option 1 100K audio taper pot with twin cntrols, audio tapers usually have poor channel-channel tracking, the twin shafts let you manually adjust to correct this. the tradeoff is > at each volume level the level will be mismatched. BTW the original had a custom taper > if you notice the tap has its own resistance built in its trace length also in series with an external 10K, so some calibration was possible by the OEM> this wont be the case with a replacement so the problem will be unique to whatever new part you select. ( FWIW audio taper is usually pretty bad that's why custom 4 pin parts existed in 1st place )
option 2 faking a linear taper > since this requires a shunt on the wiper usually 10:1. This requires a higher value linear pot since the shunt is now in parallel. So looking at the highest position, the load on preceding stage is now ~220K // 22K . then as a compromise use 47K shunt. IMO using a simple calibration and modifying one shunt can give the closest tracking hassle free for life.
also 22K shunt may also be used b/c its rare to set the gain at maximum so loading isn't severe as worst case above.
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Unfortunately the concentric pots proposed and other ones I found on Ebay do not match the dimensions of the OEM pot. Bummer.
So really that leaves us with option 2 i.e. linear 220K with a shunt 47K resistor to fake log law. I was thinking of using a trimpot for the shunt resistor to do the 1-off calibration you were talking about to improve tracking between channels. 27 turn 100K trimpot should be good.
Thanks infinia I think i understand, it's 220K//47K so as to maintain the input impedance / loading of the preceding stages. Makes sense.
FWIW I measured the resistance of the carbon track for the tap and that was in the ~200 ohm range, which is not much compared to the 10K resistor after the tap point in the original OEM setup.
So really that leaves us with option 2 i.e. linear 220K with a shunt 47K resistor to fake log law. I was thinking of using a trimpot for the shunt resistor to do the 1-off calibration you were talking about to improve tracking between channels. 27 turn 100K trimpot should be good.
Thanks infinia I think i understand, it's 220K//47K so as to maintain the input impedance / loading of the preceding stages. Makes sense.
FWIW I measured the resistance of the carbon track for the tap and that was in the ~200 ohm range, which is not much compared to the 10K resistor after the tap point in the original OEM setup.
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That would be a good explanation but I don't understand why have chosen to join the 2 grounds right where the pot is - there's plenty of space elsewhere on the board.
The original pot has a 9th leg connecting the pot case to pcb ground, so maybe the purpose of the capacitors is to decouple the pot from pcb ground?
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MADE IN JAPAN ALPS 16mm 100K DUAL LINEAR CONTROL POT WITH LOUDNESS TAPER | eBay
That's the pot I ended using up - very similar to the original part but to be honest could have used any standard lug type.
That's the pot I ended using up - very similar to the original part but to be honest could have used any standard lug type.
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The Sony STR-313 receiver from the late seventies had a switchable loudness circuit without using a tapped volume potentiometer. Trying to attach this part of its schematic ...
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She sings beautifully!! What a great little amp 
The replacement linear ALPS pot worked a treat. Panasonic FC for most places and Nichicon for recapping are always a good choice. I used EPCOS (TDK) for the main filter ones this time, they're great... plenty of kick!
The replacement linear ALPS pot worked a treat. Panasonic FC for most places and Nichicon for recapping are always a good choice. I used EPCOS (TDK) for the main filter ones this time, they're great... plenty of kick!
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She sings beautifully!! What a great little amp
The replacement linear ALPS pot worked a treat. Panasonic FC for most places and Nichicon for recapping are always a good choice. I used EPCOS (TDK) for the main filter ones this time, they're great... plenty of kick!
Nice,now let all the tweaks burning in for 2-3 months maybe more and you are fine.
Volume control
Hi Chatziva,
I have the same trouble as you did and have managed to get hold of the same vol control.
Did you just do a simple wire from circuit board to control. I also notice from your photo a wire going from pin 9 at the back, i presume this is soldered onto the rear of the vol control.
Any comments or updates please.
Mike
Hi Chatziva,
I have the same trouble as you did and have managed to get hold of the same vol control.
Did you just do a simple wire from circuit board to control. I also notice from your photo a wire going from pin 9 at the back, i presume this is soldered onto the rear of the vol control.
Any comments or updates please.
Mike
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