Old Stereo console amp repurposed for a Cigar Box Guitar

[swingarm]

[swingarm]

So the amp im building there is a stereo amp. I would like ideas if you fellas would share. I want to switch from piezo to magnetic and run one channel for each using a stereo cable. I'd also like to blend and possibly use a switch that could run one guitar pickup selection out to both amp channels. I'd like to do this from my  guitar switches and not have any foot switches. This amp will only be used with a 3 string cigar  box guitar. I guess under that last scenario there may or may not be impedance issues.  Any help from you switching gurus would be highly appreciated. this amp will be built as a combo and run 6l6 or 6v6 or mixed in parallel (each channel) with a mix pot on the amp to bring one tube forward and one faded back or both full tilt etc.
Cheers

[newey]

As I was reading through your post, my first thought was "stomp box"- but then I read you want to put all this into the guitar.

Blending the piezo and mag signals won't work very well without the use of a buffer/preamp to solve the impedance mismatch. JohnH has written extensively on this, and has a design for a zero-gain onboard buffer to do just that. And he built it all into a Strat- but I question whether you'll have enough real estate in the cigar box to do everything you want to do. Sure, a cigar box is bigger than a Strat cavity, but I assume that, given the constraints of building a guitar out of it, you won't have the whole interior available.

I want to switch from piezo to magnetic and run one channel for each using a stereo cable. I'd also like to blend and possibly use a switch that could run one guitar pickup selection out to both amp channels.

If you haven't already built the amp, adding a separate input for each channel would solve some headaches. You could then use two output jacks on the guitar, with a stereo jack for one input at each end.

I have had a stereo Tele half-built on my workbench- it's been sitting unfinished for several years now due to my work schedule overtaking my life. But the design uses two outputs with a switched jack for one of the two. One pickup goes to each channel, such that, if a mono cable is inserted into each of the jacks, each pickup goes out to its own channel, but using a stereo cable into the switched jack put both pickups into one channel. Just an idea.

[swingarm]

yes for sure, maybe i was not clear in what I was trying to achieve. A stereo jack that feeds one channel from the magnetic and one from the piezo. If each has its own volume and each has its own channel in the amp each are isolated from each other seems like it should work good.. I've seen some real cool switching and blending here and i looked at the preamp you mentioned. It looks cool. IT always takes me time to figure out beneficial switching scenarios. I figured you guys would be able to rattle something off straight away . I've read that tone controls do not work great with piezo pickups. I could not get the sound clips to work in John's thread for some reason. Anyway im going to study further what you guys have done in the past and try to figure something cool that will work for me. Im not really looking for super complicated and yes i don't see room being an issue but i do need to experiment with placement and i've not potted the piezo yet so im still in the theory stage of configuring this set up. I do have the amp started though.
 I have read that the input value of 1m to ground can be increasedsignificantlywithout affectingnoise performance. An increase to 4.7-10 meg will allow direct connection of the guitar  with little or no loss of low end response. An alternative is to use a j-fet buffer powered from dc with around 10m of input resistance built into the guitar to isolate the cable from the pickup. Thanks for your reply!

[swingarm]

I should ad the the blending would be isolated from each pick up. But I was wondering if there was a switching set up to use both amp channels for one input.

[newey]

You're right, if each input is isolated all the way into the amp and you have separate amp channels, then presumably a buffer wouldn't be necessary. But if we're blending the signals in the guitar, then the two aren't isolated.

Simplest set-up that Im' imagining would use a DPDT On-On-On to select mag/both/piezo, still maintaining separation to the stereo jack. Using a stereo cable then gets you your 2 channels; inserting a mono cable then gets you both outputs on one channels- but with the impedance mismatch as discussed.

[swingarm]

Sorry I'm not very good at these switching schemes so i'm not doing a very good job of explaining what im trying to do. The switching at the guitar would feed either a or b of the stereo amp or both. Even when both they would still be isolated , that would be my goal. Then I'd also like the option of feeding mag into 2 channels or piezo into 2 channels somehow to make use of both stereo channels for one pickup. That is what i would like to try for. I dont mind several switches on the guitar. I just dont know how to wire it to achieve the above. It seems like it would be doable. I can start to try to figure this out with a schematic but just thought some of you guys could figure this out in minutes instead of my hours

[sumgai]

swinger,

Where did this amplifier design come from? I have questions.....

sumgai