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Frankenstein preamp
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Old 4th May 2012   #1
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Frankenstein preamp

Ok guys I need someone smarter than me. I have an old sony tape machine I have no use for and the resale value isn't worth messing with. So, I took it to a local tube amp repairman to see if he could yank out the preamps so I can use them as a stand alone tube mic preamp. He said it could be done with a few mods. The ins and outs need to be changed to balanced signals, it needs a phantom power supply and an input transformer. The input now is way high, sitting at 5 megaohms. He told me the tube configuration is like a small guitar amp though. So that's my problem. Is this thing gonna have a weird frequency response or sound just way too odd? It may not be worth messing with if that's the case. I just wanted a cool point to point dual channel tube mic pre! I'll attach a schematic for those who really know what they are talking about. This is one of those things that is way over my head.
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Old 4th May 2012   #2
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Looks like a pretty standard tube pre to me. I don't think you should have any problems with it, just grab it after VR2. If you want to make a mic pre out of it you'll have to use an input transformer and the associated front end stuff that goes with it like a pad and so forth. Frankly, I'd rather build one from the ground up, but if you've got the chops I don't see a problem.
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Old 5th May 2012   #3
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Cool. The tube amp repairman is going to do it for me. He is just ripping it out of the machine and mounting in a box for me. He thought about leaving the power amp section in so I could have an output control if I wanted to saturate the tubes a little. How does this idea sound?
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Old 6th May 2012   #4
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That's fine if the guy can do it, but he has a lot of work ahead of him - you may want to find out how much he's going to charge you to do this.

I'm assuming that you are using a good quality mics so you need a good mic transformer and they are not cheap. If you can't find anything decent then try the 3195 from Sowter, which run about thirty bucks.

As far as saturating the output tubes, I'm sure that will sound good on something - maybe bass or snare. I would still take an extra output from VR2, just in case you want a cleaner sound at some point.

Anyway, I wish you all the best!
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Old 6th May 2012   #5
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I'd build from the ground up as well it is a single tube pre section not worth much to have converted to be honest I agree on taking the out from vr2 but I'd just build this

http://media.photobucket.com/image/r...eMicPreamp.jpg

your going to want good clean power as well which is another good reason to just build from scratch
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