[Tech2]

OK, I should know this, but I have questions.

I have a Little Dot II amp that has a channel imbalance. One channel is erratic and nearly cuts out completely at the very start (first 1/3-1/4 of travel) of the volume pot. This doesn't really have any effect when listening with high impedance headphones at normal volume. When listening with lower impedance headphones, I find that I am very near the start of the pot, which can be a problem since moving beyond the trouble area puts me at a very loud volume. The amp has a 50k volume pot with 6-pins, soldered directly to the PCB, which I would like to replace. So here are my questions:

- Are all pots pinned out the same? In other words, can I just pop in any 6-pin pot and solder it up?

- Is the pin spacing the same on all 6-pin pots? Are the dimensions standard as far as the height of the shaft from the PCB? This is not a major deal, since I can buy a pot with terminals and wire it with jumpers to the board. I would rather just solder one to the PCB, though.

- Can I increase the value of the pot, say to 100k, to move me into the 'sweet spot' of the pot (the middle) when listening? What would be a good value?

- Any recommendations on a decent pot that is readily available? Remember, this is a Little Dot II that I bought for $100. I don't want/need an exotic pot, just something in the $15-20 range, max. I noticed that Tangent sells a 50k alps for $15, which is right in my ball park, but I'd like to know about any other options.

Thanks in advance for any help.

 

[cotdt]

buy two alps and pick the one with the better tracking.

 

[Tech2]

Thanks, but am I to assume:

a) That any alps with 6-pins will work?...and solder directly to the PCB?

b) That when I solder it to the PCB, the shaft will align perfectly with the existing opening?

c) That increasing the value of the pot will have the desired effect on the volume?

 

[Fitz]

Changing the value of the pot has no effect on the usable range. At 10'o'clock on the knob, for example, it's going to be the same volume regardless.

 

[Tech2]

Quote:

Originally Posted by Fitz /img/forum/go_quote.gif Changing the value of the pot has no effect on the usable range. At 10'o'clock on the knob, for example, it's going to be the same volume regardless.

Then what effect would it have? I thought if you increased the resistance of the volume pot, more of the output voltage would be dropped across it and less voltage would be available to the load, which would also decrease the output current, thereby changing (lowering) the available volume.

Using your example, you would be approximately 1/3 into the full travel of the pot. At the same position on both pots, certainly the resistance would be higher on a 100k pot vs a 50k pot, approximately double, right? I don't see how that cannot have any effect on voltage/current, and subsequently, the volume at the load.

 

[Fitz]

Quote:

Originally Posted by Tech2 /img/forum/go_quote.gif Then what effect would it have? I thought if you increased the resistance of the volume pot, more of the output voltage would be dropped across it and less voltage would be available to the load, which would also decrease the output current, thereby changing (lowering) the available volume. Using your example, you would be approximately 1/3 into the full travel of the pot. At the same position on both pots, certainly the resistance would be higher on a 100k pot vs a 50k pot, approximately double, right? I don't see how that cannot have any effect on voltage/current, and subsequently, the volume at the load.

The resistance between signal and output and the resistance between ground and output would both be increased, maintaining the same ratio between them. A volume pot isn't just a variable resistor in series with the signal.

 

[Tech2]

Ok, thanks, but what effect does it have?...if I were to use a 5k pot vs a 1meg pot, for example.

 

[threepointone]

the value of the volume control pot generally sets the input impedance in most of the solid state/cmoy/etc style amps. Generally, it needs to be high enough to prevent some of the signal being filtered out (there's an RC filter that figures in somewhere in the wiring iirc) and it needs to be low enough not to be too noisy. I think 10K would sound right.

 

[nikongod]

it is worth note that a higher impedance pot will be easier for a tube preamp/phono stage to drive.

a pure tube phono stage can probably drive a 50kohm input impedance, but most dont have a very powerfull output stage and will probably struggle and fail with a 10k ohm load.

none of that matters of course if you are using an SS source, or have a buffer, or something in there.