John Curl's Blowtorch preamplifier part II

[simon7000]

Originally Posted by gpapag

This is good for you Scott. Ed’s invitation calls for liver troubles.
But if you have the chance, try smoked (fume) Grappa from Italy.




Behind the slider, with older console modules, attenuators were not simple potentiometers.

George

George,

Sip a small glass, it is not water!

A slider with carbon composition resistors! The first Yamaha mixers (PM1000) used a rotary pot with a mechanical slip roll to make it into a slider!

In one of my test setups the Lorlin silver plated rotary switch produce enough distortion you could reliably tell one of the positions!

ES

[jcx]

forget the sqrt(R) dependency?

most like to use the 4.something nV/sqrt(Hz) for 1 kOhm room or calc for operating T

Johnson?Nyquist noise - Wikipedia, the free encyclopedia

while popular with datasheet writers the "distortion magnification" completely misses input impedance nonlinearity - which often dominates today with fet input and > kOhm source

[dimitri]

Ed this is bad setup, because the capacitance between input wire and the output node is varied between setups and uncontrolled

[simon7000]

Originally Posted by dimitri

Ed this is bad setup, because the capacitance between input wire and the output node is varied between setups and uncontrolled

Can you suggest a better method? I suspect their should be some difference between C coupling and what we are looking for. (The second setup may show this.)

[simon7000]

Originally Posted by jcx

forget the sqrt(R) dependency?

most like to use the 4.something nV/sqrt(Hz) for 1k room or calc for operating T

Johnson?Nyquist noise - Wikipedia, the free encyclopedia

Typo 1 Pa across 1K, but it won't affect much!

[dimitri]

Ed, check e-mail

[jcx]

Ed this is bad setup, because the capacitance between input wire and the output node is varied between setups and uncontrolled

wire both paths with something rigid, switch source far from bridge to one or the other path - then the potential is same on all the wiring (less wire Z effects) and just the current path changes ?

another verification/calibration/control would be to replace bridge with "star bridge" 4 equal arm cross to see any coupling/phase shift effects in just the wiring, sw, setup while keeping the load conditions very similar


my guess is that you'd be looking for uV/V from mutual inductance/proximity effect at even 10 kHz - do you have the AP with the 1 MHz ADC?

[simon7000]

Originally Posted by dimitri

Ed, check e-mail

Got it.

[simon7000]

JN

I just picked 4 10.000K Dale CMF resistors. To my surprise I only had to go through the first 60 to get a match! Tolerances are quite tight. Worst I saw was 10.032K

[cliffforrest]

That should be no surprise - especially if they are bandolered as they would only be mS apart in manufacture time.

A process with enough slop in it to produce big variations from one device to the next would be very cheap and nasty, and, more to the point, difficult to keep tuned.