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jblsound
11-22-2009, 04:50 PM
Hello all, I just had a situation come up I've never had happen before.
I started playing an album and about 1/2 way through the first song a loud machinegun sound started coming from the mid-bass driver.

I then turned off the preamp and then turned on again, started alright and then the sound again.

The system; HK Citation pre-amp and power amp and custom speakers with a C-C crossover. The pre-amp was reconditioned 19 months ago, so it should be good.
So would it be the driver or the XO?

hjames
11-22-2009, 06:19 PM
So - swap amp->speaker leads and see if the sound moves to the other side.
If you disconnect just that driver, do you hear the sound in any other drivers in that cabinet??


Hello all, I just had a situation come up I've never had happen before.
I started playing an album and about 1/2 way through the first song a loud machinegun sound started coming from the mid-bass driver.

I then turned off the preamp and then turned on again, started alright and then the sound again.

The system; HK Citation pre-amp and power amp and custom speakers with a C-C crossover. The pre-amp was reconditioned 19 months ago, so it should be good.
So would it be the driver or the XO?

macaroonie
11-22-2009, 06:23 PM
Almost certainly an amp issue , often called motorboating. Get those valuable JBL's disconnected at once until you can ascertain for sure what is up.
Disconnect the pre from the power amp and let the power amp run some cheapo speakers and see if the noise starts up, If all seems well then connect the pre , still on the cheapos and see if the problem kicks off. If it does then your pre needs looked at.
:)

jblsound
11-22-2009, 07:00 PM
Thanks for the replies.

Its the left channel of the power amp. After I posted I realized I hadn't switched the interconnects between the pre/power. I had switched the TT leads to the pre and even tried the other phono input and it was always the left channel. As soon as I switched the interconnects the sound was in the right channel.
Well the entire system is going into storage, anyway, along with all the rest, until I find new living quarters in S.A.

edit: actually its the pre-amp again. I was way too tired to bother with it last night (two long days of moving). Its no longer doing the machine gun thing, but now just a constant hiss in the LC.

As I said, I had that pre-amp reconditioned 19 months ago, having all the leaky caps replaced. Guess I'll just add it to the bunch of CE gear I'm going to take over to the recycle drop off.

Tom Brennan
11-23-2009, 07:10 PM
Common problem in old HK preamps.

doodlebug
11-24-2009, 06:57 PM
Nice Citation gear, I'm sure. Which ones and have they been rebuilt?

Cheers,

David

jblsound
11-24-2009, 08:09 PM
Nice Citation gear, I'm sure. Which ones and have they been rebuilt?

Cheers,

David

Its the Citation Eleven preamp, it was completely reconditioned 20 months ago,