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Roland JX-8P high noisefloor, op-amps?
Old 10th October 2019
  #1
Roland JX-8P high noisefloor, op-amps?

My Roland JX8P is noisy. Not noisy in a gargling, crackling kind of way, it just has a high background noisefloor all the time. Would this be because of old op-amps?

(And no, its not the mn3009 chorus chip, which of course contributes with its own kind of background noise. This noise is there with or without chorus enabled.)


EDIT: I see I've asked the same question in another thread 2 months ago, lol. I really wanna know whats up with those jx8p op-amps, I suppose.
Old 4 weeks ago
  #2
More than likely the opamp's self noise is far below the conversion or samples. Swapping them would tell. Usually customers have me do this sort of synth rework to increase the fidelity, not to lower the noise floor although that does sometimes occur.
Old 4 weeks ago
  #3
I have to admit, I dont understand what you mean with "conversion or samples" in the context of a JX8P.
Old 4 weeks ago
  #4
Gear Maniac
 
becks bolero's Avatar
 

mine is pretty quiet, but once the chorus is on I can hear the faint hissing of that

( are there any mods to quiet the chorus down? )

does your noise level increase with the rest of the signal, as you turn up the volume on the synth?
Old 4 weeks ago
  #5
Yep, noise increases with signal strength. The chorus shwooshy noise is an added bonus.
Old 4 weeks ago
  #6
Lives for gear
 
Radardoug's Avatar
 

Have you measured the signal to noise ratio in dB? Telling us it is noisy actually gives us no real information.
Old 3 weeks ago
  #7
Gear Addict
 
audiospecific's Avatar
 

The best approach would be examining the signal as it passes through the stages. Also if the audio op amps are dual voltage supply, check to make sure they are within 0.01% between each other (for example, +12.04v/-12.04v) if the voltage rails are unbalanced from each other, it will cause common mode noise to be injected into the signal. Which sounds like white noise (hiss)
Old 3 weeks ago
  #8
CMRR is usually over -100 db in a good opamp. The power rails will carry far more noise and ripple, usually around -60 db down. (1 mv).
Old 3 weeks ago
  #9
Gear Addict
 
audiospecific's Avatar
 

Very true Jim, I just don't have that schematic to see if it's using split rail op amp buffering, does any have a shcematic?
Old 3 weeks ago
  #10
Gear Addict
 
audiospecific's Avatar
 

On a bad day, the whole unit is probably -60 with fx
Old 3 weeks ago
  #11
Gear Maniac
 
becks bolero's Avatar
 

Quote:
Originally Posted by audiospecific View Post
Very true Jim, I just don't have that schematic to see if it's using split rail op amp buffering, does any have a shcematic?
here is a link to the JX 8P (owners) manual

http://synthdiy.com/files/2007/jx-8p.pdf

Last edited by becks bolero; 3 weeks ago at 02:43 AM.. Reason: doh!!
Old 3 weeks ago
  #12
Gear Addict
 
audiospecific's Avatar
 

Ok, I found the service manual:
https://www.google.com/url?sa=t&sour...hzkUePh86LmZ0E
On pages 13-14 there are comments about the voltage regulator and it's vref supplies. You need to check all of the differential voltages and remulated voltages (+/- 15, 5, vref) in this unit.

You'll notice that these tolerances are tight because they use 1% parts in the power supply. I bet one of those series regulator transistors lost some of its current gain.

Last edited by audiospecific; 3 weeks ago at 03:06 PM.. Reason: Broken url
Old 3 weeks ago
  #13
Gear Maniac
 
becks bolero's Avatar
 

whoops, that link I sent was only the owners manual~

sorry, misread the link!

glad you found it
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