![]() No signs of anything burnt or scorched at all (though again, I haven't flipped the board - will tomorrow).Īny thoughts? I'm more used to things with tubes in them. ![]() Previous owner told me that a "resistor" had blasted apart, and indeed there was a small chunk of something rattling around in the amp, but that something looked like the plastic/rubber/whatever coating from an NTC thermistor, though the two in this amp aren't "blasted apart", and the amp wouldn't function at all without them. GALLIEN-KRUEGER Backline 100 gallienkruegerbackline100service.pdf: 7534 kB: 32: GALLIEN-KRUEGER. Haven't pulled the board out yet so I haven't checked for cold solder joints. Didn't bother with preamp, since it's completely disconnected for my testing. ![]() Here's the schematic for the power amp section: gallien-krueger-backline-600.pdf. Amp delivers plenty of power even while crackling, and fan turns on and off properly. Once the amp warms up enough to stop crackling (somewhere around 40☌ or ~100°f), noise at the output is around 1mv. I can see the noise when I probe Q14/18 base and emitter (perhaps it's coming from Q7A/Q7B, hmm.). Second hand GK Backline 600 2-Channel 300-Watt Bass Amp Head Bass Workshop is a small independent music shop in the South Eastern suburbs of Melbourne. Noise at the output is ~100mvP-P, and crackling can be up to 5vP-P, maybe higher (hard to catch on my analog scope). Power supply seems fine otherwise +-60v are nearly exact, +-35v and +-15v are within 10%, and no detectable noise on any of them. ![]() Scoping the power supply rails, there's a bit of ripple on the +-60v but nothing that matches the crackling at the output. Hi all, I've got a Backline 600 that's giving me some nasty crackling and noise, which sometimes goes away after the amp warms up, even without the preamp board connected at all - meaning it's the power amp or power supply. ![]()
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