Fried 700rbII!!! Help

[Tomluther]

So I bought a second hand GK 700rb and every time I turned it on while it was hooked up to my svt810e it made this really loud popping sound when the blue light cut in (when you turn it on it stays red for a second then goes blue when the power cuts in).

So to prevent this blowing the drivers in my cab and just for my own convenience, I always turned it on with the speaker cable unplugged and then plugged it in as soon as the light turned blue (not really understanding the true danger of this).

So I just went to play it then, doing the same old thing, and it fired up with a loud hum. I turned it off immediately and noticed smoke coming out the grill. Now it makes the same hum when I try turn it on while plugged in.

Can anyone speculate as to what the exact problem is and how easy/expensive it will be to fix?

Im planning on taking it to the shop asap, but I just feel i need reassurance or something.

[Jaco who?]

Originally Posted by Tomluther

So to prevent this blowing the drivers in my cab and just for my own convenience, I always turned it on with the speaker cable unplugged and then plugged it in as soon as the light turned blue (not really understanding the true danger of this).


Can anyone speculate as to what the exact problem is and how easy/expensive it will be to fix?

If you were to use the speakon outputs, you would probably get away with this, because there is no point during the connection that they short the + and - of the transformer taps together. If, however, you used the 1/4" outputs, eventually your transformer saw a zero Ω load one too many times and you now have a shorted output transformer. Similar but a little more drastic than running the poor thing with a 2Ω load one too many times.....Probably not cheap, but hey, you learned something, right?

[craig.p]

OP: I think the amp finally blew because it was experiencing problems anyway. Even though making/breaking speaker connections when power is on doesn't fall under "best practices," I see no evidence that you caused this problem in the specific scenario you describe.

[Jeff Scott]

Originally Posted by Jaco who?

If you were to use the speakon outputs, you would probably get away with this, because there is no point during the connection that they short the + and - of the transformer taps together. If, however, you used the 1/4" outputs, eventually your transformer saw a zero Ω load one too many times and you now have a shorted output transformer. Similar but a little more drastic than running the poor thing with a 2Ω load one too many times.....Probably not cheap, but hey, you learned something, right?

Uh, there is no output transformer in a 700RB.

What probably did happen is the output transistors are blown from what he did.

[craig.p]

Respectfully disagree. Output load changed suddenly from infinity to four ohms, but here's the important point: it was under zero-signal conditions, which means there was no meaningful change in final stage output current, which should have been effectively zero (not counting low-level noise) at the time the cable was plugged in. In my view any quality amp should be able to coast through this sequence. Not recommended, certainly, but cause for a catastrophic failure like this? No way.

The problem with buying used is that you don't know what the hell the amp's been subjected to -- physically, electrically, and environmentally.

[BurningSkies]

Sounds to me like you shorted the output by using a 1/4 inch, and blew the output stage of your amp. This is a good reason:

a) not to plug/unplug an amp with 1/4" connectors when the amp is on.

b) to start using Speakons that can't short across the tiny little gap between tip and sleeve.

[BassmanPaul]

There should have been a small sound as the relay kicked in to connect your speakers. that's what the delay is - it allows the amp to stabilize into its operating condition before connecting the speakers. If you were getting a loud pop then your output stage was not balanced and putting out a voltage above zero. Shorting even this small voltage by connecting a phone plug is enough to toast your amps output transistors. Sorry but it's tech time.

Anyone who has speakons on their equipment should use them.

[craig.p]

Causing an amp-jack (and therefore a final-output) short during insertion of a phone plug is an impossible scenario. Why? Because the plug can't be inserted far enough to cause its tip/sleeve insulator (let alone its sleeve) to contact the jack's tip spring contact.

[Tomluther]

Thanks for all the advice. Im going to take it into the shop now. I was using a speakon cable to 1/4 into the cab.

To me (with a lack of much tech knowledge) it seems the pop I was hearing when it kicked in was evidence of internal problems from the previous owner. Then what I did to it just pushed it a little too far.