# 1W Transformer Coupled Audio Amp

Discussion in 'The Projects Forum' started by lookitsnichole, Feb 17, 2013.

1. ### lookitsnichole Thread Starter New Member

Feb 17, 2013
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0
Hello, I'm trying to design an amplifier for a class, and I'm having a hard time getting started. The schematic below is the basic design I want to use, (it has to be transformer coupled), but I'm not sure how to even start with values. The book I found this in is really outdated and therefore I don't think I would trust the numbers given. Does anyone have some suggestions as to how I would find the turn ratios in the transformers as a start? I've also listed the project guidelines given.

2. ### MrChips Moderator

Oct 2, 2009
18,194
5,715
Are you a student in the class or the teacher?
The accuracy of the values would have nothing to do with the age of the circuit.
Why not go ahead and build it as is?
I don't know if you can still find OC81 transistors. Note that this is a germanium PNP transistor.
You might be better off to look for a circuit that uses silicon NPN transistors.

To determine the turns ratio of the transformer, apply a low voltage AC signal to the primary winding and measure the AC voltage at the secondary winding.

3. ### #12 Expert

Nov 30, 2010
18,076
9,678
To determine the turns ratio, read the drawing. The phase splitter is 3.5:1:1 and the out put transformer is 3:1 + 3:1 +1

4. ### MrChips Moderator

Oct 2, 2009
18,194
5,715
That's too easy.
The question could be:
1) How to find what turns ratio are being used (indicated in the drawing)
2) How to determine what turns ratio to use (by impedance matching)
3) How to determine the actual turns ratio of a physical transformer (read the specs or measure)

#12 likes this.
5. ### #12 Expert

Nov 30, 2010
18,076
9,678
You expanded on that concept very well.

6. ### lookitsnichole Thread Starter New Member

Feb 17, 2013
4
0
Thanks for the help. I can find the old germanium transistors, but they're about \$7 each. Does anyone know of a silicon version that might do the job?

7. ### #12 Expert

Nov 30, 2010
18,076
9,678
The only reason the transistors are germanium is that the circuit is an antique. Just choose anything that can handle the current in the output stage. 2N3906 will probably do the input stage. Change R4 to get 2 ma. Adjust R5 for minimum distortion.