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 Forum index » DIY Hardware and Software » fonik's place
Voltage Controlled OpAmp RingMod (Modulator)
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fonik



Joined: Jun 07, 2006
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PostPosted: Thu Feb 04, 2010 2:57 am    Post subject: Voltage Controlled OpAmp RingMod (Modulator)
Subject description: SOLD OUT
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harry bissell once recommended irvine's design for a ring mod. i changed the resistors to our common values, and added two VCAs to the inputs, thus giving a voltage controlled ring mod. makes a lot of fun.
refer to this thread for comments, samples and such...

there is enough interest for me to offer a professional built PCB for this project, and i am asking for advance-orders right now.
however, i won't take any money before i hold the PCBs in my hands.
the PCB will be 2.3 x 2.8 in in size. if hit the 50pcs the prize will be about 7.-USD/5.50EUR ea.
i would believe the difficulty level of this project is intermediate. to calibrate the VCAs a scope would be most helpful.
regard the Recommendations for PCB sales on electro-music.com, please.

SOLD OUT (edit: 1 DEC 2010)

the pricing:

PCB:
7.- USD / 5.50 EUR

P&P:
Deutschland: 1.50 EUR
Europe: 3.50 EUR
Worldwide: 6.- USD (1 PCB) / 8.- USD (1+ PCBs)


Documentation
VCRingMod building docs

a finished module could look like this:
Modulator_31

or like this (right part of the triple module)
triple module

here's my schematic:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

original post:
harry bissell once recommended this design for a ring mod. i built it on breadboard, changed the resistors to our common values, and added two VCAs to the inputs, thus giving a voltage controlled ring mod.
i had to remove it from breadboard, but i will built a module soon. so again, no soundclips for now. however, you could easily build it on your breadboard very fast. i just wanted to share, since i liked it very much.


Reference: Irvine, Robert G., Operational Amplifier Characteristics and Applications, p. 174-176

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Last edited by fonik on Wed Dec 01, 2010 12:14 am; edited 14 times in total
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kkissinger



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PostPosted: Thu Feb 04, 2010 8:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Forgive me if I sound like a total newb, but I'm trying to figure out the meaning of the op amp symbols at 10-9 and 7-8 ... are they just unity-gain buffers?

Also, at the IC1A and IC1B inputs, I presume the diodes are external, correct?

The voltage-control biases the modulator, correct?

Thanks!

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Blue Hell
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PostPosted: Thu Feb 04, 2010 8:35 am    Post subject: Reply with quote  Mark this post and the followings unread

kkissinger wrote:
[...]I'm trying to figure out the meaning of the op amp symbols at 10-9 and 7-8 ... are they just unity-gain buffers?


These are the LM13700 (which is an OTA and not the usual opamp) built in buffers, when you look at the data sheet it will be obvious.

Quote:
Also, at the IC1A and IC1B inputs, I presume the diodes are external, correct?


These are inside the OTAs as well.

Quote:
The voltage-control biases the modulator, correct?


The OTAs implement VCAs, so the CVs would be level controlling.

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kkissinger



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PostPosted: Thu Feb 04, 2010 8:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey, BlueHell, thanks for the info.

Incidentally, I just added a switch and a couple of capacitors to my Aries Balanced Modulator (to get rid of unwanted DC bias) and this circuit caught my eye -- looks like a neat way to get some clean modulation.

I just glanced at a recent parts order (I should take delivery tomorrow). I'm building a couple of MPS modules that use the LM13700 and I ordered 10 chips to build up my parts stock. I'll be set to mess around with this circuit Smile

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fonik



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PostPosted: Thu Feb 04, 2010 11:38 am    Post subject: Reply with quote  Mark this post and the followings unread

kkissinger wrote:
I'll be set to mess around with this circuit Smile

it took me just an hour to put it on the breadboard, it worked from the start, and then i had two hours of fun before going to bed...
so try it! it's worth it.
BTW try different waveforms for carrier and modulator, at different freq setting. it is so cool to have the modulator changing slooooowww...

