Ideas for Quad VCA project

[Joncaster]

I have a Quad VCA cause I couldn't order a Dual at the time...
I have other duals I used instead for the tremolo project I worked on a while back.

I'm wondering what I could use it for?
I'm thinking of a quasi-Leslie simulator, but that seems like quite a big undertaking.
Have the LFO control left and right sweep with two channels,
and the amplitude modulation via the other two channels,
but then get some slight frequency modulation going somehow on the Hi-Frequency signal (Low frequency can just stay tremolo-ed)
Maybe two duals would be a more suitable structure then...

Any ideas are welcome.
Thanks

[StephenGiles]

Which quad VCA is it - 2164?

[Joncaster]

Which quad VCA is it - 2164?

Sorry yes, its the Cool Audio V2164D

[Mark Hammer]

The Small Stone and its derivatives (e.g., Ross Phaser) use 4 OTAs to do its business.  Frankly, I'm surprised there aren't a slew of 4-stagers built around the V2164, since it would make for a nice compact and sweet-sounding unit.

Is EHX using those for the current issue, or are they still using a pair of 13600/13700s ?

[Joncaster]

Ahh ok, a Small Stone kinda thing would be awesome.

Nice. Thanks Mark

[StephenGiles]

Try here
https://www.njohnson.co.uk/pdf/cesyg/vcapf-sch.pdf

[StephenGiles]

And this:



ASHDOWN ENVELOPE FILTER APC054 ISSUE A
PARTS LIST FOR PCB INSERTION
VERSION B – 20/03/06
Part Name   Description   Qty   Reference
1N4002   DIODE   1   D6
1N4148   DIODE   8   D1 D2 D3 D4 D5 D7 D8 D9
         
R1/4W,100K   METAL FILM 1%   6   R2 R13 R21 R25 R26 R33
R1/4W,10K   METAL FILM 1%   9   R3 R7 R12 R17 R22 R23 R30 R50 R51
R1/4W,1K   METAL FILM 1%   5   R14 R35 R39 R40 R49
R1/4W,1M   METAL FILM 1%   2   R11 R46
R1/4W,220K   METAL FILM 1%   2   R9 R34
R1/4W,22K   METAL FILM 1%   12   R5 R6 R18 R19 R28 R29 R31 R32 R36 R43 R47 R48
R1/4W,2K7   METAL FILM 1%   1   R24
R1/4W,33K   METAL FILM 1%   2   R38 R41
R1/4W,470K   METAL FILM 1%   1   R10
R1/4W,470R   METAL FILM 1%   2   R37 R42
R1/4W,47K   METAL FILM 1%   8   R1 R4 R8 R15 R27 R44 R45 R52
R1/4W,4K7   METAL FILM 1%   1   R20
R1/4W,NOT FITTED   NOT FITTED   1   R16
Zero Ohm Link   Zero Ohm Link   24   As shown on PCB silk screen
         
33pF 50v   CERAMIC DISC 5MM   1   C20
100pF 50v   CERAMIC DISC 5MM   3   C2 C3 C24
560pF 50v   CERAMIC DISC 5MM   2   C15 C16
10nF 100v   BOX POLY 5MM   2   C21 C23
22nF 100v   BOX POLY 5MM   1   C4
100nF 100v   BOX POLY 5MM   5   C10 C12 C13 C14 C22
1uF 16v   RADIAL ELECTROLYTIC   3   C1 C11 C19
2u2 16v   RADIAL ELECTROLYTIC   2   C9 C18
10uF 16v   RADIAL ELECTROLYTIC   4   C5 C6 C7 C8
220uF 16v   RADIAL ELECTROLYTIC   1   C17
         
LM833   IC DUAL OP-AMP   1   IC2
TL062   IC DUAL OP-AMP   5   IC1 IC3 IC4 IC6 IC7
SSM2164
ANALOG DEVICES   IC VCA   1   IC5
BC549   TRANSISTOR   1   TR1
ZTX614   TRANSISTOR   1   TR2
         
PP3 Snap on Battery Connector      1   RED to BATTERY +VE
BLACK to BATTERY -VE
DC CONNECTOR   2.1mm Pin Dia
Like Farnell  224-959   1   J2
STEREO JACK    Cliff S4-BNB-PCC  or
SCJ644R5NDS0BP0   2   J1 J3
LED 3mm   Mount with tip of LED 12mm above PCB   1   D10
POT SINGLE B50K   Alpha 9mm Vertical Mount
RD901-40B
6mm 18 spline shaft L=15   5   RV1 RV2 RV3 RV4 RV5
         
