Sparked by the recent discussions of how the TS Tone Control REALLY works, and all the simplified explanations of it, I decided to model the circuit in 5Spice to try to shed some light on the function of specific components, specifically the RC filters throughout the circuit.
Here's the basic TS circuit, minus input buffers, with a few adjustments to the input output bias resisters so as not to add unwanted filtering. I used an LT1498 Model because I didn't have a 4558, and for this study we weren't focusing on that.
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/TubeScreamer.jpg)
PART I - Gain Response
First off, you can see 3 test points:
TPv1 - (RED) - Output of Clipping Amp
TPv2 - (GREEN) - Circuit Output (Volume Pot is always at Full)
TPv3 - (BLUE) - Signal after R6/C5 Low-Pass but Before Tone Control Amp.
Lets look at all three Points for Various Gain Settings, using a LINEAR Pot. Tone Pot is set at Noon, remember this is without Output Attenuation.
First, Minimum Gain. Full Treble content coming from the Clipping Amp. Nice Mid-Hump Post R6/C5. No Effect from Tone Circuit.
I think its most apparent here that the C4/R5 Frequency Cut-Off (720Hz) limits the gain to frequency OVER 720 in the clipping amp.
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/MinimumGain.jpg)
50% Gain. Less High Frequency Response from the Clipping Amp. 20dB Louder than Minimum Gain. Same Mid-Hump Post R6/C5. No Effect from Tone Circuit
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/50Gain.jpg)
Maximum Gain. Even Less High Frequency Response from the Clipping Amp. Additional 5dB louder than 50% Gain. Same Mid-Hump Post R6/C5. No Effect from Tone Circuit. So it looks as if we are seeing the effect of the 51pF Cap across the Gain Control of the Clipping Amp. I'm not going to make an attempt to explain it entirely, but I believe it is common knowledge that increasing that value of cap to 100pF or 220pF will roll-off even more highs and "soften" the distortion, but the effect is seen most at high gain settings. Again, I have not gone into details regarding the specific RC Filter/Feedback loop response.
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/100Gain-MidHump.jpg)
PART II - Tone Control
Next I will fix the Gain setting at 50%, and adjust the Tone Control Pot. The 4 curves are evenly space settings on the Tone Control Pot, 0, 1/3rd, 2/3rds and Full. As ycan see the sweep of the Pot does not have a steady affect on the frequency response. I believe this is why people have used the radical S or W taper Pots as mods instead of Linear Pots. The effect of the tone control is bunched up at the extremes on a Linear pot, whereas a W Taper allows a more rapid change of resistance near the center, and so the effect seems to have a smoother sweep. Just a theory, I don't know exactly what the W or S Taper actually does, but I have one in my TS and it works much better! Its also evident here that the Tone Control shifts the mid hump higher in its upper settings.
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/Output-ToneSweep.jpg)
PART III - Changing Values in the Tone Section
The Dubious 220 ohm resistor (R9). In some earlier simulations I did, we discovered that a resister in this configuration (Low Pass Filter) creates a High Shelf in the frequency response. This shelf levels off the 6dB/Octave created by the original R/C network, at a frequency that appears to be given by 1/(R9*C). Anyway, in this configuration its a bit more complicated, and I'm not prepared to explain it in words at the moment. BUT, I simulated the effect of shorting R9 and how it effect the Frequency Response.
First off, Tone set to 50%. R9 Does NOTHING! I believe this is because the Tone control actually has no effect at all in this setting. If we refer back to PART I, we'll see that there were no significant differences between the signal before and after the Tone Control Amp. Thus, I did not create a graph for this. What I did do is simulate the effect of shorting R9 at Minimum and Maximum Tone Settings.
1. Minimum Tone Setting (Darker Tone from TS, same as lowest curve from PART II)
Here we are seeing a slight DECREASE in Treble Content when R9 is shorted.
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/ToneMinimum-Effectof220.jpg)
B. Maximum Tone Setting (Brighter, Highest cuver from PART II).
Here the effect is most prominent. With R9 shorted, we lose a lot of upper harmonic content out of the TS Tone Control. This is the setting where the RC Filter is applied to the feedback of the Op Amp. Filtering the feedback would increase the amount of treble content in the output. Thus, a treble shelf in the feedback filtering would limit the highest treble increase, controlling the highest harmonics (usually considered harsh). Also notice that the frequency response begins to deviate significantly around 3kHz or so (3.2kHz being the 1/RC value of R9 and C6).
