Filter calibration


Built a Shruthi-1 almost a year ago, but didn’t get to calibrate the filter.
Last month, when I followed the steps for calibration I got no sine wave sound. No selfoscillation of the filter. I thought it was a bad soldering job so I reheated almost every soldering point and rechecked all components but with no success.
Today I connected the Shruthi to the Shreditorsoftware on my mac and saw there was a parameter called ‘Flavour’ in the filter section.
I put the Flavour on ‘ms’ and I heard the filter oscillate. Also if I put it on ‘whacky’.
From this moment I could calibrate the filter.

So if you are trying to calibrate your Shruthi-filter and don’t hear it selfoscillate, just turn the ‘Flavour’-parameter to ‘ms’ or ‘whacky’ and it should work if you follow the calibration instructions.
The init-patch has the Flavour set to ‘liquid’ but in that case I don’t hear the filter selfoscillate.

Now the Shruthi has a killer filter :slight_smile:

One question : if the filter is analogue how come I hear steps if I turn the knob slowly ?

Sorry for my bad English.


This is not the normal behaviour. Please post photos of your board.

> if the filter is analogue how come I hear steps if I turn the knob slowly ?

Because the filter control is digital.

Indeed not the normal behaviour, but otherwise I got no self oscillation of the filter…?
I know there is way too much solderstuff used…but no shorts whatsoever…

more pics…

We’ve seen this recently a couple of times…

Which PSU do you use? Could you try using another one?

I tried two different PSU’s. One set to 7,5V the other to 9V both with 1000mAh or more…still same behaviour…

What falls to my eye its the fact, that half of the ICs are not sitting tight in their socket and are sitting quite far to the side. May not be the problem here, but i would double-check this to avoid intermittent issues.

@nightworxx Thanks for your input. I removed every IC and put them back in their place pushing until I heard a faint click…they are surely set deep enough now. Still only self oscillation with flavour set to ms or whacky…

Anyway, I assembled Shruthi again and it’s working fine. Tuning worked very well.
Thanks pichenettes andnightworxx for your time and effort.
Happy holidays !

That’s… really strange. No one else seems to have mentioned this, but since the filter is an SMR4 mkII I wouldn’t have thought ‘flavour’ would have done anything? After all, this filter doesn’t have any different modes (that can be software controlled that is).

Yeah, you can use any of the other filter modes with any filter, but you need to use SMR with the SMR4MK2 filter to get the proper response. You can save the filer selection in the system section so you don’t have to set it each time.
As far as power supplies and resonance, 9V at 500mA or greater seems to give the most stable resonance response in my experience.

@audioharder Once I read your response, thanks for that, I checked the filter settings of the init-patch (in options > Fil ) and it was set to ‘4pm’. No selfoscillation of the filter. As soon as I set it to lpf, ssm, svf, dsp, pvk or sp the filter started to selfoscillate. (with pvk : higher pitch of the sine).

So which settings do you think I should put it on, because I didn’t see ‘SMR’ amongst the list…although it’s nice to switch between ‘flavours’ when set to ‘4pm’. The other filter settings don’t have this ‘flavour’-option…

I feel using 9V instead of 7,5V makes the voltage regulators a bit hot, should I worry or continue using 7,5V ?

Thanks in advance for any answer.

Oh, that is right, you want LPF, for low pass filter. You’ll have to excuse my ignorance. It was changed to LFP in firmware > 1.00 as the SMR mode was also used for the Tubeohm Ladder filter as well, and maybe a few others I am forgetting. Basically, set it to LPF.

If you want some info regarding using the wrong filter modes, you can read this thread. Just remember that doing this may harm your filter board. Basically, I would only worry about polarized capacitors. I would be shocked if the transistors in the LM13700 would be as fragile.

As far as power supplies, if you want to use 7.5V that is fine. Just make sure that you have tuned your filter while using a 7.5V power supply. Changing the input voltage will cause the filter pitch to change. I also use a 9V power supply as I can daisy chain a few FX pedals after the Shruthi. :)The important part is the mA. The more the better, but the minimum is 300mA. You can get by with a very well regulated 200mA powersupply, but that would cost more than a universal powersupply.

“lpf” is the right setting.

Thank you for your fast replies and interesting linked thread pichenettesaudiohoarder :^)
I saved the filter settings to LPF just not to risk any damage if I left it on ‘4pm’ and switching between flavours…

LPF sounds great by the way !

Maybe the manual could point to this issue of filter setting (lpf instead of 4pm) when calibrating the filter 'cause I worried for a while I f*cked things up with my shruthi…and it seems I’m not the only one with no oscillation of the filter using a init-patch… ?

All kits and chips I sell have “LPF” as the default setting. I am not sure how your unit got set to 4PM in the first place…

Me neither, just glad it’s working now as it supposed to…
The Anushri is a beast too BTW :slight_smile:

I was also wondering how it got set to that. As you said you had it for almost a year, I really hope you didn’t have it in 4PM mode the whole time.

If the kits are sold with “LPF” as the default setting, I must have tinkered with it in the beginning and saved it without really knowing…and yes, the filter never sounded this versatile

Yes, definitely my own fault setting the filter on ‘4pm’. I updated the firmware to 1.02 and the filter was set to ‘lpf’. The Shruthi-1 is now one of my favorite go to synths.