[JoshK]

Hola,

I got a question in regards to a motorized ALPs 100K pot I bought off of ebay.   The guy said he was going to send a PDF of the pinout but instead it was just a description/size of the pots, with no illustration of the pinouts.

I understand that a normal pot has two sets of 3 (or 4) pins with ground, out, in, (unused) as their values.   This pot has 8 pins all in a row.  Can I assume that the pins are ground c1, out c1, in c1, unused, ground c2, out c2, in c2 where c1 is channel 1 and c2 is channel 2?  This is how I have it currently wired and it doesn't seem right.  I think one of the channels is backwards somehow, but I am not sure.   I haven't plugged the preamp into my system yet, just testing it.

[mgalusha]

Josh,

You can use your meter to figure out the connections. Set your meter to a range the will read 100K ohms (assuming that it's not autoranging) and find two pins that measure 100K (+/- a few thousand ohms) between them and that doesn't change when the pot is turned. Those will be the input and ground of one channel. Very likely the pin between then will be the wiper.

Connect one meter lead to the pin between then and to either of the pins on the side and rotate the shaft. The pin that has less resistance when turning the shaft clockwise (as when you turn the volume up) is the input, the other will be the ground pin. It should act just the opposite in that the resistance will increase as you turn the shaft clockwise.

Repeat to locate the pins for the other channel.

Hope this helps.

mike

[JoshK]

Thanks Mike....I guess I sorta did that but that explanation helps me resolve what I found....

[JoshK]

For other's potential edification....

I finally figured out the pot wiring.  The diagram I had was totally wrong, and the obvious layout was pretty far off which is why i was confused.  I finally took Mike's advise and started measuring each and every pair with the pot volume up and down and writing down all the measurements.  This allowed me to deduce the wiring scheme.  My preamp I plugged in and did a listening test.  All is well!  

Here is the diagram for anyone who comes upon one of these pots.  

X I1 I2 O1 G1 G2 O2 X

Where X is a dummy pin, I's are inputs, G's are grounds and O's are the wiper/output. 1 and 2 represent the channel.   Technically the G's aren't distinguisable are far as I could tell.  Ground is ground and any measurement between one of the grounds and any other pin was the same with the other ground and that same pin.   So I don't think it matters if the grounds were switched, but I could be wrong.  

On another note, anyone know why if I turn the pot all the way down it makes a loud rude noise?  Only if it hits all the way down.  I think the easy solution is the mechanically force the pot not to be able to turn all the way down, but I wondered if someone might know why?

My 5687 single ended preamp is done.  I plugged it in and was listening to Radiohead HTTT.  Excellent vocals and crystal clean top end.  Bass is punchy but not quite as deep as the purist.  The presence is quite defined in a way I can't quite describe.  Very nice to listen to.  This is the schematic that is on diyparadise.com under simple 5687 preamp.   It is a very good starter tube project, very well explained and cheap to build.