Hammond A-102 to a Ventilator 2 Wiring Questions

[jrobinson]

To Start off, I have little to no experience with Hammond Organs. I am the tech guy for a church and we are wanting to add a Ventilator 2 box to our Hammond A-102 so that we can eliminate more stage noise. I have spent the better part of a day looking at how to wire it so that the Ventilator 2 will receive the input signal it likes and make sure nothing inside the console goes poof! I found several posts referencing a circuit designed by Geoelectro. Is this the correct diagram? If so, just to clarify, the circuit would start from each of the G and G Termainals with a 10 microFarad NP Capacitor. One leg would then go straight to the sleeve on a 1/4" plug. The other leg would go directly to Terminal 1 & 2 on the pot then terminal 3 out to a 10k resistor and then finally to the tip of the 1/4" plug. Not forgetting the 1k resistor between the signal and ground.

Sorry to be so elementary with my questions, I just want to make sure I am not missing something or misinterpreting the schematic. Another option I considered was buying a Trek II OBL-2 Output Box, but DIY would be much cheaper and possibly quicker since I could source the parts locally.

Thanks in advance for the help and also for the info so far.

[enor]

This line out circuit (from Motion Sound) works very well:

[guylavoie]

The circuit certainly makes sense (a capacitor coupled attenuator) for that application, and would be wired to the G-G terminals as you said.

[tpappano]

Enor's diagram is the best and simplest. The first would work but the bottom (ground) leg should go to chassis ground, not G. The 10uf caps serve no useful purpose and can be eliminated. The first circuit also has more attenuation, maybe more than you need.

[Jaim]

If you read Geo's comments on using the capacitors, it was for a NEO Vent. If I remember correctly, there were ground issues. I like to use a isolation cap just to protect the JFETs in what ever I'm connecting. Consider it cheap insurance.

Jim

[DrGeorge]

The connection on the A-100 preamp is to the output of a transformer so there is no dc voltage to isolate from FETs or anything. Enor's circuit is best.

[jrobinson]

Okay, I think I will go the Motion Sound route. Forgive me my circuit reading skills are weak, what size capacitor is it calling for on the 50k pot?

[DrGeorge]

And, the brown lead on the AO28 is the transformer center tap which is already connected to chassis ground. So, Enor's diagram is correct for an unbalanced output to external amplifier.

You could use the G-G connection as a balanced output as Hammond did with a modification to the circuit.

[DrGeorge]

Look at the AO28 schematic. If you connect the ground lead of an external avmplifier to one of the G connections, as in the original sketch from JRobinson, even using a non polarized capacitor, you are unbalancing the AO-28 output balanced line output. Connecting one side of the AO28 balanced output to ground can cause hum into the Leslie or other conventional Hammond speaker cabinet connected.

If if you need to feed an external balanced input amplifier you need a different circuit. Not complicated, but different.

[DrGeorge]

I read it as 0.001 microfarad. I don't understand why it is needed, it will vary the frequency response slightly

[DrGeorge]

at low level setting. I'd leave it out.

[jrobinson]

I read it as 0.001 microfarad. I don't understand why it is needed, it will vary the frequency response slightly

Gotcha, just wanted to be sure of the units, tiny little capacitor. Am I safe to use 1 watt resistors?

[DrGeorge]

Yes. Actually 1/8 watt resistors would work. Not much power in this circuit.