Tubecad preamp design

Hi everyone!

On the tubecad blog i stumbled on this mic preamp design.

http://www.tubecad.com/october99/page15.html



I hope you could help me implement a gain control in this design.
what would be the best place and value?

And if you have any comments on this design i'm open for all suggestions.
Thank you for you're time!

greetings

pretty please

first I must say that I don`t understand completely the design.
you would have to obtain some equation for the gain. surely it will depend on the condenser , resistances of cathode and the feedback network(it doesn`t seem very difficult ).

choose a resistance on the equation , change the value an look how it change the gain (frequency, headroom, distortion, etc. are also very important).

at first glance, it seems logical to me think to use the 100K resistors at the feedback network. but they can have other design considerations that I don`t know.

good luck!
Rafael

And if you have any comments on this design i'm open for all suggestions.

Click to expand...

You would need one big nasty input trafo just to overcome grid noise.
You gain some output current drive by the PP topology but IMHO not worth the trouble and extra caps. Also the feedback is crosscoupled which could lead to trouble. I would rather use a plate to cathode feedback and and a pot/switch between the input cathodes.

But by all means, build it and see for yourself. :thumb:

http://www.tubecad.com/october99/page14.html

It's been done successfully.

http://www.groupdiy.com/index.php?topic=8050

and not only by me.
I've done it "all tube" and hybrid.

Rowan

Rowan, the schematic in the link you posted doesnt show up.

/Mikael.

[quote author="Kit"]Rowan, the schematic in the link you posted doesnt show up.

/Mikael.[/quote]

The site where I hosted the schemo crashed and lost it, and I never bothered to repost.
http://www.forsselltech.com/fetcode.shtml
Take a look at that one...this topology gives you a lot more resolution and presence than you're used to from a tube unit.

Thanks! I will build up a little test to see what it does.
And the forssell fetcode did cought my attention before.
If i'm going to buy one i would consider it, but first I want to trie and build one . Could you mail/upload/post. your schematic?
I want to see as many options as possible!

Greetings!