FIXED! Stereo replacement pot for desk's control room out

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Brian Roth

Well-known member
Joined
Aug 20, 2005
Messages
3,185
Location
Salina Kansas
(See message #17 (?) in this thread for the outcome....)

Background.  More than a few years ago, one of my clients bought a small-ish Neve 5104 desk for his studio.  Well...small for a Neve broadcast desk...  LOL!  It was a bit of a "train wreck", but after a bunch of reverse engineering (little to no docs!) and a ton of mods, he's been happy with it.  My client refers it to as a "Rupert Roth desk" .  <g>

Fast Forward to now.  The control room stereo level pot was a tad wonky from the beginning, and is now taking it's last gasps.  The OEM pot is a Bourns 80-series, which is one of those blue 5/8" square conductive plastic "mod-pots" directly soldered onto a sub-card within the monitor control module.  It's a dual 50K audio taper.

While I probably can have State Electronics (aka Potentiometers.com) concoct a drop-in replacement for dozens and dozens and dozens of dollars), it dawned on me today that I have another alternative.  Directly to the left of the CR module is a blank panel, where I can mount ANYTHING with six short jumper wires onto the CR module.  Client thinks that is a cool idea, so no problem there.  ANY sized pot will fit onto that blank panel.

Now comes the question for the world-wide audience.  EGADS!  Decent 50K audio taper pots seem to be a "thing of the past" after perusing The Usual Suspects.

Mouser lists an Alpha (carbon) dual audio 50K pot for around $2.50.  No thanks....unless I buy a handful and "get lucky" on the channel-channel level tracking.

So, I went more "upscale" and poked around on the audiophile-supplier websites.  Percy Audio reminded me of the (discontinued) Noble pots (listed there at $25...if still available at all) which were not sold in a 50K value.

Percy lists a TKD stereo pot in the correct value.....at $75.00 IIRC.

Apparently the Alps "Black Beauty" stereo pots are a thing of the past.

I am dropping an email to Dale Manquen to see what a Penny & Giles pot might cost...assuming P&G even has a standard stereo pot in that resistance value.  I am scared what that might cost <g>.

I also glanced at the Goldpoint website for a stereo stepped attenuator......Egads...$175 for only 24 stereo steps.

Another idea is to find a dual 100K linear pot and "slug/load" the wiper to ground with, say, a 33K loader to make a quasi-audio-taper.  But, that assumes the dual 100K linear has decent tracking between sections.

Anyway, my client doesn't have a bazillion bucks to fix this problem...."Neve desk"or not!  <g>

BUT..I have a "wide open expanse" in the adjoining blank panel to mount whatever pot to make this work.

Bottom line.....trying to find something in between a $2.50 Mouser pot and $200 whatever...

OK...fixed with the Alps pot...

Best,

Bri

 
Bottom line.....trying to find something in between a $2.50 Mouser pot and $200 whatever...

buy a handful of cheap ones, and select the one with best l/r tracking?

only thing is - make sure you don't have ANY dc current upsetting the pot.

Jakob E.
 
These track very well: http://www.banzaimusic.com/Piher-6mm-stereo-50k-log.html

At least compared to the usual Alphas and even most Bourns I've tried. While that piher is built like a tank, the pot feel itself is oddly light and cheap.

Anyway, banzaimusic has a decent selection, maybe there are other choices: http://www.banzaimusic.com/Potentiometers/

But I can only personally vouch for that Piher.
 
I've lots of this type of pot, but in the 10K not 50K versions. They track better than +/- 0.5dB and have good feel.
http://australia.rs-online.com/web/p/trimmers-potentiometer-rheostat/2369604/

Do check that the existing pot is not a linear as Neve often used linear pots slugged to get quasi log curve.
 
Check out the Alps RK27 series.  Maybe mouser might have them or ebay?

They track nicely, feel good, probably cost about $10-$20. 
 
hey Brad, good to see you!

Bourns made some square pots, Mod Pots or something,

or radio shack alpha pots, cheap as heck but they sound good,
 
Here's a site that's got some expensive pots, there's a couple 50k in there...
http://www.hificollective.co.uk/components/potentiometers.html
 
I recently bumped into those things here, didn't yet try any myself - but they do look amazing:

http://www.ebay.de/itm/260636624590?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

http://www.ebay.de/itm/Resistor-volume-control-128-steps-stereo-P1-7-balanced-/320724270695?pt=LH_DefaultDomain_0&hash=item4aaca7fe67

http://www.ebay.de/itm/MOSFET-SE-preamplifier-plus-volume-control-128-steps-/320605477321?pt=LH_DefaultDomain_0&hash=item4aa59359c9

http://www.ebay.de/itm/MOSFET-SE-preamplifier-plus-volume-control-128-steps-/320605477321?pt=LH_DefaultDomain_0&hash=item4aa59359c9

http://www.ebay.de/itm/MV02-4Way-Motorized-Remote-Volume-Control-Input-KIT-/260720330682?pt=LH_DefaultDomain_0&hash=item3cb42487ba

http://www.ebay.de/itm/V02-Optical-Sound-Resistance-Volume-Remote-Control-Kit-/250808229157?pt=LH_DefaultDomain_0&hash=item3a6555dd25

http://www.ebay.de/itm/10K-24-Stepped-Stereo-Ladder-Type-Potentiometer-4-Poles-/260825962303?pt=LH_DefaultDomain_0&hash=item3cba70573f

Cheers,

Michael
 
I have used these Alps Blue Velvet pots before (not from this seller...) and they are superb.

http://www.ebay.com/itm/Real-ALPS-Japan-Blue-Velvet-Dual-50K-Audio-Stereo-Pot-/320693498438?pt=LH_DefaultDomain_0&hash=item4aaad27246

Peter
 
Just a quick note to say that Blue Velvet seems to be the nickname the RK27 pots get.  Peter's link is exactly what I was thinking of. 

