Power supply rebuild question

[Talldog]

Hey all. Trying to decide what to do next on my Amek Tac scorpion project. I have rebuilt/recapped the main output channel, recapped and modded 10 channels with Langley pres. Now I'm trying to decide whether to recap the 14 remaining input channels (no preamp mod) or recap/rebuild the power supply. These are all untouched since 1985. Does recapping do anything sonically to the PS? It is the 500 series if that makes a difference? Thanks in advance.

 

[cyrano]

It's hard to tell if recapping the PSU will change the sound. But I always start recapping of +20 year old gear with the PSU. Otherwise, you risk damage because the old PSU fails because mods tend to draw just a little bit more power...

 

[sweetbeats]

AFAIC its good insurance to recap the PSU and make sure the heat management is good for the regulators. I may make no difference. Recapping the PSU for my Tascam M-520 resulted in a significantly noticeable drop in the noise floor (subjective though...didn't take any before/after measurements), and recapping the PSU for my Soundtracs MX desk (along with upgrading the rectifiers and regulators and doing some significant changes to the heat management) brought a 4dB drop in the noise floor. The other interesting thing is that with the 32 inputs loaded prior to the mods I could starve the desk of power by setting the mic trims at 70~80% and channel faders to unity...bringing the group faders up would cause the outputs to go into a violent oscillation of about 6Hz as the grip faders went past unity...mind you this is with dummy-loaded inputs. Bad PSU design? Tired components? Probably mostly the latter, but heat management was kinda sad prior to the attention. Anyway, after the mods I can crank EVERYTHING to 100% no sweat. Not a real-world scenario and maybe the settings in the test prior to the mods isn't necessarily terribly real-world either, but it makes me wonoder how the mixer would have handled dynamic source material you know? Obviously the PSU wasn't up to snuff because IMO I would hope a PSU to be built to handle a reasonable margin over what the device could possibly demand. So...my point. I'd recap it, Ken. I'm sure Tac used good quality caps, and I betcha the design is good, but its been 25 years and you are going to hurt nothing by recapping it and getting in there just to kind of look at things...at the least. OR you may improve the noise floor and the mixer's abillity to manhandle transient peaks and/or save some components from undue wear or torture if something is not right in the supply. That PSU is the mixer's circulatory system. How would you do with a bad artery or valve?

Look for scorching on the PCB around the rectifiers. If things look like they've been hot then maybe some better cooling could be employed. In most cases I bet the cooling is fine. I was really surprised at the heat management on th Soundtracs mixer or rather lack thereof.

Hey...pics. Yah?

 

[evm1024]

Power supplies are part of the audio path. Any problem there....will be heard.