Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Solid State => Topic started by: Willabe on March 21, 2011, 06:10:36 pm
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I would have to switch at the input (grids) to keep the other inputs bleed path through the other channel's vol. pot and not after the coupling caps.
Can you use a relay to switch the 2 - 1st stage pre tube?
Is this too sensitive of a spot to use a relay for switching? Would noise be a problem? I'd rather not have to use an A/B box with 2 patch cords (realy 3 cords) instead of just 1.
Or can I add a second bleed path by adding a 100k/.1 uF coupling cap to ground off the relay?
Thanks, Brad :icon_biggrin:
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:w2: I need a picture to understand your question.
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Hey what just happened? I went to answer you and could'nt get back on line here for 30 min. Checked other sites no problem????
:w2: I need a picture to understand your question.
Sad to say I don't know how to do that. I've only had a computer for about a year or so. But let me try to explaine what I'm trying to get at a little better.
5E3/5G9 have interactive volume controls. Plug in #1 channel and then as you turn up the vol. on the other channel, the mids will get scooped, giving a cleaner sound, more mid scooped BF AB763 sound.
A lot of guys like to use an A/B box to take advantage of this. Set 1 ch. at say 5 and set ch. 2 at full and step on the A/B box and you go from clean to mean.
I'd like to use a relay to do the switching instead of using an A/B box. That way only 1 patch cord instead of 3 going from the guitar into the input of the amp.
If I use a relay to switch between the 2 ch's. from/off of the tail end/plate coupling cap, I will kill the "2nd path" for the signal to bleed off to ground, now the interactive controls won't work.
I think most if not all ch. switching is done at the tail end of a pre. gain stage, at least for the 1st stage, after the plate coupling cap and not at the input grid of the 1st stage pre. tube.
So if I switch the input/grid signals with the relay, it would be at the weakest signal point and noise could be a major problem. Plus now the relay would be very close to the weakest signal in the amp. can we do this?
OTOH, I was wondering if I/we could keep that "second path" intact, that's built into these amps and keep the interactive vol."FX" by tail switching the 1st stage pre after the coupling cap by some how hanging a .1uF/100k off of the relay when switching, back to/thru the power supply.
It's a new build and I have room to do this - if - > 1 it 's ok signal wise/noise and 2 > - If - placing the relay close to the first/only pre stage wont be a problem.
I'm not using 5u4 rect. tube, so I have a 5v fill. tap @ 3A to use for the relay, way more than enough.
Thanks, Brad :think1:
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OK, now I get it. Just do the switching on the grids. This will preserve all the mojo of the backward volume controls. Locate the relay close to the input jacks or tube. If you use the original board layout, there's room just below the first set of 68K mixing resistors. All wires would be short so no need for shielding.
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Well alright then.
Thanks sluckey!
Brad :icon_biggrin:
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Is this right? Also does it matter if the curent limit resistor thats in series with the LED, is before or after the LED?
Will it matter if I use a 5v or 6v relay? How much over voltage can they take? I could put in a 5v reg. chip and go with a 5 v relay.
One more, what do you do with the jack ground? N/C and just let the body frame make contact with the chassis when you fasten it in place, for shielding?
Thanks, Brad :icon_biggrin: