Can someone help me switch this amplifier from 5v to 12v?

[ExpAnonColin]

I'm basically looking for, switch this resistor to this value, etc, if that's at all possible.  Just want to make it all biased and working at 12v instead of 5.  I'm not very good with trannies.

-Colin

[gez]

You need a collector resistor to V+ for the second transistor, plus an output cap from the collector.  Don't really understand what that 10n cap is, was this supposed to be an output cap?  Or is it supposed to be in parallel with a collector resistor to cut high frequencies?

[gez]

Are you using +ve rail as ground or something?

[petemoore]

Looks like V+ is connnected throughthe cap to the base of the second transistor?
 Maybe I just don't get it, doesn't look like it would work to me though.

[ExpAnonColin]

I didn't draw this schematic, I'm not sure.

What would I need to change on this one, which I did draw:



-Colin

[gez]

Ah, didn't see the 'phones' label at the output.  The first schematic might work ok if you had high impedance headphones (2k), but it would be unwise to use normal 32 Ohm jobbies.  Even then, It's not a great idea to have DC thru phones.

Are you seriously going to use this circuit for phones (there are purpose built chips which do the job better) or do you just want to mess around with trannie amps to get some experience?

Second shematic has output cap wrong way round (assuming you're using -ve rail as ground).  Would help if you posted a link to the data sheet for 2n3904 so that resistor values can be calculated....

edit.  would help if you let us know what it's for  

[ExpAnonColin]

http://experimentalistsanonymous.com/diy/Datasheets/2N3904.pdf

It's going to be used as an amplifier.  I could use chips, but I want to use trannies, because I use chips all the time, and Iwant to expand my horizons.  Is that OK?

-Colin

[gez]

It's going to be used as an amplifier.  I could use chips, but I want to use trannies, because I use chips all the time, and Iwant to expand my horizons.  Is that OK?

Of course it's OK, just helps if you give a little more info.  For example, is this circuit for guitar?  If so, then what you've drawn isn't that suitable as it has low input impedance.  If you include an input resistor then that helps matters, but limits gain available.  

So, how much gain do you need?  Details needed before number crunching commences...

[Peter Snowberg]

This looks like a perfect place to consider an output transformer.

Transistors don't mind 1K loads in this kind of situation, but 32 ohms is asking a bit too much in the current department.

Take a look at the schematric for a pig-nose for more. I don't know if there are different units with different topologies, but the one I saw had a preamp stage driving a low power amp stage that pushed a transformer to feed the high power amp stage which is the connected to the speaker via another transformer.

If you want to use a little different topology and go push-pull then you can take a little different approach.

I wasn't going to post this just yet, but oh well.
http://www.freewebs.com/qrp/PP%20Amp.pdf (580K on a slooooooooooow server)

Best of luck!

[ExpAnonColin]

No no no, no output transformers, those are big, heavy, ugly, and expensive.  And I don't have any on hand.  And I want to build it tonight.

This will be amplifying my iPod in my car, line level->greater than line level.

The gain doesn't matter much, that's why I just wanted some simple resistor value swapping.  As long as there's no clipping, and it amplifies it a bit, because the iPod is too soft, I'm fine.

-Colin

[gez]

If you're definitely going to go ahead with the circuit you've drawn (not recommended) try something like the following for a 12V supply: 6k2 collector resistor and 390k resistor from collector to base.

No guarantee it will bias up correctly, and that's why this bias method is pants!  Including an input resistor will raise input impedance and will allow you to control gain to a certain extent (though it will be limited).  Gain (not accounting for loading effects) will be approx. 390k divided by input resistor.

[ExpAnonColin]

Thanks gez.  I'm just trying for simple here.

-Colin