Transformer Ring Modulator

[kristopher612]

interesting, have you seen the active real ring mod on ken stone's site?  it has null controls for signal and carrier, set up similar to the ring stinger clone, but it's not quite the same.  i may breadboard both of these to try when i get out there next week in order to compare them.   

[DavenPaget]

kristopher612 just swapped the modulator & the carrier around ala the Ring Stinger and it doesn't change the carrier bleed thru at all. From what I can gather si diodes from the same batch will be pretty close anyway so I'm not sure if it's even worth getting the UC3611N as it probably won't make much of a difference?? I might try Schottkey diodes (1N4001) see if that helps.

O_O schottky diodes aren't 1N4001 . You can try BAT85 , BAT42 ( similar ) or 1N5817 .

[dthurstan]

kristopher612 I'd not seen that before. Probably the best way to do lattice type ring mod. External carrier, various inputs & controls for signal, carrier & output level. I'm happy with the results I'm getting, I just want to tweak it a bit more. Once I finalise the schematic I intend to post pics and clips of the ring mod, so stay tuned.

DavenPaget I had it in my head that they where schottky diodes, doh. Oh well maybe I'll buy some 1N5817s sometime. Cheers for the heads up.

[dthurstan]

So it's been a while and I haven't done a great deal on this. I'm having trouble with the gate, getting the right value resistor to the transistor base, which will set the threshold. I got hold of some schottky diodes.

Here is a clip with different diodes;
http://soundcloud.com/dthurstan/ringmod-diff-diodes
Details are in the description. I have disabled the gate so you can hear the bleed thru pretty bad. With the gate working the bleed thru is manageable although you lose the tails of long notes, just need to set the threshold correctly.

Let me know what you think.

[dthurstan]

Hey

I don't know if many ppl have listened to the clips above, but apart from the noise it sounds like RM to me.

I have taken a method of matching diodes from electro-music forum. I connected a 68k in series with the diode and applied 9V (PSU) across that, with grd connected to the cathode. Still too much variation when measuring voltage across the diode.

I think the problem I have setting the threshold for the gate, is due the threshold voltage of the comparator (- i/p) is set at Vref which I assume is too high?
The original gate circuit is powered by 5V so Vref is ~2.5V. Im not sure if I can reduce the voltage at - i/p lower than Vref?

[charmonder]

Hey

I don't know if many ppl have listened to the clips above, but apart from the noise it sounds like RM to me.

I have taken a method of matching diodes from electro-music forum. I connected a 68k in series with the diode and applied 9V (PSU) across that, with grd connected to the cathode. Still too much variation when measuring voltage across the diode.

I think the problem I have setting the threshold for the gate, is due the threshold voltage of the comparator (- i/p) is set at Vref which I assume is too high?
The original gate circuit is powered by 5V so Vref is ~2.5V. Im not sure if I can reduce the voltage at - i/p lower than Vref?

First off this thing sounds really great! This is all a bit out of my familiarity, (Im still having trouble breadboarding phasers!)

anyhow I do have a transformer ring mod that I bought from kenstone modular, its just the two transformers and a matched germanium diode ring. I have this just as a passive box and 3 jacks. The reason I mention this is that the best thing Ive found as far as getting a sound without bleed through noise is to ring modulate the guitar by boss octave pedal. Boss octave has a pretty interesting circuit if you think about it, the amplitude of the oscillator perfectly follows the input sound. I always wanted to figure out a way to get the boss oscillator to a static pitch because it would be a great oscillator for ring modulating. just an idea...

[dthurstan]

Hey cheers charmonder. I should have got 1 of those passive boxes, then I could of just worked on the active side. Although I think a gate circuit is still needed as you just can't reduce the bleed through to nothing. The boss octave sounds interesting. I really like that pedal very underrated. So how does your idea work? You split the signal before the i/p of the RM with the carrier i/p coming from the OC-2? Does this give you octave up?

Does anyone know how to get around the high voltage at the inverting i/p of the comparator? I'm guessing in theory if you can reduce this voltage the transistor will switch off at a lower i/p signal. I could boost the signal coming into the + i/p of the comparator, it is already x11 from the gain stage before the gate which drives the modulator i/p.

Any suggestions?

