Bill and Will's Synth
Papareil Polivoks Filter Construction

May 2010 -

We think it was Gino Wong who, back in 2008, recommended that we have a Polivoks Filter in our synth.  He pointed us to Marc Bareille at Papareil Synth Labs where we got the PCB from and Gino gave us a couple Ruskie ICs to boot.  Just last month, Scott Deyo made a nice front panel - so it's time to move!

diagram M. Bareille

We want to thank Gino, Marc, and Scott for their help and support - and for the excellent work done by Marc. Thanks, guys.

Table of Contents

This page has become really long, so here's a table of contents that we hope will make it easier to traverse:

Background - presents an explanation and Marc Bareille's initial description of the Module.

Parts - presents a Bill of Materials and notes about it

Panel - presents the MOTM format panel

Construction Phase 1 - Resistors, Capacitors, IC Sockets, Power Plugs, MTA headers

Construction Phase 2 - Trimmers, Panel connections

Set up / Testing

Background

Marc Writes:

"This filter is a clone of the famous vintage russian analog synthetiser named .  Inside this synth there is an incredible and very original filter invented by Vladimir Kuzmin. Please visit his web site at http://www.muztech.com.  It is a Lowpass ( LP) and Bandpass (BP) voltage controled filter with a special design and sound . A Vodka filter...The clone contains only cheap common parts, and it is very simple to build... No calibration trimmers or accurate tempco stages required, it is not the spirit of this beast from the far East ...

"Unlike most of Voltage controled analog filters who use a combination of a fixed capacitor with a variable resistor element ( OTA, opto,etc..) the filter core here is just a pair of programmable low power operational amplifiers ( PLPOA?). At first sight, it look like a classic SVF but with a difference: there is no capacitors ! CV modulations are applied on the current setting pin (Iset) to reduce or increase the GainBandwith of the aop who act as a variable time constant RC element. It is a 12dB filter. Sound as well. A bit wild at extreme Q, remind a little bit the Korg MS20 on this point . Frequency modulation on CV inputs work well with this filter!"

On Marc's site, he shows this component overlay for the PCB:

diagram M. Bareille

He also shows this plot of the Filter's output:

plot M. Bareille

Here's his photo of his prototype build. It's important to note that the PCB is mounted so that RV1, the Cutoff or Resonance pot, is at the top of the panel. This means the PCB is installed "upside down" compared to the component overlay diagram above:

photo M. Bareille

Parts

Will and I have developed a parts-lists / bill-of-materials in the form of an XL spreadsheet.

Click here to download the spreadsheet (apx. 250K).

Click here to go to our Bill of Materials Page.

PCBs

The pcbs needed a few holes enlarged. Easily done.  First the mounting holes:

Then the holes to mount the power header:

we drilled these out with a 5/64in drill

PCB Mounting Brackets

We had a left-over stooge bracket (from Synthtech) we had prepared for an other module but didn't use - so we drilled new holes for the Polyvoks.  You could get a three-pot from Bridechamber:

Cool ICs

Here are the UD1208s that Gino sent us - we'll use them for U3 and U4:

Transistor - 2N3904

Marc notes that the transistor (Q1) needs to be CBE format to install as illustrated on the overlay. The one we're going to use, the Fairchild Semiconductor 2N3902TA - this drawing is from Fairchild's spec sheet.  The Conductor, "C," should be toward R11

Wires

During construction, we set the PCB on a bracket with a panel so we could work out the wire lengths - and we made this chart for the module's connection wiring:

Coax wire #1 will have the shield connected only at one end.

Panel

It bears noting that our panel design is different from Marc's - we added an input level pot and left off second CV INPUT jack.

Scott Deyo made the panel - and we got ours from him.

Construction Phase 1

All the stuff in Phase 1 gets soldered using "Organic" Solder.  At every break in the action, we wash the board off to get rid of the flux.

Jumpers & Resistors

Capacitors, Misc.

IC Sockets, Transistor

we installed the transistor wrong way 'round.  We corrected it later.

Construction Phase 2

All the stuff in Phase 2 gets soldered using "No-Clean" Solder and the PCB doesn't get washed off from here on.

Pots, Trimmer

We decided to install a 250K trimmer in place of R24 - we used our Ohm Meter to set the trimmer at 48k. We'll see how that works out. Here's how we set up the trimmer:

Pots, Trimmer

We prepared the wire to the Input Pot with a bit of resistor lead:

The Resonance Pot has a little anti-rotation lug so we trimmed it off:

Mount PCB

Install ICs

Correct Transistor

Input Pot

We decided to use a 100K log pot set up with a Pot Chicklet for the input pot:

Done

Set up / Testing

Use Notes