Schematics for a 500-6B Power Supply?

[MatzeMillion]

Hi everyone,

I'm new to the lunchbox thing and the start was not the best for me...
I bought a used 500-6B from a guy I know very well. He used it with 6 API preamps for some time and needed more space recently. He never had problems with the lunchbox or the preamps.

My first two modules are the Avedis MA5 and the Shadow Hills Mono Gama. After the first excitment I recognized unusual distortions with one of my microphones, a Neumann KM84. After hours of testing everything pointed to the phantom power beeing the cause.

I measure only 37VDC unloaded and a guy at Gearslutz told me that it is way out of tolerance.

So I think the power supply needs a repair and my repairtech asked me for schematics to save some time. I have the option to give the lunchbox back but I would prefer a repair if it is not so expensive, because I got a reasonable price.

Does anyone have schematics for the 500-6b power supply?

thanks in advance!

[Denyle]

Try checking the voltage on pin 15 of the elco connector with the preamps removed. That will help rule out everything else. I suspect one or both preamps are pulling down the voltage.

[MatzeMillion]

Try checking the voltage on pin 15 of the elco connector with the preamps removed. That will help rule out everything else. I suspect one or both preamps are pulling down the voltage.

With all preamps removed I get 37VDC. An ATI Tech at gearslutz told me that most likely the power supply has to be checked...

[pan60]

anyway you can get it directly to API?
were are you located, their maybe their is a API tech in your neck of the woods?

[MatzeMillion]

Berlin, Germany

anyone an idea where to go?

[pan60]

Berlin, Germany

anyone an idea where to go?

i get with API and see if they have some one they can recommend, it may take a bit, if you dont see a post, shoot me a reminder, or feel free to shoot me a emil.

[EMRR]

It may even have an adjustment trimmer. Many PSU's do.

[[silent:arts]]

just measured my lunchbox, 48,38V without any module.
pulled out the PSU, and there is indeed a trimmer for 48V adjust.
with luck it needs only to be readjusted ...

[MatzeMillion]

;1095']just measured my lunchbox, 48,38V without any module.
pulled out the PSU, and there is indeed a trimmer for 48V adjust.
with luck it needs only to be readjusted ...

Nice. thank you for that! Would be too easy...

I pulled my PSU, found the 48V adjust and carefully turned it clockwise. The phantom power (naked lunchbox) rose from 37V to 46V tops.

After I put everything together again I measuered only 42V and after plugging in a KM84, I measured only 34V, with a KM184 only 28V.
I tested the KM84 again with a loud signal and found it less clipping but still far away from the optimum. Same Mic into ISA 430mkII + same soundsource = crystal clear.

I bring the luchbox to my repairservice tomorrow and keep you posted.

[MatzeMillion]

Here is a screenshot of a four recordings of the same soundsource with different mic/micpreamp combinations. SH=ShadowHills mono gama, ISA=focusrite ISA 430mkII

http://embeat.de/lunchboxing.jpg

at the last recording, I connected a KM184 to the second pre (Avedis MA5) and just turned the phantom power on. result was total asymmetric clipping hell with the mono gama. Vice versa same result!

The powersupply definitely needs major repair.

[mikekeith]

I guess you got the phantom problem corrected??

[MatzeMillion]

Yes! It was indeed the power supply. I got another lunchbox in exchange and all the problems were gone.