In article ,
Patrick Turner wrote:
On Jul 9, 9:19*am, John Byrns wrote:
[Much off topic drivel snipped]
You may well delete "drivel" like so many others here who have awful
personalities who cannot cope with being human or nice in any way. Ah
you going senile? Just can't cope with well rounded discussions? Its
OK, you don't have to hide such characteristics.
Your drivel is a fine topic for discussion, the problem is that it is off topic
in this group and you should take it elsewhere.
I've read the tonnesoftware.com site before and there's nothing there
that works better than my circuits using tubes, and I got less wave
form distortion that they show on their oscillograms.
The detectors used in the modulation monitors, the General Radio 1931, Gates
M5693, and Belar AMM-2/3 don't appear to have any visible waveform distortion,
although your eye is probably more sensitive to this type of aberration than
mine. In my defense, back in the days before I became senile, when I worked in
the radio design factory, where we were designing "white goods" radios and
measuring power output at the 5% distortion level, I was consistently able to
set the signal level where 5% distortion occurred without reading the meter on
the distortion analyzer, looking only at the waveform displayed on the CRO.
I have two main problems with the tonnesoft web page. The first is that he uses
an ideal diode model for some of his simulations, and doesn't say what model he
used in others, although I haven't looked at the web page in two years, and if I
read it again might find that he does specify the diode models he used.
The second problem, which is very relevant to our disagreement over the use of a
cathode follower to buffer the diode from the IFT, is that he assumes that the
demodulators are driven by a zero impedance, effectively all his circuits
include your cathode follower, which confuses the issue.
I suggest you try my circuit rather than waste time trying to find
excuses not to use your soldering iron.
I probably shouldn't even be thinking about this cathode follower issue, let
alone thinking about soldering together your detector circuit. I should be
saving my solder for building an improved 25L6 amplifier, however I am curious
about the effect of your apparently pointless cathode follower, and it is
possible that I will be overcome by a desire to show it to be worthless. You
seem to possess a reverse "bean counter" element to your personality which
drives you to include circuit elements that serve no real function, thereby
needlessly driving costs up and reliability down.
I don't really mind if you are rivetted to your lounge room chair in
front of your PC, but when I ever about an idea which might be good I
rush out and try it out to see if I can replicate claims by the
inventor.
OK, what exactly is your claim for inserting a cathode follower between the
secondary of the IFT and the detector diode? On your web page you make two
claims.
Claim #1 is that "this CF isolate the loading effects of the diode detector from
the secondary of the 6BA6", however you don't say why this isolation might be
desirable? The only reason I can see is to increase the Q of the secondary of
the 6BA6, however increasing the Q doesn't seem to be your goal as you also talk
about adding 100k damping resistors to reduce the Q. You could save the cost of
the cathode follower and the loading resistor by simply using neither.
Claim #2 is that the cathode follower "provides a low impedance output to drive
the 1N914 silicon diode detector." Again you give no hint why this might be
useful, although it does seems to have some potential usefulness, on the other
hand a higher impedance output also has some advantages in detector
design/operation.
If you can't manage to build my detector circuit which uses 1 x 12AU7
tube with a few R&C then maybe you've lost your touch.
Looking at the schematic of your detector it appears to use only 1/2 x 12AU7 for
the cathode follower between the secondary of the IFT and the diode, your design
doesn't really use a cathode follower after the diode, instead depending on a
voltage divider, 330k/100k, in conjunction with a relatively high AC coupled
load of 890k, to minimize negative peak clipping. You do use cathode followers
as the audio stage, but they are not connected in a way that they have any
influence on negative peak clipping.
Your design has given me one idea that I have missed up until now. My design
uses a cathode follower directly coupled to the diode detector to eliminate
negative peak clipping. The down side of this approach for those of us who have
been influenced by bean counters is that it requires a negative supply for the
cathode of the cathode follower, impacting both cost and reliability to some
extent. On the plus side one advantage of this approach is that the AGC voltage
can be easily obtained from a tap a little way down the cathode resistor of the
cathode follower.
The idea you have given me is to float the secondary of the IFT and the diode at
a positive potential allowing the direct coupled cathode follower to operate
without a negative supply. The complication is that a separate AGC rectifier is
required, which has the potential to negatively affect the sound, especially
when a delay circuit is used.
And I have extensively discussed all this stuff before with you here
at r.a.t and I refuse to do it all over again.
Discussed it yes, unfortunately you have never offered an explanation of the
usefulness of the cathode follower between the IFT and the detector diode,
beyond the subjective claim that it provides the "best sound". Near as I can
tell the only purpose this cathode follower serves is to assuage your prejudices
against "bean counters".
--
Regards,
John Byrns
Surf my web pages at,
http://fmamradios.com/