I have a Hammond AO-29 amp that I would like to convert for guitar, I would like to keep it as close to stock as I can for now. Does anyone know how I can eliminate the expression pedal volume control? I would like to replace it with a simple volume pot but its quite a complex circuit that I have never encountered before.
The AO-29 amp was used e.g. in the M-3 organs, right? So we have the schematics here. It's quite a complex circuitry with many components which are of no use in a simple guitar amp.
The expression (= volume) pedal actuates the differential variable capacitor between V4A and V4B. You'd eliminate everything between C9 and R37 and replace it by a 1 M audio taper potentiometer, hot end tied to C9, wiper to V4B, pin 7. To start with, use terminal "A" as the input.
Have fun!
The expression (= volume) pedal actuates the differential variable capacitor between V4A and V4B. You'd eliminate everything between C9 and R37 and replace it by a 1 M audio taper potentiometer, hot end tied to C9, wiper to V4B, pin 7. To start with, use terminal "A" as the input.
Have fun!
Yes, its from a 1957 M-3. I have removed al the vibrato percussion stuff and have wired terminal "A" as my input. I was unsure how to couple V4A to V4B since they are not phyisically connected in the expression pedal assembly, its just metal plates with a gap inbetween. Also this amp has a field coil speaker I want to change to a PM, as I understand all I need to do is put a 700ohm 30+ watt resistor in place of the coil, is this correct?
I have wired up a pot between C9 and R37 and I have sound but only with the pot turned down to almost zero, it gets slightly quieter as I turn it up and goes silent about half way. How is it that more resistance equals more volume? Also whats the point of the 1.5 volts on pins 3 and 8? I have not seen this before. I am starting to think I will have to gut this thing and start over, these hammond amps are way more complex than need be.
What pins 3 & 8? I/O on Hammond stuff is labled with letters until they went to AMP connectors.
Organ players ride the gain a lot, since pushing the keys harder doesn't do anything. The variable capacitor gain on the Hammond amps is WAY more reliable than the pots used on swell in early Baldwins or the CDS cell, light bulb, and cardboard baffle, used in other brands. Why don't you buy a variable capacitor from tonewheel-general.com or some other M scrapper? You don't have to attach a pedal to it. Just put in a wood box so you don't kick it on stage and bend it.
You can change the overall gain by fooling with R25 and R26 on the captain-foldback.com schematic.
Organ players ride the gain a lot, since pushing the keys harder doesn't do anything. The variable capacitor gain on the Hammond amps is WAY more reliable than the pots used on swell in early Baldwins or the CDS cell, light bulb, and cardboard baffle, used in other brands. Why don't you buy a variable capacitor from tonewheel-general.com or some other M scrapper? You don't have to attach a pedal to it. Just put in a wood box so you don't kick it on stage and bend it.
You can change the overall gain by fooling with R25 and R26 on the captain-foldback.com schematic.
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My thoughts also!
He'd better remove everything besides the transformers and the output stage, buy one or two more 12AX7s, some potentiometers, have a proven schematic from the web and start constructing.
Best regards!
a029 hammond amp from m-3
i just picked up this tube amp and field coil rolo 12 inch speaker from an m3 organ on the side of the road
had an empty 12 inch speaker cabinet
also have a line 6 pod and a behringer tube Mic200 single 12ax7 preamp
i plugged the field coils speaker back into the amp
then hooked a 1/4 to rca jack line cord into the rca recepticle on the exprssion
pedal box .. wahlah im into the power section of the amp
perhaps not a gr8 use of electricity bypassing the entire preamp section
but damn it sounds gr8
the speaker is amazingly perfect woot love me free stuff and a 20 watt power amp/speaker ..free.. gr8 stuff
i just picked up this tube amp and field coil rolo 12 inch speaker from an m3 organ on the side of the road
had an empty 12 inch speaker cabinet
also have a line 6 pod and a behringer tube Mic200 single 12ax7 preamp
i plugged the field coils speaker back into the amp
then hooked a 1/4 to rca jack line cord into the rca recepticle on the exprssion
pedal box .. wahlah im into the power section of the amp
perhaps not a gr8 use of electricity bypassing the entire preamp section
but damn it sounds gr8
the speaker is amazingly perfect woot love me free stuff and a 20 watt power amp/speaker ..free.. gr8 stuff
Moved to Instruments & Amps since this is a guitar amp related thread.I have already gutted it. I tried to just trim away the excess but that ended up being 95% of the circuitry anyway so it all had to go. I built a 5E3 just because it is so simple but I really don't like it at all. I have 3 more of these amps, any suggestions as to what else I can turn these into? I am looking for any 6V6 cathode bias ideas. OTs are about 15watts and PTs are 320-0-320 and 380-0-380. Any ideas?
Actually I have been trying to find the specs of those small transformer for a while now. I have been holding on to them until I can figure out what they are. If you can tell me the specs and what they can be used for then I can send you some of them for a very low price. I have at least 5 of 6 swell boxes too but the variable caps have been removed for a few of them but I think the caps are here somewhere. If I do sell you some transformers you can have all the swell boxes.
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