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TVOR-Ceasar
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30/04/2020 10:46 am  

Thing is, I have a 5 volt preamp that will take that 300 mV signal and pump it up to around 2.8 volts P-P, rail flat from 20Hz on out to way beyond even bat hearing. Hell, at 10Hz, it's only down 0.2 dB. 4 resistors, 2 capacitors, and a single transistor. Pure class A. You'd need 2 for stereo. And  you could put a dual-gang pot on the input for attenuation if need be. Or you could put that pot in place of the gain resistors to adjust the gain.

But that's just my nature to make the existing work up to real specifications if I can.

-Charlie


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TVOR-Ceasar
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01/05/2020 9:10 am  

Here's what I have. Feel free to use it.

The test circuit.

5Vpreamp2N3904 test

 Here's the voltage swing.

5Vpreamp2N3904 O Scope

 Frequency response.

5Vpreamp2N3904 Bode

 This is just one channel, how to wire it.

5Vpreamp2N3904 build

 

Please note, these are all standard value 5% resistors and should be available anywhere that sells parts.

As you can see, there's a 3V P-P swing at full 300mV input.  And the frequency response is flat from 20-20kHz and even at 10Hz is only down 0.1 dB.

For the capacitors, you can use electrolytic, just make sure the positive terminal (+) is facing into the transistor.

-Charlie


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oneway
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01/05/2020 4:02 pm  

@tvor-ceasar I couldn’t tell ya one thing about it when it comes to this kinda of stuff. I haven’t even begun to get into the elections side of things but I guess ya gotta start somewhere though. No idea if something like this would be a good place to start or work up to. 


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TVOR-Ceasar
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01/05/2020 8:14 pm  

Small parts count projects like these are god-awful easy to build. I did a parts look up at Newark.com. With some of the specials they had on there, the total for 2 transistors, 8 resistors, 4 capacitors and 2 stereo RCA panels (stereo build) came to less than $3. Add in a perfboard and it comes up to around $7. Kicker is, shipping is just a bit more than the parts alone. 

-Charlie


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oneway
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02/05/2020 2:45 am  

@tvor-ceasar  the cost certainly has my attention. I’ve got a clean box I think I paid around 70$ for 


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oneway
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07/05/2020 6:46 am  

@tvor-ceasar. I think 🤔 this plate amp has gotten hot. Ran into clipping perhaps idk. I got the amp refurbished at p.e. Gave it to my brother set it up and it lasted about a year so who knows. I’m guessing for what they cost it’s not worth fixing?

if you can zoom or click on you can see discoloring and cracking on the board.

1FF28355 7447 40C9 902A 9AAB764C2DC6
28D00C0B C9BA 444C 8DA7 B12F8BCBB8EB

 


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TVOR-Ceasar
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07/05/2020 1:23 pm  

Looks like flux residue on the board, but the dark discoloration around the traces looks like the board was getting very hot. Could be shadows too....

If this was one of those "under $30" or so boards, probably not worth it. And if that was the price range, you've more than likely gotten your money's worth out of it.

-Charlie


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TVOR-Ceasar
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14/06/2020 3:53 pm  
Posted by: @tvor-ceasar

Small parts count projects like these are god-awful easy to build. I did a parts look up at Newark.com. With some of the specials they had on there, the total for 2 transistors, 8 resistors, 4 capacitors and 2 stereo RCA panels (stereo build) came to less than $3. Add in a perfboard and it comes up to around $7. Kicker is, shipping is just a bit more than the parts alone. 

I didn't mention that the smallest perfboard I found on that site was still big enough to make several of these stereo preamp boosters. That makes it less per unit cost than what I originally mentioned.

You'd have to put it in a metal container, something akin to a mint tin, tea box, or small dollar store tin. Or, a small wooden box lined with metal foil and insulating sheet (tape or plastic) to keep things from shorting (necessary with the tins). That, and a USB cord you can cut the unused end off of for powering it. 

-Charlie


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