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/ToneMaximum-Effectof220.jpg)
CONCLUSIONS
Its been said that to make a good distortion box, you need to control the EQ/Harmonics between and after gain stages. Here's a good example of what that means in a classic box. Personally I had no idea the Mid Hump was so apparent, but remember, these simulations are done with a flat frequency source, whereas an actually guitar has a lot more amplitude in the mids and lows.
From this data I believe we can conclude that the Mid Hump is induced as a combination of the C4/R5 (720Hz) cut-off in the Clipping Amp Gain, and the R6/C5 Low Pass Filter immediately following the clipping stage (cut-off also ~720Hz).
Honestly, this was just me looking for an excuse to try out a new tool. I hope you find this info useful as I did.
Very cool! Thanks for the post!
Aron
One thing I'd like to add. If the output seems abnormally large in scale (dB), its because I'm using a 1 Volt input signal. Using 100mV does not change the curves, only the overall level. For the purpose of this frequency study, the scale should be considered relative.
Does this info yield possible new mods to reduce mid hump? :)
Good work, thanks!
Quote from: grolschie on April 16, 2009, 08:27:25 PM
Does this info yield possible new mods to reduce mid hump? :)
Jumper the 220 ohm resistor to ground and the mid hump is gone when the tone control is maxed. You still lose some bass in the gain stage, but the whole tone control section goes almost perfectly FLAT. Try it! Unfortunately a tubescreamer without the mid-hump sounds pretty harsh in the highs. I still think it's a useful mod though, so I put it on a switch in my build.
That discovery is what led me to start this thread (http://www.diystompboxes.com/smfforum/index.php?topic=75576.0) where I calimed that the GeoFX article on the Tubescreamer must be wrong. The arguments on that thread were what led to Aziltz conduct his spice analysis which cleared everything up, and I thank him for that. Apparently nobody was following my original post, which is okay, because most of it is just a lot of pointless arguing and mis-communications. I was wrong about some of my initial assumptions anyway, which were just my noob explanations for what I was seeing on frequency plots that directly contradicted what I was reading. If anyone is more curious about the details, I would suggest just skipping to the 3rd page of that thread.
Anyway, carry on...
Since I never got around to posting these in the other thread, I figure I'll put them up here...
Here is a triangle wave swept over the widest frequency spectrum possible within the parameters of the synthesizer I was using as a tone generator. It represents a flat frequency response for reference:
(http://img511.imageshack.us/img511/9234/flat.jpg)
Here is the isolated tone section of the tube screamer circuit with the tone knob at max:
(http://img4.imageshack.us/img4/5642/tstonemax.jpg)
Now, here is the isolated TS tone stack at max again. The only difference this time is that the ***220ohm resistor is jumpered***:
(http://img58.imageshack.us/img58/8831/tstone220removed.jpg)
Notice that the entire tone section goes completely flat! In listening tests, it sounds very similar to a bypass of the tone section entirely. The 1k/.22uf RC filter combination in the feedback loop acts as a boost that just mirrors the cut made by the first 1K/.22uf RC filter, effectively leveling the signal. What the 220ohm resistor does is put a shelf in this boost above 3.2kHz, causing frequencies above 3.2 kHz not to be brought back up to unity from the earlier cut. So, in the end the 220 ohm resistor acts as a high frequency cut to the overall signal above 3.2kHz. This is opposite of what is claimed in the GeoFX "Technology of the Tube Screamer" article.
Just for the heck of it, here is the frequency response of the isolated gain section with the gain knob at it's lowest setting:
(http://img245.imageshack.us/img245/4024/tstotalresponsegainat0t.jpg)
And here is frequency response of the gain section at full combined with the tone section at max:
(http://img17.imageshack.us/img17/1697/tstotalresponsegainat0.jpg)
This is basically the same frequency response you should get with a stock pedal at those settings, since the rest of the circuit does little to effect the frequency response.
---
These plots are from real world analysis done with the circuit isolated between two buffers on a breadboard. A software synthesizer was used as a tone generator. I had plans to do more, but ran out of time as other priorities in my life came to my attention. I hope these are of use to someone.
