Thanks for the advice Phil.  I was just starting to think I should just do the boost in my effects loop.  I do have my circuit running at +/-15V now, so I do get a little bit of a boost there, but still a good several dB lower than the bypassed signal.  In the effects loop it is.

Thanks for the replies, guys.  I am using a TL072 (one half of it) with 12V supply.  Your circuit looks good, Phil, I might have to give that a go.  I just hope I'm not slamming the opamp input.

Hi guys, I have a preamp that I built where the tone control can be bypassed.  The issue I have is when I switch in the tonestack (passive baxandall), the volume drop is quite dramatic.  I want to put in a gain recovery after the tonestack to bring the level closer to what it is when the TS is bypassed.  I put together a simple opamp gain stage as shown here (http://www.muzique.com/lab/boost.htm) on the very bottom right (resistor values changed to what I had on hand).  The issue is that when I start to bring the gain up from unity, the signal starts to clip before very much gain is recovered.  Up to this point in the signal path, there have only been two amplification stages and then the tonestack, so I don't think my input signal is too hot to be boosted cleanly.

My question is whether this topology looks suitable for the application and whether there are any other suggestions out there.  The output of this gain recovery would go straight to volume, then power amp.  Thanks.

Thanks to both of you so much for this! I think I will probably go with spdt relays since I don't anticipate ever needing to bypass something completely, I just need to route where the signal goes (e.g. whether it goes out from the clean pre to the dirty pre or to the power amp).  This looks perfect.  I knew there had to be a simpler way, and panel switch in parallel with the footswitch is no problem, I just wanted to be able to switch channels, etc. if the footswitch is not plugged in.

Syndromet, that is a cool scheme and I may well use it in a future project where I think I am going to build several things in one box and true bypass would be nice.

I can't say thanks enough, guys.

Thanks for the response syndromet.  The structure of the amp will look like the input, clean preamp section, switch to either send that through a tonestack to the power amp or bypass tonestack into additional gain stages which then go through a tone stack to the power amp.  The effect will stand between whatever gets sent from the preamp to the power amp (kind of like an internal effects loop).  I am glad that relays seem to be the solution, now I am just really curious as to how to switch two different things on a TRS cable.  I am pretty certain that I will just need to use spdt relays (signal in on the pole and then the two throws determine whether the signal goes through the clean tonestack or through the high gain portion), but I would also like panel switches if at all possible.  That just seems to complicate things, though, so that is where my own abilities meet their match.

I will have 12 and 6Vdc available in my project.  I really appreciate all your help.  I have been thinking and dreaming switching schemes for the last several days and haven't been able to figure out how I could get panel switches and footswitches to play together (and hopefully LED's as indicators).

So let me see if I am getting this right, I will have a trs jack with sleeve being ground.  Channel switching will be on tip and effect on ring.  I will have a relay for channel switching where NC is just the clean channel and then activated is high gain.  For effect, NC will be no effect and activated for effect, right?  I guess my question is now what if I want panel switches for both? 

I found this article (http://www.geofex.com/Article_Folders/pffootsw.pdf) by RG and was wondering if this would be implementable with TRS or if I would need the same power supply in the head and in the switch (i.e. would i need four contacts as opposed to 3 to pull this off) in order for the relays to work properly.  If I can use separate power (e.g. a battery in the footswitch for 6V relays instead of 12V) then I know I can use a trs for just two channels of that method and I would be perfectly okay with that.

Hi guys, this is my first post, though I have looked around for a while.  I am in the process of building my own amp using discrete components and have a design that I like.  I have breadboarded it and all.  The thing that is troubling me is that I want to have "channel" switching.  Really what I want is to be able to send the signal either to the power amp for cleaner tones or through an extra gain section to give me a high gain tone.  I would really like to do this with a footswitch, but if the footswitch is unplugged, it just gives me clean.  I was thinking I could do it with a switched jack and a dpdt stomp switch, but I also want another button in the same footswitch to activate a single onboard effect.  The effect will also have a toggle on the front panel, so I figure I can just use a relay for that.  The problem is that I want to use a single TRS cable to flip the relay for the effect and also to route the signal from the clean stage but I don't know how I would do the routing of the clean signal with (basically) a TS connection (since the ring would be used for the relay).  I am hoping that you guys can help me out here.  Would I need to use relays for both?

Yes, it is a k-20b it looks like.  Thanks for the info regarding the power supply issue.  That makes total sense now that I think about it.  I'll see what I can do with it.

Hey, I just found this place and have a couple questions for you guys who have more experience.  In my office there was an old Dean Markley kb-20 practice amp that apparently went defunct.  As far as I know the power section in it is still good, so I took it (they've been trying to get rid of it for 2 years) thinking I could at least use the transformer and rectifier and some of the other parts like large caps, etc. 

The only problem is that I am unable to figure out what kind of transformer it is.  The amp is based around two tl072's, so I am guessing that the power section all together is putting out +/- 18V, which is in the operable range of the lm3886, as I understand it.  I am just wondering if I can use the same power section virtually component for component, or if I will be running into risks with things such as current supply, voltage sagging, etc.  I just want a decent power amp for running different low-power preamp sections into.  If anyone can help me with the transformer identification, it would be greatly appreciated.