Can hear resonance after releasing note SMR-4 mk1

I just finished building my shruthi but when I release my note I can still hear the resonance from the filter. If there is no resonance there is no problem but even with a setting of 10 on resonance I can hear the sine wave after releasing the note. The DC trim, Res trim and Lowww trim don’t do anything. Help!

Solder a 1M or 2M resistor between IC4 pin 2 and IC4 pin 11.

Is this something that I have missed or a common problem?

On some occasions this bleed thru happens, as the SMR-4MK1 is discontinued for some time this knowledge nearly got lost in time…

The logic low from the MCU is not always 0V - this varies a bit from chip to chip - so the problem does not always show up. Fixed a long long time ago in the SMR4 mkII :slight_smile:


I put a 1M resistor between 2 and 11 on IC4. The afte rnoise has gone away but filter calibration is impossible. It sounds like the filter is being constantly modulated by noise. It gets painful after a while. Turning the trims on the filter board does very little, in fact just making contact with the trims makes the behaviour even less predictable.

Can I just have a mkII filter please, this is driving me mad…

Just buy one :wink:
You probably have scrambled up some Rs. On all of my SMR-4MK1 builds everything is fine. Post a High Res Pic of your build, lets see if we can spot something.

> It sounds like the filter is being constantly modulated by noise

Are you sure you are using the “init” preset for calibration? Don’t start with one of the factory presents, some of them have some heavy modulations routed to the filter cutoff.

It’s just not worth the hassle if a resistor has gone. The control board is absolutely perfect, I don’t see any reason why the filter is acting this crazy. I have put the 1M res in and now the release of the note seems very unnatural. Cuts out before the sound fully decays.

How much to the mk2 kits cost with parts?

Yep, init patch. Also the resonance goes from nothing to fairly loud once it is set to about 2 or 3. It’s almost like the pot is acting like an on/off switch.

Maybe there’s a problem with your build then? The behavior of the resonance you describe is not normal.

I do not sell individual bags of parts. If you want the mkII, you’ll need to buy the bare board from me and source the parts yourself.

I can’t see any cold solder joints, I really have no idea where the fault would be. Where do I start with this problem? Is it possibly noise from the PSU?

Maybe. What PSU do you have?

Could you post pictures? Audio clips?

It’s just a variable DC supply. I have it set at 9v but it is running at 700mA, perhaps this is too high? It’s never caused problems on other builds I have done.

The circuit will only take from the power supply as much as needed. As long as it can deliver more than 150mA it’s fine.

Right, I’ll get some pictures together. I’ll resolder everything first. Maybe some audio if it’s still crazy.

Did you throw this in the water? I’ll take this off your hands.

If anything I’d trouble shoot it for free or buy it from you for $100.

Throwing it in a river is such as waste.