Frank's Ultimate Tube Preamp.

[G]

My apologies Frank. I didn't know that a circuit topology had already been decided on. Maybe one day I'll build that 6AS7G single stage buffer just for kicks. I'm following this conversation with great interest. Have you decided on a tube regulated supply?
or IC regulated? DC on the heaters? Just curious.

G

[fdegrove]

Hi,

My apologies Frank.

By all means, no!

Everyone is welcome to contribute in any way they want, your idea is worthy of consideration to say the least.

Tony,

Don't expect a chicken before the egg.

[apassgear]

Originally posted by fdegrove
Hi,

Don't expect a chicken before the egg.

Just putting some spice.

I'm most probably be building what eventualy will evolve from this thread.

[fdegrove]

Hi,

or IC regulated? DC on the heaters? Just curious.

The heaters will be DC and IC regulated, the B+ is silicon rectified and series regulated using tubes.

You could rectify with tubes too, just change the specs for the powerxformer accordingly + it may require a self to achieve decent filtering.

Anything prior to the reg will be a decent electrolytic cap, after the reg I recommend a film cap.

I hope to have everything ready before the end of the week, my only concern is now that the input impedance (1Meg.) may be too high for a CDP.

If anyone has concerns about this, please let me know.
It is nothing crucial but the attenuator series values and the shunt will need to be changed accordingly then.
The gridleak on the 12BH7A is 1Meg and I like to keep that value constant for the attenuator not to be compromised, its' value could lowered though.

Cheers,

[apassgear]

Originally posted by fdegrove


I hope to have everything ready before the end of the week, my only concern is now that the input impedance (1Meg.) may be too high for a CDP.


Cheers,

What does a 1 Meg Input impedance means in terms of using a 50K attenuator?

Would a 50K att be to low? Why?

[Tube_Dude]

my only concern is now that the input impedance (1Meg.) may be too high for a CDP

What is the problem of a 1M Ohm input impedance be drived by a low impedance??

Of course in a oposite case...you have a problem!

Jorge

[fdegrove]

Hi guys,

The reason I asked about the high input impedance was that with some highly capacitive cables it may cause a HF roll-off.

What does a 1 Meg Input impedance means in terms of using a 50K attenuator?

I am not sure I follow you on this one.
The idea is to use a 1Meg attenuator where the gridleakresistor would be 1Meg too.
So we would have only a series R that would be switched over 23 usable positions, the gridleak would be held constant.

A ladder attenuator built like this is ideal since it does not affect the load on the tube in any way.

Cheers,

[Tube_Dude]

The reason I asked about the high input impedance was that with some highly capacitive cables it may cause a HF roll-off.

The HF rool-off with highly capacitive cable is function of the driving impedance at the sending end...not at the receiving end!

Jorge

[fdegrove]

Hi,

The HF rool-off with highly capacitive cable is function of the driving impedance at the sending end...not at the receiving end!

Sure, I agree.
I am just trying to cater for as much product out there as possible.

If you guys say that it's no problem, then fine.

Cheers,

[apassgear]

Originally posted by fdegrove
Hi guys,

The idea is to use a 1Meg attenuator where the gridleakresistor would be 1Meg too.
So we would have only a series R that would be switched over 23 usable positions, the gridleak would be held constant.

A ladder attenuator built like this is ideal since it does not affect the load on the tube in any way.

Cheers,

So this will mean that we would have to use high value series resistances? say >1 Meg?