SSLtech
Well-known member
Surely your numbers are way off?
-120dB is a number most manufacturers would die for!
Keith
-120dB is a number most manufacturers would die for!
Keith
70's Console, noise (6k to18K hiss) troubleshooting help?
- Thread starter cannikin
- Start date
Help Support GroupDIY Audio Forum:
> Channel Strip fader +10 and channel gain turned all the way up (no group assignment). ...I assigned the channel to group A (left channel) - 67dB @1kHz
"gain turned all the way up"... how often would you do THAT?
In rock-n-roll, probably never.
If the input noise is -127dB (near theoretical), and overall gain is 60dB, I would expect noise to be -67dB at the output. (-127)+(60)= -67.
Also: are you leaving mike inputs open? Some mike inputs hiss bad when left open. Ideally you should stuff a 150Ω metal resistor up the input; for practical tests, a shorted input gives about the same result (on most mike inputs).
> all knobs cranked all the way up.
That's not a normal setting. Are there "nominal" marks on the faders? If not, put them about 7/10ths up. Do the same on the channel fader. Put a SM57 in front of your face, sing, and adust the gain-trim to get the meters touching 0VU. Now replace the SM57 with a short, and check the noise. If it is around -80 from zero VU, be happy.
> There is also a 10dB spike at 60Hz.
With mike input shorted?
Why don't you find out what power supply it really wants, and make sure the the box you got with it is really putting out the right voltages? Cleanly? With a remote power supply, there isn't much reason to have any 50/60Hz power-crap in the board. If it isn't open inputs, loose wires, or missing sheilding, it suggests a sick power supply.
"gain turned all the way up"... how often would you do THAT?
In rock-n-roll, probably never.
If the input noise is -127dB (near theoretical), and overall gain is 60dB, I would expect noise to be -67dB at the output. (-127)+(60)= -67.
Also: are you leaving mike inputs open? Some mike inputs hiss bad when left open. Ideally you should stuff a 150Ω metal resistor up the input; for practical tests, a shorted input gives about the same result (on most mike inputs).
> all knobs cranked all the way up.
That's not a normal setting. Are there "nominal" marks on the faders? If not, put them about 7/10ths up. Do the same on the channel fader. Put a SM57 in front of your face, sing, and adust the gain-trim to get the meters touching 0VU. Now replace the SM57 with a short, and check the noise. If it is around -80 from zero VU, be happy.
> There is also a 10dB spike at 60Hz.
With mike input shorted?
Why don't you find out what power supply it really wants, and make sure the the box you got with it is really putting out the right voltages? Cleanly? With a remote power supply, there isn't much reason to have any 50/60Hz power-crap in the board. If it isn't open inputs, loose wires, or missing sheilding, it suggests a sick power supply.
cannikin
Well-known member
thanks guys, I really do appreciate your tech support, thoughts and knowledge. I have to do more thorough testing, thanks for all your help. the learning curve on this has been huge. anyway I've been in contact with Cyril for the past three weeks and he just emailed me that he found the schematics, that will be a big help. once I have a better understanding of whats going on at a micro level, I'll probably have a bunch more questions. thanks again.
cheers.
cannikin
aka david
cheers.
cannikin
aka david
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