Vintage Yamaha 1204 Mixer Opamp upgrade

[radardoug]

Stand by for those Frakos to be leaky and go short. The increased cap is a sign that they are going bad.

 

[ChrisMadog]

A buddy gifted to me an old Yamaha MC1204 mixer. It works. It sounds cool. Is a little loose on the low end.
.....

Hi,
I also inherited one of these units.
I fixed up some minor issues (broken input sockets) and then attacked the power supply to include the Earthing as required by Australian Standards. I also installed a double-pole switch to replace the single pole.
After I fixed that up and I was happy (and safer), I did a frequency run over all the channels, right through to the stereo outputs.
I was surprised - the claimed 20hz to 20KHz +/- 0.1dB was 9Hz to 28Khz +/- 0.1bB !!

Noise figures with everything on full wasn't startling but not bad either at -48dBm. When would you ever run =everything= flat out ?
Hum level was at -81dBm and I will look at some new filter caps with low ESR figures as well as disc-ceramics across them (because I always do).

I thought about replacing the 4558 ic's and I don't think it needs to be done. Seriously, I don't see the need.

A friend said "What about if you get something that is very low level ?" - meaning low-level input needing tons of pre-gain - and I just looked at him.
Ï've got 5532 preamps for that if I need them.

Great mixer for non-professional users in my opinion. Probably good enough even for professional use if used properly.

My 5c worth.

Yeah, I know, the original post was in 2013 but I thought I'd throw in a some words. Just because.

 

[Snatchman]

Hello..I had the Yamaha 1604 and I had it modded by the late Timothy Smith of Weyer/Smith Labs ( man, I miss that good guy.. )..He swapped out the 4558's with the Analog Devices OP-275s through out and it really made that little console open up..!..When I first received it back from Timothy, hooked it up and turned it on, I thought something was wrong. It was so quiet..!!!... I actually used it for lots of live shows without a moment thought..!..Paired up with some great amps and speakers, it sounded a whole lot " bigger " than what it was...!

 

[abbey road d enfer]

I thought about replacing the 4558 ic's and I don't think it needs to be done.

The two places where low-noise components must be used is the mic preamp and the summing bus amplifiers.
For the mic pre, it's the discrete transistors that count, no so much the opamp. The 2SA970 transistors can hardly be improved upon.
For the summing amps, the 1204 used uPC4570, opamps that have similar noise performance and GBW than a 5532, with half the current draw. The uPC4570 does not have the output capability of a 5532, but it is not needed here.
Now, one may want to use faster opamps in order to increase "transparency", but one must make sure they don' exceed the available current the PSU can supply, and check in-circuit stability.
Quite often one needs to increase/extend power rail bypassing.