Looking for help with a 1 in 8 out guitar splitter

[simonkibble]

Hi all

I'm new here so please be nice to me! I am putting together a guitar rack which contains 7 pre-amps (I'm not sure it matters but they are a Triaxis, a Mesa Quad, JMP1, ADA MP1, Carvin Quad X, Mesa V twin rack and a Peavey Rockmaster). I will probably only use one at a time but would like to retain the flexibility to run them in parallel if the mood takes me. My plans for the switching and mixing will be put into action with rocktron patchmates and behringer rack mixers (I know they are cheap but to my damaged ears they are the best bang for buck rack mixers going - and so cheap that if they fail you just bin them and put a new one in!)

My original plan, based on advice I collected years ago from the harmony central reviews section (http://reviews.harmony-central.com/reviews/Effects/product/Rocktron/Patch+Mate/50/1), was to run the system as follows....

Depending on how many preamps you have, you'll want to get adapters or cables that are two female mono 1/4 inch into one male mono 1/4 inch. Plug these adapters into the input of your preamps and then basically daisy-chain your preamps together so it looks like this: guitar into preamp one adapter, out of preamp 1 adapter into preamp 2 adapter etc until all of your preamps inputs are connected. the last preamp will not need an adapter so for example I used 4 adapters for my 5 preamps. I'm running all mono so please keep that in mind. Next, route the preamps to the Patchmate in this fashion. I run my preamps through the first 5 loops so in loop one run the output of your preamp 1 into the return on loop 1 of the Patchmate. There should be nothing in the input or send of loop 1 of the Patchmate. Now, connect loop 1 output of Patchmate to loop 2 input of Patchmate. Then connect preamp 2's output to loop 2's return on Patchmate. Then route loop 2 output on Patchmate to loop 3 input etc. With the exception of loop one which has nothing in its input, all loops connected to preamps should have something connected to input, return and output but NOTHING TO THE SEND. You'll then want to route your effects and so on in the normal way using both the send and returns of the Patchmate.

I was concerned that if I followed this advice simply as it stands I would run into problems with the guitar signal being split into my seven preamp inputs. I've read up on buffers and my question has 2 parts I suppose...

First, if I used the routing suggestion above would a single buffer placed before the first preamp input provide a strong enough signal to feed all the preamp inputs using the daisy chaining approach? If not, would I be better off with a '1 in 8 out' style splitter, and if so, where would I find a schematic to build one? I'm no electronics genius but I have a few friends around me who could build the circuits without any hassle if I get the parts to them.

Secondly, has anyone else built a multi pre-amp set up and been able to parallel the inputs to the preamps? I know I am likely to have to deal with ground loop issues and will probably take the easy way out and buy palmer isolating transformers to solve them (rather than build my own) but I'm not sure how to deal with the input side of things. On the output side the pre amp outs will feed the Behringer mixer, which will then head for my effects rack....

Perhaps I should just buy a lap top and Guitar Rig 4?

[R.G.]

First, if I used the routing suggestion above would a single buffer placed before the first preamp input provide a strong enough signal to feed all the preamp inputs using the daisy chaining approach?

Almost certainly yes. It would be very odd if it wasn't fine with that.

If not, would I be better off with a '1 in 8 out' style splitter, and if so, where would I find a schematic to build one?

"Splitter" is one of those terms that get easily misused and misunderstood. There are two things needed for running a guitar signal to more than one destination, and both of these are consequences of the highly inductive nature of the guitar signal. The inductive nature of the signal makes the treble content be much higher impedance than the bass content. So low impedances load down the treble much more than the bass and cause "tone sucking". To combat this, a guitar needs to drive an input that is (a) quite high impedance, usually 1M but definitely over 100K resistive, and (b) NOT capacitive, which makes tone sucking worse.

The way a single guitar amp does this is with a 1M resistive input on a low capacitance cable. Early effects which did not use high impedance or which were driven by long, high capacitance cables lost a lot more treble than bass and sounded either "dull" or "brown" depending on whether you liked it or not.

A buffer which has an input impedance over 1M resistive, and which can drive several cables and input resistances needs no "splitting". You can just drive them in parallel, and something like an opamp buffer or some other concoction which has a reasonably low output impedance (10K or under) will do eight inputs for normal guitar amps plus connecting cables just fine.

There is a third issue, that being hum. This is where some real splitting may be needed. If you use a buffer which drives two amps, each of which has its own power supply and signal ground, you're open to a lot of hum. Transformer or differential amplifier isolation can subtract out the differences in the ground voltages of each amp, and get rid of much of the hum.

=> if the things being driven are already being powered by the same AC power supply, there's not much chance for hum left, so you likely don't need a splitter <=

If your preamps all share the same AC power supply, you probably don't need the isolation and a buffer will be OK. If they are in the same rack, it's less good than the same power supply, but better than two separately powered amps.

I know I am likely to have to deal with ground loop issues and will probably take the easy way out and buy palmer isolating transformers to solve them

See statement above before you buy isolating transformers.

[simonkibble]

Thanks for that very clear reply - which I suspect may save me a lot of wasted time and money! I should have the rack together and wired up over the couple of months. I was going to treat myself to a Wampler buffer but having spent a good while lately on the various DIY forums I think I might take the plunge and build my own buffer!

I'll report back on progress

Thanks again

Simon

[R.G.]

Do some looking and planning for whatever matches your pocketbook and electronic building skills.

A *very* capable buffer can be made from a $0.30 TL072, some resistors and caps. Two buffers, actually, as the '072 is a dual opamp. It's quiet, cheap and ubiquitous. But you do have to be able to solder and construct well for this to be useful. There are no magic buffers.

[simonkibble]

Thanks again

My soldering skills don't go much beyond repairing jack plugs but my dad's hobby is model building and he specialises in fine soldering work - he has soldering irons for everyday of the week, including some really fancy temperature controlled ones, plus he has loads of experience building circuits to control model railway signalling/points so his construction skills will be most useful I think!

Problem is, he's so good at it I've never had any need to learn.....