ARC SP-3 Volume Control Issue

[Jalousie]

Yeah, I would be disappointed with that too. For $125, they should sell something with the right shaft length and doesn't require modifications to the chassis. (Even if it's a traditional pot vs. a stepped attenuator.)
I hope it works out. [Btw, that's a nice looking unit. Heck of a lot cleaner inside than the one I have.]

 

[ivandezande]

It’s playing now. Can’t use the same connection scheme as the old control or max and min will be flipped. Gotta switch the out and grounds.

 

[TriodeLuvr]

They charged me $80 for a part that’s literally still in the bag from Parts Express for $15.

Did you make measurements to see if anything else would fit? Alpha makes a couple styles of dual 500K log pots, sold by AES for less than $5. I have had zero problems with their products, but maybe the shafts aren't long enough for this application.

 

[zackthedog]

They charged me $80 for a part that’s literally still in the bag from Parts Express for $15.
That’s scummy business.

Not to mention the part doesn’t even fit!!!
The stub out on the control to hold it has no where to go, and the shaft is too long.

CLEARANCE ALPS 100KAX2 100K Ohm Audio Taper Stereo Potentiometer 6mm Shaft

ALPS 100KAX2 100K Ohm Audio Taper Stereo Potentiometer 6mm ShaftThe Alps 100KAX2 is a 100K ohm stereo potentiometer of the highest quality. The 6 mm straight shaft is 25 mm long, with M8 thru-hole mounting, hardware included. The body of the potentiometer is 1.073" W x 0.97" H x 0.93" D (27 x...

www.parts-express.com

View attachment 3316578

Okay, then I take it back. ;-)

 

[ivandezande]

Did you make measurements to see if anything else would fit? Alpha makes a couple styles of dual 500K log pots, sold by AES for less than $5. I have had zero problems with their products, but maybe the shafts aren't long enough for this application.

Let me look at that site. But moot point now I guess. I really thought ARC’s part would be drop and go.

 

[TriodeLuvr]

Let me look at that site. But moot point now I guess. I really thought ARC’s part would be drop and go.

The two SKUs at AES are R-V38-2XXA and R-VA2XXA. There are links to data sheets with drawings that show exact dimensions of the bodies, bushings and shafts. I use these when I'm building gear that uses pots.

 

[ivandezande]

The two SKUs at AES are R-V38-2XXA and R-VA2XXA. There are links to data sheets with drawings that show exact dimensions of the bodies, bushings and shafts. I use these when I'm building gear that uses pots.

Yeah threading isn’t long enough on either.
On the original:
Thread: 11mm
Shaft past threading: 9mm
Shaft diameter: 6mm
Threading diameter: 9mm

These are all approx. as I don’t have a caliper.

 

[ian h]

I've been looking into replacing the volume pot on my sp3a with the Alps pot. Someone replaced the original with a stepped pot that has a terrible clunky feel to it, and the wiring been messed with.Do you have a picture of the Alps pot wiring you could post for me? I'd appreciate it!

 

[ivandezande]

I've been looking into replacing the volume pot on my sp3a with the Alps pot. Someone replaced the original with a stepped pot that has a terrible clunky feel to it, and the wiring been messed with.Do you have a picture of the Alps pot wiring you could post for me? I'd appreciate it!

I do not, but you have the schematic and all volume controls are wired the same (one wiper side to ground, wiper signal out) and you know the pinout of the Alps pot.

 

[ian h]

Ok thanks, I'll figure it out

 

[kcin]

The replacement ALPS pots available from ARC or aftermarket ( careful of fakes) don't have the correct bushing size for the ARC openings of the SP3.

You can drill out the sub chassis or you can grind down the perimeter of the bushing on the pot itself to fit. You'll also have to cut the shaft without destroying the mechanisim of the pot itself.

If you want a pot that fits off the shelf and his FAR higher quality than the ALPs and sounds like it there's this one:

TKD Potentiometer 100K 2CP-2511 Series Stereo Conductive Plastic Volume Potentiometer (50dB Audio Taper)

Get TKD Potentiometer 100K 2CP-2511 Series Stereo Conductive Plastic Volume Potentiometer (50dB Audio Taper) from Partsconnexion. Find high-quality products at great prices. Order today!

partsconnexion.com

Fits exactly through the opening of the chassis and the faceplate and no cutting of the shaft. However, if you were concerned about the price from ARC then you may not of been interested in this superior option. From my point of view , ARC are dealing with a small subset of enthusiasts for 45 year old pre amp and actually have a solution for it- they have to answer the phone, heat the place and hold stock of an obscure part-- the price is not that bad. Ask CJ for help and see what your options are.

We are dealing with EOL equipment as far as the manufacturer is concerned. ARC actually did not have a balance control replacement for the SP 3 ( they do have the tone controls!) so I had to deal with making one work on my unit. You can see the TKD pot in this thread as well as my solution for the balance control.

Audio Research SP3-A-1 the last hurdle. Balance Control

My balance control on the SP3 was "ok" but it was not tracking well. I already changed it with a standard ALPs control- but the taper and action was not exact enough. I ended up with an Audio Note 100K balance control which does have a MN taper and had to be wired in reverse of the original...

audiokarma.org

Hope your repair went well.

 

[ivandezande]

Just redid another SP-3 and I’ve very happy with the Goldpoint control.