Harry Bissell’s Guitar Synth project

[Tim Escobedo]

Those of you wanting a interesting guitar synth project, look no further than Harry Bissell, SDIY guru and BBD hater.

http://www.wiseguysynth.com/larry/guitar.htm

No construction notes. Schematic page 1 is the basic design. Multiplied by six, since this synth uses a hex pickup, one circuit per string. Waveform conversion, VCF, VCA, and Harry's unique envelope follower design profiled in Electronic Design.

OK, so it's a little more complicated than a Fuzz Face.  :wink:  Still worth a look.

[puretube]

thanks, Tim!!!

Hey guys: that is almost (though simpler coz differently approached...) similar to the barberpole envelope-follower principle like the one I mentioned a while ago:
http://diystompboxes.com/sboxforum/viewtopic.php?t=25637


edit: BTW, I thought that env-foll in ED was different!?
(have to look it up again... anybody got that link handy?)
ahh, here it is:
http://www.reed-electronics.com/ednmag/contents/images/122602di.pdf

edit2: on closer look, mr. Bissell`s circuits are the same, except for a 20 times higher "scan" rate in the newer schem...

[mikeb]

I bought the PCB that Harry produced, and am slowly stuffing parts into it as time permits ... ETA for completion is mid-2005.

Mike

[StephenGiles]

Tim, I must be psychic - I was looking at that EDN article last weekend and thought it would be nice if Harry Ever published his circuit. I think Mark Hammer has heard this synth and was very impressed. Mark - are you out of bed yet - it's 13.58GMT as I type!
Stephen

[Mark Hammer]

Seen it?  Hell, I've played it.  If the circuit is the same, a terrifically responsive unit.  Definitely NOT the same sort of beast as a Roland, and perhaps more properly described as a guitar processor than a guitar synth, since it does no P-to-V conversion.  On the other hand, the absence of lag (the very lag that is so common in the P-to-V process) is a large part of what MAKES it so responsive.  It's the sort of thing where it is still easy to feel like you're playing guitar, very organic and natural, and not one of those things that feels like you have to give the instrument instructions.

The key thing here is the use of:
a) a hex fuzz to produce a harmonically rich signal source for subtractive synthesis
b) a better-than-average envelope follower

Traditional keyboard synths used "subtractive synthesis" which meant use of a harmonically rich initial waveform that one would chisel away using filters and such.  Much like a block of granite gets turned into a sculpture by selectively removing material, the assorted waveforms that the oscillators in a synth would produce contained more harmonic content than one intended to end up with, and the filters - driven by envelope generators - would shape what harmonic content made it through over time.  Here, the use of a hex fuzz (and Harry uses a G-Vox divided pickup which he told me could be gotten cheap on E-bay - same thing as a Roland hex pickup) provides that source, which is then shaped and filtered.

Ultimately, it could be described as little more than a fuzz box an envelope controlled filter, and a Slow Gear but that would do it an injustice.  The magic happens when something as simple as that arrangement becomes integrated, optimized to work together, and harnessed to six individual strings.  The same way one person dancing looks okay, but 10 people doing the same choreography at the same time looks stunning, hex processing sounds much more impressive than the same thing in mono.

Interested parties will note that the entire circuit is not shown.  Harry uses an old 360 Systems Slavedriver for pre-treatment of the hex signal.  He explained it to me, but I have to confess that some of it (does 80% count as "some"?) went over my head.  I guess I was in too big a hurry to get my whack at the guitar itself before I had to run upstairs and turn the oven off (I was catering).

[puretube]

I hope to find my early 80`s selfmade hex-pickup soon,
for which I built 6 basic Elektor`s "Formant"-synthesizers,
to show y`all, how you can rip 6 reed-relays` coils for
a DIY 6-PU. ("sound" of the PU doesn`t matter in this case...)

:wink:

[Marcos - Munky]

I hope to find my early 80`s selfmade hex-pickup soon,
for which I built 6 basic Elektor`s "Formant"-synthesizers,
to show y`all, how you can rip 6 reed-relays` coils for
a DIY 6-PU. ("sound" of the PU doesn`t matter in this case...)

:wink:

A DIY 6-PU? Cool!!! In my case, I need a 7-PU .

[toneman]

Munky,
Use mini magnetic recording heads
from old cassette tape players.
This is similar to what the GR500 used waaaaaay back
when there were lots of free range electrons.

stayHexed.....& a boo 2 U!!
tone

[Marcos - Munky]

Did you tried it? And how it sounds? Do it need any kind of circuit to work? I'm thinking to get a cheap 6-string guitar to do some mods, and maybe this will be a cool thing to add.

[toneman]

"Sounds" ?
If U bias the heads correctly, U get "sound".
Sounds like a guitar.....
Doesn't "sound" like a synth
until U run it thru other processing elements.
U can get Roland GK2As , used, for around  100bucks on ebay.
Without using a GR30 or similar, U'll have to provide
plus&minus 7VDC for the preamps in the GK2A.
No one said this was easy...
afn
tone

[Nasse]

http://img.photobucket.com/albums/v411/Nasse/hex_pup.jpg

A photo clip from some old British electronics mag from my "archives"

Never tried it but the article mentions it needs a strong magnet put near the tape head, and preferably the pickup is best put near the bridge, because the signal is weak anyway so it must placed as close to strings as possible and at the bridge the string does not move so much that it touches and rattles to the pickup

I´ll remove the pic soon few days perhaps but thanks for the original author and the mag who might have the copyright or something, but I believe it is about 15 years old mag

(Edited) Forgot to mention it is maybe hummbucking if stereo head coils are wired certain way, which helps signal to noise ratio with low impedance and low noise opamp. I shall look the original article and author if I have some time

[StephenGiles]

It looks like Electronics Today International which no longer exists.
Stephen

[Marcos - Munky]

Looks interesting. I need to get a cheap guitar and some tape heads.

[jmusser]

So, are you saying that this little circuit would be used in the place of a pickup for each string? Are you also saying that this is something you would have to do before you could even use the synth circuity, which would also have to be duplicated 6 times?

[StephenGiles]

It may be sensible to build just one to get working from your guitar's existing pickup. It will only work one string at a time so it would be no good playing chords at this stage, as playing more than one string will confuse the electronics, or will it? We don't have any form of pitch extraction in order to derive a control voltage for driving a tracking oscillator.
Stephen

[puretube]

So, are you saying....to be duplicated 6 times?

yes...

[Mark Hammer]

The critical element of hex pickups is that they be able to sense only what is happening on one string without interference from adjacent strings.  To do that, it needs to be jammed up against the bridge where the string wiggles least.  While tapeheads CAN work, making a workable unit that can be jammed up against the bridge with each head sensing ONLY what lies above it will be hard.

As an aside, the hex pickup that came with this Guild Tri-Oct I bought a couple years ago was supposed to be able to deliver fully polyphonic octave dividing.  It CAN, but the problem is that the pickup is about the size of a Jazzmaster pickup, meaning that you can't stick it where it really needs to go to keep the string signals truly separate.  Regrettably, it results in too much "bleeding", and so false triggering.  Harry, or someone, though, suggested to me that, as a product of the 60's, it may well have been intended to be used with heavy gauge flatwound strings, which would undoubtedly extend the zone of "least wiggle" well out from the bridge, and possibly far enough that a pickup of that size could be workable.

All that being said, scoring a G-Vox is probably the safest bet for most builders.  It is apparently virtually identical to the GK-2 pickup.