Quote from: Projectile on April 17, 2009, 05:39:19 AM
Quote from: grolschie on April 16, 2009, 08:27:25 PM
Does this info yield possible new mods to reduce mid hump? :)
Jumper the 220 ohm resistor to ground and the mid hump is gone when the tone control is maxed. You still lose some bass in the gain stage, but the whole tone control section goes almost perfectly FLAT. Try it! Unfortunately a tubescreamer without the mid-hump sounds pretty harsh in the highs. I still think it's a useful mod though, so I put it on a switch in my build.
That discovery is what led me to start this thread (http://www.diystompboxes.com/smfforum/index.php?topic=75576.0) where I calimed that the GeoFX article on the Tubescreamer must be wrong. The arguments on that thread were what led to Aziltz conduct his spice analysis which cleared everything up, and I thank him for that. Apparently nobody was following my original post, which is okay, because most of it is just a lot of pointless arguing and mis-communications. I was wrong about some of my initial assumptions anyway, which were just my noob explanations for what I was seeing on frequency plots that directly contradicted what I was reading. If anyone is more curious about the details, I would suggest just skipping to the 3rd page of that thread.
Anyway, carry on...
So one could jumper the 200ohm resistor, max the tone knob, and then tack on a rat-type filter just before the output? Or maybe a runoffgroove type series of filters to roll off the harsh highs? Or does this get us back to a mid hump?
That's pretty cool. The only thing I'd say about jumpering the 220R resistor is that in the simulator doing that creates a nasty looking resonant peak at about 100KHz, I don't know what if anything this will do in the real world. If you replace the 220R with 50R then this disappears and you still get a flat response up to about 10KHz or so, making it smaller gets you a flat response up to above audio, but you probably don't need more than 10KHz. I can't hear much higher than that to start with and by the time it's gone through a guitar amp and speakers there won't be much left above that.
Quote from: slacker on April 17, 2009, 06:53:01 AM
That's pretty cool. The only thing I'd say about jumpering the 220R resistor is that in the simulator doing that creates a nasty looking resonant peak at about 100KHz, I don't know what if anything this will do in the real world.
That's strange, I haven't noticed anything like that in actual practice. I can't account for what would be causing that peak in the simulation, but it doesn't appear to happen in the real world.
I might not happen in the real world with real opamps, but generally peaks like that are bad because they can cause oscillation.
QuoteSo one could jumper the 200ohm resistor, max the tone knob, and then tack on a rat-type filter just before the output? Or maybe a runoffgroove type series of filters to roll off the harsh highs? Or does this get us back to a mid hump?
If you're going to go as far as to add a whole filter, it would be simpler to just take out the whole TS tone stack and replace it with a rat-filter, for instance.. jumpering the 220 ohm resistor could be considered as a quick and dirty mod.
That's pretty awesome to see the actual frequency response all done out like that.
I've always been one of the guys that has never liked the TS at all... I like some pedals built off of the circuit, but the sound has always been to muddy for my playing.
Now I see the big hump I can definitely see why. For some reason that frequency range while mixing bugs the crap out of me too =) (like 300-450hz)
nice work :icon_biggrin:
dave
I'm not sure the 220 (R9) on its own is the best solution for getting rid of the mid-hump. Yes, I agree that shorting it causes a "Flat" response, even in the simulations, but only above 720Hz, and only at the brightest Tone setting. Shorting 220 actually makes Treble DECREASE in the Darker Tone Setting. I think its real purpose is to shape the highest harmonics, but remember I did not show the graph of the effect of 220 with Tone at 50% because it had no effect at all, mid hump still present. Although I think its a great place to tweak to get different curves out of the tone control, we can definitely do more.
i think another way to work on the mid-hump would be to play with the R5/C4 and possibly R6/5 Values. I think by increasing C4, the lower cut off on the gain of the clipping amp would be lowered and the effect would be to broaden/flatten the mid focus. I believe this is where many tweakers put their mid/full switches (i've seen it on BYOC as well). I don't think i've seen many switchable options on C4 though, which might be an interesting place to start. By lowering C4, the cut-off of that RC Low Pass would move higher.
It seems to me that both of those points being centered around 720Hz causes the mid-focus there.
