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Question about console noise floor
Old 19th January 2019
  #1
Here for the gear
 
🎧 5 years
Question about console noise floor

Hey guys.
A very kind member suggested to move my question to this thread.
So recently I've bought an old Hill Audio Conecpt series 8400 mixing console.
Everything works fine, but I've noticed that engaging EQ section in each channel adds some additional noise. I was wondering, what would you guys suggest to upgrade to lower the noise of EQ section? And one of the channels EQ has a humming noise.

Also, another question. I've recently started cleaning pots in each channel, and noticed that some of the channels got additional Opams inserted, and some are left empty in that area. Do you guys know whats the catch?

I've added pictures of two separate channels:

Missing IC's

Input channel Schematics

Schematics2
Old 19th January 2019
  #2
Lives for gear
 
🎧 5 years
Do the channels that are missing opamps behave any differently? Are they the noisy ones or the quieter ones? It's hard to imagine that pulling an amp stage out, without otherwise bypassing it, would add noise.

The only thing I can learn from the photos, without a schematic, is that there appears to be a trimmer near these sockets. Its setting might have something to do with the noise.

And of course noise is dependent on gain staging, so you have to make sure the good and bad channels are being used the same way.

The only debugging you can do without a schematic or manual is some swapping of components between the good and bad channels, trying to isolate if it's a bad chip. And it could be a soldered component that's drifted.
Old 20th January 2019
  #3
Here for the gear
 
🎧 5 years
Hey Jay,
Thanks for response!

I didnt notice any difference behavior between channels with and without the IC's, yet it drives me crazy not knowing why most of the channels are missing these opams...

Regarding the noise - its a accumulating hiss noise when I turn on each channel EQ section (with all volume sliders set to unity). I know its unavoidable, but maybe there is a component upgrade I could to, to decrease the noise floor...?
Im kinda new to all the schematics and components stuff, yet I can solder and desolder things

I've uploaded a schematic of which I think is a input channel strip. Maybe this will help you understanding whats going on in the missing IC's stage? In the other page, featuring the list of components, its written that there should be 5532 chips.

Schematics : Imgur: The magic of the Internet
Old 20th January 2019
  #4
Lives for gear
 
nosebleedaudio's Avatar
 
🎧 15 years
You do have the inputs terminated?
Mic pres need a 150 Ohm for the typical Load..
Old 20th January 2019
  #5
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JohnRoberts's Avatar
 
🎧 10 years
Quote:
Originally Posted by tomhetas ➑️
Hey guys.
A very kind member suggested to move my question to this thread.
So recently I've bought an old Hill Audio Conecpt series 8400 mixing console.
Everything works fine, but I've noticed that engaging EQ section in each channel adds some additional noise. I was wondering, what would you guys suggest to upgrade to lower the noise of EQ section?
It is always possible to find newer op amps with slightly lower noise, it is unclear how much difference this will make, Noise in most consoles is dominated by the mic preamp and often ambient noise in the room.
Quote:
And one of the channels EQ has a humming noise.
could be faulty IC or capacitor.
Quote:
Also, another question. I've recently started cleaning pots in each channel, and noticed that some of the channels got additional Opams inserted, and some are left empty in that area. Do you guys know whats the catch?

I've added pictures of two separate channels:

Imgur: The magic of the Internet

I could also upload some schematics if that would help you to understand whats going on :}
Look at the schematic to ID the missing ICs. Does that function still work? Unlikely...

JR
Old 20th January 2019 | Show parent
  #6
Here for the gear
 
🎧 5 years
Quote:
Originally Posted by JohnRoberts ➑️
It is always possible to find newer op amps with slightly lower noise, it is unclear how much difference this will make, Noise in most consoles is dominated by the mic preamp and often ambient noise in the room.

could be faulty IC or capacitor.


Look at the schematic to ID the missing ICs. Does that function still work? Unlikely...

JR
Im still trying to understand the Schematics and which section is controlled by the IC's, yet its a bit too advanced to me...
Old 20th January 2019
  #7
Lives for gear
 
🎧 5 years
Do you want to upload the schematics? The IC numbers are printed on the PC board, so it should be easy to figure out what they do.
Old 20th January 2019
  #8
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JohnRoberts's Avatar
 
🎧 10 years
If you figure out what function is not working, that will be a strong hint.

JR
Old 20th January 2019 | Show parent
  #9
Here for the gear
 
🎧 5 years
Quote:
Originally Posted by Jay Rose ➑️
Do you want to upload the schematics? The IC numbers are printed on the PC board, so it should be easy to figure out what they do.
I've uploaded it a while ago :
Imgur: The magic of the Internet
Old 20th January 2019
  #10
Lives for gear
 
🎧 5 years
The IC numbers are almost impossible to read on the uploaded version. Please look at the circuit cards, note the numbers of empty sockets, circle them on the schematic, and upload again.
Old 20th January 2019
  #11
Lives for gear
 
The missing ICs are not shown at all on the page of the schematic you posted...they're apparently from a different portion of the schematic.
Old 21st January 2019
  #12
Here for the gear
 
🎧 5 years
Gonna try to dig deeper through the schematics later today...
Old 22nd January 2019
  #13
Here for the gear
 
🎧 5 years
So I finally managed to find the schematics for this headache.
Schematics : Imgur: The magic of the Internet
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