"meModular" Modular DIY Synth

From circuitbending to homebrew stompboxes & synths, keep the DIY spirit alive!

Moderators: Kent, Joe., analogdigital, infradead, lisa, parasitk, plord, sduck

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sat Aug 10, 2019 3:38 am

Hallo..

I have made some changes. The pulldown resistor (51K) on pin 4 of AS3340 is eliminated. IC5a (TL084A) has been replaced by OP07 with low offset.

Image

Greetings Rolf

alfa
Learning to Wiggle
Posts: 49
Joined: Tue Oct 24, 2017 10:40 pm
Location: Latvia
Contact:

Post by alfa » Sat Aug 10, 2019 10:52 am

Dear Rolf

1. It looks that R40, R44 are connected to noisy -12v.
Maybe add one capacitor 0.1 uF between those resistors to GND
to form simple first-order filter. And better to find stable negative
voltage source for offset.
2. Better to have stable sources for offset trimming R53, R15, R28, R17.
Then trimming will be more independent from +-12V noise, unstability,...
3. Some doubts, that Sync net ( serial connection C16 , D3) will work.

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sun Aug 11, 2019 2:57 pm

Thanks for tips.

I think it's better to use a 79L10 for the negative voltage.

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sun Aug 11, 2019 3:06 pm

Hello

I made some comparisons with a Doepfer A111-3 uPVCO. Here are the pictures. What I especially like a lot of the overshoot in the square wave signal in the A111-3 VCO and the different output levels :eek:

Sine meModular VCO
Image

Triangle meModular VCO
Image

Saw meModular VCO
Image

Square meModular
Image

Sub Mix meModular
Image

Triangle A111-3
Image

Saw A111-3
Image

Square A111-3
Image

Square Overshoot A111-3
Image

Greetings Rolf

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Fri Aug 16, 2019 12:59 pm

Hallo..

I have increased the amplitude of the sine wave from 8.9Vpp to 10Vpp with change of R24 R25 to 24K.

Image

alfa
Learning to Wiggle
Posts: 49
Joined: Tue Oct 24, 2017 10:40 pm
Location: Latvia
Contact:

Post by alfa » Fri Aug 16, 2019 2:06 pm

Dear Rolf
It looks, you don't need R34 and R48. You can simply short them, using corrected values
of R24 and R25.
Capacitor parallel to R24 is needed.

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Fri Aug 16, 2019 3:38 pm

Hallo..

In addition, there is now an LFO/VCO switch (IC8a). The LFO frequency can be controlled from 0.04Hz to 95Hz. VCO frequency from 8Hz to 20KHz.

Image


@alfa
How do I calculate the output voltage?

Greetings Rolf

alfa
Learning to Wiggle
Posts: 49
Joined: Tue Oct 24, 2017 10:40 pm
Location: Latvia
Contact:

Post by alfa » Fri Aug 16, 2019 11:58 pm

Dear Rolf
These part of schematic, conversion triang-》sin, is described in AD laboratory work:
https://wiki.analog.com/university/cour ... s-lab-12sg
Better to use matched transistor (AS394).

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sat Aug 17, 2019 2:19 am

A simple solution for matching two transistors:

Image

alfa
Learning to Wiggle
Posts: 49
Joined: Tue Oct 24, 2017 10:40 pm
Location: Latvia
Contact:

Post by alfa » Sat Aug 17, 2019 3:07 am

Dear Rolf
Integrated "matched pair transistors" means much more than described procedure.
Have a look on datasheets of MAT02 (AS394) ( it is not just pair transistors
with similar parameters.) , check parameters and conditions
in witch they are measured.
But if Your solution is good for your application it is Ok!

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sat Aug 17, 2019 3:26 am

alfa wrote:Dear Rolf
It looks, you don't need R34 and R48. You can simply short them, using corrected values
of R24 and R25.
Capacitor parallel to R24 is needed.
Changed circuit diagram
Image
Last edited by rolfdegen on Sat Aug 17, 2019 3:47 am, edited 1 time in total.

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sat Aug 17, 2019 3:33 am

Thanks for your tips. I think for a VCO is matched transistors 2N3904 ok. For a function generator I would take a MAT02 or AS394.

Now.. I'm testing the sync circuit again. I think there are still small problems ..

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sun Aug 18, 2019 1:09 pm

Hallo

Now.. I try sync function on my Oscillator. Sync_value (yello) on Pin6 AS3340 and Triangle Output (pink). I think Sync- value with C16 1nF is to small !?

