Tube as i/v converter

[ingram]

Hi all,
I've made a simulation using tube as i/v converter
http://www.geocities.com/aykm/temp.htm
Any suggestion?has any1 tried this kind of ciruit b4?
Anyway,im going to build this circuit but it would take a while.

[andrei]

I don't see the point of this circuit. Your tube is not amplifying anything, it is connected as a vacuum diode. If you are going to use transistors for current steering anyway, you might as well replace the tube by a resistor...

Grounded grid stage looks more interesting to me, although of course the input impedance is going to be higher than transistor's.

[till]

what about something like

[rfbrw]

Used forum search engine. It led here.
http://www.ultranalog.com/cdenhancer/cdenhancer1.html

[Guido Tent]

Hi

Cathodes are the only low impedances so look for high gm tubes, with gm as flat as possible as function of Ia.

Furthermore this converter type suffers from the same drawbacks as a cathode followers (so remeber about current sources and cascodes !)

cheers

[ingram]

hi andrei,
my thought is ,the sound will be dominate by the charateristic of the tube if use as iv converter.In simulator the wave form has the kind of distortion as described in a passlabs article:the positive half is slightly higher than negative half.Im curious how it would sound in reality.

till,
I was planning to build a similiar circuit but the operation point of tube tend to drift with age,using dc servo as shown in this website seems like a better method
http://peufeu.free.fr/audio/extremis...plement_4.html
But on second thought the IV conversion is still done by resistor in grounded grid configuration,so i assume i wouldnt differ much from a common base transitor.

[till]

My idea was to use the resistor from GND to V- and the tube to V+ with a high value for R and really high voltages for V-/V+. This way the DAC could make all the voltage needed in the whole amplifier chain, one or two source followers behind should give the necessary current for driving the speaker. This way we would have a DAC driving speakers without preamp and power amp needed.

[ingram]

rfbrw,
I've seen that website b4 but dont quite understand how it work,how come the ground is floated??

Guido,
5687 seems like the best choice here,it can operate at low voltage,with decent gm, cheap,readily available,and also sound good when used in preamp.
6H30 have better specification but cost more,my second choice
5842 have highest gm but need higher operating voltage.And it's songle triode.
Vacuum diode doesnt have my desired voltage swing and im not sure of its sonic when use in signal path.
The safe bet would still be 5687.
Can you elaborate more on the "same drawback" of cathode follower?
May i also ask do a digital expert like you use tube amp?

[rfbrw]

Originally posted by ingram
rfbrw,
I've seen that website b4 but dont quite understand how it work,how come the ground is floated??

It is the same as the Pass D1 circuit without the follower on the output or the ability trim the input to 0v.
The circuits you linked to do not look to be servoed to me in that there is nothing keep the input impedance seen by the dac as close to zero as possible. A sevoed variant of the tube iv would look something like the circuit below.

[Guido Tent]

Originally posted by ingram
rfbrw,
I've seen that website b4 but dont quite understand how it work,how come the ground is floated??

Guido,
5687 seems like the best choice here,it can operate at low voltage,with decent gm, cheap,readily available,and also sound good when used in preamp.
6H30 have better specification but cost more,my second choice
5842 have highest gm but need higher operating voltage.And it's songle triode.
Vacuum diode doesnt have my desired voltage swing and im not sure of its sonic when use in signal path.
The safe bet would still be 5687.
Can you elaborate more on the "same drawback" of cathode follower?
May i also ask do a digital expert like you use tube amp?

Hi

CFs distortion habbits from

1 - current modulation (mostly the low cathode resistor value)
2 - voltage modulation (anode - cathode)

both can be understood when studying thecharateristics

1 is worse than 2 (mu times) and 1 is also affected by external load like input impedance of next stage (but often high with tubes

Applying a current source as a load for the CF, decreases distortion, also when drive at the cathode.

2 can be reduced by applying cascoding on top of the anode, but again, yields less results

consider penthodes like E83F or E55LL as well

Try it, you'll like it......

cheers