How can i stop the pop when i flip this switch.

noworrybeefcurry · Post by **noworrybeefcurry** » Fri Oct 28, 2011 11:20 pm

This was my own take on a mid-boost switch, i basically wanted something with a bigger mid-boost than the standard dumble boost has. I am using a 2-way DPDT switch with one common terminal going to the slope resistor and the other common terminal going to the treble pot. Then on one side of the switch i have a .001uf cap and a .0022 cap on the other side of the switch. I love the way it works with the exception of the loud pop i get when flipping the switch. Does anyone have any suggestion for eliminating the pop?

John_P_WI · Post by **John_P_WI** » Fri Oct 28, 2011 11:43 pm

It's Friday after a crazy work week, I'm tired and having a hard time visualizing exactly what you are saying, but my guesses are this.

1) When you are switching the slope resistor you are switching DC. You would need a DC blocking cap before the tone stack to stop the pop.

2) When you are switching the caps, you are opening one of the legs allowing a differential charge to build. Using a high value resistor (10 meg) or so between the open leg and the switch pole may help the pop here too.

If we had a drawing, we could help you better.

Good luck, John

LeftyStrat · Post by **LeftyStrat** » Sat Oct 29, 2011 12:02 am

Like John, I'm having a little trouble visualizing what you have. But here's my take. You are basically changing the capacitance between the slope resistor and the treble pot, to either .001 or .0022, correct?

If so you want to wire it differently. Instead of switching between .001 and .0022, you want to have .001 in the circuit and then have the switch add an additional .001 in parallel, which will give you .002. The additional cap should be permanently connected on the treble pot side, and the switch should just close the connection between the other end and the first cap.

Alternately, connect two 4.7 M resistors between one terminal of each cap and ground. This will drain any charge on the cap.

The caps are charged and discharging when switched into the circuit, causing the pop.

LeftyStrat · Post by **LeftyStrat** » Sat Oct 29, 2011 12:25 am

Actually that first suggestion wouldn't work, you still get a pop. Looking at the original Dumble mid boost, you can achieve the same effect by using two .0022 caps in series, which would be .0011, with the mid switch bypassing one of them to get .0022. The 4.7M resistor to ground between them will discharge the one left dangling.

Luthierwnc · Post by **Luthierwnc** » Sat Oct 29, 2011 2:53 pm

I'm not sure I get the schematic either but the top picture is as close as I can figure. If so, yeah, it is going to pop and you also have DC on what might be a very light-weight switch.

To do what I think you have in mind, I'd put the caps in series on a switch. The first two in the diagram below could be .0022. In series that's .0011. I throw that into the usual mid circuit. You'd need two anti-pop resistors since there are now three series caps. If you are always in boost mode, you can skip the middle part and up the small cap value.

The stock circuit just bypasses the second series cap so you never get more than .0022 going to the treble pot. If I misunderstood what you are doing (and you have your .0022 and .0011 in parallel), you could just use a .0033 cap in the first position and a .0022 in the second -- or any other combination that gets you where you want to go. That comes to .00132 in series. This might come in handy:

http://www.electronics2000.co.uk/calc/s ... ulator.php

Good luck -- and your luck will improve if you don't have 180VDC on a Chinese mini-switch, Skip

Luthierwnc · Post by **Luthierwnc** » Sat Oct 29, 2011 5:08 pm

There are also possibilities with this using either a toggle or a rotary switch, sh

noworrybeefcurry · Post by **noworrybeefcurry** » Sat Oct 29, 2011 9:03 pm

Luthierwnc-

the first schematic you posted is exactly what i have in place now. I think i might try the dumble type mid boost with two .0022 caps in series and just short across one of them. Ill let you guys know how it turns out!

Luthierwnc · Post by **Luthierwnc** » Sat Oct 29, 2011 9:29 pm

Most of all, you really don't want rail voltage on anything but a heavy-duty switch. More bettah to have the first cap block the DC and let the switch do the finesse work. In my lower schematic and on the originals, the most boost you get is when the second cap is bypassed so if .0022 hits the tonestack hard enough, you just dial the second one in for your non-boost position.

The Matchless schematic works well in a lot of situations -- especially pentode front-ends. Notice the 5m1 resistors between each to keep them from popping. You end up only using one or two in the middle since the really small ones and the really big ones are on the outside of the bell curve -- at least in my hearing.

Cheers, Skip

sharkboy · Post by **sharkboy** » Sun Oct 30, 2011 12:57 pm

Funny you should say that. I just use the more extreme positions, depending on which guitar I'm playing (in the Vox cap switch circuit ). Then again, I'm not really all about subtlety.

Luthierwnc · Post by **Luthierwnc** » Sun Oct 30, 2011 1:24 pm

I'm sure they are there for a reason. I've cloned the DC-30 and still have the same amp in a 15 watt version -- although I didn't put the biggest cap on the rotary switch. It just seemed too much for the rest of the circuit. Now the brilliance/cut on the other side of the inverter is really handy for taming a squealing Tele.

I suppose we are out of the Dumble realm now but back to the mid-control, adjustable first coupling caps can be useful when you have different guitars in a gig setting (only one amp). The point I really wanted to emphasize was that you don't want B+5 voltage on a mini switch. The data sheets claim they can handle more but I just don't trust them and I don't want to be flipping a metal lever with just a few millimeters between the internal contact points.

sh

noworrybeefcurry · Post by **noworrybeefcurry** » Mon Oct 31, 2011 3:41 am

Luthierwnc-

so when i do wire up the mid boost circuit, id would basically want to short across the second cap (closest to the treble pot) in order to avoid high B+ voltages contacting the mini toggle switch?

Luthierwnc · Post by **Luthierwnc** » Mon Oct 31, 2011 11:16 am

Yeah, those mini switches aren't designed for the old school (obsolete in modern terms) voltages we use. You also want to keep those voltages on the board rather than run a hot wire among your signal wires around the front panel controls. Whenever possible, you want to keep the rail and the signal wires separate or crossing at angles so they cause minimal hum and oscillations. This doesn't only apply to Dumbles.

The rotary switch idea I posted could also be a toggle. With an ordinary SPDT you could use either of them. With an on-on-on it could be either or both in parallel. Use different values that add to the boldest sound you want: like a 680pf and a .0015. Just remember to put the switch on the friendly side of the caps and use anti-pop resistors. sh

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