I’m currently converting an integrated amp into a preamp.
All is good apart from the noticeable amount of hiss when I am between taps on the 250k centre-tapped volume pot.
little to no hiss at full CCW position, centre, and Full CW positions...
Noticeable hiss anywhere in between these positions.
I’m guessing this is happening because the path between the pot and the preamp state is acting more like an antenna between the taps where it’s
62.5k ohm away from the signal or ground at the 25% and 75% positions...
Would using a lower resistance pot solve my issue? or using a relay-array volume control? (I would lose the “loudness” function of the centre tap however)
I’ve tried lining the inside with copper for RF/EM blocking material but it didn’t seem to help much for the hiss. It did help for the blips and bloops coming from the Wifi router.. I’m using the LM4562 for the preamp stage which I hear is very sensitive.
All is good apart from the noticeable amount of hiss when I am between taps on the 250k centre-tapped volume pot.
little to no hiss at full CCW position, centre, and Full CW positions...
Noticeable hiss anywhere in between these positions.
I’m guessing this is happening because the path between the pot and the preamp state is acting more like an antenna between the taps where it’s
62.5k ohm away from the signal or ground at the 25% and 75% positions...
Would using a lower resistance pot solve my issue? or using a relay-array volume control? (I would lose the “loudness” function of the centre tap however)
I’ve tried lining the inside with copper for RF/EM blocking material but it didn’t seem to help much for the hiss. It did help for the blips and bloops coming from the Wifi router.. I’m using the LM4562 for the preamp stage which I hear is very sensitive.
I’ve eliminated most of the interference coming from nearby devices, the shielding made a difference with that, original enclosure is wood. The hiss still remains, which i’m guessing is everything else along with all the stuff coming from galaxies far, far away. Wideband noise i’m guessing it’s called?
250k is very high value, so its probably Johnson noise (and likely quite a bit of excess noise from the carbon track).
10k is a much more usual value for a pot in a low noise preamp running at line-level.
High values like 250k are the domain of high impedance circuitry (valve, not solid state).
10k is a much more usual value for a pot in a low noise preamp running at line-level.
High values like 250k are the domain of high impedance circuitry (valve, not solid state).
Now that I look at the schematic for the preamp stage i’m using, looks like it’s normally a 10k pot that comes before it.