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Old 20th September 2006, 03:46 AM   #1
Pyre is offline Pyre  Canada
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Default Alps 250k in a Pas-3 Question


Total newbie question here. I have a pas-3 that the volume control is going bad on here. I bought an Alps 250k control and went to install it. The original Dynaco volume control has three lugs on one side and an extra lug on the other side (attached to a wire and a cap) for each channel. The Alps 250k control only has three lugs for each channel. I thought that this would be a direct drop in but it seems that I a, missing something. Can anyone tell me how to install this and where this extra left over wire should go?

Thanks in advance
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Old 20th September 2006, 04:29 PM   #2
kevinkr is offline kevinkr  United States
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Whoever told you the Alps 250K pot was a drop in replacement gave you a bit of a bum steer..

It's not all bad however, the missing tap is used for loudness compensation and if you don't use that then you can ignore that wire.

Otherwise to use loudness contour a simple rc network connected to the cold end of the pot (gnd) with a switch to short it out can be used instead. You wire the cap, resistor, and switch in parallel, connect one end to ground and the other to the cold end of the pot. You might start with 10K and a 0.12uF cap in parallel.

Loudness control preferences are a personal thing - if you need more boost increase the value of the resistor, if there is too much boost in the mid bass increase the cap value, (lowers inflection point making boost end at a lower frequency) to increase boost without changing the response increase both equally.. etc. The inverse is true as well.
It's not a perfect solution, but it will work well.

The pre-amp might sound a little better with the alps pot as well.
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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Old 20th September 2006, 08:24 PM   #3
Pyre is offline Pyre  Canada
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Thanks so much Kevin!

I see now that the third tab does indeed go to a large black cap and a resistor then to the Loudness switch. I definitely do not need loudness compensation. When I hit that switch before even at low volume levels the bass was way too prominent to be enjoyable. I will wire it up after work and hope that it makes a difference.

Thanks for answering my question I really did not want a puff of smoke and my preamp dead.

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