|
Still they are publishing specifications that pertain to typical
audio performance, such as frequency response and THD. They can't
combine both quirkiness and normality.
Or can they?
Typical "I designed it that way because I could".
IMO it justifies disdain.
Le 20/02/2025 à 16:55, John Woodgate a
écrit?:
toggle quoted message
Show quoted text
I suspect that the weirdness is intentional.
Weird designs have existed from? the earliest day of DIY radio
receivers, before 'electronics'? was in the dictionary. I
recall a report of a circuit that had the 2 V lead-acid cell
apparently in series with the antenna circuit. Objective
performance measurements are typically not to be applied to
such designs. DO a web search for 'Bravo Audio reviews'.
On 2025-02-20 15:36, Jerry Lee Marcel
via groups.io wrote:
Le 20/02/2025 à 15:27, Carlo a
écrit?:
On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
There is some feedback from the audio signal
into the heater voltage. Was that intentional?? Or just an
undesirable side-effect?? I don't expect it would have
very much effect on the heater's temperature (and from
there to the triode's characteristics), but it looks
undesirable to me. Should there be filtering?
Sorry, are you asking whether the audio signal feedback into
the heater voltage comes from a design intentional choice ?
Actually I don't know since I took it from the schematic of
a commercial audio amplifier (Bravo Ocean).
It's extremely unlikely.
Heater temperature varies extremely slowly compared to audio
signals.
It could result in distortion at very very low frequencies,
definitely out of the audio band.
Now this design is weird from the start. Choosing to power a
tube circuit from 24VDC is a major flaw, unless the goal is to
create distortion.
--
OOO - Own Opinions only If something is true: * as far as we
know - it's science *for certain - it's mathematics
*unquestionably - it's religion
|
BTW, I did another run of .TRAN 10m (without UIC or Startup) this time flagging the checkboxes "Noopiter" and "Skip Gmin stepping" under Tools->Control Panel->SPICE (basically it amounts to add the .options noopiter Gminsteps=0 directive in the schematic).
?
This time both Normal and Alternate solvers return a good DC operating point (ITS) to start the transient from. The initial DC heater pin's voltage and current are 5.85V and +149mA respectively (the heater acts indeed as a load/sink). Maybe source stepping method succeeded in finding/pick a good ITS !
|
Yes, easily. Consider, for example, these two
amplifiers:
a) Output power 30 W, THD 0.1%
b) Output power 35 W, THD 5.2%
Which would you buy??
They are the same amplifier. Similar games are
played with signal-to-noise ratio and frequency response.
On 2025-02-20 16:05, Jerry Lee Marcel
via groups.io wrote:
Still they are publishing specifications that pertain to
typical audio performance, such as frequency response and THD.
They can't combine both quirkiness and normality.
Or can they?
Typical "I designed it that way because I could".
IMO it justifies disdain.
Le 20/02/2025 à 16:55, John Woodgate
a écrit?:
I suspect that the weirdness is
intentional. Weird designs have existed from? the earliest
day of DIY radio receivers, before 'electronics'? was in the
dictionary. I recall a report of a circuit that had the 2 V
lead-acid cell apparently in series with the antenna
circuit. Objective performance measurements are typically
not to be applied to such designs. DO a web search for
'Bravo Audio reviews'.
On 2025-02-20 15:36, Jerry Lee
Marcel via groups.io wrote:
Le 20/02/2025 à 15:27, Carlo a
écrit?:
On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
There is some feedback from the audio signal
into the heater voltage. Was that intentional?? Or just
an undesirable side-effect?? I don't expect it would
have very much effect on the heater's temperature (and
from there to the triode's characteristics), but it
looks undesirable to me. Should there be filtering?
Sorry, are you asking whether the audio signal feedback
into the heater voltage comes from a design intentional
choice ? Actually I don't know since I took it from the
schematic of a commercial audio amplifier (Bravo Ocean).
It's extremely unlikely.
Heater temperature varies extremely slowly compared to audio
signals.
It could result in distortion at very very low frequencies,
definitely out of the audio band.
Now this design is weird from the start. Choosing to power a
tube circuit from 24VDC is a major flaw, unless the goal is to
create distortion.
