My goal is/was to put this Neve 1783 in a box with a PSU and XLR connectors so I can experience vintage discrete op-amps, transformers, and unity gain stereo width mix. So far so good.
After etching some circuit boards and reverse engineering some of the pin-outs, fixing a broken pin on one of the op amps (oh the horror), tracing down two wires that had become separated from where they were soldered, checking all in-circuit ESR on all caps, all fine, just a few minor electrolytic caps exceeding tolerance on the high side, I've managed to get this thing producing unity gain via stereo pairs of XLR in/out on the scope. I can also see some harmonics on the spectrum analyzer. It looks like it works. I've yet to wire it to my RME interface, however. Soon.
I've one question though, regarding pin "H" on the Amphenol connector: I am not using it. What is it?
Internally pin H is soldered to both the (+) side of the 470µF electrolytic cap and cap has (-) soldered to the output transformer. Pin H is also soldered to blue (ch.1) or green (ch.2) wire that disappears into the maze of bundled wiring. So many wires.
Two channels, pins wired like this:
A +IN
B
C
D -IN
E 0V many blue traces heading into bundles
F
H blue (ch.1) green (ch.2) wire to somewhere, also (+) side of 470µF cap to output transformer
J
K
L
M
N
P
R +OUT
S
T -OUT
U +24 IN
V chassis
From some notes I have from somewhere (?) I jotted down that Neve 1272 and 1073 H/F is +/- Line In. On this 1783 unit, however there's nothing internally wired to "F" and as indicated above, "H" connected to 470µF connected to output transformer and blue or green wire. Input? Output?
In some schematics from other devices I've noticed around the same area of those pins there are gain boost RC circuit specs but I don't think that is relevant here.
Some more info:
I fed it 100mV 1kHz sine wave input signal into both channels and got same back out plus harmonics from pins R and T. There was a slight attenuation.
I raised the input sine wave to 1V line level and got back a smidge more than 1V plus harmonics, no clipping from pins R and T.
Lets say somewhere around 1V there is unity gain. Below that there is attenuation. Above that there is modest gain. Pins A and D seem to be able to handle line input. I was curious about this because on some Neve devices ABCDE are for mic input and H/F are for line input. There are no input transformer windings options, just A and D go to the input trans, I think.
In two of the photos of one channel you can see red wire soldered to pin A and large black cap soldered to pin H.
I built an XLR test/patch box for experimenting before I make the permanent case. So I am wondering if I should have an additional XLR connection for pin H and just what that is.
I guess I'll connect scope to H and see what I get as output. (But if I did that first you all would not have had as much fun reading all this.)
After etching some circuit boards and reverse engineering some of the pin-outs, fixing a broken pin on one of the op amps (oh the horror), tracing down two wires that had become separated from where they were soldered, checking all in-circuit ESR on all caps, all fine, just a few minor electrolytic caps exceeding tolerance on the high side, I've managed to get this thing producing unity gain via stereo pairs of XLR in/out on the scope. I can also see some harmonics on the spectrum analyzer. It looks like it works. I've yet to wire it to my RME interface, however. Soon.
I've one question though, regarding pin "H" on the Amphenol connector: I am not using it. What is it?
Internally pin H is soldered to both the (+) side of the 470µF electrolytic cap and cap has (-) soldered to the output transformer. Pin H is also soldered to blue (ch.1) or green (ch.2) wire that disappears into the maze of bundled wiring. So many wires.
Two channels, pins wired like this:
A +IN
B
C
D -IN
E 0V many blue traces heading into bundles
F
H blue (ch.1) green (ch.2) wire to somewhere, also (+) side of 470µF cap to output transformer
J
K
L
M
N
P
R +OUT
S
T -OUT
U +24 IN
V chassis
From some notes I have from somewhere (?) I jotted down that Neve 1272 and 1073 H/F is +/- Line In. On this 1783 unit, however there's nothing internally wired to "F" and as indicated above, "H" connected to 470µF connected to output transformer and blue or green wire. Input? Output?
In some schematics from other devices I've noticed around the same area of those pins there are gain boost RC circuit specs but I don't think that is relevant here.
Some more info:
I fed it 100mV 1kHz sine wave input signal into both channels and got same back out plus harmonics from pins R and T. There was a slight attenuation.
I raised the input sine wave to 1V line level and got back a smidge more than 1V plus harmonics, no clipping from pins R and T.
Lets say somewhere around 1V there is unity gain. Below that there is attenuation. Above that there is modest gain. Pins A and D seem to be able to handle line input. I was curious about this because on some Neve devices ABCDE are for mic input and H/F are for line input. There are no input transformer windings options, just A and D go to the input trans, I think.
In two of the photos of one channel you can see red wire soldered to pin A and large black cap soldered to pin H.
I built an XLR test/patch box for experimenting before I make the permanent case. So I am wondering if I should have an additional XLR connection for pin H and just what that is.
I guess I'll connect scope to H and see what I get as output. (But if I did that first you all would not have had as much fun reading all this.)
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