RM-1 Woes...

[A.J.]

Howdy;

Built the RM-1 from Topo...sounds like a Ring Mod should, but I just can't get rid of:

1) what sounds like a thin distorted version of my input
2) a constant whine - gets higher pitched as the pitch control is increased - it's pretty loud

I've twiddled every trimmer every which way, to no avail

I used the project voltages for reference and can more or less dial all of them in except:

IC4:
I read 0 on pin 8, instead of +/- 0.15
Can't get -0.03 on pin 6

Also
- I ended up using a pretty big transformer - all I could find in a pinch - I think it's 25V ct, 1A - I only used the centre tap half and my supply voltages are all good
Could this bad boy add noise?  I'll be using something smaller next chance I get out to pick one up....
-Used a NTE326 for the FET - seems ok....(from memory - I think that's what it was)
-Used a 100K dual gang in place of the 150K dual gang pot
-Kept my off board wiring as short as possible, but there are wires running all over - tried to keep them from crossing, but it happens.....
-Checked all components, traces - all seems good.
-Switched out all ICs - no change
-No jacks, all is internal

When tuning it, I can't adjust for 5.5V peak to peak with Pitch Range on high, as indicated in the instructions - must be on low - It reads from about -4.6 to .9V at test point A.

I've spent hours with the multimeter minutely turning the trimpots - it came pretty close to defenestration somewhere around 2am last night - I know I'm pretty close with it and that I should just put it down for a while and come back to it later, but it's really driving me around the bend - never had this much trouble with a build before.

I'm going to try retuning and will recheck everthing and voltages - any experience out there with this one?

A.J. 

[John Lyons]

This circuit is a Bitch to tune! I did it manually by ear as described in the build instructions and tuning procedures. I get a very small whine but it's not bothersome.
The fet is what controls the bleed through of the whine. It works like a noise gate turning the ring tone on when you play and off when you aren't playing. I used a 2n3820 which has a different pin out than the other Fet in the Bill of materials. Maybe this is your problem since the while never stops. Look up the pin out of youe fet and check this with the layout.

The transformer: as long as you get correct voltages at the powersupply won't make a difference because the power supply is voltage regulated. Do try and keep the transformer as far away as possible from the input. Try and move it around to see if the noise changes. I don't think this is the problem though.

Not sure about the voltages or distorted output. Could be the Fet though with the distortion. Since the fet mutes the ring tone it's possible that the fet is not the same pin out as the circuit needs. This may cause distortion...

John

[A.J.]

Thanks John - and thanks for the power supply layout - I think that was yours, right?

FET seemed ok, but maybe I'll try twisting it around - NTE has given me the wrong pinout in the past - maybe I'll try ordering some 2N3820's instead.....

Your RM-1 sound clips are great.....

A.J.

[John Lyons]

See if you can look up the NTE fet and pinout. I can't imagine it would be wrong online. Even just typing it into google should come up with what you need. Unless it's some miswire the FET seems like the likely suspect. Hopefully the distortion will clear up with the FET redo as well!


John

[A.J.]

Ok - quick update and a question....

FET seems ok - gating happily - absolutely no noise when I'm not playing - still needs a tweak to make it a little less abrupt, but I'm in the ballpark, so that's ok....

Bleedthrough is a little more under control as well......

But, I've still got what sounds like my guitar signal distorted in a bad way running through everything - doesn't seem right - don't hear it in any sound clips I've heard - so here's my sort of stupid question:

At test point B - what sound should I be getting when tuning and the osc. is off?

Thanks,

A.J.

[A.J.]

Gave up on the old build - but felt that I had invested enough time in the project - also have the habit of buying 2 of everything (just in case), so I had the parts and some spare time, re-etched the board, threw a new one together last night - turned it on - tuned by ear in about 20 minutes - works great - a little bleedthrough at high pitch, but otherwise really good - sounds like a gamelan, gets the low frequency tremolo, cool phone tones - what a pain of a project, but well worth it in the end....can't figure out what was wrong with the first one....

Call that one closed.....thanks Topo and Basicaudio!

A.J.

[John Lyons]

Ha! I do that as well. I buy 2 of everything in case I fry a part or something breaks etc etc. Good to have the spare parts around for something else...

Glad you got your Maestro RM-1  going! it is a tough build and tune in but if you are patient it comes together. You might try to use grounded input wiring if you happen to get some bleedthrough in bypass as well.

Did the FET need to be reversed of what made the bleedthrough clear up in the first build?

If you have any sound clips let me know and I'll put em up on my site if you want. www.mrdwab.com/john/soundclipspage.html

john