[HAM] C3 rumbling

[David Anderson]

A properly functioning AO-28 should be able to drive a 147 amp with no problems, assuming the load resistor on the 147 amp is set to 'Open.' The connection is usually made with one of the 'G' terminals and Ground from the preamp. The input impedance of a 147 amp should be ~10k Ohms with the load resistors out of circuit.

If your AO-28 can't do that, it's time to have it serviced by a qualified tech, whether amateur or professional. I get a little concerned with some of the suggestions I read for a little tinkering here, a little jerry-rigging there. You need someone who understands the how the entire circuit functions as a system.

After all, the newest of these preamps is now 34 years old... I read a lot of wringing of hands and gnashing of teeth on these lists about the costs of repairs, but if we object to such costs and expect them to keep working perfectly with no maintenance, it's my opinion that we are growing increasingly detached from reality. Of course, I'm a confessed miser, so I taught myself how to do it ;-) All this stuff is old technology, and the knowledge is out there in libraries.

David Anderson

-----Original Message-----
>From: Jerry Fowler <jerryinaustintx at gmail.com>
>Sent: Jan 15, 2008 8:57 AM
>To: The Hammond Forum <hammond at zeni.net>
>Subject: Re: [HAM] C3 rumbling
>
>As far as the 145/147 level goes, you could add any sort of amplifier
>between the c3 g-ground and the leslie amp. the 145/147 amp is designed to
>accept 'speaker level' signal. the c3 puts out 'hammond level' signal which
>is significantly hotter than line level, but lower than speaker level. your
>m is putting out 'speaker level' signal to the leslie amp, which is why its
>so much louder. try any amp you have laying around between the c and the
>leslie. guitar amp, pa power amp, etc.
>-jerry