SMR-4 MKII No self-oscillation


I got both of these boards and everything is running. But I’m still not sure about SMR-4 MKII board… I simply don’t get it self-oscillating at all (By the way, in which direction do I have to turn the trimpot?) no matter what I do whereas the ssm2044 seems to sound perfect without doing anything. Do you have an idea since?
Thanks a lot!

Which trimpot do you refer to? The SMR4mkII self-oscillates without adjustment and does not have a resonance trimpot.

Ok, I hoped that maybe the only trimpot on the board influences the resonance somehow. So can you imagine why I have no self oscillation?

No self-oscillation or no resonance at all?

Check that all parts around IC3 are correctly soldered, and check for swapped values.

remove IC3, set your meter in current measurement mode, put one probe on IC3.1, another probe on IC3.6, and tell me what is the maximum current flowing between these pins when reso = 63.

no self-oscillation at all. I hear a veeeerrrry quite noise, but only on my headphones not on my monitors (krk rp8 g2). But that’s nothing compared to the ssm2044 resonance.

The parts are correctly soldered.
The IC3.1 displays -17,74 (I have to check how to interpret the scale…I set it to 20k), and the IC3.6 -18,71.

You need to measure a current, not a resistance or a voltage.

are you sure, you messured a current (= strom) which is messured in Ampere (in this case probably milli ampere mA) ?

your messurement results seem strange to me. no matter if you messured resistance (widerstand) which should not have a negative result, voltage (spannung) which should be between +/- 5v at max. or current which should not be in the 20k range

in the …K range? it shouldn’t even be in the Ampere range.

@rosch : K range = resistance :confused:

@rosch: i think he messured resistance. because thats the only think that should be in the k range. i still don`t get how a resistance can be negative. maybe some kind of Perpetuum mobile… (or am i missing something here? if a resistance can be negative i misanderstood something about electronics big time…)

At school we learn everything, in physics we’re currently learning (imho unnecessary things like) how to add harmonic wave functions, but we don’t learn these simple things. It’s a shame.

Maybe just to make it clearer. Resonance works and filter board in general as well, but I don’t get self-oscillation at all as I hear it on the ssm2044.

I measured some values but these don’t seem to be correct, because they don’t change if I change the resonance value (For example IC3.1 remains at 0,11 all the time). Here is a picture of my multimeter. Can you say me which is the correct measurement mode? The manual says it’s only able to measure DC no AC - maybe that’s important.

Thank you

Black probe (COM) on IC3.6, red probe (VmAOhm) on IC3.1, mode set to A, 20m. You need to do 1 measurement (current flowing between 2 points).

The multimeter displays 0.00 after having it tried over and over agian and I definitely did it correctly according to your instructions.
The synth itself works and sounds well but the resonance reaches no self-oscillation or these “screaming” resonance levels at all.

Can you take a photo of the measurement process to make sure it’s not a measurement error? Since the resonance control does something (right?) you shouldn’t read 0.00.

I wasn’t able to make to probes touch the pins while I took the photo, but you can trust me that I’m able to touch these two pins (The first and sixth one). This demonstrates how I measure. Interestingly it did not even show a flow of current when I touched the output expansion “5v” and “ground” solder joints. Probably the mistake is caused by a defect multimeter?

Thank you very much for your help

See my original message:

remove IC3

Voltage is measured in parallel, current in series. The current needs to flow through the meter.

General Tip: tidy up your Workbench. With all these Wires flying around you could easily drop down to the 165fryers Caste of the ShruthiVersum because of shorting anything on a PCB…

I put the red probe into the IC3.1 and the red one into the IC3.6 pin header and there is no possibility for the current to take another way than going through the multimeter, but anyway it just shows 0.00 !? My unhandiness is unbeliveably discouraging.

@fcd72: Yes you’re right, I will take your advice to heart :slight_smile:

Are you shure you used the right pins? You start counting on the upper left counterclockwise where upper means the direction the Notch on the PCB is printed.
Maybe you have to plug your Red Probe into the Blue Hole, some Meters don’t switch automatic.