Adding CV Ins to Ring Mods (Frequency Analyzer in this case)

[expanoncolin]

I had a tutorial for this on the site a LONG time ago, but took it down because I tried to make it too vague even though it wasn't that vague of a mod.

A CV in, or "Carrier Voltage" or "Control Voltage" (depending on your preference) to your ring mod allows you to use odd signals to modulate your input signal.  Most commercial ring modulators consist of two main parts: An oscillator and a way to modulate that oscillator with the input signal, creating the ring mod effect.  This "way to modulate the oscillator" is often either an AD633 analog multiplier, a LM1496 balance modulator (not so common), or an LM13700/LM13600 operational tranconductance amplifier.  Most ring mods come with built in oscillators that usually output one or two waveforms, normally triangle and square if not just triangle, but Ring Modulation is possible with a variety of signals, from the output of your oscillating feedback loop to your radio to your voice to your drum machine, all sorts of fun effects can happen, and most ring modulators are capable of doing these effects, with a few limitations.  It is normally pretty easy to do-find the oscillator, find where it connects to the modulator, cut the trace at the right spot, put in a switched stereo jack, input a properly sized signal (normally around 8v peak to peak) and go crazy.  Here I am going to show how it is done with the Electro Harmonix Frequency analyzer.

Before we start, you must know that by cutting PCB traces you are doing irreversable damage to your PCB board.  Damage that can be easily fixed by a wire, but the board will never be the same.

The Frequency Analyzer uses an 8038 waveform generator to create the waveform used to ring modulate your input signal (guitar, whatever).  It then uses the AD633JN to do this modulation.  To create a CV in, we need to cut the trace between the two and insert a switched jack (stereo or mono) in between.  This way, when there is nothing plugged in, the AD633 will be connected to the 8038, while if something is plugged in, the 8038 is disconnected and the input signal is sent to the AD633.  If you need any switched jacks, ask me, I have a ton I can let go of for really cheap.

Here is a picture of the circuit board with the proper point cut:


Simply connect the pin shown on the AD633 to the NON switched lug of the jack, and then connect the lug shown to the SWITCHED lug of the jack.  Don't forget to ground the jack.

Here is how I mounted it:


I hope it works out for you.  If you do this to another ring mod, please post the results below.

-Colin

[arnehepp]

my friend tipped me about this one, and I've been thinking about it a bit...

because I'm using it in a feedback loop, I would like a 3-way switch that changes betwen cv-in, cv-in/qaveform generator, and waveformgenerator. this way I can use the cv in from aux from my mixer and dont have to worry about pulling in and out a cable, and especially dont have to worry about big differences in volume when changing from cv to waveform. OR DO I??  

that is the question. never mind the level of the cv input because that is aux controlled, but the 8083, will that be too loud (or to low) compared any normal signal? is this anything more I should think of or consider?




hey, thanks for helping us creative minded who would have ended up breaking even more stuff if you didnt exist. (my usual way of doing reverse enginering is to take the pcb's and rub them against each other to get glitch effects).

-Trrg

[expanoncolin]

You could certainly mix the CV in with the normal oscillator, but to do this safely you'd probably want to build a simple active mixer like this one:
http://generalguitargadgets.com/diagrams/mixer_sc.gif

You coudl remove input 3 and 4 and their respective pots/caps/100k resistor.  If you didn't want volume controls, simply remove the pots and connect the inputs directly to the cap.  You could then just have two switches, one to turn each the CV In or the internal oscillator on/off.  That would work pretty well for your purposes.

-Colin

[danobeavis]

This is an awesome mod--thanks for the details.

I'm a bit confused about the photo. What is the dashed green line?

[expanoncolin]

This is an awesome mod--thanks for the details.

I'm a bit confused about the photo. What is the dashed green line?

The dashed line just shows where a jumper is on the other side of the board.  Just to help you visualize what is happening on the ciruit board.

-Colin

[danobeavis]

This is an awesome mod--thanks for the details.

I'm a bit confused about the photo. What is the dashed green line?

The dashed line just shows where a jumper is on the other side of the board.  Just to help you visualize what is happening on the ciruit board.

-Colin

Got it. Thanks much.

[danobeavis]

I just complete a re-house/true bypass of an FA for a local player. I added your awesome CV mod and it works great! Thanks so much for the research on this, and for sharing.

Here are some pics of the process and completed project:

[expanoncolin]

That is awesome!  Your rehouses pay very much attention to the details, I can tell a lot of care is taken.

-Colin

[nicholaslaughterer]

Thanks for the great tutorial, this was a snap.

Danobeavis, where did you find a suitable point, to power the LED?
Also how did you make it true bypass?

[danobeavis]

Thanks for the great tutorial, this was a snap.

Danobeavis, where did you find a suitable point, to power the LED?
Also how did you make it true bypass?

Just pull 9V+ off the adapter and run the negative of the LED to the new 3pdt switch.

As for true bypass any of the standard diagrams will work. Make note of where the in and out lines are on the pcb and work from there.

[nicholaslaughterer]

okay, true bypass, makes sense, I got that.

how do I pull 9v+ off the adaptor?

[maxime]

I discover the website right now,


wow !   (':juggle:')

I was thinking about modding a frequency analyzer for CV input too. I would like to modulate the carrier frequency with a external VCO. I don't think the mod is the same as yours, right?
this one is about getting external carrier to modulate the multiplier, isn't it?

keep on modding !!

very inspiring

maxime

[expanoncolin]

I discover the website right now,


wow !   (':juggle:')

I was thinking about modding a frequency analyzer for CV input too. I would like to modulate the carrier frequency with a external VCO. I don't think the mod is the same as yours, right?
this one is about getting external carrier to modulate the multiplier, isn't it?

keep on modding !!

very inspiring

maxime

I don't THINK the FA is using the 8038 in a way that makes for easy voltage control.  You will probably have to implement some sort of LED/photocell (or much better, H11F3) setup to modulate the fine/shift resistance (perhaps in parallel).

-Colin

[maxime]

I 'll try this!

thanks a bunch

maxime

[superttramp]

hello
that mod seems interesting , but what exactly should I plug in the CV jack ? should I plug something while playing guitar in the ring mod.?
thx
Rémi/France