(good to see you CJ as well!)

 
Hi Brian: Haven't been on analog console forum for awhile but recognized you from there. I will check my stock of pot tomorrow; may have a 50k dual w log taper will let you know as soon as I check it.

Bill W.
 
the alps rk27 that brad recommended is a very nice pot -- good feel and nice tracking.  mouser does have them in 100k but not 50k unless you order a bunch.

tangent's headphone amp parts shop has the dual 50k audio for $16:

http://tangentsoft.net/shop/

or you could get them off eBay.  i've even bought quad versions there.  shaft may be 6mm rather than 1/4", so depending on the knob you may need a small shim to even it out, or a different knob.

ed
 
The Alps rk27 pots look like a good answer, and there are several USA sources for those in the 50K value.  Thanks for all the suggestions!

Best,

Bri

 
So I'm on the hunt for a 6 gang level control (surround sound...) any ideas!? Those of you who've used the alps rk27/blue velvet pots, i see they are bolted together. Anyone seen inside and know if it's easy to strap a few together? I see there's 4 gang versions on ebay, not 6 gang though
 
UPDATE:  My client ordered two of the Alps RK-27 50K pots from one of the sources we found online (I don't recall which one, but both had the same price of $16.00).  He decided to order a second pot to keep as a spare for such an important component.

When I did my initial measurements last month, the DC resistance made it LOOK like the crappy Bourns "modpot" had an audio taper.  The part number on the pot was not a stock number, either. 

But, once I totally dismantled the module today so I could actually remove the defective pot from its circuit card, I discovered it actually was a dual linear!  I would have seen that fact if I had schematics for the CR module, but alas....

Obviously, Neve had resistors to load the wipers to ground to fake a log taper.

So, after some circuit tracing, I found the two "wiper load/slug" resistors.  Interestingly, Neve also had each "slug" in series with trimmers to ground, apparently so they could "tune" the L/R tracking of the dual linear Bourns modpot.  I removed both slug resistors (which obviously disabled the trimmers), and ran two pieces of shielded cable to the externally mounted Alps.

Yes indeed, it works great, the L/R tracking is excellent, and the Alps pot has that really "creamy" feel as you rotate the shaft.  Client is going to find a new knob for the 1/4" diameter shaft of the Alps, since the Bourns had a 1/8" shaft.

One final note is a second pair of trimmers on the Neve PCB wired in series with the "low" end of each side of the dual pot.  Those trimmers set the minimum audio level when the pot is cranked fully counter-clockwise, which means the CR pot cannot go fully "off".  I had noticed the Bourns never went full "off", but assumed it was because the pot was in such horrible condition.

Since this desk was intended for TV/radio broadcast studios, I guess Neve did that so you couldn't accidentally cut the CR speakers off during a hectic live show.

Thanks for all the suggestions...and those Alps pots sure seem nice if you have the approx. 1" square space to mount them.  Time will tell how long they will last in a studio environment.

Best,

Bri
 
Hello All,
My last experience with dual track pot level.
To replace on my Accuphase home HIFI amp I bought this recently, from Hificollective, in UK.
TKD 2CP-601/S Potentiometer TKD-250
New for hificollective, the 2CP-601 and the 2CP-601S (stepped version) taper stereo volume controls.
A superb alternative to the Noble with a greatly improved sound over the Alps blue. The stepped version offers 21 steps.
PRICE : 10K, 100K, 250K  - £25.00 (601) & £29.00 (601S)+vat+p&p

A superb alternative.....well, a big deception for me when I turned on the amp again, the pot is...noisy ! on about 30 degres of one track.
No DC here, just a bad quality pot.... :'(  and £30.00 lost... :'( :'(
Best,
Guy


 
Those 'Blue Velvet' (what a great film, eh?) / RK27 pots are all over certain items I work on. I've replaced quite a few, but only after a *lot* of abuse, i.e. tens of thousands of rotations.  I have them on my personal gear and am constantly amazed at how well the stereo tracking usually exceeds the quoted tolerance. I'd say they average out at around 0.3dB stereo match - pretty stellar, really. I also have a stack of the now-discontinued RK40, the predecessor. The 'Black Beauty' (not such a good film) uses a novel multi-finned wiper to give excellent matching between channels. As a rule it's only a little better than the RK27.

What is remarkable, IMHO, is that whereas the RK40 is carbon and the RK27 'plastic film', the RK40s tend to last a great deal longer. I've seen ones that are many decades old, which are still quiet and don't even need a blast of FaderLube. They are incredibly durable - which could partly explain their discontinuation... One of the nicest pots ever made IMHO. The fantastically expensive TKD 'Ko On', whilst quoting better matching tolerance, does not channel match better than the RK40 in reality - I've compared batches.

The RK40 is also quieter in terms of surface noise in operation than RK27. CP pots are marketed as quieter and more durable than Carbon pots, yet in this scenario, the older carbon pot totally trumps the later CP pot. I guess we're not comparing apples with apples. The RK40 is from a generation of more expensive pots. 

Justin
 
Well, the RK-27 Alps is SOOOOOOOOO much better than the "shot" Bourns modpot!

I hadn't worked on that Olde Neve desk for several years, and was shocked how BAD that CR pot had become.

My friend/client was REALLY suffering..and the Alps fixed that problem!

Again, it was NOT a 'drop-in'....I added the Alps pot onto an adjacent metal "filler panel", since the Alps was so much larger than the OEM Bourns.

Best,

Bri
 
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