Re: Weird results DC operating point for Tube amplifier
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?:
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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
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Re: Weird results DC operating point for Tube amplifier
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.
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Re: Weird results DC operating point for Tube amplifier
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
|
Re: LTspice 24.1 Simulation Errors
The symbol file I used was extracted from 74LVC1G.zip. sorry for the typo.
Steve
?
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On 2025-02-20 10:42, info@... wrote:
I am now running 24.1.3. I just installed 74LVC1G.lib and used symbols from 74LVC.zip found in the "files" section.? As long as I connect the power pin to each symbol to VCC, connect VCC to the logic voltage, and add .param VCC=5 or (whatever voltage is your logic voltage) everything runs fine with no errors detected. I checked a '14 Schmitt trigger with 5 volts and the positive going and negative going thresholds were right on.
I'm not sure the library and symbols need changing at all to properly run with 24.1.3.
Steve Hogan
?
On 2025-02-20 09:39, Tony Casey wrote:
On 20/02/2025 15:19, Andy I via groups.io wrote:
Well, there may be one caveat.? If I remember correctly, Mike Engelhardt said that parameter values do not descend infinitely far down into their subcircuits, like you think they ought to.? I think he said it goes down only three(?) levels deep.
?
That was and is really disturbing.? I never took the time to verify it.
That implies that different code is executed after a certain depth. That doesn't sound like the right thing to do. That "recursive" thing has popped up again. Proper recursive sub-routines should, in principle, recurse to infinite depth, limited only by memory. I guess one might add a sanity check at some level of arbitrarily defined depth. But three sounds way too conservative.
As a practical bloke, I might check your theory.? :-)
--
Regards,
Tony
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Re: LTspice 24.1 Simulation Errors
I am now running 24.1.3. I just installed 74LVC1G.lib and used symbols from 74LVC.zip found in the "files" section.? As long as I connect the power pin to each symbol to VCC, connect VCC to the logic voltage, and add .param VCC=5 or (whatever voltage is your logic voltage) everything runs fine with no errors detected. I checked a '14 Schmitt trigger with 5 volts and the positive going and negative going thresholds were right on.
I'm not sure the library and symbols need changing at all to properly run with 24.1.3.
Steve Hogan
?
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Show quoted text
On 2025-02-20 09:39, Tony Casey wrote:
On 20/02/2025 15:19, Andy I via groups.io wrote:
Well, there may be one caveat.? If I remember correctly, Mike Engelhardt said that parameter values do not descend infinitely far down into their subcircuits, like you think they ought to.? I think he said it goes down only three(?) levels deep.
?
That was and is really disturbing.? I never took the time to verify it.
That implies that different code is executed after a certain depth. That doesn't sound like the right thing to do. That "recursive" thing has popped up again. Proper recursive sub-routines should, in principle, recurse to infinite depth, limited only by memory. I guess one might add a sanity check at some level of arbitrarily defined depth. But three sounds way too conservative.
As a practical bloke, I might check your theory.? :-)
--
Regards,
Tony
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Re: Weird results DC operating point for Tube amplifier
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.
|
Re: Weird results DC operating point for Tube amplifier
On Thu, Feb 20, 2025 at 06:55 AM, Andy I wrote:
OK -- so the question still remains:
Does the output signal look "not good at all", as you claimed earlier?
I apologize, it was just a mistake/misunderstanding from mine.
?
Why do you say it doesn't look good?? What about it does not look good?
?
Admittedly it has more distortion, especially in the even harmonics.? But is it bad enough to not be acceptable?? The waveform looks good in a waveform plot, but human eyes are not good about spotting imperfections with our eyes.? Why do you say it is not good?
Yes, I can say that the output signal waveform looks pretty good (although its mean/average value changes slightly even after 60 seconds). Sorry, sometimes I'm in trouble with English :-(
?
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Re: Weird results DC operating point for Tube amplifier
On Thu, Feb 20, 2025 at 09:43 AM, Carlo wrote:
Yes, sorry for the confusion, you are right. The averaged voltages & currents about 60 seconds from the beginning of both .TRAN 60 UIC and .TRAN 60 Startup analysis look right. As you highlighted "what I get is what I get", maybe just the circuit design is the reason !
OK -- so the question still remains:
?
Does the output signal look "not good at all", as you claimed earlier?
?
Why do you say it doesn't look good?? What about it does not look good?
?
Admittedly it has more distortion, especially in the even harmonics.? But is it bad enough to not be acceptable?? The waveform looks good in a waveform plot, but human eyes are not good about spotting imperfections with our eyes.? Why do you say it is not good?
?
Andy
?
?
