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How do I select volume pot for ef1? Active volume control. What does this mean.

post #1 of 5
3/6/09 at 1:24pm
Thread Starter 
I got my first full sized amp this year (besides the stax 2050). I really love the amp but the pot is seriously imbalanced in the low volume range which is predominently where i do all my listening. I find it very annoying, I just got d7000 headphones which are even more sensitive than anything i have, when i turn the volume down 1 channel will go up for a nano second.

anyway, i want to fix this. Ive seen alot of threads that seem to indicate this is quite common. how do i select a new pot that will work with my amp and improve on this problem?

these are the specs for this amp.

Opamp: OPA275
Tube: Sylvania 12AU7 (CONN branded)
Frequency Response: 20-30K Hz
THD+N: less than 0.2%
S/N: more than 95dB
Input impedance: 50K Ohm
Output impedance: 2–2K Ohm headphones
Output signal strength: up to 15 Volts at 32 Ohm
Input: RCA*1
Output: 1/4 headphone jack*1
Dimension: 110mm(W)*50mm(H)*270mm(D),
or 4.33inch(W)*1.97inch (H)*10.63inch (D)
Weight: 750g (without power supply)
Acessory: 12AU7 tube, 18V AC power supply.

any help at all would be appreciated.
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post #2 of 5
3/8/09 at 8:22pm
Thread Starter 
Allright changed the title of this thread hoping to get some reply. My ef1 amp has active volume control supposedly to make a cheap pot sound like stepped attenuater.

I have low impedance headphones, D7000 that with dvd source the volume I can comfortably listen to them is between 7:00 and 8:00 where there is some channel imbalance and scratchiness. I am thinking of replacing volume pot.

Is there a pot that would increase the range, have higher resistance but would keep sound quality high?

thanks for your help.
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post #3 of 5
3/8/09 at 9:43pm
I'm not quite sure what they mean by "active volume control" but I am guessing that this is just a shunt arrangement (perhaps). Got a link to the amp?

From your description, it doesn't sound like replacing the pot will do anything for you (other than perhaps better tracking at low levels. You probably need to investigate lowering the gain to put the D7000s more up into the 9:00-10:00 or higher range, where pots track much better. A pot (or stepped atten.) is just a voltage divider; going from a 10K to 100K pot does nothing in terms of how the pot works (and its range).
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post #4 of 5
3/8/09 at 10:11pm
Thread Starter 
here is the link to the amp. Head-Direct.com | YUIN

Pars, lowering the gain was something that i really wanted to do. Is this a feasable thing to do? Is it something like adding resistors?
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post #5 of 5
3/9/09 at 1:24am
It should be feasible, though in this amp, I'm not sure how you would do it. This is a hybrid opamp//tube architecture it appears. Normal opamp based amps typically use a feedback loop; this is where the gain can be set via the feedback resistors.

One thing you could try fairly easily would be padding the input via inline resistors. There should be threads here dealing with that; probably search on attenuate to find them.
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