--
OOO - Own Opinions only If something is true: * as far as we
know - it's science *for certain - it's mathematics
*unquestionably - it's religion
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
|
Yes, it's a circuit that works, somehow. However there are many
more efficient and stable ways to bias a MOSFET and to provide
voltage to a 6V heater from a 24V source.
BTW, source-follower it is not. It's actually a common-source
stage.
A source fiollower has about unity gain, this common-source has
about 15dB gain.
Le 20/02/2025 à 17:00, Carlo a écrit?:
toggle quoted message
Show quoted text
On Thu, Feb 20, 2025 at 07:36 AM, Jerry Lee Marcel wrote:
Now this design is weird from the start. Choosing to
power a tube circuit from 24VDC is a major flaw, unless the
goal is to create distortion.
I'm not an expert. However I believe the LM317 in "current
source" configuration actually fulfills two functions. First it
is employed to bias the source of the IRF510 mosfet in common
drain (aka source follower) configuration. Second such a
constant current is employed to drive the 12AU7 triode heater.
|
There really isn't any point in criticizing
the design. It's deliberately weird. An LM386 makes a good
headphone amplifier, but it might be difficult to sell for $130.
On 2025-02-20 17:17, Jerry Lee Marcel
via groups.io wrote:
Yes, it's a circuit that works, somehow. However there are many
more efficient and stable ways to bias a MOSFET and to provide
voltage to a 6V heater from a 24V source.
BTW, source-follower it is not. It's actually a common-source
stage.
A source fiollower has about unity gain, this common-source has
about 15dB gain.
Le 20/02/2025 à 17:00, Carlo a
écrit?:
On Thu, Feb 20, 2025 at 07:36 AM, Jerry Lee Marcel wrote:
Now this design is weird from the start. Choosing
to power a tube circuit from 24VDC is a major flaw, unless
the goal is to create distortion.
I'm not an expert. However I believe the LM317 in "current
source" configuration actually fulfills two functions. First
it is employed to bias the source of the IRF510 mosfet in
common drain (aka source follower) configuration. Second such
a constant current is employed to drive the 12AU7 triode
heater.
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
|
No more difficult than 1m of coax and 2 gold-plated phono plugs.
People still buy them because they hear something on that Alice
Cooper LP they didn't hear before. It's probably tinnitus, but don't
tell them.
--
Regards,
Tony
On 20/02/2025 18:31, John Woodgate
wrote:
toggle quoted message
Show quoted text
An
LM386 makes a good headphone amplifier, but it might be difficult
to sell for $130.
|
Le 20/02/2025 à 17:33, John Woodgate a
écrit?:
Yes, easily.
Yes what?
Consider, for example, these two amplifiers:
a) Output power 30 W, THD 0.1%
b) Output power 35 W, THD 5.2%
Which would you buy?
I don't care, but Bravo Audio seems to care about
figures that are long accepted as performance indicators.
They are the same amplifier. Similar games
are played with signal-to-noise ratio and frequency response.
On 2025-02-20 16:05, Jerry Lee Marcel
via groups.io wrote:
Still they are publishing specifications that pertain to
typical audio performance, such as frequency response and THD.
They can't combine both quirkiness and normality.
Or can they?
Typical "I designed it that way because I could".
IMO it justifies disdain.
Le 20/02/2025 à 16:55, John
Woodgate a écrit?:
I suspect that the weirdness is
intentional. Weird designs have existed from? the earliest
day of DIY radio receivers, before 'electronics'? was in
the dictionary. I recall a report of a circuit that had
the 2 V lead-acid cell apparently in series with the
antenna circuit. Objective performance measurements are
typically not to be applied to such designs. DO a web
search for 'Bravo Audio reviews'.
On 2025-02-20 15:36, Jerry Lee
Marcel via groups.io wrote:
Le 20/02/2025 à 15:27, Carlo a
écrit?:
On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
There is some feedback from the audio signal
into the heater voltage. Was that intentional?? Or
just an undesirable side-effect?? I don't expect it
would have very much effect on the heater's
temperature (and from there to the triode's
characteristics), but it looks undesirable to me.
Should there be filtering?
Sorry, are you asking whether the audio signal feedback
into the heater voltage comes from a design intentional
choice ? Actually I don't know since I took it from the
schematic of a commercial audio amplifier (Bravo Ocean).
