acmp 1081 - fully functional or not?

[cannabis]

Should we be looking at replacing these crap transformers with good ones at this point?

That can't be THAT big a job.

replacing it would be easy


finding a good one

that is compatible

electrically and physically

would be the hard part


I think a smaller one

that could be mounted vertically

on the sidewall toward the rear

instead of horizontally

in its present location

could go a long way toward

reducing the emi

 

[antichef]

here you go:

http://www.recursor.net/ACMP-81-talking.wav

(and for the bandwidth challenged)

I want to replace the transformers in my 73s -- I'm kind of in the mood to leave the 81s alone for now. Anyone know of good drop in replacements?

 

[cannabis]

that's good

i hear no noise



do you have the output gain

cranked all the way up?

 

[drBill]

that's great!

is there anyone near you

that can compare the electronics

of these to the ones with hum

to see if differences exist?



were these late arrivals

that may have been among those

that had the delayed shipping

due to quality problems?

These came at the same time mine did. I WAS in a different envrionment (studio), so there were variables. To do a scientific test, I'd need them at my place. But I can safely say they were useable and worked fine for what they were designed to do.

 

[antichef]

that's good

i hear no noise



do you have the output gain

cranked all the way up?

Yes - the output gain was definitely all the way up. Unfortunately, I didn't write down where the input gain was, but I'm sure it wasn't also all the way up [or almost so] because I would have clipped my converter.

I got my units shortly before Xmas - not in the first few batches to go out, certainly, but not at the end (has that happened yet?) - [and to make sure I'm not answering the wrong question -- let me state that the samples I posted were done after the transistor swap.]

 

[pohaku]

Yes - the output gain was definitely all the way up. Unfortunately, I didn't write down where the input gain was, but I'm sure it wasn't also all the way up [or almost so] because I would have clipped my converter.

I got my units shortly before Xmas - not in the first few batches to go out, certainly, but not at the end (has that happened yet?) - [and to make sure I'm not answering the wrong question -- let me state that the samples I posted were done after the transistor swap.]

Did you just use braid to de-solder when you did your transister swap? I've got my parts, I've just got to find some time. It'll likely be a couple weeks from now as I have a trip to a warm place planned for next week and I'm not taking any pres in my luggage.

 

[Steve Hogan]

replacing it would be easy


finding a good one

that is compatible

electrically and physically

would be the hard part

I designed a new drop-in replacement power transformer that has low stray magnetic flux and both a Faraday (electrostatic) and magnetic shield. It drops the noise about 20 dB relative to the old power transformer. The power supply PCB needs all new caps and some other mods as well, due to wrong values, wrong voltage ratings, no protection diodes, etc.

The original Chinese power transformers have cores made from multiple scraps of steel spliced together instead of a single continuous strip of (known quality) steel. The hum level in any one preamp is a crap-shoot depending on the quality of the particular core that ended up in your preamp. Some are REALLY bad and others are almost OK. None of them are as quiet as the replacement. Note that the 73 and 84 use the same power tranformer, but the 81 has an extra 24V secondary.

For more info visit http://www.prodigy-pro.com/diy/index.php?topic=27791.msg391935#msg391935

 

[P. Glaser]

Nice to see you drop in over here, Steve. What's the latest on the mods/repairs? Thanks.

Paul