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Switching opamps on Gallien Krueger amps

mouthmw

mouthmw

Jul 19, 2009
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Croatia
#1
I found this thread a whole while ago, but really started thinking about doing this on my 700RB II just now:

[Invalid or Expired Link Removed]

Apparently, when you switch LF353 or TL072 opamps with pro opamps like say AD823 opamps, you get a better frequency response, fatter growl from your boost, better articulation and more headroom. And less noise, not that I really had noise problems with mine though.
Sounds great!

Anyone here tried that?

Here's a link for the opamps that guys used:

Invalid Link Removed
 
#2
Not with GKs but I did switch out the TL072s in my Thunderfunk with TLE2072s and the noise level dropped by half. The tone was clearer but in losing the haziness it also lost some of that "phatness". Practically speaking it did not make any difference in a live setting but if you are sitting in a quiet room you do hear a difference. The most stunning difference was when I replaced the input 5532 op amp in the Thunderfunk with an LM4562. I think this was mainly because the 5532 was unstable in the Thunderfunk circuit and was oscillating, killing dynamics and tone. The TLE2072 will probably be more compatible with the LF353 and is a direct upgrade replacement for the TL072 for not a whole lot of money, so you may want to check them out.
 
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#7
BassmanPaul said:
You could well swap them all and notice absolutely no difference except in your wallet. The amp could even turn into a nice oscillator.
Click to expand...
+1 to that, and if/when it does turn into an oscillator, it could happen at a frequency well above audible range, which is the worst kind of oscillation because now you've got an amp in serious trouble and you can't hear the symptoms.
 
#8
mouthmw said:
Apparently, when you switch LF353 or TL072 opamps with pro opamps like say AD823 opamps, you get a better frequency response, fatter growl from your boost, better articulation and more headroom. And less noise, not that I really had noise problems with mine though.
Sounds great!

Anyone here tried that?
Click to expand...

Although I don't have a GK, I've tried a number of different op amps in my Eden WT-500, replacing the original JRC 072Ds. It can indeed make a difference to the sound, though whether or not that is an improvement may be subjective.

IMO, the ADA4627-1 sounds quite nice. Not much of a fan of the AD823.
 
#9
Hi.

I haven't tried that with GK, but I did swap the OP amps on my SWR ST220.

The reduction in static noise was noticeable, no other differerences to me. But then again, the Op amps Steve used were nothing special.

Paul makes exellent points.

While some OP amps are somewhat noisy, the noise usually comes from somewhere else. Unless the OP amps are used outside their designed parameters and the noise floor rises over time as a result.

If the Op amps aren't on sockets, don't even think of swapping them unless You're equipped with a desoldering device of some sort, or do this for living. The traces are delicate.

Regards
Sam
 
#10
This started a while ago when chatting with a younger bassist. I replaced the TL072's and LF353 with BB OPA2134's when they were still available (before TI took them over). It made a marked improvement in my 800RB. He choose the almost most expensive current option.
They NOT socketed so anyone thinking about this should install sockets. Yes higher bandwidth opamps can oscillate so bypass caps should be used on VCC and VDD.
If you think there is no difference, the sockets will make the change back easy and you will have a reference to compare to.

(Of course all tubes sound the same too ;))
 
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#15
As an alternative to swapping op amps you could try to replace or bypass the coupling caps in the amp. This can give a noticable improvement of clarity and micro-dynamics.

In the amps I have seen scematics of so far, there are several coupling caps in the signal path of the preamp section, and they are often very cheap ones, not good for audio signals. Replacing them by good quality poly propylene is the best solution, but can be expensive and since poly propylene caps are bulky there might not be room for them. A good solution can be to bypass the existing coupling cap with a small polypropylene or polystyrene type cap. For instance, if the coupling cap is 1 uF then bypass with 100nF. Try it out :)
 
#16
Morten_B said:
As an alternative to swapping op amps you could try to replace or bypass the coupling caps in the amp. This can give a noticable improvement of clarity and micro-dynamics.
Click to expand...

Replacing/bypassing interstage coupling capacitors can also help to clean up the sound. Not sure about GK, but Eden uses a number of electrolytics in the signal path which add a bit of "grunge" to the sound. I replaced/bypasses the electrolytics in my WT-500 and it opened things up somewhat. Although I haven't looked at schematics, I got the impression that GK used some discrete circuitry in their amps rather than op amps?
 
#17
12bass said:
......Although I haven't looked at schematics, I got the impression that GK used some discrete circuitry in their amps rather than op amps?
Click to expand...

Owning both a 400RB and 800RB, at least those seem to have a mix of discrete w/op amps.

I recently added more capacitance to my 800RB's power supplies (an extra 10,000 uF) and noticed a distinct improvement in performance. Nope, no before and after MP3s to post, sorry. I like it enough to do on my 400. But I've done this mod, as well as bypasses etc to other audio gear in the past w/generally noticeable improvements in sound, noise floor, etc.

From my own experience swapping opamps to improve performance really depends on the overall circuit design of the amp to begin with. Some designers are really good at taking the proverbial sow's ear (in terms of specs) and making a silk purse.
 
#18
dhsierra1 said:
I recently added more capacitance to my 800RB's power supplies (an extra 10,000 uF) and noticed a distinct improvement in performance. Nope, no before and after MP3s to post, sorry. I like it enough to do on my 400. But I've done this mod, as well as bypasses etc to other audio gear in the past w/generally noticeable improvements in sound, noise floor, etc.

From my own experience swapping opamps to improve performance really depends on the overall circuit design of the amp to begin with. Some designers are really good at taking the proverbial sow's ear (in terms of specs) and making a silk purse.
Click to expand...

The addition of 40,000 μF to the supply in my WT-500 definitely made a noticeable improvement to headroom, especially in bridged mode. Old amps from the 80s may have pretty tired supply capacitors, so that may also explain some of the improvement in the RB.

There are some stock/modded Eden comparison clips here: http://www.talkbass.com/forum/f15/eden-wt-500-circuit-modifications-improvements-762982/
 
#19
It's amazing that GK doesn't add another 10,000 μf themselves.
How could they overlook such a design flaw?
Why didn't you do 20,000 or 5,000 ... :rollno:

Often repeated on this forums is "no pic no proof"
So "No measurements no proof" ;)

Just a clip, a wave file is better an mp3 and simple.

Ear witness testimony will get you about as far as it'll cost you to repair the amp after damaging some other part. Caps have inrush and what else is affected?

Oh, but look - you can Pay somebody to mod it for you. And these people make a living repairing amps. How convenient :D
 

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