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opamp bypass caps Modular Synthesizers
Old 18th December 2010
  #1
Lives for gear
 

opamp bypass caps

hi guys,

i want to try some op-amp changes/ i'm going to install sockets and .1uf caps across power rails from op-amps.

infact i've already done 1 channel + right master channel, interestingly there are two tl072's on the board and one already has the .1uf caps across the power rails to ground but the other doesn't/

I'm not going to go crazy and do all the channels yet, although I am still fixing a few niggling problems with a few boards and if i have to take a board out I am installing sockets and putting the original op-amps back and installing the .1uf caps.

I only have some OPA2134's to try at the moment.

question:
Ceramic caps?
Does quality matter?
Is OPA2134 power consumptions mucher higher than tl072?


Any other recommendations for replacing Ne5532 or Tl072? ( i don't really want to mod other than bypass caps)

Anything else to be ware of?

thanks
Old 18th December 2010
  #2
Hi oxide54

For .1uF bypass, use high quality ceramic. By high quality I do not mean NP0, I mean reputable manufacturer such as Kemet.
I use 20% Kemet "Golden Max". They come in at some of the lowest prices by the 10,000 lots that I buy, but still some of the very best quality.

You do not need film here.

I just can't begin to tell you of all the low and high end gear I have repaired that simply had faulty bypass caps. Both digital and analog circuits...

TL072- +/-5mA
TLE2072- +/-4.4mA
OPA2134- +/-10mA
NE5532- +/-16mA
OPA2604- +/-12mA
OP275- +/-5.5mA

As you can see there are not many choices for low power to replace the TL072.

Best
Roger
Old 18th December 2010
  #3
Lives for gear
 

hi roger,

thanks .


1 more question know anything about JRC 4580D??

just i have another device, a dj mixer that has a really high noise floor, i've read 4580d is cheap and nasty? could i replace with something like a tl072 or ne5532?? as funnily enough i have a few spare

thanks
Old 19th December 2010
  #4
Isn't the 4580 in a SIP?
IIRC, some old Mackies used them.

In nay op amp replacements, try to avoid op amps that are very much faster than those being replaced.

Also, in bypassing, I always use 2-.1uF per IC package. One from each supply rail to gnd. Across both rails works too, but I am not sure it works as well.

rf
Old 19th December 2010
  #5
Lives for gear
 

The 4580 is not likely to be the source of the noise, the circuit topology is.

You might be able to reduce it some by opamp swaps, but without diving into
the circuit values just shot-gunning isn't likely to help much.
Old 19th December 2010
  #6
Lives for gear
 

Quote:
Originally Posted by Dan Kennedy View Post
The 4580 is not likely to be the source of the noise, the circuit topology is.

You might be able to reduce it some by opamp swaps, but without diving into
the circuit values just shot-gunning isn't likely to help much.
oh okay thanks,

its a stanton sa3 . can't find a schematic anywhere, i might email stanton on monday see if they have one. have my doubts though might have insist i'm not trying to copy it!

i know without seeing a schematic is like looking on the dark, but any general suggestions for anything to look at on the circuit?
Old 19th December 2010
  #7
Lives for gear
 

Quote:
Originally Posted by Dan Kennedy View Post
The 4580 is not likely to be the source of the noise, the circuit topology is.

You might be able to reduce it some by opamp swaps, but without diving into
the circuit values just shot-gunning isn't likely to help much.
just swapped, stupendous difference!!!!!
Old 19th December 2010
  #8
Lives for gear
 

Quote:
Originally Posted by RogerFoote View Post
Isn't the 4580 in a SIP?
IIRC, some old Mackies used them.
Its DIP.

Quote:
Originally Posted by RogerFoote View Post
Also, in bypassing, I always use 2-.1uF per IC package. One from each supply rail to gnd. Across both rails works too, but I am not sure it works as well.

one from each supply rail is what I've been doing, with the cap pin going to suppy pin shorter than the ground side.

thanks
Old 19th December 2010
  #9
That's fine, with the speeds we are talking here, there's no need for extreme fussiness about lead dress. Close to the IC pin is fine.

Check for oscillation at the outputs before you put the lid back on...
Old 19th December 2010
  #10
Lives for gear
 

Actually I'm rather surprised if there was a significant difference, the 4580 is not particularly noisy.

The 2134's are good amps, but not hugely quieter.

I'll bet the 4580 was defective or oscillating.
Old 20th December 2010
  #11
Lives for gear
 

Quote:
Originally Posted by Dan Kennedy View Post
Actually I'm rather surprised if there was a significant difference, the 4580 is not particularly noisy.

The 2134's are good amps, but not hugely quieter.

I'll bet the 4580 was defective or oscillating.
it might have been, I added the 0.1uf bypass caps as well, so maybe that fixed it.

you may well be right about the 4580 being defective, as it was a 2channel dj mixer and that half was more noisy than the other side, although with new opamps and bypass caps it is now less noisy than the other side.

I may add just the bypass caps to other side and use the original 4580's and see what happens, if so I may well put the 4580's back in the altered side and use the 2134's elsewhere.


I've ordered an array of different op-amps to try in my main console. i really should stop messing about now its all working and get on with making some music!

trouble is the electronics side of things has become quite interesting, and thanks to everyone past and present on this forum, not only for replys to my posts but other peoples posts as well as there is a wealth of valuable information hidden under the search button.!
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