i wanna run other stuff through my leslie - DIY preamp combo

[Marc Alan Goodman]

wouldn't using the speaker output of your amp be taking the load off the output? what kind of amp is it? I've been using a '65 bandmaster head to a cut-down drum. I was sure to match the impedance, but otherwise i can't imagine why it won't be fine.

There are two kinds of leslies. Some have onboard amps, a few rarer ones don't. The ones that don't have one built in require an external amp, in which case the speaker output is a good idea, as the leslie speakers will provide the load.

However if you plugged a guitar amps speaker output into the input of a Leslie with an onboard amp you'd end up with one less guitar amp and one less leslie amp. It would be like plugging the speaker output of one amp in to the instrument output of another one. It's a bad idea if you like having functioning gear around.

[James Anderson]

yes! He didn't mention going directly into the amp section of the leslie, it sounded to me like the tech bypassed the amp since he is now using another amp.

i'm not helping so I'll step aside. as you were...

wouldn't using the speaker output of your amp be taking the load off the output? what kind of amp is it? I've been using a '65 bandmaster head to a cut-down drum. I was sure to match the impedance, but otherwise i can't imagine why it won't be fine.

There are two kinds of leslies. Some have onboard amps, a few rarer ones don't. The ones that don't have one built in require an external amp, in which case the speaker output is a good idea, as the leslie speakers will provide the load.

However if you plugged a guitar amps speaker output into the input of a Leslie with an onboard amp you'd end up with one less guitar amp and one less leslie amp. It would be like plugging the speaker output of one amp in to the instrument output of another one. It's a bad idea if you like having functioning gear around.

[Darlington Pair]

So how I'm understanding this is that the tech bypassed the amp so you could directly power the speakers through the crossover.

Is this correct?

I don't remember what the impedance of leslie speakers are but I'm going to bet that it's an 8 ohm horn and an 8 ohm 15 wired parallel to give you 4 ohms. I would check with your tech, or take the back off to confirm this.

You won't need a dummy load, just unplug the amp's speaker and the leslie will be the load.

This is assuming that he hacked a jack to the crossover, if he put in something like a FET DI that will handle an amp level out then your amp will blow it's output transformer from not being loaded properly. I wouldn't guess this is the case because adding an amp in jack would be so much easier. He could have also hacked in a line level in to the preamp of the amp, but your mic pre should have been able to drive that.

Ask your guy to see what he did and we can confirm what is safe.

[joninc]

my leslie is a 710: http://www.dairiki.org/HammondWiki/Leslie710
there is an amp onboard (i think there are 2 - one for bass and one for top) - there is a way to turn up the amp on the back with a screwdriver.

i believe that my tech wired the 1/4 inch jack as an input to the amp.

i tried using a boost pedal but i still get next to NO signal out of it - the boost was 35 db but it's like a whisper.

i have a call into my tech for more info but if i recall correctly it was more on an impedance issue than anything else.

btw - we tried using mic pre amps to drive the signal as well (great river) and it still wasn't working. a voc ac30 or ampeg b15 head on the other hand, sounds and works well but i am leary of damaging stuff....

[LowG]

Obviously for the op the tech that installed the jack must be consulted.

But for other people in similar situations, check out Dead Duck products. Just had a unit delivered from them to run my 147 off any mic/instrument pre. Decent prices and seems to be solid build quality.

[joninc]

so i am working on this with my tech right now.

a lot of this is over my head but the jist of it is that the output of the amp head is only about 1 volt and we looked at the schematics of some of the combo preamps and they are outputting 5 volts.

basically - they are giving a lot more juice.

my tech made a load resistor and that allows me to use the amp head but there's pretty loud hum happening and it's not as clean as i'd like.

still working on it...

(trek II on ebay used for $500!! crazy)

[joninc]

update: i think we have realized that having both the organ and an amp head into the amp is creating an impedance bottleneck.

when we disconnect the organ - it's WAAAAY louder.

now we just need a proper step up transformer to deal with the hum, which is fairly bad right now.

making progess....

[LowG]

(trek II on ebay used for $500!! crazy)

This is why I suggested the Dead Duck products. They have a bare-bones model that lets you use whatever preamp you want with it - - nice for studios that already have plenty of preamps lying around.