Filter tuning

I can’t get the filter of my lovely Shruthi synth to be in tune from octave to actave. I tune to middle C, fine, but the next octave up the filter is tuned to B, a semitone below where it should be, and below middle C I get A#?

Weird, not really an issue for me, but it would be nice to have the filter correctly tunned!

Any help will be much appreciated, thanks :slight_smile:

You get exactly C, A# and B? Or C, A#, B +/- some cents (which would explain things).

Try turning the trimmer until you get an octave up and down…

I get A# Middle C and B + a few cents, I am tweeking it now and cannot get a full octave :confused:

I will keep persevering!

Thanks pichenettes

If you have windows and a MIDI interface, using this will save you a ton of time!

When you get it tuned, it will track perfectly over 5 octaves at least. My 4PM tracks over 7, and my SSM tracks over 8.

Do you know that the trimmer is a multiturn? You have to turn it 25 times to go from one side to the other.


I had to put the Mixer into ‘Duo’ mode, any other mixer setting and the filter is always a semitone away from being in tune over an octave.

Is this normal?

No. I’m sure that there’s something you are doing wrong, but I can’t think of what it is…

Okay, I made a video to see if that helps anyone identify what I am doing wrong!

Excuse my dusty keyboard, it never gets used as I almost entirely write by programming

First, thing: don’t use “duo” mode. In duo mode, filter tracking is disabled.

I had a look at your video. It’s sometimes hard to know what’s going on. It looks like at one extreme, you have less than one octave, and at the other extreme, more than one octave - which means that inbetween there’s a position that should work!

At the risk of repeating myself, the goal of tuning is not to get “C” when you play middle C. The goal is to get the same note, only one octave higher, when you play middle C and the C one octave higher.

Thanks pichenetts, I am aware the goal is to get the filter in tune over the octaves, but not necessarily in exact pitch with the relevant keys on the keyboard.

I will keep trying to tune the filer

My apologies for burdening you with the technical issues

I think I know what the problem is! The trimmers were around the wrong way, the 5k timmer was where the 20k one should have been, there is another issue aswell.

The trimmer does not come to a stop point on either of the trimmers. When I re-soldered both trimmers to the control and filter board, I now get all LED’s lit and no display. ‘sigh’

I think I need to buy new trimmers from somewhere

@Adam You should feel a slight click then the trimmer exceeds either the upper or lower limit. You can still turn it though, it just won’t change the resistance value any more. I’ve found trimmers to be quite delicate in the past. Turn them too much, and they can break. I’ve had problems tuning filters in the past, and have ended up having the replace the trimmers.


@toneburst Thank you :slight_smile:

I just soldered the 5k display trimmer, but I could only find a 10k for the filter which should be 20k, not sure if that will be adequate or not. Also, I am having power problems, the filter/power board is getting all the right voltages, but the control board is not illuminating the LED’s :confused: