GK Fusion 500 - Control Pots Soldered or Plug-In?

[CoffeeLove]

Hi. Title says it all, but I also included a picture for reference. Are these little control pots "soldered" to the board, or are they plug-and-play?

Both "gain" knobs are problematic, so hoping to replace them.

Thanks

 

[agedhorse]

Soldered, don't damage the PCB or you will end up with a doorstop. It's a double-sided PCB with plated holes. You will need a suction type solder remover and skill to avoid damaging the thru-hole plating. Since you asked this question, it tells me that you do not have the experience.

 

[groovaholic]

Both "gain" knobs are problematic

Can you expand on what you mean by "problematic"?

Many amps (including several older GK's that I've owned) will develop crackling sounds when a pot is nudged or rotated - and any user can generally alleviate that issue non-invasively by rotating the pot from maximum to minimum repeatedly (think of it like stretching after you've been sitting at your desk too long)

But if someone has sprayed contact cleaner into the pot, they've probably flushed out all of the lubricant - this tends to make the pots turn too easily at first, then corrode and get worse...eventually requiring replacement by someone who has the tools and skills described by @agedhorse.

So, if it's not already too late, try turning each knob a bunch of times first...

 

[agedhorse]

Spraying "miracle cure-all spray" isn't going to help and will just create entirely new issue. That's a sealed pot.

 

[shoot-r]

Hi. Title says it all, but I also included a picture for reference. Are these little control pots "soldered" to the board, or are they plug-and-play?

Both "gain" knobs are problematic, so hoping to replace them.

ThanksView attachment 7126641

I'm guessing what you have is a "MB" Fusion 500?

(I've been having the same problem with the pots in my MB Fusion 800.)

You will have to locate a Authorized G.K. Service Center and take or send the head to them for repairs. A list of service centers can be found on G.K.'s website.

The G.K. factory in Stockton, Ca. no longer offers repairs for amps from the MB series or any of the earlier models before the MB's.

Only amps from the Legacy and Fusion "S" series are now serviced/repaired at the Stockton factory.

 

[Pizza Frog]

I had 3 crackly pots so I rotated the pots on my MB Fusion for a few minutes and the crackling went away and never came back on 2 of them. I was hoping for 3 out of 3 but 2 out of 3 ain't bad.

 

[CoffeeLove]

OP here. Good news, just purchased a new preamp section (control pots included) for $50, direct from GK. After I have the amp running again, will buy just the "pots" to see if I can get the old preamp running, maybe.

Yes, I have been doing the "rotating knob" trick to get rid of crackling for 3 years now, it's time. Beyond happy GK still sells the preamp, looks like a fairly simple install, mostly plug and play.

Swapping out the tubes at the same time. Let me know if anyone has suggestions for the new preamp install.

Thanks everyone for the response.

 

[WRM]

Is there a problem with the tubes?

 

[agedhorse]

I would leave the tubes alone, if they are good there’s no reason to create a potentially new issue with a possible defective tube.

 

[PeaveyPlayer]

OP here. Good news, just purchased a new preamp section (control pots included) for $50, direct from GK. After I have the amp running again, will buy just the "pots" to see if I can get the old preamp running, maybe.

Yes, I have been doing the "rotating knob" trick to get rid of crackling for 3 years now, it's time. Beyond happy GK still sells the preamp, looks like a fairly simple install, mostly plug and play.

Swapping out the tubes at the same time. Let me know if anyone has suggestions for the new preamp install.

Thanks everyone for the response.

I’ve been asking my dealer to just replace the preamp

But they keep repairing it
Scratchy pots and noise in the chain

Once again I took it in and they send it away. I get it back and they don’t even tell me what they did

 

[PeaveyPlayer]

I would leave the tubes alone, if they are good there’s no reason to create a potentially new issue with a possible defective tube.

Agreed
Unless your trying to tonallychange it

I tried an ECC803S which I moved to my Aguilar Db680 V1


The gallien Krueger fusion 500/800 is
V1: First gain stage and contour.

V2: Post “Gain control” /“Bright switch”, High Mid.

V3: Low Mid, Bass and Treble.

With the ECC803S in V1 it felt more sparkly and smoother but it seemed like something was missing.. not in a bad way but it wasn’t As in your face

all though some note the Fusion 500/800 doesn’t make much of a difference
On the gk site it says the run the 12ax7 as full plate voltage I think

“The signal path for gain, EQ, contour and the DI are 100% tube driven, achieving classic tube performance with 300V plates.”

So why wouldn’t it respond well to different tubes

Different tubes are subjective and even yet tolerances are gonna be so different across the board. Generally tubes are warm so with the fusion 500 your getting a warmer/ deeper version already of the m500/800

I’d keep them stock with JJECC83S/ JJ ECC83 for the original voicing

 

[agedhorse]

I would leave them alone to avoid creating new and unrelated problems. Change the tubes and the preamp, now the amp doesn’t work… what is the cause???

 

[fdeck]

I've replaced pots on my amps, but I'm an experienced tech. But this is a pet peeve of mine. Worn out pots. Really? I looked up some Bourns pots of the same form factor in Digi-Key, and they're rated for 15000 turns. That's like 30 years, for how I use amps. It's not like I'm twiddling the pots all day.

And over the past couple decades or more, scratchy pots have been the most common failure mode I've experienced in my amps.

Maybe I'll build a pot tester this weekend.

 

[agedhorse]

I've replaced pots on my amps, but I'm an experienced tech. But this is a pet peeve of mine. Worn out pots. Really? I looked up some Bourns pots of the same form factor in Digi-Key, and they're rated for 15000 turns. That's like 30 years, for how I use amps. It's not like I'm twiddling the pots all day.

And over the past couple decades or more, scratchy pots have been the most common failure mode I've experienced in my amps.

Maybe I'll build a pot tester this weekend.

Often, pots fail due to circuit deficiencies, environmental contamination, impact and folks cleaning them improperly. Every once in a while I see a defective pot, but not often with the 4 main brands.

 

[fdeck]

Often, pots fail due to circuit deficiencies, environmental contamination, impact and folks cleaning them improperly. Every once in a while I see a defective pot, but not often with the 4 main brands.

That's good to hear. I haven't cleaned one improperly in years. Learned my lesson.

Long enough ago that the spray can is from Radio Shack.

 

[6thplanet]

Maybe I'll build a pot tester this weekend.

I'll get you my buddies number, he tests pot all the time.

 

[CoffeeLove]

Hi all, just an update. The preamp arrived and has been installed. Works like new, and GK even through in a new "power button/switch" for free, easy install. And once again, this thing sounds amazing.

Peace

 

[chiplexic]

Often, pots fail due to circuit deficiencies, environmental contamination, impact and folks cleaning them improperly. Every once in a while I see a defective pot, but not often with the 4 main brands.

What is the proper way ? I need to clean pots in my 1980’s GK 400rb.

 

[agedhorse]

DeOxit D-5, only the tiniest amount possible sprayed into the slot the terminals exit. Less is more.