As Picard hinted at, a conductive panel helps. In fact, it is absolutely necessary in this filter. This is the first time I’ve used a temporary plastic panel, and probably won’t do it again. With the plastic panel, if I touched any of the pot shafts or bodies, I would get hum. I accidentally touched the Emphasis shaft with one hand and the ground for the output with the other and the hum disappeared. So, that kinda gave it all away. Last night I whipped up an aluminum panel and installed it, no more hum.
While I was trying to figure out what was going on, I used some unmatched transistors in the ladder instead of the SSM2210 ICs (I was trying anything). They work but might be contributing to some other oddness, that may actually be correct, I really don’t know. The audio inputs affect the resonance, which seems odd. I may do another video, but Picard, can you tell me if yours does this?
@piscione Congratulations sir!
I always go for metal.
Could you describe the resonance effect? Matched transistors are absolutely required for the intended filter characteristic. Otherwise resonance and slope of the transfer function will drop (plus other strange effects maybe). You have single transistors just now?
Yup, six single transistors. Most of the examples I have seen of this filter are using individual transistors. Here’s the continuing saga.
We absolutely need pairwise matched transistors. That can be single transistors which have been manually picked out of a batch like Mr. Moog did or monolitic integrated transistor pairs like the SSM2210. The Yusynth circuit I did in the pics above is kind of hybrid - the current mirror and the differential amplifier is integrated (CA3046) and the ladder is discrete (3 matched pairs of BC547C).
So I’d suggest you to replace the transistors and then let’s face the resonance problem - if it’s not already gone. BTW I myself skipped the input pot and feed the full oscillator signal.
I’m a bit leery of desoldering all of those transistors (yup, I removed the sockets too, just trying anything I could think of). Maybe I’ll just order another board, I have most of the parts already around to build another one.
I’ll take the ham radio filter if you no longer want it after building a second one. It can go with my other equipment that dreams to be a ham radio.
Oops, I fixed the radio problem. Although, get rid of the metal panel and it would come back.
Ah, I just watched the other video you linked to. Not as obvious as an embedded one. I would assume that the same resonance/input behavior happens with input 1 as well? If so, I doubt it would be a crossed wire.
As Picard said, the transistors should be matched. You may have ended up with an arrangement that just happens to phase cancel the resonance. I do think that the timbral change with no resonance is actually pretty cool though. You may want to try this filter configuration on some more subtle moving sequences where resonance may not be as important before “fixing” it.
Funny you should say that, I was doing something like that. That’s why I’m thinking about getting another one. I figure I could leave one a bit, uh, unusual, and the other a bit more standard. It’s an easy build and not very expensive. I’ll probably post one more video, just to demo it actually working. I have no idea how to embed Youtube videos or Soundcloud stuff on here.
The matched transistor thing confuses me a bit. I remember finding a thread on Muff’s (which is down now unfortunately) that mentioned not bothering with matching the transistors, and that Moog didn’t match them either, just pulled them from the same batch (which I did). Could be anecdotal 'though.
I have two more or less normal filters, a Ripples and an MMG. The others are a bit rougher around the edges, a CGS Synthacon and Discrete SVVF. I tend to use the crazier ones more than the normal ones.
Moog for sure used matched transistors, even in the service manuals there are tutorials to match them.
Apropos matching - did you actually use matched capacitors for the ladder, piscione?
If you finally go for a new board, we really could start a batch of 3 of my layout (incl. audiohoarder) since I spent some effort to route the signal traces as short as possible and it has a ground plane - so the ham radio should be minimized.
I did not use matched caps, nothing in the build docs suggested that. Or, I just missed it. Now I’m really curious to build another one, using the SSM2210 ICs and matched caps. What do you suppose one of your PCBs would cost, and whereabouts are you located?
I’d be interested in getting in on a nicely routed MM filter PCB too. Although, I’m on the other side of the pond from Mr Piscione.
I just remembered (I’m getting old) that I bought the kit from Bridechamber so the caps may have been matched.
i really like what ive heard of the hearn Morley stuff https://sites.google.com/site/hearnmorley/synth-diy-resources
The dual ssm2040 filter sounds very nice, i believe thats what hes done - clone the SSM 2040
@Dogma, the filter we’re talking about here is a transistor ladder filter based on one of the Minimoog filter designs. The filters on the site you reference don’t seem to match this design, at least from what I can see.
Sorry @piscione I shoud have made that clear
I would love to try one of PCBs Picard had - very nice.
Sounds like a grounding issue of some type or another - very strange problem…
Yup, it was grounding, although I haven’t figured out why. Metal panel solved it.
Well, it looks like a run of Picard filter boards is in demand. Just let me know the price.
Yeah! Looks like we are one man per continent. I’m in Germany…
I usually take Jackaltac, a batch of 5 would be around 17 EUR / piece.
My domestic supplier would do a batch of 10 for 20 EUR / piece - in this case I could label it Made in Germany…
Don’t forget to check the original Yusynth page for build instructions. Also check my derived schematic if it fits your needs and tease yourself with a pic of the actual module…
You really simplified the panel. Count me in for one PCB plus shipping to Canada. I have the SSM2210 ICs already from the first build, just need to get matching caps I suppose.