String ringer quite scratchy.

[dubiousss]

So after a year of shelving this project I came back to it now I had those mouser transformers. (42TM006-RC).
Ive loaded it all up but its terrible scratchy. I did an audio probe and the VCO/LFO thing works fine, guitar signal travels to the transformer board fine. Its when it comes off the second board that its all scratchy. So its either the transformers which is a bummer cause I got the exact right ones now, or its the diodes, which I read in another post should be matched up?

In the drawing http://homepage.ntlworld.com/paul.nelson666/StringRingerv12r.pdf it shows to use 1n4148 diodes, the list says 1n34, in the schematic it says use 1 1n4148 and 3 d1n60/5dg. I socketed the diode slots but results are varied and havent got anythign smooth yet. Any help would be welcome.

[nexekho]

I'm assuming it's a fairly standard dual audio transformer ring modulator with some kind of synth/LFO?  Looks like it.  Anyway, though I've never built a real one, I found using four Zener diodes worked best in the simulator and made a smooth signal.



Also, it seems to distort a lot - 100mv on both inputs seems to be the limit at least in the simulator.  Maybe try dropping the input volume?

[dubiousss]

update, So its pretty much clean until very low volumes. low volumes works best on my powered pickup that has a very clean signal. Still some scratchyness at the very tail end of notes, hopefully this will reduce when I clean up some of the wires, but i think im gonna have to live with it, no good fade outs. I did try lowering the input volumes of the carrier and guitar but it didnt help. I really need to buy a scope one day..


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OK looking over the demos and sound clips of the real ring stinger I see they have a scratchy sound and the end of notes also, I think its the nature of the diode ring, its just most of the demos constantly hits notes and dont let things ring. Also reading about how hard it is to match up this circuit I think im happy where it is. Once I've finished this I can move back to completing the maestro that i coupled with a sequencer.. has taken me ages to get a +15-15 +12-12 power piece.

[Taylor]

Diodes don't conduct until you cross their forward voltage threshold. That means that you will have no signal through the diode ring when the signal is smaller than the Vf of the diodes you're using. Germanium diodes have a lower forward V than silicon ( about .3v vs. about .6v) but Schottky diodes are even better, sometimes .15v or .2v. Using a matched quad Schottky array (TI part number UC3611) will give you the least gating and best matching, as the diodes are formed on the same wafer.

You can get over this by amplifying the signal, but the problem in this circuit is that you then clip harder because of the diode clippers. I haven't done this mod, but looking back at this project I'd want to have a switch to turn off diode clipping. That would allow amplification into the diode ring without increasing distortion (why this circuit includes its own clippers is beyond me - by the time one has a ring modulator, has one not also a generic distortion?).