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O'Conners Preamp & Reverb Unit

12/22/1997 7:52 PM
Greg O'Conners Preamp & Reverb Unit
Has anybody built the O'Conner Guitar Preamp or Reverb Unit from "Tonnes of Tone"? Opinions? Advice? Tips? Etc. These look like good novice projects. Thought I might try one or the other.  
12/23/1997 8:20 AM

These are good novice projects, and they are based on proven circuits. I spoke to Kevin O'Connor about this reverb circuit. He said that it wasn't anything special, but it does work and he included it as a fairly simple beginner's project to demonstrate the principles of spring reverb.  
I have not built any of these circuits (yet), but I had tentatively planned to put together a preamp with reverb, maybe using his London Power "standard preamp" which has a switchable gain boost stage, a power supply of course, and this spring reverb circuit.  
Then yesterday, the mailman dropped off my copy of "The Ultimate Tone vol. 2". In there (p.6-35) is a push-pull 12AT7 reverb driver! This circuit has advantages similar to a P-P output circuit, such as lower distortion, more natural reverb sound, hum cancellation due to balanced windings of a P-P output trans, and a wider frequency response. Back to the drawing board!  
By all means, build what you can. In addition to the great learning experience it's simply a great feeling to play through some gear that sounds great, and you built it yourself.  
12/23/1997 1:10 PM

I just built the "All-Tube Effects Loop" in TUT, volume one. All I can say is that it is a very fine addition to any amp--it does all the things he says it will, and it does them quietly and transparently. I know this doesn't directly address your question, but I just wanted you to know that I did this circuit and I'm a relative newbie to electronics myself. Just take your time, double check all your connections for accuracy, and be prepared to enjoy the fruits of your labor.  
Idyllwild Brewing Company
12/24/1997 1:03 AM
John Kos

What type of transformer does the push-pull reverb driver circuit use? I am wondering if it could be used as a small power amp (with appropriate preamp circuitry).  
John Kos
12/27/1997 8:18 AM
Bob K.

John asked the same question I was going to ask. I have the TUT II book and O'Conner doesn't mention what xformer he uses for the push-pull reverb driver. Does anybody know? Also, in my copy of the book the value of the cathode resistor of on the 12AX7 driving the xformer is unreadable due , I think, to a printing error. Can anybody make this value out?  
I would like to try this reverb mod as it sounds promising. I also am curious about John's question as to whether this circuit could be used in a low wattage amp as I thought that reverb xformers typically put out about 1 watt.  
12/30/1997 7:41 AM

The transformer is a 150K/8ohm , made special for London Power by Hammond. This info came from the book's author. I'm not sure if it will be available to us experimenters, either through Hammond or London Power, but I hope it will be.  
1/9/1998 1:06 AM
Kevin O'Connor

As Wayne stated, the reverb driver transformer is custom made for London Power by Hammond. We also use it as a half-watt tube headphone driver in preamps, and as a choke splitter in the Studio amp.  
It is a small epoxy-potted toroid in a plastic case. Short buss wire leads allow mounting on a PCB or eyelet card.  
The cathode resistor value is 2k2-1W. Sorry.
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