[sdiy] Group buys: Alpha-style, dual pots, and Joysticks (WAS: RE: Dual-gang reverse-log pot group buy ?)

[flightofharmony]

Comments inline

-> -----Original Message-----
-> From: David G. Dixon [mailto:dixon at interchange.ubc.ca]
-> Sent: Monday, November 17, 2008 10:43 PM
-> To: 'flightofharmony'; 'Andre Majorel'
-> Cc: synth-diy at dropmix.xs4all.nl
-> Subject: RE: [sdiy] Group buys: Alpha-style, dual pots, and Joysticks
(WAS: RE:
-> Dual-gang reverse-log pot group buy ?)
-> 
-> flightofharmony asked:
-> 
-> >> I don't know - what markings do they have on the case? <<
-> 
-> They have no markings on the metal canister (which is a gold color), and
-> "B100K" in white letters on the top front of the plastic pc-board part of
-> the pot.  (I only have B100K versions of this particular pot.)  I have a
-> feeling that they are the same pots that Futurlek sells (they look
exactly
-> the same based on the pictures of the latter I've seen on the web).

A good rule of thumb: Always avoid unmarked components, with marked ones at
least you know who to avoid should they be garbage.
Futurlec sells Alphas though. In my quest for pots I found  14 different
manufacturers that make pots identical to Alpha - does anybody know who
developed this design first? 

Anyway, the Song-Huei pots  have a stylized "SH" stamped in the back cover,
and GH have a - wait for it - "GH" stamped in the back cover.

-> The problem with them is that they do not appear to admit desoldering and
-> reuse, and I'm not really even sure that they work terribly well the
first
-> time.  It would seem that the resistive strip becomes disconnected from
the
-> riveted metal pins after soldering.  Perhaps some of the plastic from the
-> pc-board part of the pot is getting between the two and breaking the
contact
-> (some of the plastic seems to "boil" if the soldering iron is held on the
-> lug long enough to flow the solder joint -- these are all pc-mount pots,
by
-> the way, including the Alphas).  If I pull on the wires, I can sometimes
-> reestablish the connection.  For example, if this pot is a frequency knob
on
-> a VCO, then pulling on the wires causes the frequency to go sharply up or
-> down as the contact is reestablished and rebroken.  Sometimes, just
jiggling
-> the wires causes the same effect.
-> 
-> At least 33% of these pots failed to work after rewiring a panel.
However,
-> none of the Alpha pots I used (all the non-B100K pots on the panel, as it
-> happens) failed to work upon reuse.  I'm sold on Alpha pots, and every
-> synth-diy'er I know swears by them, so they seem like a very safe buy.  I
-> would say that it's definitely worth an extra dime or two per pot to get
-> reliable performance and avoid having to redo panels!

I remember when you posted about those issues.

To be honest, I have always disliked Alphas. The construction is erratic,
stamping tolerances are sloppy, even the rotational torque is widely
inconsistent (from tight to almost freewheeling). In one bag, direct from
the Thailand factory, some had gold covers, others silver; some stamped with
the little "a" in a circle, some with the word "alpha", some with the value
stamped as well (but only the B100k, none of the others), and some that were
not press-stamped, just ink-stamped; two different shaft lengths when I only
ordered one; nuts and washers of different materials and stamping processes;
some with mangled mounting pins - a couple had the pin-mount portion of the
PCB broken completely off; loose rivets on the PC pins, and different styles
of said rivets.

Hell, even the font and ink used to print the resistance value on the front
PCB vary greatly. The same for shaft wobble.

I ordered some of the 0.25" round shafts from Mouser once. They came with
much nicer quality nuts & washers than any others I had seen on other shaft
styles, so yet another incongruity. The washers were still sloppy and, when
I tightened the nuts, the threads stripped out of the nut before they were
anywhere close to being tight enough to prevent movement of the frame. The
0.25" shaft uses the same bushing as the 6mm shafts,  but the shaft is ~6.35
mm. Allow for manufacturing variances and you have around 0.2mm-0.3mm height
of thread (made of low shear strength pot metal) to fix the pot.

Alpha has factories in Thailand, Taiwan, Hong Kong, and Guangdong & Shanghai
in China, maybe others as well. You never know what you will get.

Both the Song Huei and the G&H pots have some tiny features that show a bit
more attention to usage issues that the Alphas I have seen did not: The PC
mounting pins have anti-rotation bumps around the rivet point (the
electrical connection can be greatly compromised if you force the pin to
rotate around the rivet); the aforementioned I.D. tolerance on the panel
washer; and, from what I've seen, consistency!

Your Alpha mileage may vary : )

I just like to make sure to keep everything in perspective. By the way, did
anyone here check out the GH booth at NAMM 2008 in LA and have an opinion to
share?

~flight
flight at flightofharmony.com
http://www.flightofharmony.com