Guitar Input

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Guitar Input

I am interested in running a guitar through the Werkstatt. Is this possible? I was considering using the VCO LIN IN - could it be this simple? Has anyone tried this?

D. Vollkasko
D. Vollkasko's picture
Audio-In from other Instruments

Hi Keith,

VCO Lin In is not a Line-In, but a linear control voltage input. You'd run an external controller's CV Out to VCO Linear Input to control the pitch of the Werkstatt.

Take a look at, esp. page 20f.:

"In general, the Werkstatt is designed so there are no “illegal” patches, though not all make musical sense. In experimenting with the Patchable Header, there are some ground rules/best practices that apply."

Page 26 on Audio Inputs in the Patchable Header: "VCF AUD IN: Filter Audio Input" -- I think this is what you want to use to turn Werkstatt into an awesome filter/effect for your guitar.

Page 22 has a pointer on having the guitar amp and Werkstatt on the same mixer to achieve a common ground (literally), and on making the required cables.

I like your idea. I did something similar with a crappy five bucks junkstore keyboard run through the Aux In of a Stylophone Gen-X1, which also offers filters and stuff, to live enrich (or mangle ;-) ) the cheapo sound of the keyboard. Great fun, especially with the ridiculous-sounding default rhythm section of the keyboard.

Let me hear how it goes!

D - this is fantastic

D - this is fantastic information - thanks a bunch! I will certainly post back how it goes, along with my other mods (which mostly include re-housing the Werkstatt in a bigger wooden box and externalizing some of the controls using oversized nobs and levers. So far I have replaced the on-board pots with external rotary and linear sliding pots and everything is working. Once I get this guit input working as an option, it's gonna be a fun addition to my band's setup for both experimentation, and live performances! Cheers, Keith

Wow, I forgot about this forum...

Thanks for bringing it back!
You can plug the guitar audio directly into the VCF_Aud_In but... the LFO is always connected to the filter so you won't be able to use it as a pure filter, only a modulated filter. However...
From this page:
you can cut a trace on the board, insert a shorting jack in there and disconnect the LFO whenever the instrument is plugged in.

But there are also some caveats:
1. Your guitar signal is unipolar, meaning it goes from 0V (gnd) to whatever voltage your pickups will produce (around 3V). The werkstatt, on the otherhand, is bipolar and the voltage signals traverse the range of -5V-0-+5V. This means that filter will work on only the top half of the waveform. You need to build a converter circuit on the little kludge area on the werkstatt's PCB. You can make one with a single opamp and a few resistors.
Here is a good lesson:
2. The signal input from your guitar may not be of sufficient strength to be audible. Looking at the user manual for the Grandmother we see there is an instrument input on the back and, according to page 34, it gains up the signal 10db. You can use another opamp to create a simple non-inverting gain stage to make that up. If you use a dual opamp you can fit both circuits in the kludge area.

Here are some more links to modded werkstatts:

And here is a link for another circuit you may need:
I used a couple of these circuits when I built my sequencer:

Erix, a wealth of information

Erix, a wealth of information - thank you! i have some work cut out for me now. stay tuned... I may need some more help as I get a design together.

... and ERix that sequencer

... and ERix that sequencer mod and build is beautiful - NICE!


I'm working on a new version now, arduino based.

I forgot another good site for mods:

Hey Erix, I've been doing

Hey Erix, I've been doing some calculations and trying to design a circuit, and I could use some guidance. Aiming to boost the signal by 10db would mean a voltage boost of about 3.16x. should I boost the signal before the UniPolar to BiPolar converter circuit, or after? The reason I ask is if my math is right using the formulas from Adrian Nastase on I can do the bipolar conversion and get to the correct voltage with one circuit:

Vout = Vin * Gain - Voffset

If Guitar In Voltage = 0v to +3v --> a 3v range
Required Voltage = -5v to +5v. --> a 10v range

Then I need a gain factor of 3.3, and a Voffest of 5v, which would yield the correct Vout of -5v to +5v, right?

Vout = Vin * Gain - Voffset

+5v = 3v * 3.3 - 5v
0v = 1.5v * 3.3 - 5v
-5v = 0v * 3.3 - 5v

I calculated values for the resisters in the circuit to be:
R1 = 6kOhms
R2=R3=R4= 10kOhms

am I on the right track? or missing something?

Thanks, Keith

Looks right to me...

...but I’d breadboard it to be sure. You’ll have to power the opamp with bipolar power so it can swing below ground. There are pads on the Werkstatt pcb with -9v, +9v, +5v, and ground.


and thanks for that note on powering the op-amp - that makes sense, and I was wondering what to do there. Any suggestion on which op-amp (component-wise) I should use, or specs to search out on Digi-Key?


FYI: I was planning on going with this guy:

It has two op amps, so could also go with the single op amp version...

OPA2134 is a great part...

But an 072 will work just as well.

I've been thinking about this project some more and I might be making it more complicated than it needs to be. I have a schematic that purports to be the MF-101 and the instrument input on it is just a non-inverting opamp, fed by +/- 9V, going straight into the ladder filter. Instrument input goes:
10n cap --> 10K res -->470p cap to ground --> 1M res to ground --> + input of opamp.
It has a 50kA pot in the feedback loop labeled "DRIVE" with a 15K to ground.
Output of opamp --> 220n cap -- 47K res --> filter section.

Do you have a breadboard to whip this up?

Success... sort of

I got it to work. Though my 0-3V output estimation ended up being way high (like an order of magnitude I think, though I do not have an oscilloscope to verify it with), it works. It just doesn't do much. Not exactly Pete Townshend playing through his ARP... Here is a video of the results. You can also see in the video a bit of the augmentation I have done with external ridiculously oversized controls.... We call her Tobias.