PCB - APC054      1   
         
PARTS BELOW -   NOT ON PCB      
FOOTSWITCH DPDT   Double pole change over   1   S1 Connected to PCB with 6 x 100mm wire links
VU Meter    Componex 35mm round face (as used on original Peacemaker combos)   1   Connected to PCB with 150mm wire links 1 x RED 1 x BLACK
         
         
         
         

ISSUE AB -    R9 220K (was 22K), R45 47K (was 22K), R49 1K (was 10K)

[StephenGiles]

And this:

https://www.sowa.synth.net/modular/vcf.html

[StephenGiles]

And here:

http://synthdiy.fonitronik.de/files/3514/7392/5080/TH_2164VCFVCA-v1.pdf

[Joncaster]

Stephen, that's amazing thank you!

[Mark Hammer]

Yeesh, I asked the same question 9 years ago!   
https://www.diystompboxes.com/smfforum/index.php?topic=95152.0

[ElectricDruid]

Frankly, I'm surprised there aren't a slew of 4-stagers built around the V2164, since it would make for a nice compact and sweet-sounding unit.

The trouble is you need two further op-amps per stage. So your four stages on one chip turns into one chip plus eight op-amps (at least two more chips).
Apparently there is an alternative arrangement for the 2164 VCA all pass stage that only uses a single op-amp, but I've not seen it.

For compact phasers, the 3320 (AS3320 or V3320) is a better bet. Then you really do have all you need for four phaser stages on one chip. You only need op-amps for the in/out at the ends. You even get VC control of resonance.

I've been experimenting with this, but found it a bit noisy. That's just the curse of OTAs, I suppose. You don't notice using the chip as a lowpass/highpass/bandpass filter because so much signal is removed, there's not much noise left either. As soon as you turn it into just a narrow notch that is removed, you can hear gently phased hiss while you're not playing. Still, there might be a way. Or stick a compander on it, like you suggested.

[Mark Hammer]

You're right, Tom.  I knew there was a reason I bought a few 3320 chips from Small Bear a while back! 

[Joncaster]

Yeesh, I asked the same question 9 years ago!   
https://www.diystompboxes.com/smfforum/index.php?topic=95152.0

Haha I found that too, thanks!

[Joncaster]

I'll get this all together and put something together once I've cleared the breadboard.
I've still got a spring Reverb sitting there to hack at. And another parts order, but funds are limited what with this lockdown.

At least I'm finally boxing up my tremolo though. Progress.

[ElectricDruid]

How about a quadraphonic panner? V2164 for the four VCAs, phase-shift oscillator to provide four sine waves at different phases.

"You spin me right round, baby, like a record baby..."?

Ok, maybe most of us don't have that many amps. Still, it would have been fun. Until you got queasy.

[PRR]

Which quad VCA is it - 2164?

While CoolAudio has a spec-sheet, it is a less-rich copy of the SSI and Analog Devices' 2164 sheets, which have gut-plans.
http://soundsemiconductor.com/downloads/ssi2164datasheet.pdf
https://www.analog.com/media/en/technical-documentation/data-sheets/SSM2164.pdf

[rockola]

How about a quadraphonic panner? V2164 for the four VCAs, phase-shift oscillator to provide four sine waves at different phases.

"You spin me right round, baby, like a record baby..."?

Ok, maybe most of us don't have that many amps. Still, it would have been fun. Until you got queasy.

I've been thinking of whipping up just this. Many older home theater amps had analog inputs for 5.1 audio. David Gilmour's guitar solo on a Pink Floyd tour (I forget which one) was run through a quad panner so that his guitar was coming from all corners of the venue in sequence.

[ElectricDruid]

How about a quadraphonic panner?

I've been thinking of whipping up just this. Many older home theater amps had analog inputs for 5.1 audio. David Gilmour's guitar solo on a Pink Floyd tour (I forget which one) was run through a quad panner so that his guitar was coming from all corners of the venue in sequence.

Trust the Floyd to go for a quadraphonic system at a gig!

It shouldn't be too difficult. The potential issues I foresee are designing and building an oscillator that can produce four outputs 90 degrees out of phase, and designing a equal-power panner so that the perceived volume of the signal doesn't dip (or peak) as it travels from one speaker to another. Given that the 2164 has a log control law, I need to think about the maths of that, and I can't do that without the back of a *large* envelope and a pencil!
Neither problem is insurmountable, or un-previously-solved.

[swamphorn]

Constant-power panning for two VCAs is pretty ugly in the analog domain¹ but it's far from impossible. On the other hand, it should be easy enough to bake a pan law into a wavetable and generate four phase-shifted modulation waveforms with your choice of microcontroller.

¹http://www.thatcorp.com/datashts/dn120.pdf