[ericj]

Quote:

Originally Posted by tangent Try several hundred. I just measured a Sennheiser HD-600 cable a few days ago, and got around 500 pF, with two different meters. That comes out to about 50 pF per foot.

Yeah, had it been some other time of day, I'd have realized that. I've never tried to test a long cable, but I'm painfully aware that in it's lowest range, my LCR's capacitance results are skewed widely by whether probes are attached, and which way they happen to be jumbled around. I still need to take some time and put together some 1-inch-long probes with aligator clips . . .

People talk like a series 47ohm metal film resistor on the output of an amp is going to make some massive negative impact on either the quality or the volume, and it just isn't so. You probably won't notice any difference in loudness, and often it actually improves the sound quality. And you don't need to use one that big, either.

 

[amb]

Quote:

Originally Posted by ericj People talk like a series 47ohm metal film resistor on the output of an amp is going to make some massive negative impact on either the quality or the volume, and it just isn't so. You probably won't notice any difference in loudness, and often it actually improves the sound quality. And you don't need to use one that big, either.

If the load impedance is a 32Ω headphone, then a 47Ω series output resistor will cause almost 8dB loss. That's pretty big. Not only that, if the headphone's impedance curve is not ruler flat with respect to frequency, then such a resistor will introduce frequency response aberrations.

 

[dsavitsk]

Quote:

Originally Posted by amb No, but you will get undesirable noise that could be avoided simply by re-thinking about placement of the transformer.

Have you done any experiments/measurments placing a shielding box either around the transformer, or around that circuitry? Might that be a solution to keep things close together?

 

[amb]

Quote:

Originally Posted by dsavitsk Have you done any experiments/measurments placing a shielding box either around the transformer, or around that circuitry? Might that be a solution to keep things close together?

Shielding magnetic fields is tricky business and I tend to simply avoid it by keeping things far apart. The fields have a way of finding its way around the shield unless you've completely boxed it in with mu metal or something.

 

[robzy]

What would happen if you did a total redesign of the power section?

Firstly get an IEC socket with an inbuilt fuse holder and then instead of the dual power supply you have at the moment - a single power supply with a TLE? (Afterthought: how much current draw would the opamp have?)

That might give you just enough room to move all of the audio components as far left as posible (cramped around the pot) and the transformer mover just a little bit more to the right.

Rob.