It's extremely unlikely.
Heater temperature varies extremely slowly compared to audio
signals.
It could result in distortion at very very low frequencies,
definitely out of the audio band.
Now this design is weird from the start. Choosing to power a
tube circuit from 24VDC is a major flaw, unless the goal is
to create distortion.
--
OOO - Own Opinions only If something is true: * as far as we
know - it's science *for certain - it's mathematics
*unquestionably - it's religion
--
OOO - Own Opinions only If something is true: * as far as we
know - it's science *for certain - it's mathematics
*unquestionably - it's religion
|
Le 20/02/2025 à 18:31, John Woodgate a
écrit?:
There really isn't any point in criticizing
the design.
Maybe there is. The OP is probably on a wild
goose chase.
It's deliberately weird. An LM386 makes a
good headphone amplifier, but it might be difficult to sell
for $130.
On 2025-02-20 17:17, Jerry Lee Marcel
via groups.io wrote:
Yes, it's a circuit that works, somehow. However there are
many more efficient and stable ways to bias a MOSFET and to
provide voltage to a 6V heater from a 24V source.
BTW, source-follower it is not. It's actually a common-source
stage.
A source fiollower has about unity gain, this common-source
has about 15dB gain.
Le 20/02/2025 à 17:00, Carlo a
écrit?:
On Thu, Feb 20, 2025 at 07:36 AM, Jerry Lee Marcel wrote:
Now this design is weird from the start.
Choosing to power a tube circuit from 24VDC is a major
flaw, unless the goal is to create distortion.
I'm not an expert. However I believe the LM317 in "current
source" configuration actually fulfills two functions. First
it is employed to bias the source of the IRF510 mosfet in
common drain (aka source follower) configuration. Second
such a constant current is employed to drive the 12AU7
triode heater.
--
OOO - Own Opinions only If something is true: * as far as we
know - it's science *for certain - it's mathematics
*unquestionably - it's religion
|
RE; Yes, what? You asked, 'Or can they?', and
the answer is, 'Yes, easily'. Well, of course Bravo wouldn't
give figures that showed less than excellent performance. The
THD with 33 ohm load is admitted to be rather high, and we don't
know what the output voltage or power was at that THD. That is
why I gave the two pairs of amplifier figures as an example.
On 2025-02-20 18:14, Jerry Lee Marcel
via groups.io wrote:
Le 20/02/2025 à 17:33, John Woodgate
a écrit?:
Yes, easily.
Yes what?
Consider, for example, these two
amplifiers:
a) Output power 30 W, THD 0.1%
b) Output power 35 W, THD 5.2%
Which would you buy?
I don't care, but Bravo Audio seems to care
about figures that are long accepted as performance indicators.
They are the same amplifier. Similar games
are played with signal-to-noise ratio and frequency
response.
On 2025-02-20 16:05, Jerry Lee
Marcel via groups.io wrote:
Still they are publishing specifications that pertain to
typical audio performance, such as frequency response and
THD. They can't combine both quirkiness and normality.
Or can they?
Typical "I designed it that way because I could".
IMO it justifies disdain.
Le 20/02/2025 à 16:55, John
Woodgate a écrit?:
I suspect that the weirdness is
intentional. Weird designs have existed from? the
earliest day of DIY radio receivers, before
'electronics'? was in the dictionary. I recall a report
of a circuit that had the 2 V lead-acid cell apparently
in series with the antenna circuit. Objective
performance measurements are typically not to be applied
to such designs. DO a web search for 'Bravo Audio
reviews'.
On 2025-02-20 15:36, Jerry Lee
Marcel via groups.io wrote:
Le 20/02/2025 à 15:27, Carlo
a écrit?:
On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
There is some feedback from the audio
signal into the heater voltage. Was that
intentional?? Or just an undesirable side-effect?? I
don't expect it would have very much effect on the
heater's temperature (and from there to the triode's
characteristics), but it looks undesirable to me.
Should there be filtering?
Sorry, are you asking whether the audio signal
feedback into the heater voltage comes from a design
intentional choice ? Actually I don't know since I
took it from the schematic of a commercial audio
amplifier (Bravo Ocean).