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slacker



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PostPosted: Thu Feb 04, 2010 1:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for sharing this Matthias, it's very cool.

I've only breadboarded the modulator part without the VCAs but it works really well. You get really nice ringmod sounds with 2 audio signals and I like the fact that you can drop the carrier right down to below audio and it acts like a VCA.
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fonik



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PostPosted: Thu Feb 04, 2010 3:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

slacker wrote:
I've only breadboarded the modulator part without the VCAs but it works really well. You get really nice ringmod sounds with 2 audio signals and I like the fact that you can drop the carrier right down to below audio and it acts like a VCA.

cool. did not think of that.

the VCAs are just a benefit to fill the front panel. however this is a little bit of anti-modular.

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fluxmonkey



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PostPosted: Thu Feb 04, 2010 4:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

just straight (w/out the VCA modulation), how does the sound of this compare to other ring-mod designs, like 633 or even passive transformer/diode?
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widdly



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PostPosted: Thu Feb 04, 2010 11:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

Does the ring mod work with DC inputs and AC inputs?

If it works as a VCA with a DC input, you couldd loose the 13700 and duplicate the ring mod part twice for the left hand side VCA's. Then it could also work as a 4 input ring mod.

Last edited by widdly on Thu Aug 05, 2010 10:00 pm; edited 1 time in total
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fonik



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PostPosted: Thu Feb 04, 2010 11:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

yes. it works DC. great idea, widdly.

as in comparison to other ringmods: i have a AD633 ringmod, i will be able to compare them as soon as i built a module from our new circuit.

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BOB-SNARE



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PostPosted: Fri Feb 05, 2010 1:48 am    Post subject: Reply with quote  Mark this post and the followings unread

bbob wrote:
just straight (w/out the VCA modulation), how does the sound of this compare to other ring-mod designs, like 633 or even passive transformer/diode?


This looks like a "switching mixer" i.e. when the modulator is -ve the phase of the carrier is inverted and when +ve the carrier is non-inverted. This is for the case where the amplitude of the modulator is greater than the carrier. When the carrier is larger than the modulator, part of the carrier will be clipped at 0V.

Where as the 633 is a 4-quadrant multiplier, so it has amplitude modulation too.

So they should sound different.

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PostPosted: Fri Feb 05, 2010 11:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Here's a couple of quick soundclip of the modulator, I haven't made any attempt to do anything musical, it's just to show what it sounds like.

One input's a fixed frequency saw and the other is a triangle that sweeps from below audio and back again, in the second clip I change this to a saw half way through.

If you look at the wave form you can see that it works how BOB-SNARE explained. At slow modulation speeds the ramp up saw morphs into a triangle and then into a ramp down saw. If you use a triangle wave it morphs into one twice the frequency.


ringmod1.mp3
 Description:

Download
 Filename:  ringmod1.mp3
 Filesize:  1.18 MB
 Downloaded:  673 Time(s)


ringmod2.mp3
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 Filename:  ringmod2.mp3
 Filesize:  1.25 MB
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fonik



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PostPosted: Thu Feb 11, 2010 5:33 am    Post subject: Reply with quote  Mark this post and the followings unread

PCB could look like this. however, i will have to build my SMT version first. so stay tuned...

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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LektroiD



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PostPosted: Sun Feb 14, 2010 11:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

I need 4 of these! I love this effect. I also have the Moogerfooger MF102.

Would this also have low & high impedance to work with mic, guitar or line level (presuming this is the purpose of the VCA), or would I need to modify?

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fonik



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PostPosted: Mon Feb 15, 2010 12:26 am    Post subject: Reply with quote  Mark this post and the followings unread

LektroiD wrote:
Would this also have low & high impedance to work with mic, guitar or line level (presuming this is the purpose of the VCA), or would I need to modify?

unfortunatley not. the purpose of the VCA is to have voltage control over the inputs.

