PEC pot tracking issue

[crackaddict]

Hi,

I'm about to build my second Crack. (My buddy liked my first one so much I sold it to him at cost so I could build an upgraded one for myself.) I did upgrade the volume pot to the PEC model folks recommend due to the left/right tracking issue at low volume (left channel faded out sooner than right). However, the PEC pot did not help. I have now picked up an Alps Blue pot, hoping this is a better upgrade.

I noticed the final comment by PB in this thread (http://bottlehead.com/smf/index.php?topic=1632.15), stating that "you can add a 100k resistor in series between the center pin of your input RCA jacks and the potentiometer." Could someone clarify what this means? Does this mean one per channel, and where would I put the resistor(s)? And what rating would I need on the resistor (1/4W?)

Is there any other impact from this? Reduced overall output volume?

Thanks,
Derek

[Paul Birkeland]

Yes, one per channel. 

I would more recommend to put a resistor across each pair of outboard lugs on the level control (47K), then a resistor between the white wire and where it mounts on the pot (75K) and the red wire and where it mounts on the pot (also 75K).  There is a fair amount of flexibility in these values, but putting everything on the volume pot will help keep the noise floor low.

Wattage is supremely unimportant here, go for low wattage parts because they are small and easy to squeeze in wherever you need them.

[crackaddict]

Thanks for the quick reply. I'll plan for this.

Can you clarify what you mean by "between the white wire and where it mounts on the pot? Do you mean to cut the wire a bit short, add a resistor to the end of the wire, and then connect that resistor to the lug instead of the wire?

Regards,
Derek

[Paul Birkeland]

Yes, you have the idea.  I would recommend just removing the wire without cutting it, just in case you change your mind down the road.

-PB

[crackaddict]

OK, I'll try this when I put it together.
Does this reduce volume, given that it's 75K in-line with the input?
Thanks again,
Derek

[fullheadofnothing]

Yes, the purpose if this mod is to reduce the volume. Some people will do it to decrease the hair-trigger sensitivity of their volume control. Others will do it because with less voltage going into the pot, you will need to turn it up further, where the tracking is more even.

[crackaddict]

Hi,

That makes sense. I've spent the evening reading up on stepped attenuators and saw the same thing written about on Goldpoint's web site.

Thanks to both of you for the advice.

Derek

[jlucas]

Yes, one per channel. 

I would more recommend to put a resistor across each pair of outboard lugs on the level control (47K), then a resistor between the white wire and where it mounts on the pot (75K) and the red wire and where it mounts on the pot (also 75K).  There is a fair amount of flexibility in these values, but putting everything on the volume pot will help keep the noise floor low.

Wattage is supremely unimportant here, go for low wattage parts because they are small and easy to squeeze in wherever you need them.

Do you have a picture of this?  (particularly trying to clarify the part about the outboard lugs)
Also, why different resistor values than listed in #3 of the FAQ?

Thanks!

[Paul Birkeland]

The single resistor can be noisy, though not always. 

The outboard lugs are the lugs that aren't in the middle of the pot. 

-PB