Sunn Concert Slave Question

[Mosthigh]

Hello, I recently bought an early 70's Sunn Concert Slave secondhand. When I plugged it in with my Alembic F-1X preamp and 15' speaker, it seemed to have a real lack of power, and a certain crackle I attribute to a dirty volume pot. I did clean the pot several times, but I still only get volume after I turn it to noon, or 2V, on the dial, it doesn't go very loud, and sounds 'fizzy'. I took it to a questionable electronics repair guy, and he says it needs a preamp or a equalizer to boost the input levels. Since the Alembic pre has no wattage of its own, I find this an inconclusive assessment, but I'm not an expert. Thoughts?

[Isaac]

He may well be right.

According to Alembic's website*, the F-1X is a unity gain preamp. In other words, the signal out is no stronger than the signal you put in, so it's like plugging your instrument straight into the slave amp. A guitar can't generate enough voltage to properly drive a power amp, and a power amp such as the Concert Slave isn't designed to have enough gain to amplify such a low level signal.

What other gear do you have access to that could function as a preamp? That's where I'd start.

*http://www.alembic.com/prod/f1x.html

[Isaac]

Okay, I misread the Alembic text. The effects loop is unity gain. The text implies that the preamp as a whole has positive gain, but never says how much, nor what its maximum output is. So maybe it has enough gain to drive the Concert Slave, or maybe not. But why not turn the Sunn's volume control all the way up, and control the volume with the Alembic? The only real reason for the CS having a volume control on it at all is to turn down an input that is too hot, to keep from overdriving the slave. Doesn't sound as though that's a problem with the Alembic.

[Mosthigh]

Thanks for the reply. I don't think the issue is the preamp, because when I do turn the volume all the way up on the Sunn and the Alembic, it just doesn't seem to be putting out the power that it should, and sounds thin. I did plug in a SWR Interstellar Overdrive pre, which has a 5w amp, but the result was similar (although it is in need of tubes change). I think the Sunn has power supply issues.

[Isaac]

Certainly possible. "Thin" is not normal for a Concert Slave.

[ryco]

It is probably something wrong in the Slave.

Just for fun I'm running a Concert Slave with nothing more than an old '70s 9v battery powered Barcus-Berry 1330-1 Standard Preamp into a Marshall 412 bass cab 4Ω and it is ridiculously LOUD and full.