Jensen reamp/guitar splitter combo

I built a Jensen reamp a few weeks back. I Would also like to have the Jensen passive guitar splitter that uses the same transformer. I doubt I would ever need to use both at one time so I figured it would be a simple thing to combine the two circuites with a three way switch and save the extra cash of buying another transformer and case. It seems simple, but I'm not an EE so If you all could take a look at my plans and see if I missed anything I would appreciate it.

Here are the originals:
http://www.jensentransformers.com/as/as092.pdf
http://www.jensentransformers.com/as/as013.pdf

mine:



Also, in the splitter schem it uses a 680p cap. what type of cap would you use for this. I found only a few types in that size:
http://store.yahoo.com/webtronics/21cd680.html
http://store.yahoo.com/webtronics/dm15-681j.html

Thanks

I think it all seems to be in the right place.

The 680pF is probably going to end up being a ceramic and will look like a disc with legs.
You can always change it later if you find something more interesting.

One of the caps I found was ceramic but it had a 20% tolerance. The other was Silver Mica with a 5% tolerance. Would there be anything wrong with using the Silver Mica since it has a tighter tolerance?

Can anyone tell me what the purpose of this part of the circuit is (--13k--680pf--)?

Anyone have an opinion on the silver mica?

take a look at my plans and see if I missed anything

Click to expand...

FWIW, you could skip the lower third section of the 3PDT-switch and connect everything together - only a DPDT required.

Also, note that the input impedance of this box might be too low for a gtr/bss with passive pickups. It won't do an 1M input impedance.

Finally, it might be convenient to have a second jack input, wired in // with the XLR & jack connectors.

Anyone have an opinion on the silver mica?

Click to expand...

Not from own experience, but based on the various cap-articles these will always be better than ceramics (if at all noticable here).

Bye,

Peter

Use either the ceramic or the mica. Really makes no difference: you are damping the supersonic resonance of the transformer. You could probably omit it and never hear the difference.

You do not need a 3-pole switch; a 2-pole is plenty.


I strongly suspect you don't need the switch or 13K-680pF network. Leave it in guitar-amp mode. When using as a direct box, keep the 10K pot up to maximum volume, the 20K pot down to zero resistance (maximum volume).

As a guitar-amp driver, you sometimes need lower signal and significant output impedance to emulate a gitar pickup; that's what the pots do. As a direct box, you want a little loading on the transformer, mostly so supersonic response graphs look "good". The 13K-680pF is some kind of "ideal" loading for this transformer. In real life, that 10K pot will load it just the same, unless you take precision measurements.

And theory aside: in Real Life, switches fail. Usually in the middle of an important gig.