John Curl's Blowtorch preamplifier part II

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#89,741
Hi Scott,
We're really splitting hairs here, I doubt anyone here is instrumented to measure the difference especially with S102's.
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I completely agree with you!

I would go with 4., 16k // 16k as it is easier to fit and will probably bring you closer to the true value you wanted. This will also give you the highest power capacity if that is important to you.

-Chris
 
#89,742
Without more details on the application the resistor stuff seems like arm waving.

An S102 type (metal foil) is very like a wirewound resistor. They have essentially no excess noise, noise from passing a current through them. They have virtually no distortion above 50 Hz. Below 50 Hz the thermal time constant between the foil and the substrate seems to modulate the resistance a very small amount. (Tese are from measuring S102s with a Quan-Tech and a Radiometer CLT-1) .

However Samuel Groner has demonstrated you can use a network of MELF resistors to get to the same place.

The S102 does have really good frequency qualities. They worked out the pattern to balance inductance and capacitance. Above 100 MHz they are too big so less relevant.

Real question, aside from audiophile feel goodness, is what are you trying to do? In a voltage divider, decent resistors, all the same value, will actually cancel some of the error terms. Excess noise from a resistor is most likely way less than the noise floor of the signal unless your cooking a resistor.

S102's arengreat for precision instruments. They are extremely stable. I have an AC calibrator that's 40+ years old with probably 70 S102's in it and still meets state of the art current specs. That is beyond overkill for audio products.
 
#89,744
jan.didden said:
I agree spreading the power over multiple units gives lower distortion. There is a secondary effect whether the voltage coefficient is larger or smaller than the temperature coefficient so it may be wise to spread the voltage rather than the dissipation.

The other thing Patrick and I were discussing is whether you can optimise noise this way. My take on it is that the noise depends on the thevenin resistance, but not absolutely sure.

Jan
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Yes, Thevenin equivalent network. As to voltage vs. thermal, in this case option 5 is still the best, no? And lower than a 4k+4k. On any specific resistor, it has the best voltage and thermal sharing of those listed. Yes, 3 series 2k6 resistors would be even better, but that's not an option.
 
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#89,751
Anybody want any 2013 Ridge Monte Bello Cabernet $185

I just got Ridge's 2016 Holiday Giving brochure as a member of their ATP. They're selling the 2013 Monte Bello to members for $185 per bottle, plus shipping. I suspect this is a pretty good deal but I might be badly mistaken.

If anyone would like me to order them a few bottles at the member price, drop me a PM. There are a few States that don't allow wine to be shipped in from California, so check to see if you're on the list.

"Order by December 12th to ensure delivery by the 25th" says the brochure.

Mark Johnson
 
#89,756
Hi hitsware,
feedback cannot work
perfectly because of the
transit time of the amplifier
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You do know that this isn't true - right? The frequencies you are talking about are the ones used with travelling wave tubes. Way, way higher than broadcast FM frequencies. At audio frequencies (let's call that 1 MHz and below), this does not happen.

-Chris
 
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