I went ahead to simulate this. Now that I've got the circuit built it takes 2s to explore ideas like this.
Here's what happens when you increase C4. Stock, 2x and 3x. (Same values as the BYOC Mods). It seems to pull the mid hump down a bit, into the 400Hz range.
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/MidHump-C4.jpg)
Changing C5 (Decreasing) I chose Stock (.22uF), .16uF and .1uF. It looks like the mid hump is pulled up, over 1kHz.
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/MidHump-C5.jpg)
Here's both at the same time, raising C4 and lowering C5 TOGETHER. This looks a lot more broad, while still centered in the 6-700Hz "Mids", with a lot more output. Keeping things relative, a quick comparison would be to look at what point the amplitude drops 5dBs from the peak. In the stock setting, that happens a lot sooner than in the "Maximum" test values setting.
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/MidHump-C4andC5.jpg)
I don't think we're gonna get anything near a FLAT response out of this puppy, and I suppose that is ok because the guitar is a mids-instrument. I would like to suggest that the idea of mid-hump is the relatively sharp hump in the stock settings, and simply broadening that will reduce the effect on our ears.
Does anyone have any suggestions for how to create a signal source that models the frequency content of a guitar? That might give us a better real world picture out of something like this.
Just my $.02, I put a trimmer in parallel with the 220Ω resistor in my TS-7, drilled a hole to make it externally adjustable, and found that shorting the 220Ω did "practically nothing" except in the very brightest setting of the tone control. In that setting, it makes a very harsh treble boost. I'd agree that something like 50Ω is probably a good value if you want a bit more brightness at max treble without things getting too crazy.
Nobody here is interested in phase response? :P
Quote from: Cliff Schecht on April 17, 2009, 01:09:27 PM
Nobody here is interested in phase response? :P
I wouldn't say nobody! but phase can take a while to explain if you haven't had a basic AC electronics intro... whereas I think even the newest of newbs can understand the amplitude no problem. But check one box when you run these simulations and you can get the phase response as well, as I'm sure someone like you knows. Something i'll do when I make this into a article/website.
People don't see the immediate purpose of phase plots and tend to ignore them completely. At least from what I've seen, a lot of people really don't know how to interpret phase - especially when it comes to guitar type effects that are looking for distortion and not specific phasing sounds. Filters aren't hard to understand in terms of amplitude vs frequency response - that I completely agree with - but they can get a bit more fishy when you start looking as phase plots, group delay (negative derivative of phase), linear and nonlinear filters, etc.. The tonestack of a tube screamer is a good example of a nonlinear filter, essentially meaning that the filter sections can't be rearranged in any way without altering the response (it doesn't obey the principle of superposition).
It's always easier to apply this stuff to synth style circuits, because the waveforms typically used are so much less harmonically complex (e.g. square, triangle, ramp, sine) and the effects of phasing can be easily seen. The best example of phasing is running a square wave through a filter with a bad phase response (Butterworth, Chebyshev, Elliptical). You can watch the harmonics of the square wave literally shifting in time (phasing can be equated to a time delay at a specific frequency). You slowly start to see the third harmonic, fifth harmonic, etc start to appear as you raise the cutoff of the filter - this is what causes ringing. It not only looks cool on a scope, but it sounds fantastic!
I'm one of those who tend to ignore the phase plots. But seriously, what does it matter? I thought the human ear can't hear a difference in phase anyway. I get it that phase differences can be used to advantage in phasers, etc. but in a distortion circuit such as this one, is there a difference anywhere else than the screen of the scope?
Quote from: earthtonesaudio on April 17, 2009, 09:37:18 AM
Just my $.02, I put a trimmer in parallel with the 220Ω resistor in my TS-7, drilled a hole to make it externally adjustable, and found that shorting the 220Ω did "practically nothing" except in the very brightest setting of the tone control. In that setting, it makes a very harsh treble boost. I'd agree that something like 50Ω is probably a good value if you want a bit more brightness at max treble without things getting too crazy.
