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Re: O'Connor Preamp

4/7/1998 2:08 PM
R.G. Re: O'Connor Preamp
You might use the Keen(tm) Vintage AC Adapter - that is, use a second transformer to lower the AC line into the primary of the power transformer to get the filaments back in line.
4/10/1998 8:46 PM
Paul P

A good insulated socket is made by Cliff in England. You shouldn't have any trouble finding them, they are used by Marshall, Ampeg, Crate, ART, Alesis, Dunlop etc, etc. Any retailer or professional, repairing these brands and many more should have them in stock or be able to get them in. The sockets are made from fiber filled high impact plastic. They come in mono and sterec switched and unswitched, with a plastic fixing nut or a chrome dress nut, these are the ones you see on just about every wah pedal on the market.  
4/12/1998 7:20 AM

HEy Mang,  
I Had the exact same problem with a new amp I bought. im a tech by navy training and  
was thinking of all kinds of problems that it might be. so instead of doing the warranty work myself and not get paid for it i took it back to the store tech. It turns out all it was was a bad preamp tube. the hum was outrageous. I dont know if this is your problem especially with the high filament voltage but it might be a problem later on.
4/14/1998 11:11 AM
Greg Re: O'Connor Preamp (solved)
Well, I figured it out, for what it's worth.  
The preamp diagram in the book shows wiring to be used w/ the book's "Experimenter's Power Supply" which has a DC filament supply. Basically, has one 6.3vdc wire to pin 9 and the other to ground w/ pins 4 & 5 connected to ground. Well, I wired mine exactly the same way except that I'm using an AC filament supply. Plus, I had the filaments referenced to grnd w/ two 100R resistors. So, essentially, one side of my filament supply went to the 100r res to grnd and on to pin 9. While, the other side went to a 100r res to grnd and on to grnd again. Doh!  
Solution: Ran directly to pins 4 & 5 and disconnected the pin 4 & 5 connection to ground as per the DC version.  
Anyway, it sounds good but I do have a question. I don't have a seperate power amp so I'm just running into the front end of my regular amp and I can't turn the preamps volumes up very much at all before it's just too loud. And this is w/ my amp's volume low (about 2 or so). I have to keep the preamps volume barely on. That seems a little odd to me.  
Also, it's a little bright sounding on the distortion channel. Clean side is pretty nice.  
Any thoughts...  
4/15/1998 7:41 AM

Sounds like you're running the output of a preamp (signal voltage of .5 - 1volt) into a guitar amp that's looking for a maximum signal strength only one-tenth of that. By turning down the volume controls so far, the frequency response is suffering due to impedance mismatches.  
If you can locate a spot in your amp's circuit that is after the first or second gain stage, and inject your new preamp's output there, you won't experience the same problem.
4/16/1998 9:40 AM
Jack Orman
Time to build that DiY Champ to go with your preamp.  
4/18/1998 8:56 PM
Yep. Well, that's what this preamp project was really about. I didn't really need it but I thought it was a good way to get my feet wet w/ tubes. Course you probably wouldn't want to get your feet wet w/ tubes but I digress....  
Ultimately, I've had this goal to make an amp for about 6 years now and I'm finally making some progress due largely to this forum and a few websites and some book learnin'. I'm very patient, so I'm in no particular hurry. I'll just keep learning little by little and then one day...  
Tell you one thing. I would not have learned nearly as much if this project would've worked right out of the gate.  
Right now, in case anybody's interested, I run it direct into an ADA Microcab II into my desk and it sounds pretty nice.  
Thanks for all the help!  
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