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PostPosted: 25 Oct 2009, 23:00 
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Joined: 25 Oct 2009, 22:52
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Location: Barrie, Ont, Canada
Hello all - I am a total newbie here and to most of this stuff. I play harmonica and am looking to boost the output of a low-z mic into my 67 champ amp. Would this pre amp do the trick? It looks like a fun project.

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PostPosted: 26 Oct 2009, 17:39 
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Location: Dartmouth, Nova Scotia
This preamp will work as a mic preamp, and if some values were changed it would make for a really good mic preamp but as it is, I tried it, and it amazingly works! :D

I am not sure what values would need to be changed but I can give some help, you could also just use a single 2N3904 pre mic stage to drive the tube preamp, you would get more gain that way and you could still use the preamp for other purposes as well.

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PostPosted: 26 Oct 2009, 18:57 
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Joined: 25 Oct 2009, 22:52
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Location: Barrie, Ont, Canada
Hey Thanx for any ideas you have - Like I said I am a complete novice at most of this stuff - I have built a mic that I really like the sound of but it needs to be boosted up a bit to get that overdriven "chicago" sound. That's why tubes are so important. Plus I like to "McGuyver" stuff together just to use up what I have. So any "simple" gear that would do that for me would be really appreciated. And hey HI!!! :D to the right Coast from the newest "have not" province.
talk soon - jawbone

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PostPosted: 26 Oct 2009, 19:17 
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Location: Barrie, Ont, Canada
Hey Craazy - I've been doing a bit of studying and that Transisor thing might just do the trick - do you have a schematic? Something that would work with a dynamic cartridge.

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PostPosted: 27 Oct 2009, 18:04 
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Location: Dartmouth, Nova Scotia
Here are a couple of ideas for you jawbone;

ESP mic preamp: http://sound.westhost.com/project13.htm
The real simple mic preamp: http://www.epanorama.net/circuits/micamp.html

The second link is the simple one I am talking about, and is about as simple as you could get. :)

Good luck! :D

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PostPosted: 28 Oct 2009, 00:11 
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Location: Barrie, Ont, Canada
Hey Craazy - Thanx - If you hear of a big hole burned into Ontario just North of Lake Simcoe you'll know it didn't go well :blush: :D :blush: - I'll keep you posted. - jawbone

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PostPosted: 02 Dec 2009, 16:41 
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What is the reason for putting the two 12v trannies back to back? couldn't you rectify the line voltage coming in and use one transformer to feed the filaments? I'm sure there's a good reason, I just don't know enough about transformers to know.


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PostPosted: 03 Dec 2009, 13:39 
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Hi lmillis, welcome to the forum.
Putting two transformers back to back like that may be a cheap way to may an inexpensive 120V isolation transformer if you have access to inexpensive 120V to something V transformers.

lmillis wrote:
What is the reason for putting the two 12v trannies back to back? couldn't you rectify the line voltage coming in and use one transformer to feed the filaments? I'm sure there's a good reason, I just don't know enough about transformers to know.

:!: Please do not do this. It is NOT SAFE and could destroy some equipment or worse, hurt or kill someone. Always use a transformer to provide isolation. :!:
Gio

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PostPosted: 03 Dec 2009, 21:34 
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Location: Rochester, NY
Gio wrote:
:!: Please do not do this. It is NOT SAFE and could destroy some equipment or worse, hurt or kill someone. Always use a transformer to provide isolation. :!:
Gio
For more thoughts around audio safety see Things that make you say Ouch! or Electrical Safety.

Alan

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PostPosted: 04 Dec 2009, 10:30 
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OK thanks for the info. I've built of couple of tube based amps and have always used a step-up transformer to power the plates of the tubes but have never needed to have a straight 120 volt for a project. OK thanks for the info, I'll be happy to not shock the $#!* out of me. :)


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