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Re: Weird results DC operating point for Tube amplifier
On Thu, Feb 20, 2025 at 06:30 AM, Andy I wrote:
My thought is that if the average voltages look about right, then probably what you simulated is reasonably accurate, and "what you get is what you get" - meaning that if it looks bad, it probably really is bad.? If it's bad, maybe the circuit design is the reason.
Yes, sorry for the confusion, you are right. The averaged voltages & currents about 60 seconds from the beginning of both .TRAN 60 UIC and .TRAN 60 Startup analysis look right. As you highlighted "what I get is what I get", maybe just the circuit design is the reason !
?
Thank you.
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Re: LTspice 24.1 Simulation Errors
On 20/02/2025 15:19, Andy I via
groups.io wrote:
Well, there may be one caveat.? If I remember correctly, Mike
Engelhardt said that parameter values do not descend infinitely
far down into their subcircuits, like you think they ought to.?
I think he said it goes down only three(?) levels deep.
?
That was and is really disturbing.? I never took the time to
verify it.
That implies that different code is executed after a certain depth.
That doesn't sound like the right thing to do. That "recursive"
thing has popped up again. Proper recursive sub-routines should, in
principle, recurse to infinite depth, limited only by memory. I
guess one might add a sanity check at some level of arbitrarily
defined depth. But three sounds way too conservative.
As a practical bloke, I might check your theory.? :-)
--
Regards,
Tony
|
Re: Weird results DC operating point for Tube amplifier
Carlo,
?
I am still confused.? Earlier you wrote that your output signal "doesn't look good at all" with .TRAN 60 UIC.
?
Later you wrote that .TRAN 60 Startup "looks good either".? Huh?
?
To me, they look exactly the same.
?
You also wrote that the "DC" (average) voltages near 60 seconds look right.
?
I am trying to determine whether the signals look good, or not good.? Can you please explain?
?
My thought is that if the average voltages look about right, then probably what you simulated is reasonably accurate, and "what you get is what you get" - meaning that if it looks bad, it probably really is bad.? If it's bad, maybe the circuit design is the reason.
?
Andy
?
?
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Re: LTspice 24.1 Simulation Errors
Hello All:
?
I learned from experience.
24.1 flagged a slew of my user.xxx type .models as bad.
And they were; mostly missing spaces between parameters and parenthisis issues.
This never happened before.
I've had those user libraries for a long time and no previous version ever complained.
?
It's appearant that 24.0.x and backwards only parsed .models that were used in a design.
If any unused models in the same file were bad, one would never know.
Now I realize that 24.1.x parses all .models within the entire file, for example all transistors in user.bjt.
24.1 also found errors in my user.jft file and I had no junction FETs in my project.
It appears that 24.1 has changed to parsing every .model in every user.xxx file.
?
Perhaps this new syntax checking behavior now extends to .subckt libraries as well?
Broken .subckt models may have not been parsed in the past because they were unused.
?
Mathias probably knows the answer.
?
All for now
?
?
Sent:?Thursday, February 20, 2025 at 7:54 AM
From:?"Mathias Born via groups.io" <mathias.born@...>
To:[email protected]
Subject:?Re: [LTspice] LTspice 24.1 Simulation Errors
On Thu, Feb 20, 2025 at 12:26 PM, Tony Casey wrote:
If a top level parameter is not re-defined beneath the top level, its value will cascade down the hierarchy. Perhaps, it is this behaviour that has changed in 24.1? I haven't had the chance to investigate this further yet. This would represent a significant change in the assumed architecture.
--
Regards,
Tony
That's exactly what happens. Nothing was changed.
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Re: Weird results DC operating point for Tube amplifier
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).
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Re: Weird results DC operating point for Tube amplifier
On Thu, Feb 20, 2025 at 08:46 AM, Carlo wrote:
A different timestep employed by .TRAN card for transient analysis can't explain that weird (non physical/nonsensical) result for the ITS solution.
You're right about that.
?
Andy
?
?
?
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Re: LTspice 24.1 Simulation Errors
On Thu, Feb 20, 2025 at 08:57 AM, Tony Casey wrote:
I don't believe that LTspice 24.1 shouldn't have complained, if VCC was assigned in the top-level schematic. It is not re-defined anywhere in the 74LVC1G library. That being so, it is perfectly legal syntax to use it anywhere.
Well, there may be one caveat.? If I remember correctly, Mike Engelhardt said that parameter values do not descend infinitely far down into their subcircuits, like you think they ought to.? I think he said it goes down only three(?) levels deep.
?
That was and is really disturbing.? I never took the time to verify it.
?
Andy
?
