From http://www.runoffgroove.com/thunderbird.html
(https://i.postimg.cc/fy3GkbTP/ROG-dynamic-clipper.png)
Output varies with time. Initially there is more amplitude
(https://i.postimg.cc/jj6trcMF/ROG-1.png)
Waveshape in first few ms (sine wave 1000Hz, 3V peak fed in)
Soft clip on positive cycle due to series resistor near positive clipping diode. Even more compliance in the bottom cycle
(https://i.postimg.cc/GhXX6RL8/ROG-begin.png)
Waveshape after 800ms
The cap has built up a charge, shifting the signal waveform more positive. The top becomes broader since the diode clips at a fatter part of the sine wave. The bottom becomes smaller since there is less signal being presented below 0V.
(https://i.postimg.cc/FRhc9fG9/ROG-end.png)
Is that a real circuit or modelled? And if modelled, are there components subject to thermal drift and/or leakage?
An apparent DC drift may only be the wave shape "centering". The centre of an assymetric waves' amplitude is not 50% of peak to peak.
Quote from: anotherjim on October 30, 2020, 05:32:45 AM
An apparent DC drift may only be the wave shape "centering".
That's the same thing as a DC drift.
A dynamic shift is more important to a good overdrive tone than almost anything else, so I have to applaud the OP for pursuing this route instead of wasting time with different coloured LEDs. However, for a true tube-like distortion (which most people seem to like best) you want the dynamic shift to have the opposite effect -initially
less amplitude, then a little
more after 50ms or so. Better yet, clipping that is initially asymmetrical, then grows more symmetrical with time. Keep it up! :icon_biggrin:
Quote from: anotherjim on October 30, 2020, 05:32:45 AM
Is that a real circuit or modelled? And if modelled, are there components subject to thermal drift and/or leakage?
An apparent DC drift may only be the wave shape "centering". The centre of an assymetric waves' amplitude is not 50% of peak to peak.
That bit of circuit is from real circuit from THUNDERBIRD at ROG.
but I analysed it with LTSPICE.
Its not just wave centering because
The peak to peak amplitude changed with time
The wave shape changed with time.
Quote from: merlinb on October 30, 2020, 06:21:26 AM
A dynamic shift is more important to a good overdrive tone than almost anything else, so I have to applaud the OP for pursuing this route instead of wasting time with different coloured LEDs. However, for a true tube-like distortion (which most people seem to like best) you want the dynamic shift to have the opposite effect -initially less amplitude, then a little more after 50ms or so. Better yet, clipping that is initially asymmetrical, then grows more symmetrical with time. Keep it up! :icon_biggrin:
I understood
Sag = cleaner, higher amplitude signal initially and then dirtier and less amplitude signal
Bloom, Swell etc may be the opposite
But I cannot seem to find raw data of waveshapes or oscilloscope snapshots or WAV files on the internet that show these characteristics of a tube amp. Hence it is so hard to study.
So far I only saw very few DIY circuits, some Crate Amps, some Levin amps that try to emulate change in waveshape over time. and they do it is somewhat similar fashion of a cap collecting charge over time. They dont have that cap reducing charge over time.
While it appears that almost no AMP IN A BOX or Distortion pedal has implemented this feature.
About initially asymmetrical ie pleasing even harmonics, progressing to symmetrical clipping , I feel this could be related to instantaneous signal level rather than integration over time. I need to read to old patents more carefully, but I was thinking of implementing this in a second clipping stage which clips earlier asymmetrical clipped waveform to be symmetrical if above a particular value.
Or maybe this circuit already does this, if I input sine waves with envelope approximately same like a guitar input. Right now I posted input = Sine wave 3V peak, 1000Hz fixed
I actually have a pedal circuit in my unfinished pile that does this, based on the ideas in the expired SLM (Crate) patent:
(https://i.imgur.com/8UEgFHVm.jpg)
Jack Orman also explored the main part of the SLM circuit a bit on his page (I'll try to dig up the link).
