Vintage Studiomaster Mixer output clips at 0VU - Recap?

[outoftune]

Working on a vintage Studiomaster Series II console for a client.

I have a sine wave going into channel one Line In at +4, fader at 0, master fader at zero. It's measuring lower than 0.01THD until it gets to around 0VU and it immediately starts hard clipping. This happens on the master out, monitor out, and any group / aux out. Same if I use a different channel of input, or even with a lower input signal, as soon as the output is near 0VU it hard clips.

I've measured the outputs of the PSU voltage at the correct +/- 15VDC. I've worked on many other consoles with this same voltage / headroom and none of them did this.

The PSU has never been recapped, before I dig in, I was wondering if this could be the cause of the issue? Anything else I should check for? Aside from measuring the capacitance / ESR of the caps, is there any other way I can verify the PSU as the cause?

 

[moamps]

Have you tested insert out on a channel for THD?

 

[outoftune]

Have you tested insert out on a channel for THD?

Not yet but I will, thanks for the suggestion

 

[radardoug]

Sounds like 0 VU out is its maximum level, especially if it occurs everywhere. Or does it have low mix gain and you are actually clipping the channel? Get in there with a scope.

 

[gyraf]

..readjust vu-meter?

 

[JohnRoberts]

Working on a vintage Studiomaster Series II console for a client.

I have a sine wave going into channel one Line In at +4, fader at 0, master fader at zero. It's measuring lower than 0.01THD until it gets to around 0VU and it immediately starts hard clipping. This happens on the master out, monitor out, and any group / aux out. Same if I use a different channel of input, or even with a lower input signal, as soon as the output is near 0VU it hard clips.

I've measured the outputs of the PSU voltage at the correct +/- 15VDC. I've worked on many other consoles with this same voltage / headroom and none of them did this.

The PSU has never been recapped, before I dig in, I was wondering if this could be the cause of the issue? Anything else I should check for? Aside from measuring the capacitance / ESR of the caps, is there any other way I can verify the PSU as the cause?

Pretty unlikely to be caused by an old tired capacitor. Have you checked frequency response? Weak bass might point at a cap.

As already suggested is the direct out clean?

If you drop the channel fader -10dB and push the master fader +10dB does it still clip at 0VU

Does EQ bypass or trims make a difference...

Are sends similarly clipping?

JR

 

[Rob Flinn]

Sure you don't have a massive eq boost at the frequency of the sine wave you are injecting ?

 

[gyraf]

Again, have you checked adjustment of its VU-meters?

What analogue level in e.g. dBm or V does 0VU correspond to in your case?

(best way to measure is to send through a 100Hz sine, then measure with AC voltmeter most voltmeters are not precise at higher frequencies)

/Jakob E.

 

[outoftune]

thanks to everyone for the input, it has been a while since i’ve posted but i’m always glad to have all the help.

i’ll try these suggestions and let everyone know.

according to the manual the outputs are listed as Max out +20dbm

 

[gyraf]

listed as Max out +20dbm

..yes, this is measured in dBm, and of realistic magnitude - but it tells you nothing about how this correlates to your VU-meters. It may very well be set so that 0Vu=+16dBu or even weirder 

you NEED to have fixed a reference in order to use a VU-meter - by itself it's just a relative measure

/Jakob E.