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Re: Weird results DC operating point for Tube amplifier
It's been discussed and argued, and stated by Analog Devices's experts with the LTspice code, that LTspice should be entirely deterministic, with no randomness in simulations unless the user actually adds it.? One of the tools sometimes used to solve systems of equations, is adding a little randomness into the mix.? The randomness can steer the solver one way or the other, thus potentially avoiding difficult solutions.? But we are assured that LTspice does not do that.? As far as I am aware, SPICE itself (from Berkeley) did not either.? As far as I know, "numerical noise" also does not exist in the sense that repeated runs through the same code should be exactly the same, down to the very last bit.? Even "round-off errors" are exactly predictable and repeatable.
?
If I remember correctly, ADI also said that LTspice code did have some unintended non-determinism, and that these have been (or are being) cleaned up in recent LTspice releases.
?
Over the years I have seen cases where LTspice simulated differently on repeated runs.? We know it should not have done that.? My guess is that I was witnessing some of those unintended bugs that ADI has been fixing.
?
Maybe they are not all fixed yet.? (And as they say, you can't get rid of ALL bugs.)
?
Or maybe you (Jerry Lee Marcel) had certain settings set, the first time you tried this simulation, which caused your simulation to converge correctly right "out of the box" the first time, but not a day later when you fired up LTspice again and it had reverted back to your default settings.? Who knows?
?
Andy
?
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Re: Weird results DC operating point for Tube amplifier
On Thu, Feb 20, 2025 at 05:40 AM, Andy I wrote:
What I mean is, what do the steady-state DC voltages look like, and are they correct or incorrect for your circuit?? I was not referring to the INITIAL voltages at the start of the transient simulation. When the simulation is near 60 seconds and reached steady-state, do the bias voltages look right, or wrong?
Ok, by "bias voltages" you mean actually the mean value of the voltages averaged for instance over a time period of the source signal (e.g. averaged over a 1ms interval for a 1Khz source signal). Near 60 seconds from the beginning of .TRAN 60 UIC analysis, the heater's voltage and current looks good.
?
I meant the voltages in your circuit, at some or any or all circuit nodes. ?Were the FET's gate and source DC (bias) voltages about right, when near 60 seconds? ?Or were they wrong?
Ok yes, for instance the MOSFET's gate and source mean (DC bias) voltages (and current) near 60 seconds look good.
?
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Re: LTspice 24.1 Simulation Errors
On 20/02/2025 14:57, Tony Casey wrote:
I
don't believe that LTspice 24.1 shouldn't have complained, if VCC
was assigned in the top-level schematic.
It should be obvious, but due to a typo, it might not be - it should
have been:
I don't believe that LTspice 24.1 should have complained, if VCC was
assigned in the top-level schematic.
--
Regards,
Tony
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Re: LTspice 24.1 Simulation Errors
On 17/02/2025 09:22, herman.vos via
groups.io wrote:
The highlighted VCC should actually have been VCC3 and
after this correction, LTspice 24.1 will not complain (at least
not for the 2-input nand gate).
?
Do you know what previous LTspice versions have filled in?
Did it assume something like: "ah there's only one parameter
which comes close to VCC which is VCC3 so let's use that one?"
or did it fill in just some positive value (3V3 or 5V? or zero?
Were ALL simulations with this library just wrong??
I don't believe that LTspice 24.1 shouldn't have complained, if VCC
was assigned in the top-level schematic. It is not re-defined
anywhere in the 74LVC1G library. That being so, it is perfectly
legal syntax to use it anywhere. It may well be that it was intended
that the highlighted VCC should have been VCC3, but in actual fact,
it makes no difference as VCC → VCC1 → VCC2 → VCC3 as you descend
the hierarchy. This feature of the library was inherited from the
74HC and 74HCT libraries, originally written by Helmut Sennewald. I
suspect this was deliberately done as an aid to debugging as the
design of the library hierarchy evolved, and was never changed. So I
saw no reason to change it either. The CD4000 libraries were
similar, except that the base parameter used was VDD, instead of
VCC.
It can cause problems, particularly if users either deliberately, or
by accident, don't use the accompanying symbol library with the VCC
parameter named in each symbol, with users then trying to figure out
what parameters should be specified in the top level schematic. If
they would use the example schematic as a template, it would never
arise.
This is a fuss over nothing.
--
Regards,
Tony
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Re: Weird results DC operating point for Tube amplifier
On Thu, Feb 20, 2025 at 05:44 AM, Jerry Lee Marcel wrote:
I thought I suggested small differences in (a) settings or (b) algorithms.? I do not suggest gremlins in the computer!? :-)
?
Andy
?
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Carlo
John Woodgate
Tony Casey
eewiz