Info: Level on CH2 is 2V not 200mV (My probe was seleced to 10x ). C18 100pF is taken away.

Sync+ with C16 1nF
Image


Sync- with C16 1nF
Image


Sync both with C16 1nF
Image




Sync+ with C16 10nF
Image


Sync- with C16 10nF
Image


Sync both with C16 10nF
Image

alfa
Learning to Wiggle
Posts: 49
Joined: Tue Oct 24, 2017 10:40 pm
Location: Latvia
Contact:

Post by alfa » Sun Aug 18, 2019 2:12 pm

Dear Rolf
Looks strange presence of C18 and D3.

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sun Aug 18, 2019 2:19 pm

Ok. C18 100pF is taken away. D3 is only for negative Sync puls for SoftSync on Pin9 !? I will try this without D3.

alfa
Learning to Wiggle
Posts: 49
Joined: Tue Oct 24, 2017 10:40 pm
Location: Latvia
Contact:

Post by alfa » Sun Aug 18, 2019 2:30 pm

Dear Rolf

About D3. Usualy , in low frequency networks, serial connection of capacitor and diode
don't work (C16,D3).

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sun Aug 18, 2019 2:34 pm

The same problem I have with the sync- function. At low frequency sync- does not work.

alfa
Learning to Wiggle
Posts: 49
Joined: Tue Oct 24, 2017 10:40 pm
Location: Latvia
Contact:

Post by alfa » Sun Aug 18, 2019 3:25 pm

Dear Rolf
About D3. It looks better to short it.

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sat Aug 24, 2019 11:46 am

Hallo..

Sync modification

Image



Sync Plus. Yello is Triangle Out. Pink is HardSync Pin6
Image


Sync Minus. Yello is Triangle Out. Pink is HardSync Pin6
Image

Sync Both. Yello is Triangle Out. Pink is HardSync Pin6
Image

Soft Sync. Yello is Triangle Out. Pink is SoftSync Pin9
Image

Soft Sync looks a bit strange. I think D3 is better. It prevents glitch on triangle tip (red circle) :hmm:

Image

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sat Aug 24, 2019 12:20 pm

SoftSync with D3

Image

alfa
Learning to Wiggle
Posts: 49
Joined: Tue Oct 24, 2017 10:40 pm
Location: Latvia
Contact:

Post by alfa » Sat Aug 24, 2019 11:08 pm

Dsar Rolf
If D3 works then it is Ok!
What are the levels on Sync input?

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Sun Aug 25, 2019 12:55 pm

SoftSync input level is asymetric +11.40V (SQU out from A111-3). Yellow is Square output from A111-3 and Pink is Softsync input on Pin9 from AS3340.


Sync frequency 248Hz
Image


Sync frequency 2.130Hz
Image

Greetings. Rolf

alfa
Learning to Wiggle
Posts: 49
Joined: Tue Oct 24, 2017 10:40 pm
Location: Latvia
Contact:

Post by alfa » Sun Aug 25, 2019 11:21 pm

Dear Rolf
It looks you allow too high voltages to be applyed to soft synchro input.
Positive level must be avoided, negative limited till 5v.
So, you must think about potection/limitation for these input.

User avatar
rolfdegen
Common Wiggler
Posts: 81
Joined: Sat Jan 12, 2019 6:48 am
Location: Wuppertal (germany)

Post by rolfdegen » Mon Aug 26, 2019 1:46 pm

The level at Pin9 (SoftSync input) of AS3340 has a voltage of + 3.44V unloaded. The negative SoftSync pulse is slightly larger at high frequencies than the positive voltage at Pin9 (see picture).

I calculate negative level at pin9 must be limited to -3.33V (+10V supply voltage). :hmm:


SoftSync with 632 Hz. SoftSync level (pink) is ok.
Image


SoftSync with 9.133 Hz. SoftSync level (pink) is to high.
Image

alfa
Learning to Wiggle
Posts: 49
Joined: Tue Oct 24, 2017 10:40 pm
Location: Latvia
Contact:

Post by alfa » Mon Aug 26, 2019 10:40 pm

Dear Rolf
Level at pin9 is defined by positive supply volrage and internal divider.
If you don't allow positive spikes come to these pin and limit negative, then at
these place all is Ok!

Post Reply

Return to “Music Tech DIY”