Edit: Here it is. About 2/3 of the way down on this page:
http://www.muzique.com/schem/projects.htm
"Tubetype Distortion"
My circuit is different from Jack's, but the main bits are very similar. Ignore Jack's last bit about the patent, by the way. The knowledge belongs to everyone, as the patent is long expired.
Thanks for pointing that out!!
(http://www.muzique.com/schem/louis2.gif)
Yes I had earlier input that circuit into Spice and analysed it too. It has somewhat similar buildup of charge on the Cap. So the overall amplitude graph was similar as what I posted earlier. It does not do "Bloom", "Swell"
The interesting thing is the DC gain resistor 42 that can be converted into a pot, to change the effect of the DC shift
But the circuit needs pre-dist EQ and post-dist EQ since the patent only tried to show the way to get a DC shift
https://patents.google.com/patent/US5032796A/en
It would be nice to see your schematic
PS: Crate and Levin Amps have 2 stages with this DC shift, to increase the effect.
Levin schematic with 2 stages that show DC shift
I would feel that the second stage integrates the signal that already has been clipped by the first stage and hence shows less dynamic range. It might have been interesting to feed the second Opamp the DC control signal generated by the first IC.
(https://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=42442&g2_serialNumber=1)
Quote from: Vivek on October 30, 2020, 08:22:45 AM
It would be nice to see your schematic
This is still unfinished, but here you go. Feel free to suggest improvements. The JFET portion is a rather crudely cobbled bit, so go easy judging that. :icon_razz:
(http://i.imgur.com/HJolvgO.jpg)
(http://i.imgur.com/6zqAsFf.jpg)
Wow, Interesting, thanks for sharing !!!
That patent DC shifter needs fairly high input signal voltages to be able to do its stuff.
What is the peak voltage of signal that reaches R5 ?
I found in the simulations that one way to reduce the requirement of big input signals is to scale everything down ie 2 or 3 diodes in series for the clipping instead of zenners, and a schotty for the DC integration diode.
Please help me to understand the subcircuit A,B,C,D. Thanks
Quote from: Vivek on October 30, 2020, 09:06:05 AM
Please help me to understand the subcircuit A,B,C,D. Thanks
The subcircuit is lovingly ripped out of the Klon and scaled a bit differently. I wanted to feed some additional bass signal forward around the distortion portions and mix it into the output to have more bass content without more mud. I thought it would be fun to just see what would happen dropping that existing bit in. It sounded interesting enough in my initial testing that I haven't bothered changing it yet. Another crudely cobbled bit that looks more sophisticated than it is. :icon_wink:
Couldn't IC1B & IC2B be incorporated in a single stage, Eric..??
P.S.
"Honey Butter Biscuit".. ??? !!! :o
(you didn't give your best, did you..??) :icon_lol: :icon_lol:
Quote from: antonis on October 30, 2020, 09:22:27 AM
Couldn't IC1B & IC2B be incorporated in a single stage, Eric..??
No. You see, this one has two stages. It's one louder. :icon_lol:
Quote
P.S.
"Honey Butter Biscuit".. ??? !!! :o
(you didn't give your best, did you..??) :icon_lol: :icon_lol:
The very first prototype of the circuit, which was a lot different at the output stage, sounded sweet, rich, and warm to me. That's what inspired the name. This iteration is (sadly) less warm, but I've kept the name.
Quote
P.S.
"Honey Butter Biscuit".. ??? !!! :o
(you didn't give your best, did you..??) :icon_lol: :icon_lol:
The very first prototype of the circuit, which was a lot different at the output stage, sounded sweet, rich, and warm to me. That's what inspired the name. This iteration is (sadly) less warm, but I've kept the name.
[/quote]
I do like the name, though.. :icon_mrgreen:
I need to know what all these adjectives for tone are. I now feel like creating a pedal named "food" or something like that and having a "sweet" knob, "bitter" knob, "spicy" knob, etc.
Quote from: EBK on October 30, 2020, 09:14:14 AM
Quote from: Vivek on October 30, 2020, 09:06:05 AM
Please help me to understand the subcircuit A,B,C,D. Thanks
The subcircuit is lovingly ripped out of the Klon and scaled a bit differently. :icon_wink:
Does one end of R25 need to go to an AC ground like VBias ???
