M-208 Power Supply voltage regulators

[Laszlo]

Hi Tascam Funs,

as in another post I already mentioned, I am in the middle of restauring an M-208 mixing consol. The consol elctrically is in quite a good shape, but I am planning to recap the power supply unit as well as the monitor PCB and two input channels along with upgrading one input cards operational amp ICs to the newer NE 5532. The last mods aim to make some demonstrations and measure the changes in audio parameters and compare them with those of the channels with the old components. The report is planned to be shared in this forum. But this is the vague future..
My actual question is regarding the PSU. I realised that it uses older NJM78/79XXA voltage regulator ICs. I tried to compare them with the latest L78/79XX units and found that the A series of them have much less output noise, while their ripple rejection is significantly lower (58dB vs 70dB). Now I am puzzled, which one is more important in order to get a mixer with less audible noise. I suspect the newer units should be better, but this is rather a circuitry matter.. Can anyone help sort this out.
Cheers,
Laszlo

 

[SkywaveTDR]

Hi Lasxlo,
I don't know if regulators are getting worse or not but the fact is that all they do is give DC power to the rails the rest of the circuit uses. The amount of noise on these is not usually that much an issue as the noise that gets through would be from decayed or low value Electrolytic capacitors.
Sometimes specs of a part are picked on when that part of the part does not matter. I think the LM7812 or 24 are at least as good as they were in the past and any new stuff with greater technology can be less grade wise as the mighty dollar or Yen in this case, rules where better parts are not what is looked at but how to make the product cheaper. The Porta Studio I saw from China is a significant down grade from the earlier version with more plastic and over all more junk in it. Items made with junk parts will last less long than those good products made in the past. It is always better to get a Japanese product over that made in China.

 

[Laszlo]

Hi Sam,
Thanks for your response. In the meantime I decided to leave the original regulators, except for the 6V one which looks like burnt and dead. I wonder why the designers put regulated voltage for the VU meter lights (kindof surge protection?)..and unregulated ones for the headphones amp..
On another note, I replaced all the electrolitic caps in the PSU and tested the old ones. I dont have an ESR meter, but their capacity all were within tolerance. Maybe good as a preventive measure, but for now it lookes like I did it in vain. I never recapped anything before, except for the 122 MKIII capstan servo PCB (BTW, they were also within tolerance too, although I am aware of the leakage issue), do you think the ESR would show a different picture?
Cheers,
L