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Double Bass GK 200mb repair

Earl

Earl

Supporting Member
Jan 29, 2000
2,003
2,232
Ridgefield Park, New Jersey
www.yourlifeblueprint.net
#1
I have a GK 200mb that started distorting/crackling/buzzing. Took it to a local GK authorized service center - the first time it came back with the same problem, the second time they said they tightened a screw on the woofer. It is slightly better but still distorts especially on low notes. I called GK and they said they could not repair it because it is too old (1987).

Does anyone have any suggestions or experience with repairing this amp?
 
#2
Try turning off the internal speaker on the 200MB and plugging the amp into an external speaker cabinet. If the problem goes away, then there is a problem with the internal speaker. After many years the foam surround on the woofer breaks down, which makes it sound very bad. If the foam surround is bad, a new woofer is available from GK or it can be repaired. If the amp still sounds bad through a known good external speaker, then the problem is with the amp electronics. Besides the chorus circuit, everything is fairly standard with readily available parts, and can probably be repaired by someone competent.

There is also a thread in this forum about replacing the speaker in these amps.
 
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#3
robgrow said:
Try turning off the internal speaker on the 200MB and plugging the amp into an external speaker cabinet. If the problem goes away, then there is a problem with the internal speaker. After many years the foam surround on the woofer breaks down, which makes it sound very bad. If the foam surround is bad, a new woofer is available from GK or it can be repaired. If the amp still sounds bad through a known good external speaker, then the problem is with the amp electronics. Besides the chorus circuit, everything is fairly standard with readily available parts, and can probably be repaired by someone competent.

There is also a thread in this forum about replacing the speaker in these amps.
Click to expand...


Nicely done. Answers like this are a big part of the reasons that, despite its many flaws, I still love Talkbass. :)
 
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#4
I've had issues with the jacks getting dirty and the same thing happens. Lots of crackling and poor sound output and quality.

I take it in to a local guy who has been doing electronics repairs for 40 yrs or more and he cleans them up for me once a year for 20 bucks.

He says the GK's are the best he has worked on electronics wise but they use cheap damn 1/4 jacks that get dirty.

You can usually get it working by repeatedly shoving the cord in and out of the jacks but they will need cleaning and while it is in for that they will clean all the pots etc as well.

Well spent money each year............
 
#6
fdeck said:
Here's an idea. Unless you have a use for the effects loop, next time you have the amp in the shop, have the tech bypass it with a wire.
Click to expand...

This would remove the option of bypassing the input jack and preamp section of the amp by plugging in through the effects return (using an aftermarket preamp) as some, including me, choose.

Although, for convenience's sake, sometimes I'll forego (leave at home) the aftermarket preamp and opt to use the GK's preamp and EQ sections. That option was recently temporarily removed when, while the amp was being used for a keyboard at a jam, someone tripped over the cable and screwed the input jack. I was bummed, momentarily thinking I'd have to take the amp to the shop, be without it for a few "travel light" piano trio gigs. Then I remembered: I don't need the front jack, I can use the effects return instead. Had a private event trio gig last night, used the "broken" GK. Worked great.
 
#7
Here is another consideration.
A few years ago, I had a friend that used a combo 300 Bass amp. The amp developed a loud buzzing noise at certain frequencies(only when he played specific note).
He had taken it to an electronic techneshion no less than three times. Issue still wasn't resolved.
He brought it to me to look at. I discovered one of the internal cabinet braces was just slightly loose enough to cause vibrasion. All it needed was some woodworkers glue. "walla"!!! problem solved !!!:hyper:
 
#8
Thanks everyone! I haven't been able to try an external speaker, and it's not a dirty jack. Someone pm'ed me the name of a repairman who re-foamed his GK speaker but he never returned my call. I guess I'll just try taking it to a different repair place.

Oh, and I did have another amp recently that was vibrating loudly on a certain note, and it turned out to be a loose screw. I wish the fix on the GK was as easy!
 
#11
Hey Earl, I have the same vintage GK. Has an input jack problem after falling over on it's face just like Keyser Soze describes. Had it fixed once, problem came back. I retired it to the garage. While convenient, never was in love w/ it's sealed cab sound or its electronics. Those big old 400 to 800 watt GK heads that all the sound guys insist on supplying as backline also sound cold and brittle to me as well. Get a new amp, 1987!, that goes back to Gulliver's days :p. It doesn't owe you anything :help:

Say hello to John B. for me.
Hope you've been well, Brian Glassman
 
#13
Earl said:
Hahaha! Hey Brian! Oh, I have other amps (and 80% of my gigs are ampless anyway), but I do like to keep that one around, you can't beat the size and weight. I think those original 200mbs sound MUCH better than the mb150 that came after (I couldn't stand those).I took it to another repair place so we'll see what happens. Keep swingin'!
Click to expand...