[slacker]

Instead of wiring the 100k resistor from the - input to vref, connect it to the wiper of a pot wired as a voltage divder across 9 volts. That will let you move the comparator threshold up and down, this might be useful as a control, or you could use a trim pot or a couple of resistors to set the voltage where ever you like.

Sounds good by the way.

[brett]

Hi
Schottkey makes lots of sense. Highly matched, low Vforward.
Note that 1N4001s are not Schottkey diodes.
The most common is something like a 1N5819 (from memory, might be wrong, look it up).
cheers

[dthurstan]

@slacker

I tested that yesterday and tonight. It doesn't work, because it varies Vref. I've tried a 100k trim between 9V & Vref with the wiper at -i/p, and 9V & grd wiper at -i/p. Doesn't work. I think I need to vary the signal at the +i/p, I've tried putting a 10k trim in but that didn't work. I'm not sure what else I can try.

@brett yeah I got some 1N5817 schottkey diodes. Thats what I'm using in the clip they don't sound as good as the 1N914s to my ears maybe they need less gain.

Anyone know if upping the signal at the +i/p of the comparator will allow the gate to switch off  at a lower guitar signal?

[slacker]

I tested that yesterday and tonight. It doesn't work, because it varies Vref. I've tried a 100k trim between 9V & Vref with the wiper at -i/p, and 9V & grd wiper at -i/p. Doesn't work. I think I need to vary the signal at the +i/p, I've tried putting a 10k trim in but that didn't work. I'm not sure what else I can try.

Sorry didn't explain myself very well, I meant like this



This should let you adjust the comparator threshold, without affecting anything else.

[dthurstan]

Hi slacker thanks for making it a bit clearer. I've been playing around with it, it's very difficult to set it to the right point. It seems to go from 1 state to the other with a very small turn. I may try varying the resistor to the base of the transistor too see if that helps.

[dthurstan]

Hello again

I think I've got something ready to build. Finally! It's not perfect but it's what I'm going with. Here's the schematic;



Biggest thing is I replaced the triangle with a sinewave generator with a good range I got this from the ESP website. I also got rid of the gate as I just couldn't get it to work how I wanted it too, lower threshold and longer decay. I decided to try and reduce the bleed through instead. I have put a 38k feedback resistor from the RM o/p to the diode ring. Then I added a 0.1uF cap across the RM o/p. The cap does remove a lot of highs but it still sounds good. Here is a clip showing the effect of the resistor and cap.

http://soundcloud.com/dthurstan/ringmod-bleed-through

Another element I have been working on is matching diodes, not getting very far with this. Here is what I'm using, but my volts are too low. Increasing the amps is difficult as going to far heats everything up.
http://www.electronicpeasant.com/circuits/diodemch.gif
also
http://www.qrp.pops.net/general-electronics2010.asp
found some more info here
http://mysite.du.edu/~etuttle/electron/elect61.htm

Even though bleed through is still audible I think it works well. It's difficult to get the circuit just right, especially with my limited electronic knowledge  . The gate is a good way to deal with bleed through but I think it may need to be more complex, with trims to set threshold and decay. Thanks to everyone who has given me a helping hand I really appreciate it. Cheers

Let me know what you think?

[dthurstan]

Hey

If anyone has any thoughts on this I'd like to hear them?   

What do you think of the bleed through, could you live with it? My thinking is that I'll be using it as a noise effect or playing tuned so the bleed through becomes less important.
Also I have the octave switch which I haven't tested yet.

There isn't much on the forum about diode matching, however those links above provide some information about how to go about it. I used the popular electronics circuit which at one point I had 9v straight through the 100Rs which was producing a lot of current so I could measure more voltage. I realised this probably wasn't very good the 100Rs got hot and I wasn't measuring stable voltages. Does any one have any advise?

The oscillator circuit is pretty cool. Took me ages to breadboard it, all those feedback & feedforward paths. I may build one just to use on it's own. I found it on ESP website and the circuit itself is originally from Wireless World, February 1982.

Cheers

Dave

[Fernando]

I know the thread is old, but for the archives:

You have to use very well matched germanium diodes and good transformers with wide freq response, not those tiny ones (just look at their specs)
Matching the diodes is critical and it has to be done very carefully, even your breath will alter the reading.
The transformers should be 1:1CT, 3k:3k or higher (10k, 15k etc)

Cancelling the bleed with trimpots is also important