Problems With My Anushri

Anushri Trouble Shooting Values

1) Input DC voltage = 8.2V with a little ripple
2) Input DC voltage post protection diode = 7.35 with a little ripple
3) Output of Voltage Inverter = -6.4V with a little ripple
4) Red Points = I get 4.98V for all of them but they all drop to 4.97 one second later ( not sure why
5) Green Points = I get -4.98V and the remain constant not like the red points
6) Purple Points = For R9 I get 4.1V and for the other purple point (at the resistor) I get 4.08V
7) Cyan Points = it mover between -4.08 and -4.09

First of all I really wanted to solve all the problems by myself but I have come to a dead end and require a little bit of assistance from the pros. ( you guys ) thanks in advance.

So the problems I am having with this synth is

  1. When I turn the synth volume knob fully clockwise I can here the analog oscillator even when I am not playing anything.I know its the analog oscillator because when I move the mix knob between square and saw wave I can hear it change.
    2)When the synth is playing a sequence (any sequence triggered by itself by pressing the run/stop button ) and when i turn the cut off knob (filter) fully anti clockwise I still can hear the oscillator , But its completely distorted. But as I turn the knob clockwise its sounds fine. At this point the envelope mod and lfo mod for the filter are turn completely anti clockwise so they are not affecting the filter at all.
  2. The synth button ,clk/kbd and drums button work from time to time and sometimes it switches by itself without me pressing anything
  3. The drums section doesn’t work
  4. Sometimes when I put the volume knob for the synth at the center position I can hear a really high pitch sound and when i turn the knob fully clockwise the sound disappears.
  5. The good news is that I hear sound and it kinda works but It doesn’t sound like a anushri yet

If you need picture let me . Thanks In advance again.Have a nice day

Hi Ashvin,
your voltage measurements look very well. Maybe the -6,4V (point 3) should be closer to the voltage at point 2 (but negative). But as long as you get the -5,0V (±1%) from the LM7905 there is no problem. How much mA can your power supply deliver?
Have you already done the vco/vcf calibration?
For further trouble shooting pictures would be helpful!

1) ; 2) Could you post a recording?

3) Check for a bad connection between the two boards ; a bad solder joint on the resistor network or on the 74hc165.

4) Make sure that you have pressed “Start” and that the drum density settings are set to non-zero values. Start by listening to pin 5 of the MCU. Then the signal should be present on one pin of C4 - then on the panel jack output, then on the mixer.

Hey Guys, Thanks for the fast replies and here are my replies to your questions-


  1. The LM7905 is outputting -4.99V
  2. My power supply can output 500ma, Its is one of those cheap china variable voltage things, It has two knobs. Ones to control its voltage(3,6,9,12) and the other one is to control its polarity.
    3)No I haven’t done my VCO/VCF calibrations. For now I have just been relying on software tuning. Which works fine. I was thinking of solving all the problems first and then do the VCO/VCf calibrations. Cool ?
    4)For the pictures can you give me your email address? the files are too big to upload. Sorry


  1. Recording posted here (
  2. I did a continuity test here all the way to pin 4 on the 74hc165 and its fine. Should i try something else ? I also did a continuity test for the resistor network and 74hc165 pins and they are all fine.
    3)I somehow got to the drums page for a bit and the drums work fine , its just that i can’t access that page because that button only works from time to time.

The sound is certainly distorted. Do you get such distortion at other points in the signal chain (such as straight at the filter output, or even straight at the VCO output - see the test points in the build instructions)?

Regarding the problem with the buttons, it could be a bad connection between the two boards. Try probing each pin of the resistor network - it should be at +5V and go to 0V when you press a button. Are there pins which are stuck at different voltages or which do not react to button presses?

Hey, so after checking the board here are the results.

Point E = -4.6v constant , tested with multimeter
Point F = 1.2V tested with multimeter
Point L = 0.1V fully opened and fully closed 2.2V (multimeter)

Furthermore I can hear the distorted sound at Point O. So I have uploaded the sound clips from Point F, G, H, V, and K.(

Thanks and I hope to hear from you soon . Have a nice day bro

Can you make a recording with the filter closed (and even better: with an envelope, like in the middle of the first recording you made).

Today Ashvin emailed me these pictures of his Anushri mainboard. Checked all resistors (all the right values in the right place). Everything looks good for me. Except for one thing I have highlighted in red. The two solder points on the back may have contact (R41/R42). Could you check this?

Hey Guys,
Pichenettes I put a new recording for the env affecting the filter, I did it in a few different ways with different pitches, I hope its what you wanted ! And cj55 those two points on the board are not touching each other , Its just the camera angle…

Hello Anyone there ?

One problem at a time… have you solved the drum page button problem?

Yeap Its working brother ! All good…

So what’s the next problem on the list?

So the next problem is my filter section. When the filter is in BP or HP mode, the frequency cut off knob affects the pitch a little bit. Next when the filter is low pass mode. When I turn the knob anti clockwise the audio just disappears. If the envelope is affecting the filter then the filter works a little bit.

Hey can someone please explain to me what does ref _-4.096 at resistor R66 in the schematics means ? How does it effect the circuit ?

It means that it’s connected to a voltage reference that generates -4.096V. So you must read a -4.096V voltage at a side of the resistor (the other point being at 0V). This resistor is involved in shifting up/down the cutoff frequency of the filter so that it remains in a musically useful range.

thanks Pichenettes. So I did some checks on my board today and found 2 values to be a little bit funky. The first one is on resistor 59, I get -3.7 on one end and 0V on the other. The next one is for Point L, I get 1.7V when the filter is fully closed and 0V when the filter is fully open.
Any Ideas why ?

Why do you think your reading on resistor 59 is strange?

Reading on point L looks alright - this could be a consequence of keytracking shifting the cutoff range a bit up.

Because when I was checking the schematics, I saw that the value there should be -4.096V. or thats what I thought. Currently everything works fine on my Anushri except for the filter cut off range pot. When I turn the filter Knob anti clockwise, after the center position the filter stops working and there is no more sound. So I have just been checking all the values on the board to see whats wrong but I still have no idea at all.
Any thoughts ?
Thanks …

> Because when I was checking the schematics, I saw that the value there should be -4.096V.

The -4.096V reference signal arrives at R74, not at R59.

> after the center position the filter stops working and there is no more sound.

Does it sound like an sudden change or is it simply the filter totally closing?