It's extremely unlikely.
Heater temperature varies extremely slowly compared to
audio signals.
It could result in distortion at very very low
frequencies, definitely out of the audio band.
Now this design is weird from the start. Choosing to power
a tube circuit from 24VDC is a major flaw, unless the goal
is to create distortion.
--
OOO - Own Opinions only If something is true: * as far as
we know - it's science *for certain - it's mathematics
*unquestionably - it's religion
--
OOO - Own Opinions only If something is true: * as far as we
know - it's science *for certain - it's mathematics
*unquestionably - it's religion
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
|
That is not the subject.
The subject is that they try to justify their quirky "design"
with objective arguments.
Enough said now.
Le 20/02/2025 à 19:45, John Woodgate a
écrit?:
toggle quoted message
Show quoted text
RE; Yes, what? You asked, 'Or can they?',
and the answer is, 'Yes, easily'. Well, of course Bravo
wouldn't give figures that showed less than excellent
performance. The THD with 33 ohm load is admitted to be rather
high, and we don't know what the output voltage or power was
at that THD. That is why I gave the two pairs of amplifier
figures as an example.
On 2025-02-20 18:14, Jerry Lee Marcel
via groups.io wrote:
Le 20/02/2025 à 17:33, John
Woodgate a écrit?:
Yes, easily.
Yes what?
Consider, for example, these two
amplifiers:
a) Output power 30 W, THD 0.1%
b) Output power 35 W, THD 5.2%
Which would you buy?
I don't care, but Bravo Audio seems to care
about figures that are long accepted as performance
indicators.
They are the same amplifier. Similar
games are played with signal-to-noise ratio and frequency
response.
On 2025-02-20 16:05, Jerry Lee
Marcel via groups.io wrote:
Still they are publishing specifications that pertain to
typical audio performance, such as frequency response and
THD. They can't combine both quirkiness and normality.
Or can they?
Typical "I designed it that way because I could".
IMO it justifies disdain.
Le 20/02/2025 à 16:55, John
Woodgate a écrit?:
I suspect that the weirdness is
intentional. Weird designs have existed from? the
earliest day of DIY radio receivers, before
'electronics'? was in the dictionary. I recall a
report of a circuit that had the 2 V lead-acid cell
apparently in series with the antenna circuit.
Objective performance measurements are typically not
to be applied to such designs. DO a web search for
'Bravo Audio reviews'.
On 2025-02-20 15:36, Jerry
Lee Marcel via groups.io wrote:
Le 20/02/2025 à 15:27,
Carlo a écrit?:
On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
There is some feedback from the audio
signal into the heater voltage. Was that
intentional?? Or just an undesirable side-effect??
I don't expect it would have very much effect on
the heater's temperature (and from there to the
triode's characteristics), but it looks
undesirable to me. Should there be filtering?
Sorry, are you asking whether the audio signal
feedback into the heater voltage comes from a design
intentional choice ? Actually I don't know since I
took it from the schematic of a commercial audio
amplifier (Bravo Ocean).
It's extremely unlikely.
Heater temperature varies extremely slowly compared to
audio signals.
It could result in distortion at very very low
frequencies, definitely out of the audio band.
Now this design is weird from the start. Choosing to
power a tube circuit from 24VDC is a major flaw, unless
the goal is to create distortion.
--
OOO - Own Opinions only If something is true: * as far
as we know - it's science *for certain - it's
mathematics *unquestionably - it's religion
--
OOO - Own Opinions only If something is true: * as far as we
know - it's science *for certain - it's mathematics
*unquestionably - it's religion
--
OOO - Own Opinions only If something is true: * as far as we
know - it's science *for certain - it's mathematics
*unquestionably - it's religion
|
On Thu, Feb 20, 2025 at 12:17 PM, Jerry Lee Marcel wrote:
BTW, source-follower it is not. It's actually a common-source stage.
A source fiollower has about unity gain, this common-source has about 15dB gain.
No, it is a source follower.? Its voltage gain is unity.? Input applied to gate, output from source pin.? Almost the same output voltage, but shifted 4.2 V lower.
?
The overall circuit has voltage gain (~23 dB), but all of that comes from the 12AU7, in its common-cathode configuration.
?
