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Fonitronik Thomas Henry SSM2164 VCA/VCF
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Fonitronik Thomas Henry SSM2164 VCA/VCF
Teusa Rass
Before I get trouble with desoldering:
There is a footprint for R10 the normal size for resistors.
The BOM assigns R10 as a 2k/+3500ppm/C tempco,(which is much
fatter in size).
I don't know now which part might need to get temperature compensated,-
like say on the TH X4046 the tempco is stuck over the LM394, which makes sense to me.
I use to see Fonik's designs as immaculate, so I wish to get some
enlightment from somebody more experienced than me.
Teusa Rass
edit and up
I looked at the project on the website and to me this doesn't make sense. Typically you'd put the tempco on the part of the circuit that is temp sensitive. In a VCO it will be the matched transistor pairs if they have them. Here the expo converters are in the 2164. But the tempco and 2164 are pretty far apart on the board. So I'd question if the tempco really does any good. Usually with filters that use a expo transistor pair if you aren't going to use them as oscillators you can leave the tempco out of the circuit and the tracking will be good enough. Probably should put this in the original project thread.

2164 Filter Project

Good luck.
The tempco is definitely supposed to be compensating the CV of the 2164 -- see the schematic. emmaker is right that it is probably not super effective or necessary, but you might as well put it in. You could consider epoxying it to the top of the 2164 and running wires to the pads on the PCB, as Dave Brown does in a different build here:
Teusa Rass
Thank You for the answers,-
this is exactly what I was thinking, but feeling insecure about.
As I built two of these, I now will go and put in a normal 2k resistor
into one and wait what will happen.

After finishing a module I always am so anxious to blow it that sometimes
I dare not testing it for days.
Procrastinating, rearranging modules, start building another one
Did anyone have problems with using TL072CP in the circuit? It caused resonance problems for me. Works good with TL082 and NE5532.

edit, sorry I should post this on the main thread/
I'm having a few issue with it, I'm using ne5532s but the module doesnt respondas it should. Course, fine and res just seem to act like volume controls and on lowpass I'm getting heavy bass frequencies with res at full clockwise. I've reflowed the whole board and even swapped out the 5532s for new ones, could it be a faulty audiocool chip or does anyone else have ideas as to what to look for to resolve the problem?
i did not find it necessary to have tempco on this module, nonetheless, i designated the parts as thomas henry did in his original documentation. i should amend the documentation accordngly.
BTW the temco resistors i use are even smaller than your common 1/4W resistor wink

@staticcharge:the NE5532 is not 1:1 replacement for the TL072. it just has the same pinout, but does not work the same in all situations. if you want lower noise, larger bandwidth go for the OPA2134.
NE5532 is not a JFET input opamp has has an input resistance sigificantly smaller than JFET opamps.

@sammy123: i am puzzed. all TL072s are decoupled and even have a cap in they feedback path. i really don'T know how this could possibly happen.
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