[sdiy] Dead Unobtainable Concentric Pot, What to do?

Brian Willoughby brianw at audiobanshee.com
Wed Jan 20 02:51:17 CET 2021

Here's a worst-case workaround:

Since the pots control input and output levels, just wire the internal PCB with a 10 kΩ resistor and 500 kΩ set to full volume. Then, use other equipment in your studio to control the input and output levels external to the reverb.

I was trying to think of why you can't just substitute other resistance values, and the only answer I came up with is that 10 kΩ and 500 kΩ were probably chosen to provide the correct input impedance, and output impedance.

Yeah, it's not ideal, but a good mixer should have Send and Return level controls sufficient to keep things under control, volume wise. You won't be able to patch just anything in to the reverb, but it would work with extra gain stage patched in.

It will be confusing to have the concentric pot there on the panel, but nonfunctional, but at least you'll have the rest of the reverb.


On Jan 18, 2021, at 20:20, James Coplin wrote:
> The concentric pot sets input and output levels.
> James
> On Jan 18, 2021, at 9:51 PM, ColinMuirDorward wrote:
>> How about a two-pole, multi position switch plus mini PCB populated with appropriate SMD resistors?
>> What does the pot do?
>> -Colin 
>> On Mon, Jan 18, 2021 at 10:28 PM James Coplin wrote: 
>>>   I have an Orban 111B Spring Reverb here that has had scratchy pots 
>>> since I bought it ages ago. It had gotten progressively worse to the 
>>> point that I decided it was time to open up the pots and see what was 
>>> up. The carbon tracks on one of the decks had worn through and was 
>>> flaking off. Basically, the pot is dead. Unfortunately, it's a 
>>> concentric 10k/500k CCW Log pot which I can't find a suitable 
>>> replacement for. There are other concentric pots available but not in 
>>> that split value -100k/100k, 500k/500k, . I really don't want to drill 
>>> the front panel out unless that's an absolute last resort. Anyone have 
>>> any thoughts on what I could do instead to get it back up and running? 
>>> James

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