8 Channel, 3U NEVE 1073 completed

CJ said:

congrats on getting the phantom up!

your ohms for the xfmr look good,

let us say you hve 24 ohms for each pri coil,

with 24 in series you get 48, now when you run the 300 ohm setup, the coils are in parallel,

anytime you have 2 parallel resistors of same value, the calc simplifies to just dividing 24 ohms by 2 = 12 ohms so everything is cool so far.

use the DMM on ohms and connect to pins 2 and 3.

you should get 12 and 48 ohms again.

i bet the 48 ohms was too much for your continuity checker to say yes,

but it liked the 12 ohms ok, so everything looks go for takeoff at 08:00.

that LED across the 48 volts, i figure it is a 48 volt LED or a lightbulb, unless you have a series resistor on a regular LED?

otherwise the LED would have smoked like a chimney, get me?

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CJ said:

transformers have two kinds of ohms which can be confusing, DC resistance of the windings, and impedance ohms, DCR will always be way lower than the impedance or "Z"  ohms, which is the 300 and 1200 ohms

Z ohms is the resistance to AC due to inductance, which is formed by the turns of wire round the core, DCR is the actual resistance of the copper wire, Q is quality factor, you want a Hi Q, (not poetry)    for audio transformers, that is you want DCR less than Z, usually by a factor of 10 or better, so a Z of 1200 ohms might have a DCR of 1200/10 = 120 ohms, so your Q on the Neve input is better, 1200/48 ohms = a Q of about 24 which is good, you find a Hi Q on transformers with nickel lams since you get more inductance  for the same amount of turns that  you would on lets say a power transformer which uses steel lams,

so when you ohm out the XLR pins 2 and 3, you are ohming out DCR, not Z,

if you wanted to check Z ohms, you would inject AC and measure the current, then divide the AC voltage injected by the ac current, this would give you your Z in ohms,

a little current is used to run the xfmr, so your Z ohms will be off by a small factor due to some of your measured current being used to excite the core. this is called core loss, nickel lams have less core loss than steel, so your Z measurement will be more accurate than if you were to check an output transformer which uses lower perm lams,

so the bottom line is DCR = DC ohms, and impedance (Z) = AC ohms,

your ohm meter uses batteries, or DC, to measure DC ohms, an inductance meter uses AC to measure  Z ohms which then gets computed into Henries, a measure of inductance.

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desol said:

Cool! I was kinda suspecting that it might be that cable, but i wasn't sure if you had installed the DI's?
Regardless, great work! Now the biasing....!?

I think it's great that CJ contributed some good info...he's forgotten more than i'll ever know. 

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