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Re: How to hook a Hammond organ reverb amp/tank to an amp

10/6/2005 9:37 AM
GlennW Re: How to hook a Hammond organ reverb amp/tank to an amp
Hi Peter,  
I posted the wrong link last time but couldn't edit it, but I'm glad you noticed.  
I'll try looks different to me. Once again, it's the one marked "R":  
I think that's the one I referred to earlier, but I'm not sure if mine's hooked up that way.  
Are you saying that I can put a pot between the reverb output on the tank and the reverb amp to get some control over this?  
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10/6/2005 1:47 PM
This is getting weird, in a good way.  
Either yesterday or the day before when I was trying different speakers and heads I was using a slapped together test cab which will hold two 10's and one 12", or any combination of those. At first I tried two 16ohm speakers, a 10 and a 12, in parallel to work with amp set for 8ohms (no reverb). Then I tried different 8ohm speakers to get a 4ohm load to work with a Silvertone 1484, one 10" and one 12" in parallel (no reverb).  
This is when I started fooling with the reverb.  
This way the guitar amped speakers didn't get any reverb, but the separate reverb speaker just took over the sound and was trebly.  
Today I went to a pair of 16ohm 10"'s in parallel for 8ohms, and used a 8ohm 12" for the separate reverb speaker. You'll notice that the link in my last post shows the signal to the reverb amp coming from a 16ohm speaker (not an 8ohm speaker like I used before). Anyway, like this ALL the speakers seemed to have reverb, and it sounded pretty good, definately usable.  
Does this make any sense? Maybe I was hearing things...  
There's enough room in this test cab for two 10's and two 12's, so this weekend I plan on making another baffle and trying four 16ohm speakers to get 4ohms for the 1484, and will have to just set the separate reverb speaker in the floor for the time being. Looks like this reverb unit will end up looking like a 1x12 combo by the time it's done.
10/7/2005 11:09 AM
You can put the pot right on the output of the tank, which is at least easy, but you might get slightly better noise performance if you put it after the first gain stage in the amp, which probably isn't much harder to achieve.  
Just replace R7 in the circuit diagram with a 1M pot, connecting the wiper to the grid of V1...
10/9/2005 8:14 AM
Thanks again, Peter. I'll attempt to get a pot in there sometime soon as you said.  
The 4-speaker cab project got rained out this weekend.  
There were a few other possible contributing factors to make the reverb sound good:  
1) different separate reverb speaker  
2) reverb speaker mounted in cab instead of setting on floor  
3) different guitar amp  
4) different guitar amp speakers
10/12/2005 12:22 AM
Dr. Photon
Re: How to hook a Hammond organ reverb amp/tank to an am
I have an AO-35 reverb amp, which is an older version of the reverb amp. The AO-44 you have is a newer, cheaper version. The one in that M100 schematic (they'd come with all three reverb amps, depending on vintage) that sucks power from the main amp is an AO-66 I think. The AO-35 uses a 5Y3, 2 X EL84, a 12AX7 PI and a 12AX7 as two gain stages. the AO-44 uses those pentode/tetrode tubes to put the PI in the same bottle as the power tubes, and uses a transistor as the voltage gain stage. the AO-66 is exactly the same, but without a power supply.  
With my AO-35 I built a 1 x 12 open back with some Bladwin Alnico organ speaker (sounds awsome!) and a generic "hammond" 4-spring fender style reverb tank. I used an L-pad on the output of the amp for volume. I basically had a box with a speaker level input that would give any other amp reverb. there was also an input to plug a guitar into the input of the amp (they take guitar level signals well).  
these things are designed so that the "sig input" go directly to the main speakers. the "driver" terminals go directly to the reverb tank input terminals (no need to bother w/ shielded cable here). the output on the reverb tank goes to the RCA on the chassis (shielded cable). then you connect your reverb speaker to the output terminals (8 ohms). These things are designed to use a low impedance (fender-style) tank with a floating/isolated input. I used a high-impedance grounded input tank and it worked fine (I shuffled around the resistors and bulbs in the input circuit. the AO-35 has a different input network. the bulbs ar used as a sort of compression/power limiting things. they don't light up unless the input is real hot). use a big variable resistor or (better) a 8 ohm high power L-pad. on the output as volume. you can also replace R7 with a 1M log pot.  
On mine, I got tired of the verb and removed it. I took off the cap and resistor on the input and made two inputs (bass sounds mellow with the load, guitar wants the unadultered input). I also replaced the grid resistor between the two gain stages in mine with a pot (equivalent in yours is R7). I also added a line out pot from the speaker outputs. I like having both the L-pad and gain control for a guitar amp, it gives good distortion. I sold the amp to an acoustic player since he loved the clean sound with an electro-acounstic.
10/16/2005 7:32 AM
That's pretty cool. I've seen the AO-35 on ebay from time to time, think it's the one with the "necklace" reverb spring setup...not sure.  
Glad to hear that someone had good results with it.  
That little light...the first time I played it I thought something had combusted. It does get bright sometimes.  
Where would you hook up an on/off footswitch?  
I'd guess in the reverb output line between the tank and the reverb amp.  
10/20/2005 8:47 AM
>>>Where would you hook up an on/off footswitch?  
I'd guess in the reverb output line between the tank and the reverb amp.  
Yes, ground the input of the reverb amp...

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