Two Different Coupling Cap Values on a Switch... Will This Work?

syscokid

syscokid

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I want to try to mellow out and alternate the overall bass response on my Allen Amp Sweet Spot by altering the coupling cap value that's between the reverb recovery stage of V3b to the grid of the V4b P.I. grid. I also don't want the electrical pop when flipping the switch. Original coupling cap value is .0047uF. The alternate value I'm seeking is .0015uF. I'm thinking of replacing the original .0047uF cap with a .0015uF cap. I'll add a .003uF in parallel on a switch, for a total of .0045uF, which is pretty close to the original value. Also on the switch, I'll add a 4.7M to ground to prevent the electrical popping. Will this work as shown in my second pic?

Original layout:
ALLEN AMP'S SWEET SPOT V3 TO V4 COUPLING CAP.jpg

Proposed layout with two new caps in parallel, one new resistor to ground, a SPST mini switch, a grounding lug, and one new piece of wiring:
ALLEN AMP'S SWEET SPOT V3 TO V4 COUPLING CAP.jpg

I guess I could also ground the 4.7M resistor to the speaker jack instead of adding that grounding lug!
 
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New illustration...

If my proposed switching wiring is correct, I realized that I could create a much cleaner mod by putting the caps in Series with each other instead of Parallel with each other. The original .0047uF cap will remain the same for one position of the switch, and the new second cap will be .0022uF for switch position #2... which the new capacitance value will add up to .0015uF. I don't think I'm going to need that big value resistor to ground anymore. Hopefully somebody will chime in!
ALLEN AMP'S SWEET SPOT V3 TO V4 COUPLING CAP SERIES.jpg
 
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syscokid said:
I want to try to mellow out and alternate the overall bass response on my Allen Amp Sweet Spot by altering the coupling cap value that's between the reverb recovery stage of V3b to the grid of the V4b P.I. grid. I also don't want the electrical pop when flipping the switch. Original coupling cap value is .0047uF. The alternate value I'm seeking is .0015uF. I'm thinking of replacing the original .0047uF cap with a .0015uF cap. I'll add a .003uF in parallel on a switch, for a total of .0045uF, which is pretty close to the original value. Also on the switch, I'll add a 4.7M to ground to prevent the electrical popping. Will this work as shown in my second pic?

Original layout:
View attachment 106610

Proposed layout with two new caps in parallel, one new resistor to ground, a SPST mini switch, a grounding lug, and one new piece of wiring:
View attachment 106631

I guess I could also ground the 4.7M resistor to the speaker jack instead of adding that grounding lug!
Click to expand...
"I want to try to mellow out and alternate the overall bass response on my Allen Amp"

The bass response is determined by the two cathode bypass caps that connect to pin(s) 3 and 8.
You can use this simulation to test and see the frequency response result.
use the calculator to plug different bypass cap values which produce the low frequency roll off

Cathode Bypass Capacitor Calculator

www.ampbooks.com www.ampbooks.com

other than that you need a resistor I think to keep it from popping and the wires to the grid should be shielded.

coupling cap.png
 
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Amp Mad Scientist said:
The bass response is determined by the two cathode bypass caps that connect to pin(s) 3 and 8.
You can use this simulation to test and see the frequency response result.
use the calculator to plug different bypass cap values which produce the low frequency roll off

Cathode Bypass Capacitor Calculator

www.ampbooks.com www.ampbooks.com
Click to expand...
Thanks, AMS! Agree with your statement, and I am familiar with those various amplifier calculators at ampbooks.com. But one can still manipulate the amp’s low end by messing with the coupling caps. Depending on the overall circuitry and layout of the circuitry, sometimes I see an easier and cleaner path to achieve whatever it is that I’m trying to accomplish by following my curiosity. But I have to admit that I’ve also have failed many times when sitting at the “Tinker’s Table”.

Amp Mad Scientist said:
other than that you need a resistor I think to keep it from popping and the wires to the grid should be shielded.
Click to expand...
What minimum resistor value would you suggest here?

Do you think that grounding the resistor at one of the speaker jacks is good enough? Or maybe add a grounding lug to the switch’s mounting hole?

Shielded wires: That’s a good suggestion too. Because of the location of the switch, the grid wire from the original coupling cap to the P.I.’s 1 Meg cathode bias resistor will be extended by about six inches, and it will also cross under a few voltage infused wires.

Thanks for verifying my switching ideas again… :cheers:
 
I meant to post this a few days ago and close this adventure out. Anyways… I set up the wiring as illustrated in post #3, and it works nicely. I did not need to add a resistor-to-ground to prevent electrical popping when switching. Perhaps it’s because the coupling caps are blocking dc voltage, and ac voltage that passes through is very small. Also did not need to use shielded wiring because I’m not noticing extra noise. The layout of the new wiring is avoiding being too close to the ac heater wiring and the wires carrying high dc voltage.

IMG_1981.jpeg


IMG_1980.jpeg
 
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