..hmm maybe the one in my garage is the mb 150? I'll have to look. 80% ampless! good for you. wish I had the stones (or gut string chops?) to do that more often. Lemme know who you brought it to. I could use a good repair guy for another dinosaur I have hanging around...gee maybe we're the dinosaurs at this point, talkin' about 25 yr old amps, pining for ampless gigs and long gone Jazz clubs :bassist:

Be well!
 
#15
CTForde said:
why would that remove the crackle?
Click to expand...
The RETURN jack in the effects loop is a switching-type jack. The switch contacts can get dirty or oxidize causing noise, an intermittent or complete loss of signal at that point in the circuit. Besides cleaning this switching jack with a high-quality contact cleaner like Caig Deoxit D5, the solder connections between these jacks and the PC board should be checked and possibly re-soldered. This is pretty typical stuff, and applies to several other amps also.
 
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#18
CTForde said:
it kind of depends on what parts we're talking about - some stuff specific to the 200mb is indeed hard to come by a source I consider reliable has told me - but I generally agree with teemuk.
Click to expand...

I just got my 1980s GK 200mb back from the shop of my usual tech guy. He has always been very good, but he couldn't find the fix for my amp problems this time: Three of the four EQs and the Chorus were not working at all. The main thing he says is that the 15 volt rail (whatever that is?) signal path is shorted and he can't find it. He didn't charge me a dime and I know he spent an awful lot of time on it. I feel bad about it. Guilty. But, my question is: Do I buy something new or go with another tech guy? I love the amp and it has served me well for many years of hard, steady gigging. Do I give it another shot?
 
#19
gerry grable said:
I just got my 1980s GK 200mb back from the shop of my usual tech guy. He has always been very good, but he couldn't find the fix for my amp problems this time: Three of the four EQs and the Chorus were not working at all. The main thing he says is that the 15 volt rail (whatever that is?) signal path is shorted and he can't find it. He didn't charge me a dime and I know he spent an awful lot of time on it. I feel bad about it. Guilty. But, my question is: Do I buy something new or go with another tech guy? I love the amp and it has served me well for many years of hard, steady gigging. Do I give it another shot?
Click to expand...

It's a tough call isn't it. I owned two 200MB's ( a Series I & a Series II). They both sounded great for Double Bass, the EQ points on those earlier GK combos was, IMHO ideal. You'll be hard pressed
to find another amp that sounds like that one, especially now that pickups have improved. Understand here, I don't currently have one, but I'm always scouring the TB classifieds to see if one pops
up. In my search for a comprable replacement, I went with a Headway EDB-2 into the QSC K8. This combo sounds great, but it's more expensive, and has more moving parts. The Genz Benz Shuttle
3.0's and 6.0's were the logical replacement, until the company folded. Since I've recently had to have my Walter Woods Ultra repaired it's become apparent to me how difficult it is to source parts
for older, discrete component, solid state amplifiers. Lot's more B-15N's still in service than 200MB's because their simpler, easier to repair, they had larger initial production, and parts are readily avaliable.
I'm not saying that you should run out and purchase a 25 watt, 75 pound Ampeg Portaflex amp, but these days, it's far easier to repair that amp than it is the 200MB.

Ric

You could get a newer GK MBS, which is about as close as you can get to the old 200MB's
 
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#20
Close, but no banana. The old 200 series GK has a much warmer and present sound, ime, imho. Maybe because GK opted for more power with the MBS? Kind of silly because adding 40 more watts to that little box didn't really equate to any usable volume past the point were the rig sounds good. The power amp in the 200 series was perfectly matched to the cabinet.

EDIT: For repairs on that old 200MB, the buck stops at The Amplab in Campbell, CA. Keith was working for GK when that amp was being produced, he knows the circuit.

Rick, it's true about the old B-15, not only are the parts available, but the sound is unparalleled. Mated with a more efficient and upright friendly box, it could be the ultimate in amplified tone coming from a production line amp.

Can't wait for the rant here about how wrong I am... :-) :-) :-)
 
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