AN7 prototype- variation?

fdegrove · 2004-02-19 1:43 pm

Hi,

But I do like the White follower somehow, possibly good for driving nasty power triodes

Or a mile of cable capacitance...

Tube_Dude · 2004-02-19 2:10 pm

fscarpa58 said:
I have to disagree

When point A is at virtual ground
for AC the first tube does not see
the output tube
period

Federico

Me to...

Why the point A become a virtual ground for AC Signals??...because you feed to this point signal from the output in a postiif way...that increase the gain... as if the cathode bypass was there...

periode!

fdegrove · 2004-02-19 3:51 pm

Hi,

that increase the gain... as if the cathode bypass was there...

You both seem to be in agreement without realising it appears...

Cheers,

Tube_Dude · 2004-02-19 4:00 pm

fdegrove said:
Hi,

You both seem to be in agreement without realising it appears...

Cheers,

You too seem to agree that is positf feedback...because in post # 10 you say that is positif feedback:

True, but that's not a problem per se.

and you post a J. Hiraga circuit that is also a positif feedback circuit...

So a i can not see what such issue is all about!!!

fdegrove · 2004-02-19 4:11 pm

Hi,

You too seem to agree that is positf feedback...because in post # 10 you say that is positif feedback:

Yes, of course it is and I don't think Federico disagrees with that.

because you feed to this point signal from the output in a postiif way...that increase the gain... as if the cathode bypass was there...

That was the point of the entire exercise in the first place.
The first stage acts as if it's cathode is bypassed for AC signals without the non-linearities of the capacitor.

Anyway, that's how I read it.

Cheers,

Tube_Dude · 2004-02-19 4:15 pm

fdegrove said:
The first stage acts as if it's cathode is bypassed for AC signals without the non-linearities of the capacitor.

Yes ..without the non linearities of the capacitor...

But..with the nonlinearities of the open loop circuit...

fdegrove · 2004-02-19 4:16 pm

Hi,

But..with the nonlinearities of the open loop circuit...

No such thing as a free lunch, right?

Tube_Dude · 2004-02-19 4:19 pm

fdegrove said:
Hi,

No such thing as a free lunch, right?

Right....Frank!!!

fdegrove · 2004-02-19 4:27 pm

Hi,

Now that we're on the same page, if we consider the entire stage, distortion won't be bad at all and Zo will still be at acceptably low levels...

All it now needs is a very stiff PS, preferably a nice regulated one, no?

Cheers,

EDIT: In the context of a CDP based system I'd rather pick a lower gain, more linear tube such as the ECC99, 12B4A, 12BH7A etc...

Tube_Dude · 2004-02-19 4:32 pm

fdegrove said:
Hi,

Now that we're on the same page, if we consider the entire stage, distortion won't be bad at all and Zo will still be at acceptably low levels...

All it now needs is a very stiff PS, preferably a nice regulated one, no?

Cheers,

EDIT: In the context of a CDP based system I'd rather pick a lower gain, more linear tube such as the ECC99, 12B4A, 12BH7A etc...

Are you talking about the Hiraga schematic or the one at the post #1?

fdegrove · 2004-02-19 4:35 pm

Hi,

Are you talking about the Hiraga schematic or the one at the post #1?

I'm referring to Federico's idea.

While the Hiraga is fine for a phono preamp, it has way too much gain to be useful as a linestage.

The circuit of post #1 is errrr....boring?

Cheers,

Tube_Dude · 2004-02-19 4:40 pm

fdegrove said:
Hi,

I'm referring to Federico's idea.

The circuit of post #1 is errrr....boring?

Cheers,

But the circuit with Federico' idea is the same circuit with some positif feedback...that will cause...increased distortion and increased output impedance...

In my vue a step behind...

fdegrove · 2004-02-19 4:45 pm

Hi,

But the circuit with Federico' idea is the same circuit with some positif feedback...that will cause...increased distortion and increased output impedance...

Which is why I suggested more linear triodes in the second place, you know less gain more often than not means increased linearity.

In case you never toyed with PFB, give it a try. it can be tricky to get it just right but when it's working it's great ( soundwise that is).

Ciao,

Tube_Dude · 2004-02-19 4:56 pm

fdegrove said:
Hi,

Which is why I suggested more linear triodes in the second place, you know less gain more often than not means increased linearity.

And why not, the simpler more elegant solution...if we do not need mouch gain...take out the cathode bypass capacitor...

Bingo!!...less gain ...no capacitor...increased linearity...

In case you never toyed with PFB, give it a try. it can be tricky to get it just right but when it's working it's great

Of course...PFB is good for increased gain...but at the expence of distortion...they are also much used in Bootstraped load resistors in the voltage gain stage in solid state amps...and in fets for overcome the input capacity...

PS: there are few things that i had never toyed in my life...

fdegrove · 2004-02-19 5:08 pm

Hi,

Bingo!!...less gain ...no capacitor...increased linearity...

Certainly...But I think Federicos' idea was about how to preserve the gain of the first stage and lose the decoupling cap all in one go.
Within that context, PFB is the only sollotion I can come up with...

PS: there are few things that i had never toyed in my life...

Tssssssssskkkkkkkkkkkkkkk.............. :smash:

Cheers,

Tube_Dude · 2004-02-19 5:26 pm

fdegrove said:
Hi,

Certainly...But I think Federicos' idea was about how to preserve the gain of the first stage and lose the decoupling cap all in one go.
Within that context, PFB is the only sollotion I can come up with...

But once again...the only remarked that i have done, is that it used PFB...but it can be used...of course...eveybody must use the circuits they want...

I allways use the circuits i like...and all the people must do the same...but that don't change the laws of design...and the names of the things ...

fscarpa58 · 2004-02-19 6:15 pm

that increase the gain... as if the cathode bypass was there...

infact: zero feedback.

Yes, of course it is and I don't think Federico disagrees with that.

In fact: I see the positive feedback … cancels the negative feedback, thus zero feedback.

That was the point of the entire exercise in the first place.
The first stage acts as if it's cathode is bypassed for AC signals without the non-linearities of the capacitor.

Yes, this was the point.

But..with the nonlinearities of the open loop circuit..

I agree, Jorge
Cancellation is not complete, so the first tube does not see the output tube only as a first approximation. Point A is at AC ground only referring to fundamentals not in respect to distortion products, but ...

...that will cause...increased distortion

not noticeable.

and increased output impedance...

true.

I'm referring to Federico's idea.

It is not a my idea. rather a Broskie one.

And why not, the simpler more elegant solution...if we do not need mouch gain...take out the cathode bypass capacitor...

Bingo!!...less gain ...no capacitor...increased linearity......

I completely agree, Jorge.

I think to that circuit only because some people fear the solution without bypass capacitor. They say: “Naaaaa, negative needback, never.”

ciao

Federico

Tube_Dude · 2004-02-19 6:44 pm

fscarpa58 said:
ciao

Federico

Ok ...lets eat a carbonara and drink some Lambrusco...to much positif feedback for a day!!
:drink:

fdegrove · 2004-02-19 7:14 pm

Hi,

Ok ...lets eat a carbonara and drink some Lambrusco...to much positif feedback for a day!!

Salute a tuti...Saludade a todos...( Not sure if I got it right).

Cheers, :drink:

ErikdeBest · 2004-02-19 7:42 pm

in Portuguese: Saúde a todos

AN7 prototype- variation?

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