EHX EH-8000 Guitar Synth (Schematic)

[Scruffie]

Redrawn schematics for the rack mount EH-8000 guitar synth, mods included to replace the CA3094 with LM13700 and the TL607 with standard CMOS (not sure if this will work in practice, perhaps someone else can advise).

Don't have a schematic for the power supply but it puts out +/-12v from recollection.

[Mark Hammer]

Holy moly!!!!!

[bluebunny]

^^ What he said! 

[StephenGiles]

Holy moly!!!!!

or to put it another way - "well strap me to a tree and call me Brenda"!! Excellent drawing - a veritable work of art.

Here is the power supply circuit I have:

[StephenGiles]

I also have a sample & hold circuit designed by John Williams at EH UK which I'll try to find.

[Scruffie]

Holy moly!!!!!

or to put it another way - "well strap me to a tree and call me Brenda"!! Excellent drawing - a veritable work of art.

Here is the power supply circuit I have:

Thank you very much, Brenda! While this design is slightly different to the 2 x TL601 version you have the schematic for, this still seems to match up to the photos I have of the power board in the unit I repaired from a quick peruse.

I also have a sample & hold circuit designed by John Williams at EH UK which I'll try to find.

Colour me extremely intrigued

[StephenGiles]

I also have a sample & hold circuit designed by John Williams at EH UK which I'll try to find.

Here you go!

[Scruffie]

I also have a sample & hold circuit designed by John Williams at EH UK which I'll try to find.

Here you go!

Oh I see! I was thinking you meant a stand-alone effect, that being the case, I better get building a guitar synth.

Thank you very much, Stephen!

[bean]

Badass Scruffie. Thanks for the share.

Here's a vid I found that does a bit of a deep dive on the compressor/adaptive filtering input section:

[StephenGiles]

Fantastic, last time I saw those waveforms was at EH Uk 40 years ago!!! Where did you find the video?

[bean]

Fantastic, last time I saw those waveforms was at EH Uk 40 years ago!!! Where did you find the video?

It was the only thing I could find on youTube searching for the EH-8000. I don't even know what this thing sounds like. 

There are some other interesting guitar synth related videos on that channel, as well.
https://www.youtube.com/c/AirgunShootingAndRelatedActivities-ASRA/videos

[bean]

Here's the calibration instructions for the EH-8000. This came from a Reverb listing:

[Scruffie]

I'll have to check the video out in a little bit.

Fantastic, last time I saw those waveforms was at EH Uk 40 years ago!!! Where did you find the video?

I don't even know what this thing sounds like. 

It's been about a year since I played with it, but it really does sound like a proper synth and is insanely fun to play with. This is the only demo I know of it online which is far more out of tune than it's capable of and doesn't really show off many of the voices, modulation effects or the portamento http://jeffcreamermusic.com/eh-8000-guitar-synthesizer/

Here's the calibration instructions for the EH-8000. This came from a Reverb listing:

Ah, I was going to have to type up the copy I had, thanks for that

[StephenGiles]

 I did record a few things on reel to reel back in the 1980s using my diy EH Guitar synth in pink BASF tape I remember, which I doubt that I still have yet alone a working reel to reel tape recorder.

[StephenGiles]

Badass Scruffie. Thanks for the share.

Here's a vid I found that does a bit of a deep dive on the compressor/adaptive filtering input section:

fuzz box fanatics might look at this guy's facebook page, linked in the youtube video!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[StephenGiles]

Here are my drawings from the 1980 circuits I was given by the designer.

[StephenGiles]

If anyone is interested, I drew those in MS Excel 1997!!!!!

[Scruffie]

I should point out so it's clear, Stephen's drawings are for an earlier version (schematic dated August '78), identified by the use of 2 x TL601 chips instead of the 1 x TL607 in my drawings (from a schematic dated June '79).

I've seen inside a few Guitar Synth's but have only ever seen the TL607 variant.

[StephenGiles]

Perhaps they had supply problems back then, we shall never know. I wonder if there ever was an official factory schematic. The synth I played with, which was bound for Steve Howe of Yes, I never saw inside.

[Scruffie]

Perhaps they had supply problems back then, we shall never know. I wonder if there ever was an official factory schematic. The synth I played with, which was bound for Steve Howe of Yes, I never saw inside.

I did have a small correspondence with Julia a little over a year ago and if my memory is correct, I think she was unaware of the redesign but suggested it was probably just done as a cost saving measure/circuit refinement.
If you look at the original drawings, the change to TL607 managed to save a 311 & 3140 too which was probably a fair saving back then.

There was a couple of other small tweaks throughout the circuit I seem to remember.

Oh and this was redrawn from an official factory schematic.