G9 Preamp Help

[barthman.de]

Sorry this should not be a poll - I've only a question  :

I've a question to the G9 circuit diagram. It shows the following output transformer part:

The output transformator ought to be wired 2:1. To get 2:1 I think the secondary of the transformer must be wired as follows: connect Pins 6 to PIN 9; (+)"hot" to PIN 7; (-)cold to PIN 10.

In the circuit above I think the output is wired only to one winding of the secondary. Why that? 2+2:1=4:1 not 2:1 ?!

At the layout of the printed circuit board (look at http://www.barthman.de/bilder/g9_pcbs.pdf) the output transformer is not wired as shown in the circuid diagram isn't it?

The second question I have is: How must be wired R32 and R44?

I drawed the following circuid from the printed circuit board:

Is this connection of R32 and R34 right?  

Why two of this 10k resistors? Would not be adequate one 10 k resistor to load the transformer?

 

[Matthew Jacobs]

Hi

Do you realize that the transformer is reversed?

So pins 6,7,9, 10 are actually on the "primary" side. That's what makes it step down 2:1.

This setup works fantastic in my G9. I'm using OEP transformers BTW

J

 

[barthman.de]

Yes I realized that it is reversed. OEP transformer is a 1:2 transformer Lundahl is 2:1 so the OEP must be reversed for 2:1. My problem: I think the circuit diagram is different to the layout of the printed circuit board  ???

The numbers I wrote to the pins are for Lundahl transformer wiring.

 

[zebra50]

I had a quick look at the layout again and I thought it looked like the secondary windings are in series, not parallel as shown in the diagram. If so it may be a simple cut-paste error from an earlier design. So for the Lundahl you have 1+1:0.5+0.5, or 2:1.

Anyway, the circuit works very well with that layout and either transformer - I've built both.

I think the use of two resistors either side of the switch means that the preamp always sees a load, and the input of whatever is next also sees a load. This will minimise pops and clicks when switching.

 

[barthman.de]

Thank you for your answer. I want to build my own PCB's for the G9 so I was insecure after looking at the diagram. Could somebody check wether R44 is on the right place in my drawing after the phase switch?