Quote from: antonis on October 30, 2020, 09:22:27 AM
Couldn't IC1B & IC2B be incorporated in a single stage, Eric..??
I think IC1B clips asymmetrically since the zeners are not the same value
Then the output of IC1B is inverted
and 1C2B clips the inverted signal asymmetrically ie clips the other side of the signal
All this cannot be done with one opamp
(https://www.trueaudio.com/images/eet_fig1.gif)
Quote from: Vivek on October 30, 2020, 09:45:59 AM
Quote from: EBK on October 30, 2020, 09:14:14 AM
Quote from: Vivek on October 30, 2020, 09:06:05 AM
Please help me to understand the subcircuit A,B,C,D. Thanks
The subcircuit is lovingly ripped out of the Klon and scaled a bit differently. :icon_wink:
Does one end of R25 need to go to an AC ground like VBias ???
Yes. I corrected that, but didn't take a new pic after I drew it in. I'm still looking for my latest copy. I believe I scaled some resistors and caps differently too....
EBK, it would be a good idea to estimate the peak signal value at various stages in the circuit
I feel that in case Vcc was infinity and there were no zeners, IC1B should have output maybe 200 times the bigger zener voltage. Then the zeners clip the output at around 1/200 of peak at max gain.
PS : Input DC decoupling cap needed ?
PS : Cutting bass before clipping needed ?
I'd also recommend taking a look at this paper for another take on emulating triode DC shifting:
https://www.researchgate.net/publication/290534843_Triode_emulator_-_Part_2
I think Peavey may have done something similar in some of their amps.
Quote from: Vivek on October 30, 2020, 09:59:59 AM
EBK, it would be a good idea to estimate the peak signal value at various stages in the circuit
Still looking for my notes. I'll post whatever I find.
Quote from: EBK on October 30, 2020, 10:36:55 AM
https://www.researchgate.net/publication/290534843_Triode_emulator_-_Part_2
Thanks !!!
Takeaway 1 re charge buildup on coupling cap : "For guitar amplifiers the charge time constant is about 2-10 ms, and discharge time constant is ten-twenty times larger. "
But the circuits I analysed seem to have charge time constant in the order of 80 ms !!!!
Takeaway 2 : The graphs presented are different in shape than the ROG circuit, the Peavey patent and the Levin design
All above have bigger output signal at beginning and then smaller signal
But the paper you posted shows smaller signal first and then bigger amplitude as time goes on. Maybe it is also more distorted initially and less later on.
I always linked "Sag" with "bloom"
Does anyone know how to find waveforms, graphs and measurements of real tube amps exhibiting sag, bloom etc ?
Any PhD thesis available on the internet ?
Or only way is to buy a tube amp and measure yourself ?
Guitar Amplifier Overdrive First Edition by Ulrich Neumann (Author), Malcolm Irving (Author)
https://www.amazon.com/Guitar-Amplifier-Overdrive-Ulrich-Neumann/dp/132959665X/
Thank you, sir Paul!
https://books.google.ae/books/about/Guitar_Amplifier_Overdrive.html?id=41gdCwAAQBAJ&printsec=frontcover&source=kp_read_button&redir_esc=y
Richard Kuehnel's book on the 5F6A Bassman goes into the nitty-gritty on that amp's response to a signal, from quiescent to full power. Even if you're not totally into that particular amp, you'll learn a lot: https://www.amazon.com/Circuit-Analysis-Legendary-Tube-Amplifier/dp/0976982250
if you swap the orientation of the 2 clipping diodes i think it'll do the sag/bloom thing, start smaller and get bigger as the cap charges?
I did some internet search to try and understand how do people define Sag, Bloom. Swirl
Tube rectifiers have a delayed note response, known as "sag". When you hit a note on the guitar forcefully, the rectifier tube is temporarily overloaded, which reduces the volume of the attack slightly. As the tube recovers from the overload, the note will get louder. This phenomenon is known as "bloom". Amps with tube rectifiers are described as "smooth", "spongy", and "forgiving".