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richardc64



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PostPosted: Mon Feb 15, 2010 2:45 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
LektroiD wrote:
Would this also have low & high impedance to work with mic, guitar or line level (presuming this is the purpose of the VCA), or would I need to modify?

unfortunatley not. the purpose of the VCA is to have voltage control over the inputs.


Could not the left-over op amp be used to boost low-level signals such as guitar or mic?

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fonik



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PostPosted: Mon Feb 15, 2010 3:46 am    Post subject: Reply with quote  Mark this post and the followings unread

wouldn't we need two actually? one for the carrier and one for the modulator?
anyways, i'd liked to leave it as a synth module. maybe i should/could bring out the left opamps pins to pads? the one could use it for whatever he wants to...

BTW i once had the MS20 external in circuitry on my breadboard and i found it quite useful. i especially liked the idea of using a 1M potentiometer to change input impedance and amplification. worked fine for me.


MS20_extin.gif
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MS20_extin.gif



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a100user



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PostPosted: Mon Feb 15, 2010 4:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Matthias,

Bringing the pins out to pads is a very good idea.

Thanks for posting the MS20 circuit, agree that could be very useful.

David
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Dave Kendall



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PostPosted: Mon Feb 15, 2010 4:28 am    Post subject: Reply with quote  Mark this post and the followings unread

+1 for pads for the spare Opamp.

Maybe if board space permits, include pads for the couple of additional components to make a simple attenuverter?
They're always useful to have around....

cheers,
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PostPosted: Mon Feb 15, 2010 4:37 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
wouldn't we need two actually? one for the carrier and one for the modulator?


Well, yeah, if both modulation and carrier are low-level, like voice modulating guitar, or vise versa. But as a synth module, one or the other is likely to be at a high enough level. I was avoiding adding another package.

A low-budget way to do it might be to change the attenuation at the OTA inputs by increasing R4 and/or R8. A.C. coupling might be desireable.

Quote:
anyways, i'd liked to leave it as a synth module. maybe i should/could bring out the left opamps pins to pads? the one could use it for whatever he wants to...


Excellent idea! Should be incorporated in all future projects with unused devices. Frankly, I have doubts that non-logic inputs (op amps,) even need termination.

Quote:
BTW i once had the MS20 external in circuitry on my breadboard and i found it quite useful. i especially liked the idea of using a 1M potentiometer to change input impedance and amplification. worked fine for me.


Ah. I knew I'd seen a circuit something like that. You saved me the trouble of digging through my old magazine clippings.

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fonik



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PostPosted: Mon Feb 15, 2010 5:58 am    Post subject: Reply with quote  Mark this post and the followings unread

richardc64 wrote:
Excellent idea! Should be incorporated in all future projects with unused devices. Frankly, I have doubts that non-logic inputs (op amps,) even need termination.

Very Happy
be this as it may, i've done it on the PS3100 PCB in a way one could use jumpers to set the spare opamp as inverting buffer without input OR use the pads for utilizing the opamp for other puposes.

however, i will have to build my SMT version first, PCBs are on their way!

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fonik



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PostPosted: Wed Mar 03, 2010 3:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

built the SMT version tonight. worked from the start. sound samples will follow as soon as i got the frontpanel and put it into the system. BTW, i enjoy SMT more and more...

RingMod Components Side

RingMod

RingMod front panel side

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haxster



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PostPosted: Thu Mar 04, 2010 12:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Very nice Design. I love no Wires! what kind of Jacks are those? Are those BI potentiometers also?
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fonik



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PostPosted: Thu Mar 04, 2010 12:56 am    Post subject: Reply with quote  Mark this post and the followings unread

jack sockets are from china (chuangjiebao), potentiometers from taiwan (song huei). both direct orders from manufacturer (MOQ 1000psc).
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adambee7



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PostPosted: Thu Mar 04, 2010 7:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Another excellent piece of work Matthias. When you get either version ready for sale I'll have 4. Cool.
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