DC on a switch

[C Moore]

I rebuilt a friends Bassman. It has a switchable cathode on V1 of the Bass Channel. Is there a reasonable method to avoid the popping when using the switch while playing.?
Thank You

[selloutrr]

1meg resistor from the switch to ground

[C Moore]

I did not give you all the dope.....
This is a DPDT that switches between two different sets of resistor and cap.
The choice is between:
1.5k//.68uf and 820//10uf
So how would I accomplish this.?
Thank You

[rdjones]

Keep the 1.5k and .68u in circuit and add values in parallel to make the modified values.
You still need a high value resistance across the switch to keep the cap charged but effectively out of the circuit.
I've seen Fender use values as high as 10Meg in this position.

reddog

[John_P_WI]

Here are a couple of examples out of one of my hi gain designs...

[C Moore]

Here are a couple of examples out of one of my hi gain designs...

OK.
The top example looks like it will wok for me.
Thanks
I probably have the title of my OP worded wrong. My switch is always at ground potential, there is no DC on it. Is that right.? I am currently just switching the ground connection between two sets of Cap//Resistor.
Is the popping I hear while playing just from instantaneously changing the bias of the tube while it is on.?
Thank You

[rdjones]

When the switch is open there is DC on the side that's not grounded.
The pop comes from the cap charging or discharging.

rd

[C Moore]

When the switch is open there is DC on the side that's not grounded.
The pop comes from the cap charging or discharging.

rd

Bare with me please.....I am still learning.
When the switch I am currently using is open, the cap couldn't charge could it.? Wouldn't the cap discharge through the cat resistor.?
And that is what made me think there would not be DC on that part of the switch.
Obviously I am wrong somewhere...
Thank You

[John_P_WI]

Think of it this way, the "bottom leg" of one cap is at ground potential, the other cap has its' bottom leg "hanging in the air". This allows the ungrounded cap to charge up and hold a charge. When you switch between the two caps there is a "dc shift" which causes the thump. A resistor between the two caps more or less will keep them at the same potential minimizing the thump.

[C Moore]

Keep the 1.5k and .68u in circuit and add values in parallel to make the modified values.
You still need a high value resistance across the switch to keep the cap charged but effectively out of the circuit.
I've seen Fender use values as high as 10Meg in this position.

reddog

Sorry.....coming back to this.
As in your post, and as in Johns first schematic.
Why is it better to use a SPST switch and parallel the parts than it is to use a SPDT switch and use separate values.?
Could I use that 47k across the DT of the SPDT switch to stop the popping also.?
Thank You

[rdjones]

Keep the 1.5k and .68u in circuit and add values in parallel to make the modified values.
You still need a high value resistance across the switch to keep the cap charged but effectively out of the circuit.
I've seen Fender use values as high as 10Meg in this position.

reddog

Sorry.....coming back to this.
As in your post, and as in Johns first schematic.
Why is it better to use a SPST switch and parallel the parts than it is to use a SPDT switch and use separate values.?
Could I use that 47k across the DT of the SPDT switch to stop the popping also.?
Thank You

Using the separate values creates a greater likelihood of a pop due to the time the switch is open during switching.
As the switch is operated the tube's cathode circuit goes from 1.5k to 47k to 820 (using your values).
It's the opening of the circuit to 47k that's going to create an audible pop.
This is in addition to the sound the cap is going to make during discharge.

I predict using a SPDT switch like you suggest will create quite a noticeable thump.

reddog

[John_P_WI]

Even if it does thump, it appears that this will incorporate a manual switch and does not appear to be a"during performance" switching concern. Give it a try, it is only a resistor, switch and an extra piece of wire or two.

This can be a simple strat boost or other to be used when switching guitars.

[Structo]

Another method is to put a 4K7 resistor between the switch contacts.

[C Moore]

Another method is to put a 4K7 resistor between the switch contacts.

Yes, that is what I was proposing.
All good advice above.
And, as John says, if it does not suffice I am only out a few parts and some wire.
I already have the DPDT wired as a SPDT with a 47k across the DT. I will see what happens.
Thank You All