Guitar signal splitter

[ckeene]

[I tried UtSF but I couldn't find anything quite appropriate to my question]

I'd like to build a guitar signal splitter that will work for 4-6 outputs. I assume transformers will be necessary to provide some isolation, but when driving 4 or more loads might I also need to contend with signal loss? Are there other noise issues I should be aware of? Surely there's a schema out there from someone who's tackled this problem, though I can't find anything.

Thanks

-ck

[covert]

Transformers are not the only choice, but might be the best. Way back in the old days, Craig Anderton did a diy column for Guitar Player. Among the projects was a splitter/buffer. The thing as designed was only 2 channels, but could probably be modified easily for more. I think it was in his, Electronic Projects For Musicians, book, and I think you can still get that book.

[ckeene]

Thanks, it looks like there's an online version here:
http://www.generalguitargadgets.com/ind ... Itemid=122

...which would involve a series of parallel switches to n-number of the buffered output modules.

Anyone care to explain the buffering circuit to me? The caps I imagine provide some rejection of noise, right? DC filtering?

The op-amp - is it strictly for impedance matching or are we getting any gain out of it as well?

[brianroth]

Thanks, it looks like there's an online version here:
http://www.generalguitargadgets.com/ind ... Itemid=122

...which would involve a series of parallel switches to n-number of the buffered output modules.

Anyone care to explain the buffering circuit to me? The caps I imagine provide some rejection of noise, right? DC filtering?

The op-amp - is it strictly for impedance matching or are we getting any gain out of it as well?

The buffer in the circuit you posted is a unity gain circuit. It provides a high input impedance and low output impedance.

The 741 chip is sucko, however. You would be better off with something like a TL071 (or TL072, which is a dual channel version).

Bri

[ckeene]

Brian,

If I use either of the chips you recommend, would the rest of the schema remain the same?

Thanks,

-Chris

[kayagum]

If you got $ :

http://www.radialeng.com/di-jd7.htm

[brianroth]

Brian,

If I use either of the chips you recommend, would the rest of the schema remain the same?

Thanks,

-Chris

Yes.

Bri

[ckeene]

ok, so I build two of these buffers on a project board, connected them in parallel and sent a guitar signal out to 2 amps. The sound was ....
unimpressive. There's a significant signal loss (maybe around 3dB?) at both amps and noise has increased.

[brianroth]

Try this mod. Use just ONE C1 (0.05 uF) and ONE R1 (1 Meg) to feed the non inverting inputs of BOTH opamps. IOW, where C1 connects to R1, wire that to the "+" input of both opamps (pin 3 of a TL071, or a 741 for that matter).

That will make the input impedance into the pair of buffers 1 Meg versus 1/2 Meg (which would be the case when wiring two of the circuits shown in the article in parallel).

I would suggest a metal film resistor for R1.

Bri

[ciminosound]

Some ideas for slitting guitar signals.

Jakob from Gyraf Audio came up w/this

http://img.photobucket.com/albums/v172/ ... litter.gif

Then there are transformer versions from

http://www.jensen-transformers.com/apps_sc.html#musical

http://geofex.com/fxprojex.htm

[brianroth]

I notice that the Gyraf circuit uses the same "common" bias resistor for all four opamps, as I described. 10 Megs seems high me, however. 1 Meg is more typical for the input of a guitar amp.

Bri

[Scodiddly]

The buffer in the circuit you posted is a unity gain circuit. It provides a high input impedance and low output impedance.

This begs a bit of explanation - there won't be any voltage gain, so the output won't be louder than the input. However, the point of a "buffer" is to provide more available current - more power than the guitar itself provides. So you can split the signal more times without dragging it down with a heavy load.

[gyraf]

[quote="brianroth"] I notice that the Gyraf circuit uses the same "common" bias resistor for all four opamps, as I described. 10 Megs seems high me, however. 1 Meg is more typical for the input of a guitar amp.
Bri [/quote]

Yup - I agree that it looks strange, but real-life tests showed that many - specially old-old - guitars benefit'ed significantly from raising the buffer input impedance above the usual ?-1MOhm. Can't really tell you why - but there were several cases of notably better top-end definition when raised to more than 3M3. 10M was selected "just-in-case"

TL074 shouldn't care about the resulting low input biasing current.

We have used several of these splitters in our studio for the past 10-15years, and we are frequently asked by clients to build them one too. So it's a known-working thingy, even though it seems over-simplified..

:-)

Jakob E.

[ckeene]

Just wanted to say thanks to everyone for the help, links and advice. I think I'm going to go with Jakob's design and will keep you posted.

Just a couple questions on building it:

Should I be fussy about what capacitors I use on the on the outputs of the TL074?

Also, for the 12V rail-splitter power supply, are there specific diodes I should use?

http://img.photobucket.com/albums/v172/ ... litter.gif


Thanks again for the help!

- Chris

[ciminosound]

Should I be fussy about what capacitors I use on the on the outputs of the TL074?

The best you can afford. Electrolytics are cheap. Musicaps or Solen cost $$$.

Also, for the 12V rail-splitter power supply, are there specific diodes I should use?

The power supply diodes? 1N4001 should be fine. If you have higher current ones just use them.