Vademeccum pre.

[Kit]

Thanks guys!

Rotation;

The OEP can be bought from RS components for 339 sek which is
about 36 Euro.

I think thats pretty cheap for a shielded chassi mount 1:13 ratio transformer.

why you need 50k secondary?

We want as much step up as possible so that noise in dominated by source, not circuit.

Otherwise your wiring is very nice, i didn't think it will be so...

Now, what makes you say that? :razz:

 

[rotation]

[quote author="Kit"]

why you need 50k secondary?

We want as much step up as possible so that noise in dominated by source, not circuit.

Otherwise your wiring is very nice, i didn't think it will be so...

Now, what makes you say that? :razz:[/quote]

Could you please explain more about the step up? Is it important to have as high as possible secondary "impedance" compared to circuit's impedance or is it pri:sec ratio?
And what is your amp's input impedance? I think that's the parameter that tels us how much step up we need.

I'm wondering about it because ioaudio's preamp which is based on EF86 and ECC82 has much lower pri:sec ratio, but probably the same input impedance as yours. There must be something i don't understand...

Why i thought your wiring is not as nice as it is? That's because you didn't show the pictures from begining, so it was just a thought and joke

 

[Kit]

Could you please explain more about the step up?

Ill try.........

Is it important to have as high as possible secondary "impedance" compared to circuit's impedance or is it pri:sec ratio?

That depends if your matching Power or if (as in this case) we mostly want to step up the small signal from the microphone to impove S/N ratio.

Remember that a "perfect" transformer only reflects the secondary load
to the primary. Divided by ratio of course.

The transformer only adds noise proportional to its DC resistance which is usually to small to matter (for me at least). It can pickup hum if its not properly shielded, though.

And what is your amp's input impedance? I think that's the parameter that tels us how much step up we need.

No, in this case the only thing we need to worry about is not loading down the secondary to much. In my preamp the load seen looking in to the secondary is 1M and the plate to grid C of the EF86.

 

[ChrioN]

"Förstärkning" :green:

I don't know why that looks funny

Skål! :sam:

 

[Kit]

I don't know why that looks funny

It does, doesnt it? :?

We are all victims of anglicisation, Im afraid. :razz:

:sam:

 

[tommypiper]

Hi Kit,

Nice project! Nice audio. Can you say something about your PSU?

 

[rotation]

[quote author="Kit"]

Could you please explain more about the step up?

Ill try.........

Is it important to have as high as possible secondary "impedance" compared to circuit's impedance or is it pri:sec ratio?

That depends if your matching Power or if (as in this case) we mostly want to step up the small signal from the microphone to impove S/R ratio.

Remember that a "perfect" transformer only reflects the secondary load
to the primary. Divided by ratio of course.

The transformer only adds noise proportional to its DC resistance which is usually to small to matter (for me at least). It can pickup hum if its not properly shielded, though.

And what is your amp's input impedance? I think that's the parameter that tels us how much step up we need.

No, in this case the only thing we need to worry about is not loading down the secondary to much. In my preamp the load seen looking in to the secondary is 1M and the plate to grid C of the EF86.[/quote]

Well, thanks for the explanation. I think i finally understand what's going on here

 

[Kit]

Nice project! Nice audio. Can you say something about your PSU?

Thanks!

About the PSU..................not sure what you want to know. Its pretty straight forward. One trafo feeds two channels via a full wave bridge, on to a resevoir cap (22uf) then two voltage drop resistors to the two different channels. Depending on which transformer one uses and which voltage you end up with, you would have to adjust these resistors so you have about +300V on top of the ECC82 plate resistor.

The heaters are twisted AC.

Anything specific you were thinking about?