Designing a Hexaphonic breakout box. Some questions.

[Rodgre]

Hi all.

I have been toying with this concept for many years and I am once again trying to wrap my head around how to best accomplish this.

I would like to make a breakout box/mixer that will accept the input from a Hexaphonic pickup and simultaneously mix the six pickups into a stereo mixer with panpots for each string as well as normalled insert points on each string, just for fun, and ALSO have separate outputs for each string as well. There will probably be a dedicated output to drive my Arp Avatar too, but that's a whole other topic.

Anyway, I was looking at schematics for Roland GK pickup systems and I am assuming decent buffers/preamps will be required for each pickup, to start. That's probably nothing too crazy to implement. What I am wondering, though, is the best way to split the signal the three ways: to the stereo mixer, to the individual outs and to the Arp Avatar cable. Should I use isolation transformers? Should I put separate buffer circuits on each leg of the split?

I'm worried about the different simultaneous outputs affecting each other. I am worried about impedance issues.

It might be worth it for me to draw up a block diagram of what I'm imagining, but basically, my question is how best to split each pickup output to three splits without interaction between them.

Thanks all!

Roger

[ElectricDruid]

Assuming a single-string pickup behaves pretty much like a "normal" six-string pickup (which I don't know to be the case) I'd say that your buffers can be similar to the sort of thing we'd use on a typical pedal (so >500K input impedance would be nice, and BJT, FET, or op-amp as you see fit).
The mixer part is a simple stereo op-amp mixer. You'll fins loads of schematics for such a thing. Ones with panpots for the inputs are less common, but they're out there too. For example:

http://www.all-electric.com/schematic/simp_mix.gif

The one in the bottom right is the one you want. It shows various types of input you could implement, but for your application, you'd need six of the "mono input with pan". You can also leave out the second "re-inverting" op-amps (the ones with 10K/10K/47pF round them) since you don't care which way up your output signal is. So it's a simple job with one dual op-amp, plus a lot of pots!

If you want insert points for each string, I'd put those between the buffer and the mixer. Since the stuff you insert should have a low output impedance, the mixer's >10K input impedance won't be an issue.

Splitting the signal after the buffer really isn't a problem, despite your worries. The load that the buffer sees will be the parallel combination of the three destinations (assuming you have all three plugged in, which you won't always). Parallel combinations of resistance or impedance always reduces the overall value, but since a typical op-amp can drive loads of a few KOhms without too much sweat, it's very unlikely to be a problem.

If the Arp is going to be fed a signal which contains all six strings, then it would be best if it had its own separate mixer circuit, which could be a super-simple affair with no individual level controls or panpots, just the six signals mixed down to a single mono output to go to the synth. That's a one op-amp job.

I definitely agree that you should draw a block diagram. It'll get it clear in your head, and if you post it here, we can tell you if you're on the right lines. I often think I've got something worked out, but then when I start sketching it out, I realise there's several things I hadn't thought of. Seeing it in front of my eyes makes it far more obvious, at least for me.

HTH,
Tom

[Mark Hammer]

I wonder if there's a schematic somewhere for the Ripley guitar, that Eddie of blessed memory endorsed.

[Rodgre]

Thank you! Tom, you relieved a lot of my concerns, for sure.

Mark, I knew about the Ripley guitar as well. I figure that the simple concept of panning and mixing a stereo signal from the pickups shouldn't be too hard to implement. I mean..... famous last words, ha!!

I'll keep you posted, as I'm sure I will need more advice at several points.

Is anyone else out there interested in this sort of thing?

Roger

[Rodgre]

[Mark Hammer]

To what extent do you anticipate needing all possible output types available simultaneously?  Would having one at a time simplify things in any way?

[Rodgre]

That's a good question. I was just trying to cover all the bases at once, but honestly, I could run the six separate outs into an external mixer and do it that way. I guess I was trying to anticipate any possible use I might have for such a thing, and trying to keep it so I wouldn't need to patch in so many cables and a mixer just to do stereo. Still a work in progress....

Roger

[Processaurus]

That's a good question. I was just trying to cover all the bases at once, but honestly, I could run the six separate outs into an external mixer and do it that way. I guess I was trying to anticipate any possible use I might have for such a thing, and trying to keep it so I wouldn't need to patch in so many cables and a mixer just to do stereo. Still a work in progress....

Roger

I helped a friend with a similar hex breakout, and this was the solution- buy an inexpensive mixer, don’t build one. The breakout consisted of a hi-Z discrete JFET buffer (circuit from GGG) for each string, and quarter inch outs to the mixer. It was pretty cool, he got it going with two amps and the stereo-ness was amazing and so was the clarity from distorting the low notes separate from the high notes.

I suppose in retrospect, where panning was the main use of the mixer, it could have been built with 6x 3 position toggle switches, and done an LCR thing, but the behring3r mixer left a lot of options for science projects.

[pinkjimiphoton]

if i were gonna do this i'd probably see about using a hex inverter like a 4069 or something to do it. you're gonna want something to iso each string, so it would need 6 opamps

shoot. that would work for a hex fuzz, but not what you want.

i gotta agree, a cheap mixer would probably be the easiest way to get the stereo deal.

sounds like more of a pia than worth it sorta...

guitar synthesis stuff requires a lot of compromises... this project seeks to combine what i'd think may be several projects into one.

you'll need an in and out for each string, so that's at least one semiconductor per,  then a summing mixer stage, i'd think for a "stereo" output, and i have no idea what would be required to drive an avatar.

but... you may find some useful stuff on https://www.joness.com/gr300/ that can explain some of the hex stuff that's out there.

[Rodgre]

Thank you. It doesn't take much to drive the Avatar. Just the straight pickup signals. It takes a hexaphonic input straight from the pickup (no electronics) and each string goes through a filter to try to focus it's signal to a frequency range that makes sense for it's likely signal. They also go to mixing, stereo hex fuzz and filtering on the Avatar as well. That's the least of my issues with this project.

I was just picturing some simple buffer circuits for each string, either an op-amp or a single transistor, and then a stereo mixer circuit with two more op-amps and simultaneously, 6 direct outputs, buffered, I suppose? A total of 12 simple buffer circuits and two mixer circuits for stereo outputs.

This is all in my head and on graph paper at this point, so I haven't worked out the schematic in any sense.

By the way, my renewed excitement in hex pickups and my Avatar are inspired by Alex Ball's fantastic walkthrough of the Arp Avatar, (https://www.youtube.com/watch?v=AIOLKwWmHpQ) which is the first time I have seen anyone on YouTube actually play one with a guitar in any way that makes it sound good. The stereo hex fuzz is killer!

[Mark Hammer]

These folks seem to make a variety of hex breakout boxes:  https://www.synquanon.com/products