Circuit switching

[Zenabi]

Hi all.  I am in the planning phase of a multi channel amp and would like to run some ideas by you guys first.

When using relay switching, typically we will use a coupling cap to decouple the DC and a resistor to ground to avoid pops. I was originally planning to use more typical values of 0.1uf/1M but am now contemplating in using bigger values, ie 1uf/10M. Using bigger values will allow me to use a wider variety of circuits without doing a bunch of recalculations (series capacitance or parallel resistance etc...). I will be using this same pattern between multiple stages in the amp.

Will the 10M resistor increase noise or hiss of the amp?
Will the 1uf coupling cap create problems?
Other than cost and size, are there any other disadvantages of using the bigger values?

Thanks.

[acheld]

Will the 10M resistor increase noise or hiss of the amp?

No.  It's not in the signal path.

Will the 1uf coupling cap create problems?

I don't know about "problems," but it will pass more bass signal and definitely will change the voicing of the amp. 

[Zenabi]

Thanks, acheld.

I don't know about "problems," but it will pass more bass signal and definitely will change the voicing of the amp.

Yeah. The point was to pass the whole signal into whatever circuit gets switched in and then have that circuit do its tone shaping.

Come to think of it, I might as well add a 10k/10M stopper/leak on the grid as well. This way the grid is grounded when it's not in use.

I'm just trying to come up with a template for having different channels switch in and out with minimal fuss.

[acheld]

trying to come up with a template for having different channels switch in and out with minimal fuss.

I'm not the big dog around here (or anywhere, nowadays) but have been poking around Dumble inspired amps over the past year.   Dumble used relays and switches to do this in his amps.   There are schematics available over at http://ampgarage.com/forum/viewforum.php?f=5 within the Dumble section.  His switching schemes work well, but I don't think they are unique to his designs.

One thing is clear:  having multiple circuits in an amp and switching in and out of them dramatically increases the complexity of said amp.   

[d95err]

1u is overkill in this position for any normal guitar tube circuit. You should be able to use 0.1u or even lower, without audible impact on the following circuits.

For example, Engl amps (lots of relays and options…) typically use 47n/2M2 after gain stages, to decouple them from relays and following circuits.

(Note: official looking Engl schematics found online are full of deliberate errors, but you can find schematics traced by people on various forums which should be accurate.)

[Zenabi]

Thanks for the link, acheld.

d95err, you're right. 1u is overkill. I've redone some calculations and like you've said, even 0.1u is probably overkill. I'm going back to 0.1u.