I wonder why you saw only 15 dB gain, and why you saw that in just the MOSFET.
?
Not that the following has any significance - but I vaguely recall reading about operating valves (vacuum tubes) at much lower than "normal" anode voltages.? ?There were specialized miniature valves designed for it.? But it was also applied to more traditional valves too, ones like the 12AU7 that are capable of hundreds of volts.? It does not appear to be a sure-fire way to generate distortion, as this simulation demonstrates, if you trust the SPICE models.? I can't recall what were the advantages (if any) of using such low voltages - other than easier battery power.? Lower noise?? ?Longer life?? I dunno.
?
Andy
?
|
On Thu, Feb 20, 2025 at 12:32 PM, John Woodgate wrote:
There really isn't any point in criticizing the design. It's deliberately weird. An LM386 makes a good headphone amplifier, but it might be difficult to sell for $130.
Yeah, but then it would not have that "tube sound".
?
?
|
Any tube sound this design gives you is weird tube sound. ?
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> On Behalf Of Andy I via groups.io
Sent: Thursday, February 20, 2025 5:23 PM
To: [email protected]
Subject: Re: [LTspice] Weird results DC operating point for Tube amplifier? On Thu, Feb 20, 2025 at 12:32 PM, John Woodgate wrote: There really isn't any point in criticizing the design. It's deliberately weird. An LM386 makes a good headphone amplifier, but it might be difficult to sell for $130.
Yeah, but then it would not have that "tube sound".
|
I have to confess that I was misled by this at
an early age, about 13 I think.? The valve doesn't know what the
supply voltage is with zero signal. It only knows the voltage
between anode and cathode, which can be quite small, yet even a
triode still can give gain. I simply didn't believe a DAC32
would work with a 470k anode load, so I used 4.7k, which gave
hardly any gain. What this low Vak does, of course, is limit the
maximum output signal amplitude, but if only a volt or two is
required, there is no problem.
OT observation: With small-signal pentodes,
such as EF33 or EF50, very low anode and g2 voltages can be
used, with megohm values of feed resistors, giving very high
gain.
On 2025-02-20 22:20, Andy I via
groups.io wrote:
Not that the
following has any significance - but I vaguely recall reading
about operating valves (vacuum tubes) at much lower than "normal"
anode voltages.?
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
|
Oh, I get that by putting a 10cm long
unobtanium tube over the headphone cable.
On 2025-02-20 22:22, Andy I via
groups.io wrote:
On Thu, Feb 20, 2025 at 12:32 PM, John Woodgate wrote:
There really isn't any
point in criticizing the design. It's deliberately weird.
An LM386 makes a good headphone amplifier, but it might be
difficult to sell for $130.
Yeah, but then it would not have that "tube sound".
?
?
--
OOO - Own Opinions only
If something is true:
* as far as we know - it's science
*for certain - it's mathematics
*unquestionably - it's religion
|
You're correct.
Le 20/02/2025 à 23:20, Andy I via
groups.io a écrit?:
toggle quoted message
Show quoted text
On Thu, Feb 20, 2025 at 12:17 PM, Jerry Lee Marcel wrote:
BTW, source-follower it is not. It's actually a
common-source stage.
A source fiollower has about unity gain, this common-source
has about 15dB gain.
No, it is a source follower.? Its voltage gain is unity.? Input
applied to gate, output from source pin.? Almost the same output
voltage, but shifted 4.2 V lower.
?
The overall
circuit has voltage gain (~23 dB), but all of that comes from
the 12AU7, in its common-cathode configuration.
?
I wonder why you saw only 15 dB gain, and why you saw that in
just the MOSFET.
?
Not that the following has any significance - but I vaguely
recall reading about operating valves (vacuum tubes) at much
lower than "normal" anode voltages.? ?There were specialized
miniature valves designed for it.? But it was also applied to
more traditional valves too, ones like the 12AU7 that are
capable of hundreds of volts.? It does not appear to be a
sure-fire way to generate distortion, as this simulation
demonstrates, if you trust the SPICE models.? I can't recall
what were the advantages (if any) of using such low voltages -
other than easier battery power.? Lower noise?? ?Longer life?? I
dunno.
?
Andy
?
|
Carlo
John Woodgate
Tony Casey