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HELP PLEASE! problems with GK 400RB-III

B

bass349

Aug 18, 2003
376
2
#1
Hi Everyone,

I'm having some serious issues (yet again:hmm:) with my GK 400rb-III 2x10 combo amp. A few months back i was doing a recording when the amp started "farting" and distorting. I automatically assumed that i had blown a speaker and started to make arrangements for a replacement to be shipped over to Australia.

Then for some unknown reason, the farting/distorting sound went away... :eyebrow: now, it was apparent that it can't have been a blown speaker..

I didn't use the amp for a while (unfortunately funds are kind of short at the mo, otherwise i would've taken it to the tech ASAP). The other week i started playing through it at home, just kinda testing it to see if it would hold up - and low and behold it sounded fine, no indication that there had ever been a problem..

HOWEVER.. unfortunately, yesterday it started doing it again..

I have managed to eliminate the speakers as the problem, because I tried it through an extension cab and it made the same weird low distortion type sound (note, it only "distorts" on the lower notes, seems fine in the upper register).

I tried putting a patch lead connecting the effects loop send and returns (this has been an issue before, and as I understand it, fairly common with the GK's) but to no avail...

Out of curiosity, I plugged my bass directly into the effects return (I THINK, bypassing the voicing filters, eq.. the preamp?) and VIOLA ! the sound went away. So i'm assuming there is a problem somewhere in the preamp section...

I was hoping somebody could help me out here as to what this problem may be.. I have had some issues with this amp before, and with the kind assistance of Daniel Elliot from GK, the preamp board was replaced around about this time last year. (Feel frime to chime in Dan!).

Thanks in advance for any help :)

Andy
 
#2
Try inserting a short 1/4" instrument cable between the effects send and effects return. I had an old 400 RB that used to cut out the way you decribe and this solved the problem. It could be the jacks are dirty or defective. If this solves the problem and it doesn't happen again as long as the instrument cable is in there, that's what needs to be fixed. It's worth a try anyhow.
 
#6
All I can think of is to closely inspect the circuit board with bright light and magnifying glass. Also take a real close look at the input jack and its solder joints. By the way, the effects loop problem you mention is not confined to GK amps of that era, but any amp that used those Neutrik phone jacks. I think Neutrik improved the jack design since then.
 
#7
I should also mention, if this is the second time with the same failure, it may be the power supply wiring running up to the preamp. Again, bright light and magnifying glass. And I assume you won't open the case unless you know how to avoid getting fried.
 
#8
thanks fdeck for your very informative answers!

i definately don't trust myself tinkering around inside the amp.. unfortunately it looks like i'm going to have to take it in to the tech to have a look. (this would be about the fourth or fifth time this amp has been in for repairs now :rolleyes:)
 

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