I've been doing a bit of searching regarding linearization of individual
stages before feedback is applied. One interesting old techinque was
discussed at diyaudio.com, where a diode tube inversely predistorts the
input to the triode (see "The long lost linear gain stage" thread in the
tubes forum).

Another thing I came across is this:
http://www.wolcottaudio.com/WA_whitepapers.htm
The problem is that a) there's no schematic, and b) it's hard to get
through all the marketing BS. Nonetheless, I'm interested in figuring
out what exactly is being done, specifically with the 2nd stage. I'm
amazed Wolcott didn't actually list the patents being referred to.

USPTO's website doesn't search properly pre-1975 patents, but,
ironically, the German patent site does (for US patents at that). From
the 1960s, I found the following amplifier patents by the guy: US3111630,
US3328711, US3361981, and US3428912. Of the two being referred to on the
website, the second one from that list (US3328711) is clearly one of them
(fig. 6), but the other one I'm not sure. By the way, the best way to
view patents is by downloading them as PDF files from
free.patentfetcher.com.

My goal in posting here is to get comments on a) how this design has been
upgraded to fit the description on the website, as I failed to get a
clear idea; b) the merit of the idea overall; and c) how well it stands
on its own, in terms of me being able to use a similar stage in an OTL
amplifier, as he's got feedbacks from various other stages, including the
output transformer (my tube amplifier plans relate to driving high
voltage plasma and electrostatic panels directly, as well as Berning's
high frequency switcher-based impedance matching output that he calls
ZOTL).

Hi,

I've fought my way through the description and am of the opinion that
there's nothing outrageously new about the Woolcott circuit. If I
understand it correctly, it (1) has a dedicated gain/splitter circuit
for a positive feedback loop sourced from a tertiary winding on the
output transformer, (2) has a second phase-splitting stage per
push-pull half to drive (3) a set of McIntosh-inspired final driver
stages, and (4) a conventional pentode output stage.

So, marketing hype aside, it's defintely quite an involved circuit for
any amplifier. However, even assuming that the designer has come up
with a listenable product (I suspect it'll have a rather solid-state
like quality to it), getting such a complicated circuit stable will
require very, very careful attention to power supplies, grounding, and
precise component values. There's an awful lot happening to the audio
signal already, and an amplifier of this complexity runs a serious risk
of instability.

At any rate, this is an interesting idea - but I'd really need to be
convinced that it's practical and desirable!

Best regards,

Russ Sadd

Prune wrote:
Another thing I came across is this:
http://www.wolcottaudio.com/WA_whitepapers.htm
The problem is that a) there's no schematic, and b) it's hard to get
through all the marketing BS. Nonetheless, I'm interested in figuring
out what exactly is being done, specifically with the 2nd stage. I'm
amazed Wolcott didn't actually list the patents being referred to.

Referring to fig. 6 in the patent (US3328711), I was interested in the
triode/tetrode second/third stage as driven by the cathode follower
input. I quoted this particular patent as the second and third stages
essentially correspond to the website description (in the webpage, the
first stage is replaced with White cathode followers, and there is only
feedback signal and no input at e1, and the connection to the output
stage is DC coupled with current mirror, and there is stuff on the
secondary 119). Now, there's probably more to it, given a comment at
audioasylum (http://www.audioasylum.com/scripts/t...ubediy&m=51536),
but...

Now I have four specific questions, please:
a) About the cross-coupled phase splitter -- the way I understand it, a
mere CSS loading of the triode also has the benefit of appearing like
infinite plate impedance, so what's the point of doing it the way in the
patent? The only thing I see is that the positive feedback from the third
stage cathodes makes for very high gain, allowing very high feedback (and
very high frequency problems from this are dealt with by the feedback
from the output through capacitors 122).
b) Capacitors 104 can be replaced by DC coupling through level shifting
such as by a zener(as in other figs in the patent); what about capacitors
123 -- given it's in a local feedback loop, it's still in the signal
path; any way to do away with it?
c) What about using this configuration in an OTL amp? Adding a negative
rail, the load could be connected between the output devices, like the
balanced single ended Aleph-X amps (see diyaudio forums/Pass Labs). But
what if the output was to be unbalanced? How would the third stage
outputs be properly coupled to a single output device? I'm asking because
I have specific applications in mind.
d) In an OTL, since there's no tetriary winding 120, where would the main
NFB be sourced? And in a way so that balanced input can be done without
input transformers -- where would the main NFB be injected?

