Date: Sun, 2 Oct 2005 23:17:30 -0500
To: “analog heaven”
From: “Paul Schreiber”
Subject: Re: [AH] Choosing pots and switches

I am a firm believer of “you get what you pay for”. I have no idea where people
get the idea that DIY synth construction is cheap. As far as modern “craft”
of hobbies go, it’s quite expensive to do *properly*. The good news is the
Mouser and DigiKey catalogs here in the US at least are thick as phone books.
eBay has driven *down to almost zero* the value of test equipment (I routinely
see $55,000 pieces of HP test equipment sell for $300).

When building any sort of electronic project, the ‘UI’ panel is ALWAYS the
majority of the cost (and headache!). I’d estimate that the average MOTM module
has 85% of the overall cost in the panel ‘stuff’
(pots/knobs/jacks/switches/panel). However, when something breaks or is
aggravating flakey, chances are it’s not a cap or IC. It’s a panel component.

Pots and knobs: this is where I spend the most dollars overall (over $180,000
date). I spent over 4 months of research and product testing before I selected
the 2 pots that I use. And I *really did not* want 2 different vendors, because
you are immediately forced into having 2 different torque (the pot’s ‘feel’)
values on 1 panel. However, for the VCOs I wanted cermet pots for minimal
drifting (even though used ratiometrically cermet drifts 100X less than carbon)
and wanted conductive plastic (super long life) for the others. I also need
panel mount (being able to solder wires) and pcb mount (trying to get *rid* of
wiring!). So, for panel pots I use Bourns Series 95. These are the MOTM ‘blue’
pots. Newark Electronics (www.newark.com) carries them. I order 1000 at a time
so I have a direct factory account. I have long history of reliability data
using these: I used to work for a company that had over 500,000 of these in the
field over a 20 year period. Their records indicated that in this period less
than *30* ever needed replacing. And in the application, 40% were washed down
with hi-pressure *steam* every day. Should be OK for a synth 🙂 I have about
25,000 of these in the field and have yet to replace one.

The other pcb mount pots are made by Spectrol and carried by Mouser
(www.mouser.com) The 149 series is cermet, the 148 series is conductive plastic
(like the Bourns). The Spectrols are a ‘step up’ from the Bourns in terms of
quality. They have all metal shafts and use gold-plated leads and contacts.
also cost $1 more. The leads are long and pliable enough to solder wires to
(used in the MOTM-300 VCO) but these are really for pcb mounting. I have not
seen a better pot for <$5, period.

If $$$ are a factor, then the Alpha-branded pots from Mouser are fine. I prefer
Noble pots, but they are harder to find. If you are a student and just want
*something that works*, get the Alpha pots. If I was doing my Masters/PhD, I'd
get the Bourns at least 🙂

MOTM uses the Tyco PKES90B knobs which are about $1ea. They use brass insets
hex set screws. If you get Alpha pots with what is called a "spline" or
'D-shaft', then you can get knobs that simply push on/pull off for about 30
cents. Quite a cost savings when say making a sequencer.

Switches: NKK is it. All others are crap. The Mouser 'Mountain' switches are to
be avoided at all costs. C&K has *long-term* reliability issues (likes to break
in 3 years). I've *never* seen a NKK switch failure in 27 years of using them.
used 6 *million* of them at Tandy. They just make a fine pruduct. BTW: if you
want the best rotary switches, these are made by Grayhill. Quite expensive but
these are the standard by which all others are judged. Every Boeing aircraft
about 200 in the cockpit.

Jacks: Nothing beats the Switchcraft 112A. My Moog 55 has some from 1968 and
they still work prefectly. However, recently I have been testing some other
for pcb mounting. I've found some but not telling yet 🙂

Paul S.