L-1 Stereo VC Mixer

L-1 Stereo VC Mixer replaces the Verbos Scan & Pan for my output mixer.

Features

  • 4 stereo channels with voltage controlled level and panning
  • Voltage controlled sum out level
  • Stereo level bar graph, 10 LEDs per channel
  • Headphones out
  • Audio signal flows only through VCA chips and summing amps, all controls through CV

Why switch?

Verbos Scan & Pan is a nice, compact VC mixer,  having four channels with VC level and VC panning for each channel.  It also features a scanning function that I didn’t use much.  I liked it a lot.  But it has a few drawbacks.  The knobs for panning are tiny.  The channel level sliders are inoperative when a level CV is patched in.  And there’s no global output level control.  I never took advantage of the input preamp overdrive feature.  So, not to disrespect the Scan & Pan.  It just didn’t have the right feature set for me.

I heard Paul Schreiber, of Synthesis Technology, raving about the quality of the L-1 VCA designs, based on THAT 2180 chips, and that influenced me to switch.  The L-1 is larger than the Scan & Pan, partly because of its large knobs.  It also had to be larger to accommodate all of the circuitry, which lives on two PC boards that plug together.  The functionality is straight-forward:  Each of four input channels has a level pot and and pan pot, with corresponding CV inputs.  The interaction of the pots and CV inputs turns out to be very useful.  Unity gain is set on each channel with no CV in, the level pot full and the pan pot fully left or right.  If you add a CV, the panel controls impart an offset (an initial) setting.

Construction

A partial kit can be purchased from the designer, Aleksei Laman, at L-1.  Please see the L-1 Stereo VC Mixer page.  I purchased a full kit from SynthCube.  The SynthCube kit at $395 is a good value, considering that the module is $600 assembled.  Assembly is greatly simplified by all SMT parts being already soldered to the boards.  Your job is to solder the through-hole components and assemble the two boards together with the face plate.  It seems simple enough, but there are some things to watch out for.

Assembly Tips

Follow all the assembly tips on the L-1 page.  The jacks legs need to be cut off, as well as tabs on the pots.  There need to be thin washers (not supplied) under the standoffs going between the boards.  This helps to raise the separation just a tad, to keep the trim pots from hitting the board above.  I have more assembly tips.

  • Mount the boards together, using the standoffs, for soldering the headers that connect the two boards.  This can be done early on.  Having them together while soldering insures alignment.
  • The back board can be soldered with organic, water-washable solder.  I used Kester 331, which is getting harder to find.
  • Before soldering them, check the 1uf 50V electrolytic capacitors to see if they are short enough to clear the front panel.  I had to replace the ones that SynthCube supplied.
  • To solder the jacks and pots, mount them all loosely at first, affix the front panel over them and put washers and nuts over all the jacks, and a washer and nut on the two corner pots.  Holding the panel flush to the parts, solder the corner jacks and pots.  Recheck alignment.  Now solder all the jack and pot leads.  This way you are assured of alignment.
  • Leave the LEDs for last, after you’ve soldered all the jacks and pots.  Put all the LEDs in place (the long lead goes to the + symbol), then reassemble the panel.  You can adjust the height of all the LEDs at this point.  I set them to protrude just a bit above the panel.  Watch out for LEDs that expose one of the leads at the side, which can short to the panel.
  • Look carefully at all of the photos, to make sure you’re soldering things on the correct side of the front PC board.  (All parts insert from the same side on the back board.)

PC Board Photos (click to enlarge)

Top of the front board.  I put the LED driver chips in sockets.

Back side of the front board.  Notice the washers underneath the standoffs.  You can also see flux residue from the no-clean solder I used.

Front side of the rear PC board.  Notice I did not use IC sockets.

Back side of the rear PC board.  Squeaky clean, due to washable flux.  This side faces the rear.  Notice the little holes for accessing the trim pots.  This board will be covered by a protective metal plate.

The back of the assembled module.  The screws were not supplied, but are standard m3 panel screws.

Here is a side view of the sandwich.

The Custom Power Header

Because the power has to connect to the front PC board, the rear board and its cover plate have rectangular holes for the header to poke through.  And, since this height is needed, Aleksei supplies a custom header, pictured to the left below.

To the right is a normal 10-pin Eurorack keyed header.  If you did use one of these, it would be difficult to connect the power cable.  Unfortunately for me, the custom header did not get included in the kit.  I had to wait for three weeks for one to arrive from Aleksei, mailed from Belarus!  He was quick to send it, free of charge.  I let Synthcube know about the omission, and they were responsive, but didn’t have the custom header.

 

 

 

 

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2 Responses to L-1 Stereo VC Mixer

  1. Edgar Brocke says:

    Hi Richard,

    Thanks for posting your experience about the l1 stereo mixer build. Do you recall about how many hours it took to build it? I’m thinking about commissioning someone to build it for me, but I would like to know what I might be looking at for time charged. Thank you!

  2. Richard says:

    Edgar, thanks for visiting my site. Well, since I’m not in the business of building modules for other people, I don’t have much idea how a builder sets prices. I don’t track my time when building. Since the L-1 is available assembled, why not buy an assembled one? Sure, it costs $200 more, but you know it will be assembled and calibrated properly. Finding a builder who would do it for less than $200 might be difficult. I think the assembled price is a fair one.

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