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February 28, 2020, 04:19:09 AM

Author Topic: Need to Replace Volume Pots  (Read 883 times)

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Offline arturo7

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Need to Replace Volume Pots
« on: July 29, 2018, 12:24:35 PM »
I just broke one of the volume pots on my Foreplay III. I took the knobs off the clean the pots and the knob didn't want to go back on. I applied too much pressure and the pot blew up. I guess I should replace both of them while I'm at it.

This may be too broad of a question, but what are my options?

Thanks

Offline Natural Sound

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Re: Need to Replace Volume Pots
« Reply #1 on: July 29, 2018, 01:15:58 PM »
The FPIII didn't use potentiometers. It used a stepped attenuator called, "sweetest whispers." Unless of course yours was modified.

If you need to build a new one this switch is reported to work.
https://www.digikey.com/product-detail/en/c-k-components/A11203RNZQ/CKN10201-ND/2043157
« Last Edit: July 29, 2018, 01:21:30 PM by Natural Sound »

Offline arturo7

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Re: Need to Replace Volume Pots
« Reply #2 on: July 29, 2018, 02:12:22 PM »
Thank you, Mr Sound! That looks like a 1:1 replacement.

I think it would be better for me to replace all of the attached components rather than un-solder and re-solder. My assembly manual is long gone. I'm assuming I can download another but I didn't see a link.

 

Offline arturo7

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Re: Need to Replace Volume Pots
« Reply #3 on: July 29, 2018, 03:10:47 PM »
Cruising around the site, I see the SmashQuiet attenuator upgrade. Is this compatible with the FPIII?

Offline Natural Sound

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Re: Need to Replace Volume Pots
« Reply #4 on: July 30, 2018, 09:27:33 AM »
No, the SmashQuiet attenuator upgrade is not compatible.

If it were me I'd order replacement resistors along with the switches and not mess with de-soldering the old ones.

Since you don't have the manual for the whispers you have a little work ahead of you. Not to worry though it shouldn't take too long. The best way is to read the resistor bands and figure out the value. I'd then take a resistance measurement with your digital meter to verify your outcome. You may want to have a strong light and a magnifying glass ready since the resistors are pretty small.

Optional - Chances are you installed the recommended 33k padding resistors during construction. These are the resistors soldered to the input selector switch. If you find that your system gets pretty loud just after a few clicks now would be a good time to address that.

According to the manual 33K is the stock value to achieve an overall gain of 10dB. To pad down from the stock 10dB gain use the following guide. (From page 24 of the FPIII manual)

-6dB (80.6K ohms)
-12dB (182K ohms)
-18dB (360K ohms)

http://cdn.wonderfulengineering.com/wp-content/uploads/2014/06/What-is-a-resistor-9.jpg

I hope this helps.

Offline arturo7

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Re: Need to Replace Volume Pots
« Reply #5 on: August 01, 2018, 01:50:02 PM »
Thank you!

Offline arturo7

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Re: Need to Replace Volume Pots
« Reply #6 on: August 04, 2018, 07:00:50 AM »
Holy garbanzos!

I found the Foreplay manual, complete with SW insert.

Strike up the band!

Offline [email protected]

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Re: Need to Replace Volume Pots
« Reply #7 on: September 23, 2019, 08:54:40 AM »
Finally replacing the sweet whispers on Foreplay amp vintage 2002. I am replacing them with a double volume stereo potentiometer (ALPS RK27). Couple of questions: 1) I ordered 100K but was sent 50K pot. Is there way to use the 50K pot? It takes almost six weeks to get the ALPS from China at a good price on Ebay.   2) It has been so long since I built the amp that I am going to need a little help knowing how to connect the correct terminals on the new ALPS pot to my foreplay, especially if additional wiring and resistors are needed to use the 50K pot.
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Offline Paul Birkeland

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Re: Need to Replace Volume Pots
« Reply #8 on: September 23, 2019, 11:41:49 AM »
If you got the Alps pot from China and it has solder lugs, it's a counterfeit component.  You can still use it, but it's not an Alps.

A 50K pot will work just fine. 

If you still have the Sweetest Whispers manual (or if your Foreplay is still 100% wired up) there's a pair of resistors that go from the selector switch to each stepped attenuator.  For a 50K stereo attenuator, I would replace those with 100K resistors.  Each of those resistors goes to the "input" lug on each level of the Alps pot (if you got a PC pin mounted, genuine Alps pot, then you should also order a PC board to mount to it so you can install it properly, and the board will have labels).

The wire that leaves the center terminal of each SW attenuator and goes to the 9 pin socket will be connected to the output of the Alps pot.

Lastly the ground connections of the Alps pot can go to a ground on the RCA jacks or ground bus.  Once the SW attenuators are removed, be sure the ground buss is preserved. 

-PB
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man