preamp with output trannies.

[then_dude]

hello,

i wanna make an preamp which serves two functions: a line stage with a gain of 2; and a headphone amp.

i thought a lot about what i should do: output trannies or not. but since the design can be extremely simple with an transfo i will go for that.

so essentialy i wanna make an single ended preamp. the tube i had in mind is the d3a which i wanna put in triode mode.

so following the specs of this tube: the b+ should be around 160 volt, I=24ma; R of the tube is 1.9k.

but i have some questions, about the design.
1)the trannie will have a lot of output impedances, : can i connect the input of the poweramp to the output of the trannie at 600 ohm ?
2)if i only take a gain of 2; would that be enough to drive the headphones ?
3)does anyone has a link where i can find some theory about SE design: like what to use as plate load or ande resistor cause i'm losing it.

thanx

 

[AndreasS]

so following the specs of this tube: the b+ should be around 160 volt, I=24ma; R of the tube is 1.9k.

You have for the D3a at 24mA@160V a grid bias of -1,5 Volts; grid currents begins at -1,3V... the input signal without significant load for the source must be much smaller than 0,5 Volt.

Andreas

 

[then_dude]

hello andreas,

i'm not saying that i wanna have 24ma. i can change the bias of the grid.

but what do you mean by the input signal without significant load for the source must be much smaller than 0,5 Volt.


the input signal would be around 0.7vrms. i wanna double it; because my power amp has only 10 watt , so i don't wanna loose to much off that.

thanx

after some thinking, o yes i see what you mean. indeed, but if i change the resistor under the kathode i can make it like -5 of -10 volt or somehting. i will have to change the B+ and things like that, but since i start from the scratch, and i will have an order made to measure for the trannies, i can go all directions


thanx

ps: here are the specs
http://www.mif.pg.gda.pl/homepages/frank/sheets/128/d/D3a.pdf

 

[AndreasS]

...i'm not saying that i wanna have 24ma. i can change the bias of the grid.

You see the problem with the the D3a: increasing the bias reduces the anode current, increases the plate resistance and the tube works in the nonlinear region.

the input signal would be around 0.7vrms. i wanna double it; because my power amp has only 10 watt , so i don't wanna loose to much off that.

Input 0,7 V RMS would be a signal peak of 1 Volt, near the 0-Volt load line. IMHO a tube with a smaller transconductance will work better.

Regards Andreas

 

[phn]

How about the C3g?

http://www.jogis-roehrenbude.de/Leserbriefe/Siemens-C3g/c3g.htm

Edit: I should add no transformers. The C3g (and C3m) doesn't need them. I think I have a transformer design on my hard drive.

 

[then_dude]

thanx alot for the scheme, i think it is very interesting and is not that expensive, this is very fine thanx.

i think i'm gonna build an tubalizer or something like that as a preamp, we'll see what comes up. but by splitting up the tasks of preamp and headphone amp i have more space for other options, in everyway thanx a lot

 

[then_dude]

i have been reading a bit more. so i might drop the funtion of an integrated headphone combined and line amp. I think the headphone amp above looks very fine, so that's fantastic.

i'm will build for simplicity reasons a grounded grid preamp. it has to serve as an output tube behind a dac.
after reading some theoretical stuff (but i didn't find that much) i have seen that i need a high mu tube in order to get it right.

acutally i'm trying to fit a d3a in this scheme.
if there is anybody who can help me out on the parts. i will get myself studying those design because i go crazy that i can't figure it out myself and then ask advice. i will look on this site for some good books people are advising;

anyway thanx guys.