--http://www.hammersmith.rocks/pro-tips/2016/8/9/tube-amp-basics
I prefer "Swirl" which implies a shifting emphasis of harmonics as the note sustains and then decays. Is that what you mean?
-- https://www.thegearpage.net/board/index.php?threads/describe-amp-bloom.369114/#post-3844831
If all a cap can do is build up charge when the signal is on, and discharge when the signal is off,
Then it cannot do sag and bloom at the same time.
But yes, the circuits i posted of ROG THUNDERBIRD, Levin, Crate, Patent will create Swirl = different harmonic content based on time and past signal history (DC shift on integrating capacitor)
However there is a way to create swirl based on instantaneous signal amplitude by designing correct transfer function. Here the swirl depends upon current signal value and does not consider past signal history.
Quote from: Steben on October 30, 2020, 01:43:20 PM
I always linked "Sag" with "bloom"
" So the sag thingy, in reality, happens when the power amp transformer drops the voltage for a fraction of a second, it's a behavior that in this situation the signal sounds compressed.
The waveform starts with the full dB range of the initial signal and then it is choked out. The short squeeze and jump after happening for milliseconds, making the notes to "bloom" – all of this happens after a hard picking attack and a voltage spike on the input stage produced by the guitar signal."
-- https://www.kuassa.com/caliburn-and-matchlock-guitar-amp-engine-deconstructed-sag-and-bias/
(https://www.kuassa.com/wp-content/uploads/2019/12/Picture2.png)
> how do people define Sag, Bloom. Swirl
They don't, they just run off at the mouth. Most people can't dance about sound any better than they can sing about architecture. Partly language, but that is because most people do not hear analytically, even musicians.
Quote from: PRR on November 01, 2020, 03:07:02 PM
> how do people define Sag, Bloom. Swirl
They don't, they just run off at the mouth. Most people can't dance about sound any better than they can sing about architecture. Partly language, but that is because most people do not hear analytically, even musicians.
Very true.
A part of the "sag and spongy" thing is interaction between player and amp response, more than recorded sound.
Explain octave, they will listen, explain distortion vs clean, they will listen
Explain sag and bloom to non-guitarists and they will go like "yeah whatever"
lemme get this straight... you can get this "sag" and "bloom" characteristics of tube amps with a compressor with (probably) a short release that the volume would just "jump" right up?
Or am I missing something?
Quote(https://www.kuassa.com/wp-content/uploads/2019/12/Picture2.png)
Note that this image displays what happens to AC waveform
of power supply and not what happens to signal as a consequence.
From signal's perspective you notice "sag" as dynamic decrease of clipping threshold as supply voltage drops down and reduces headroom of signal swing before clipping. Time constants of sag are largely defined by RC filter of power supply series resistance and filtering capacitance. "Attack" time is often slo100 (as filtering capacitors decharge during loading) and recovery time very fast (as filter cap charges when loading stops).
RC filters of preamps and power tube screens are such that sag is very rare occurence unless loading is extremely sustained. (Not typical with usual guitar input, which is not continuously high amplitude).
Do note that mechanisms and effects of sag are quite different to mechanisms and effects of DC bias shifting via charge of interstage coupling capacitors.
Quote from: 11-90-an on November 02, 2020, 06:15:46 AM
lemme get this straight... you can get this "sag" and "bloom" characteristics of tube amps with a compressor with (probably) a short release that the volume would just "jump" right up?
Or am I missing something?
I would think :
Tube amp reduces volume and changes clipping characteristic due to sag. As power supply changes, the bias operating point changes and the headroom changes, leading to changes in volume and also clipping characteristics and created harmonics.
Compressor will normally only play around with envelope and volume. It should not change the harmonics. (Unless the compressor time constants are so fast that it acts as a clipper)
Hence a compressor cannot fully emulate sag.
And then there is cathode bias shift as well .... :icon_mrgreen: