Hissy GK 250 ML

[drewl]

They all this noisy and hiss like crazy?

I know the internal trimpots can vary the gain but damn this sounds noisy.

Anyone have a schematic handy?
Thanks

[Leo_Gnardo]

They all this noisy and hiss like crazy?

Yes, sounds like a steam radiator about to 'splode. Around here the habit was to run the output to a couple of 4x12's, the speakers usually didn't have as much hi end response as their built in 6's. A favorite of loud metal players, one guy blew his up about 7 times, kept bringing it in. Not much in the way of heat sink - just the chassis.

If I'm not mistook there is an FX loop, or pre out power in jacks, you could patch in a gate and/or graphic EQ to knock off noise. Nobody I knew with these amps bothered, they just let 'er rip tater chip. (put fingers in ears smiley thing here)

[drewl]

Yeah, run into the FX return and its nice and quiet.

Wondering if new op amps would help but it sounds like the nature of the beast.

[Jazz P Bass]

Pain in the butt to work on.

But then again, as your taking this oddity apart, you have to wonder at the engineering (lack of?) that went into the critter.

gallien_kruger_250ml_250rl_212scl.pdf

gallien_kruger_250ml_Layout.pdf

I have sent out more than a few to get the speakers reconed.

[drewl]

Thanks, found service manual.

[J M Fahey]

1) killer little amps, if feeding decent speakers (at least a stereo 2 x 12")
2) typical 80's metal sound, take it or leave it, in the line of the famous Rockman and not too far from Crate/Ampeg/Randall SS amps same vintage, all loved by Metallists, before dark muddy MB became the standard for most.
3) noise is fully explained by the TON of gain, but that's what the Footswitch was invented for, you turn high gain for grinding solos or shredding, instantly turn it off for "quieter" stuff.
Sort of a human noise gate and very effective, after some time it becomes second nature, and that's how it was used.
4) that said, the *first* gain stage is the key one, since it's the most amplified one, so a better Op Amp there will definitely help.

U1, an LM353 is a good Op Amp but not optimized for noise, even a humble TL072 will be better, but I'm certain USc olleagues will suggest way better ones.

Only problem is that the latest ones are only available in SMT packages, but you can mount them in an SMT>DIP adapter board.

[drewl]

Thanks, good tip.

I still have a bunch of through hole op amps, TL072, 4558, 4560, 4580 etc.

[52 Bill]

Let us know what you find out. I've got a rack mount version that I've been meaning to quiet down, someday.

[drewl]

Just to follow up, I replaced six opamps in the preamps and tone stack which knocked the noise and hiss down alot.

If you are so inclined you could probably replace all the 353's and bring the noise down dramatically.

[J M Fahey]

Just to follow up, I replaced six opamps in the preamps and tone stack which knocked the noise and hiss down alot.

If you are so inclined you could probably replace all the 353's and bring the noise down dramatically.

People wants to know:
* Which?
* What with?

thanks.

[drewl]

All the opamps before the loop.
1,3,5,6,10,12 and 13 I believe
The last two in the tone stack.
I used TL072's.
Easy to work on the preamp once you slide it out.
I did have to drill out a stripped screw.