Prune wrote:

I've been doing a bit of searching regarding linearization of individual
stages before feedback is applied. One interesting old techinque was
discussed at diyaudio.com, where a diode tube inversely predistorts the
input to the triode (see "The long lost linear gain stage" thread in the
tubes forum).

Another thing I came across is this:
http://www.wolcottaudio.com/WA_whitepapers.htm
The problem is that a) there's no schematic, and b) it's hard to get
through all the marketing BS. Nonetheless, I'm interested in figuring
out what exactly is being done, specifically with the 2nd stage. I'm
amazed Wolcott didn't actually list the patents being referred to.

USPTO's website doesn't search properly pre-1975 patents, but,
ironically, the German patent site does (for US patents at that). From
the 1960s, I found the following amplifier patents by the guy: US3111630,
US3328711, US3361981, and US3428912. Of the two being referred to on the
website, the second one from that list (US3328711) is clearly one of them
(fig. 6), but the other one I'm not sure. By the way, the best way to
view patents is by downloading them as PDF files from
free.patentfetcher.com.

My goal in posting here is to get comments on a) how this design has been
upgraded to fit the description on the website, as I failed to get a
clear idea; b) the merit of the idea overall; and c) how well it stands
on its own, in terms of me being able to use a similar stage in an OTL
amplifier, as he's got feedbacks from various other stages, including the
output transformer (my tube amplifier plans relate to driving high
voltage plasma and electrostatic panels directly, as well as Berning's
high frequency switcher-based impedance matching output that he calls
ZOTL).

The comments here won't help you as much as using a few diodes and triodes
on a breadboard set up, and then measure and observe all scientifically with
meters and CRO.

Patrick Turner.

Agreed.

"Patrick Turner" wrote in message
...


Prune wrote:

I've been doing a bit of searching regarding linearization of individual
stages before feedback is applied. One interesting old techinque was
discussed at diyaudio.com, where a diode tube inversely predistorts the
input to the triode (see "The long lost linear gain stage" thread in the
tubes forum).

Another thing I came across is this:
http://www.wolcottaudio.com/WA_whitepapers.htm
The problem is that a) there's no schematic, and b) it's hard to get
through all the marketing BS. Nonetheless, I'm interested in figuring
out what exactly is being done, specifically with the 2nd stage. I'm
amazed Wolcott didn't actually list the patents being referred to.

USPTO's website doesn't search properly pre-1975 patents, but,
ironically, the German patent site does (for US patents at that). From
the 1960s, I found the following amplifier patents by the guy: US3111630,
US3328711, US3361981, and US3428912. Of the two being referred to on the
website, the second one from that list (US3328711) is clearly one of them
(fig. 6), but the other one I'm not sure. By the way, the best way to
view patents is by downloading them as PDF files from
free.patentfetcher.com.

My goal in posting here is to get comments on a) how this design has been
upgraded to fit the description on the website, as I failed to get a
clear idea; b) the merit of the idea overall; and c) how well it stands
on its own, in terms of me being able to use a similar stage in an OTL
amplifier, as he's got feedbacks from various other stages, including the
output transformer (my tube amplifier plans relate to driving high
voltage plasma and electrostatic panels directly, as well as Berning's
high frequency switcher-based impedance matching output that he calls
ZOTL).

The comments here won't help you as much as using a few diodes and triodes
on a breadboard set up, and then measure and observe all scientifically
with
meters and CRO.

Patrick Turner.