Volume Pot Wiring

[laatsch55]

The following was a discussion on how to properly wire the wiper and stationary legs of the pots.

laatsch556 asked;

When Jer did his 700 LED lights he noticed the the leads coming off the wiper went to the RCA jacks(input). From the schematic it shows the wiper lead going to the driver board. I did not check that before I sent it to Jerry. I will from now on. Just got done checking the 700 of Suttons, it's backwards too.

Joe----- what happens when its backwards, noisier??

Gepetto answered;

Perhaps Lee it would be noisier. At reasonable listening levels it may increase the input impedance to the first differential stage and could cause it to be noisier than when the wiper is wired to it. At minimum volume setting, this wiring config would effectively short the preamp signal output to ground. At maximum volume, you would probably not notice any difference at all as that would again be straight through.

laatsch55 added;
At full volume no contribution to impedance then? If you were doing away with the pot the pre-amp would see the normal 50 K input impedfance??


Gepetto replied;

Hi Lee
If you do away with the pot, you will effectively see the 10K in series with 39K for a total of 49K (reduced only slightly by the near negligible contribution of the long tailed transistor pair input impedance).

This is the normal input impedance of the PL400 amp with the PL14 original board installed.

The White Oak board also uses this same input resistor arrangement.
Joe

 

[mlucitt]

Another consideration from my professional sound reinforcement days - I always wire the wiper of the input potentiometer to the amplifier input. I think there are two reasons: 1) wiring this way gives you the accuracy of pulling off the maximum signal when the pot is turned fully up and pulling off ground when the pot is turned fully down. Maximum signal = loud, and ground = silence (at least it should). 2) this wiring scheme also presents a constant load to the ouput of the preamplifier. The preamp will always see the value of the pot (50K, 100K, 250K, etc.) and this is good because some preamps are funny about loading (what the preamp "sees") to a short circuit (0 Ohms to ground when the pot is turned all the way down) and max resistance (such as 50K Ohms to ground when the pot is turned all the way up) if wired backwards. I think PL had it right, those guys were engineers...