D3a preamp.

[Bigun]

GroupBuild Forum - 300B SE Project, Part 9 - E180F, E280F, D3a pentodes - triode connected - Damir, March 09, 2006 at 14:19:29

 

[Nikitas]

Why?

 

[Nikitas]

Bigun thanks.
Kevin, is the transformer suitable (except for ballse) to be used as an i/v stage, or does it need more , like resistors?

 

[kevinkr]

Usually the transformer is used in conjunction with a resistor which does the actual I/V conversion.. Have a look at my old thread here:
http://www.diyaudio.com/forums/tube...r-i-v-converter-differential-current-dac.html

 

[Nikitas]

The Simple Transformer Explanation… | H i F i D U I N O

this is something I have found today. This is a kind of answer I would like to hear.
Kevin, I'm going to read your thread now.

 

[Nikitas]

Kevin, what's the purpose of r1 and c2 on the final schematic in your thread?

Edit: No need to answer that, got it.

 

[schiller]

Not trying to replace Kevin, but R1 seems to be necessary to damp tranformer resonances in higher frequencies,or compensate for rising frequency responce, or both.
Interstage transformers -especially step-up ones- are a bit sencitive in this. Secondary must be always loaded.
C2 is a power supply filter capacitor.

 

[Nikitas]

Yes, I figured it out about r1, c2 was strange to me because the source is virtual, ie you don't see the diodes,filters etc.

I still think that resistors is not a good idea for i/v duties. It is quite simple though.
The thing is the "ground" of a differential stage, especially for a dac is a digital dumpster. Everything there is unwanted. So I don't want to couple this dumpster with such a clean signal as a differential.