Differences in Resistance/Voltage check

[Clmntbnr]

Hi !

When I did the resistance and voltage check, I noticed those differences:

6: 2.486 (kOhm)
7: 3.020
9: 3.022
10: 2.488
B3: 2.985
B6: 2.991
Center pin Left: 87.3
Center pin Right: 98.4

1: 81.6 (V)
5: 80.6
A1: 80.6
A6: 81.6
B1: 81.6
B4:80.6

Everything else is normal.
I was wondering what could cause these differences, if the big 10kOhm difference between center pins could cause anything noticeable, and if I could do anything about it (rewire ? change parts ?)

Thanks a lot !

Clément.

 

[Paul Birkeland]

6: 2.486 (kOhm)
7: 3.020
9: 3.022
10: 2.488
B3: 2.985
B6: 2.991
Center pin Left: 87.3
Center pin Right: 98.4

I don't see that any of these are off.  2486 Ohms is very close to the specified 2500, etc.  Nothing to worry about here.

1: 81.6 (V)
5: 80.6
A1: 80.6
A6: 81.6
B1: 81.6
B4:80.6

As mentioned in bold and red lettering on the voltage check prompt, it's mandatory to fix resistance issues before turning an amp on.  Having said that, all these voltages should be between 75 and 90, and they are, so nothing to worry about there.

I was wondering what could cause these differences, if the big 10kOhm difference between center pins could cause anything noticeable, and if I could do anything about it (rewire ? change parts ?)

Carbon resistive elements have a bit of a wide tolerance.  In practice, this difference is not audible (though some mistakenly attribute this resistance difference as the root cause of a potentiometer with tracking issues at low levels).

 

[Clmntbnr]

Thanks for your quick answer !

But the 10kOhm difference between RCA left and right is huge ! It's a 11% difference. Okay, still under 15%, but because of U=RI, there must be quite a noticeable imbalance between left and right chanel right ?

 

[Paul Joppa]

Carbon pots are often specified +/-10%. That is an independent measure from tracking linearity, which is also sometimes specified.

What matters for gain and tracking is the ratio of resistances, bottom to slider vs. slider to top - not the absolute magnitude of the resistances. In most cases, you could use a 50K pot on the left channel and a 200K pot on the right channel, and still get good balance of gains with no audible differences between channels.

 

[Clmntbnr]

So this cannot be in any way related to bad soldering ?
One last thing, at very low volume, there is a huge imbalance. I know it's usual (also happens to my Violectic HPAV100). Can I fix that by changing the pot ? Any links, recommendations, infos on that ?

 

[Paul Birkeland]

So this cannot be in any way related to bad soldering ?
One last thing, at very low volume, there is a huge imbalance.

See the Crack FAQ sticky, item 3.  At low volumes, there isn't enough resistance used on one end of the potentiometer track to get good channel balance.  The solution is to add a couple of resistors to bring you closer to the center of the pot's travel.