who plays bass with a bassman? Sucks for guitars unless you're tuned to C but there is no meat left in the low mids where the guitar tones live.
I use the two series .047 caps for a deep. I just short out the second .047 cap. This gives me either a .02 or a .047 that approximates the different values you will see in the AB763 amps.
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Ok,I just tried a paralleled cap as a deep switch on an AB763 amp.When you add the cap in parallel and connect one end to ground like the AB165 the sound gets thinner and when you lift the end off ground it's back to normal.
so the way to get this to work is get the deep sound you want by upping the bass cap to get more bottom and then parallel a cap in until the sound is back to normal.
so to reiterate,cap in parallel and one end grounded = thinner tone.Lift ground on one end = fat or normal tone.
It works very nicely actually,it's just getting the right caps to get in place to make the effect work well and give maximum tone.Trial and error.