etheory
Well-known member
Hi there!
A quick call for a bit of help.
I've been looking over the Siemens U273b schematics (for the approx 100th time) and I've figured out that the bv.2558 listed on the schematic as the input transformer is a 10K:2.4K 2:1 input, the bv.2557 is wired 2:1 and is approx 100R:100R but wired as approx 100R:50R. This is by looking at the TAB U374a, which has those transformers also, and I found some notes from someone who measured the transformers in that compressor.
The interstage bv.1784 in the U273b, however, is a bit more mysterious. Does anyone have a U273b handy to please measure what the two primaries and one secondaries are?
A simulation suggests that the bv.1784 is probably a 2.4K:10K 1:2 wired before the output amplifier. I am pretty sure it has to be 1:2 due to the gain staging after it, but I'm not sure about the impedance. I could really be any 1:2, possibly even 150R:600R, or possibly even a much higher impedance to avoid loading the transistor voltage-controlled gm in the inter-stage VCA.
If anyone has any info it would be greatly appreciated.
Also, as far as I can tell the bv.2559 used in the side-chain is approx 1:4, or 1:3, 75R:1.2K or maybe 150R:1.2K (probably fine for either of those), it looks like a mic transformer most likely.
If anyone has a U273b I'd be greatly appreciative if you could get out your LCR meter and take one for the team!
I promise to give back something interesting for whatever help you give.
Does anyone even know which manufacturer made it? I've tried Haufe, Beyer and Telefunken internet searches but got nothing.
Thanks again!
A quick call for a bit of help.
I've been looking over the Siemens U273b schematics (for the approx 100th time) and I've figured out that the bv.2558 listed on the schematic as the input transformer is a 10K:2.4K 2:1 input, the bv.2557 is wired 2:1 and is approx 100R:100R but wired as approx 100R:50R. This is by looking at the TAB U374a, which has those transformers also, and I found some notes from someone who measured the transformers in that compressor.
The interstage bv.1784 in the U273b, however, is a bit more mysterious. Does anyone have a U273b handy to please measure what the two primaries and one secondaries are?
A simulation suggests that the bv.1784 is probably a 2.4K:10K 1:2 wired before the output amplifier. I am pretty sure it has to be 1:2 due to the gain staging after it, but I'm not sure about the impedance. I could really be any 1:2, possibly even 150R:600R, or possibly even a much higher impedance to avoid loading the transistor voltage-controlled gm in the inter-stage VCA.
If anyone has any info it would be greatly appreciated.
Also, as far as I can tell the bv.2559 used in the side-chain is approx 1:4, or 1:3, 75R:1.2K or maybe 150R:1.2K (probably fine for either of those), it looks like a mic transformer most likely.
If anyone has a U273b I'd be greatly appreciative if you could get out your LCR meter and take one for the team!
I promise to give back something interesting for whatever help you give.
Does anyone even know which manufacturer made it? I've tried Haufe, Beyer and Telefunken internet searches but got nothing.
Thanks again!