Stereo filter board for Shruthi/Phoenix - first soundexamples out

Stereo Inputs are not a great problem because i have 2 Filter. It is one IC more . But if i do a stereo input i make it jumper switchable for also for mono.
BTW , yesterday i have get the first filter running .
The first schematics comes next for people who wants to build it on veroboard.

@tffshtt , this Vocoder ?? oh , not to compare with the think i will do .
I will build my Vocoder2 in hardware ( without sampler ) but with nearly the same functions .
Here a link for additional infos .


@tubeohm is the plan to use single stereo jack sockets for in and out? I doubt there would be room for 4 1/4" sockets across the back of a Shruthi-1 (and you’d need a custom case, too).


The Eurorack sampler sounds intriguing. Any clues as to possible specs/features?


Hi Toneburst , not now. We are in the early developemen state.
I will take normal stereo audio jacks. The same like in the mono shruthi but in stereo . So you don’t need a custom case . Simply plug and play like the other voicecards .
Yesterday i have finished the filter -only the filter circut , at first without reso and VCA to control the differency of both . looks very good . Today i build the reso circuts. After i have build the VCA it gives the first stereo demo sounds …


@tubeohm cool! I have one Shruthi-1 mainboard PCB left. I’ll use it for this :slight_smile:



Hey , now news . I have build the reso circut . geil> in german - works.
here are the first pictures . Sorry the soundexample comes a little later if i have the VCA ready.
You see 2 curves , yellow= L and blue =R. The reso goes very deep - from 20…30 HZ up to 19 kHZ.
and it is not too loud .
I have here a direct output from 4Volt pp.
from left to right .
1 Picture= reso less, 2 reso full, 3 reso middle- You see also the lin of both filters is good, also the amplitude.
4 actual prorotype . Only the dual VCA i must build .
There are 5 pots . Pot 1,2 is CV1 lin/F_lin L, Pot 3,4 is CV2 lin F_lin R .
Pot 5 is the frequency bal . Move left increases Frq_L and decrease FRQ R and via versa.
Haha , i have fun here . Works good .
Tomorrow come the VCA and than …lets hear .


Ha! urst schau! wannsinn! perfekt!

News 1, schematics Degenerator nearly ready .
News 2: Stereo Filter for Shruthi nearly ready . I have build now both VCA’s .
Today i will build the input amp - stereo external input . than it is time for sound.


I am looking forward to seeing the finished product! :slight_smile:

i’m looking forward to buying the finished product

Hi , the filter board works , needs a liitle fine adjustment. I have made some sounds to look how it sounds. Comes next on Youtube or sound-cloud.
PS , i hurry up to present
the finished product … I am curious what you all say to the sound.
And now again the color question . What color should have the PCB ,?

We don’t have purple yet… :slight_smile: With a matching digital board ? :wink:

white, red or black please…and for god’s sake no blue LEDs

Hi, after a little fine tunning it works good .
Here is the first schematics. First without the power supply . and the block caps .
This is the normal POWER supply with an LT1054.
Now i make e few soundexamples


How it works ![](?
Here a short description .
On the left side you see the two log converter for both filter.
Both log converter use the same input for the cutoff, but than each of them had an additional input ,CV1 for the L channel, CV2 for the R channel.
Remember , Volt/Oct comes direct from the Cutoff output and had an influence of both filters .
the Filter ADSR also , but you can control the filter ADSR amount to zero )!
So you have only the Volt/OCT and now you can use for example the MOD matrix and set the Filter ADSR to CV 1 and the VCA ADSR to CV 2. In fact you get now different ADSR’S for each filter .
Or, set the Cutoff in the Shruthi filter menue , but use the mod matrix for the LFO.
Mod 1 is offset 10
Mod 2=LFO2 , amount 40
Mod 3 is offset , amount 10
Mod 4 =LFO2 , amount - 40 (-40 = Phase 180 degree )
In the end now you get a filter panning effect .
I have also add a stereo input .
The VCA circut is new and allows you to adjust the VCA to 0 output .

Specs : reso oscillation/cutoff from 20Hz… 30KhZ.
12 dB LP, ( PB is also possible with a jumper)
Attack VCA 1,5 ms
SNR - cant measure it , but greater than 60…70dB

BTW: there is a missing connection to the resonance control for the right filter in your schematic.

Yepp you are right . Both wires comes on the same control transistor .
I will make an update .

First Soundexamples


Some stereo effects , filtersweeps , normal Shruthi/Phoenix sounds