Yup, like I said "The tube screamer without the mid-hump sounds pretty harsh in the highs". It's not for everyone, but it IS technically flat above 720Hz when the knob is maxed, and even lower if you combine it with the fat bass mod. Once you start rolling the tone knob back the highs start getting cut again and you bring the mid-hump back. If you want a "scooped" sound when the knob is near max, then you could lower the value of the cap on the wiper. This would shift the frequency response of the feedback network up in frequency, so it doesn't start compensating for the 720Hz roll off until higher in the spectrum. I haven't actually tried it, but this should produce a dip in the mid range between 720Hz and 3.2KHz. If you are going to try this, I would also suggest doing the bass mod, or else it is just going to sound mostly like a treble boost, since most of the bass is already lost in the clipping stage. You could also play with different values for the 220 ohm resistor to determine at what frequency the high rolloff starts.
Another interesting idea would be to replace both the 220 ohm resistor and the 1K resistor after the clipping stage with trim pots, 500ohm and 5K respectively. Then you would have control over both the rolloff points of the initial 720hz rolloff, as well as the 3.2kHz high sculpting. Unfortunately you cannot also change the frequency where the feedback network boost starts without swapping out the cap, because if you change the value of the 1K resistor in the feedback network, you change the gain of that stage significantly.
Overall, I don't think the TS tone stack is a very good design. I don't know anybody who actually uses the tone knob below the first 1/4 or maybe 1/3 turn from the top of it's rotation. It's fun to discuss what happens when you turn the knob down that far, but in reality the whole bottom two thirds of the knob's range is wasted, which seems pretty pointless. The problem is that once you start messing with it, you'll find that, for that particular style of tone stack, the values that were originally chosen actually sound pretty good. If you want to have a more useful tone stack it really requires a pretty drastic re-design, which is what is discussed in the AMZ article.
You could always increase the bass after the distortion like in the Bad Monkey - that sounds much better to me than the usual bass response mod which sounds fartier.
http://www.greene-pedals.com/GEAD/newtech.html
Quote from: johngreene on April 17, 2009, 08:44:07 PM
http://www.greene-pedals.com/GEAD/newtech.html
"The third plot shows what happens to the frequency response when a 100 ohm resistor is added in series to the first .22uF capacitor (after the 1K). This results in leveling off the midrange bump somewhat and allows more variance with adjustment of the tone control. It gives it a somewhat more full sound and less harsh."Interesting. Thanks for the link.
The thing that most bugs me about the post-clipping EQ in the TS is that it really seems like overkill. A passive high-cut followed by a buffer could replace maybe a dozen parts and still work basically the same.
Quote from: grolschie on April 17, 2009, 08:59:57 PM
Quote from: johngreene on April 17, 2009, 08:44:07 PM
http://www.greene-pedals.com/GEAD/newtech.html
"The third plot shows what happens to the frequency response when a 100 ohm resistor is added in series to the first .22uF capacitor (after the 1K). This results in leveling off the midrange bump somewhat and allows more variance with adjustment of the tone control. It gives it a somewhat more full sound and less harsh."
Interesting. Thanks for the link.
I put that page up in 1997. :icon_wink:
Quote from: earthtonesaudio on April 17, 2009, 10:31:06 PM
The thing that most bugs me about the post-clipping EQ in the TS is that it really seems like overkill. A passive high-cut followed by a buffer could replace maybe a dozen parts and still work basically the same.
I think it is pretty elegant. The passive high cut rolls off the harsh overtones at just the right spot. Then the buffer with the tone control goes from additional cut to boost. The TS808 had several designs before it with different EQs. So it wasn't exactly the first try...
Quote from: MohiZ on April 17, 2009, 05:12:55 PM
I'm one of those who tend to ignore the phase plots. But seriously, what does it matter? I thought the human ear can't hear a difference in phase anyway. I get it that phase differences can be used to advantage in phasers, etc. but in a distortion circuit such as this one, is there a difference anywhere else than the screen of the scope?
The human ear CAN hear the difference from phasing, even in distortion circuits. It causes all kinds of problems like smeared bass, nasally sound, ringing, even oscillation! Look up Barkhausen Stability Criterion, understanding it can help you understand why your distortion is self-oscillating. In a fuzz circuit, phase misalignment can cause those nice square waves to become ringy, although this typically isn't a problem with passive filters. With active filters, you sometimes get humps in the group delay that can reveal problems as well. For example, with a Butterworth filter type, you have a slight hump in the bass frequencies - this means that your high frequencies are going to get delayed more than your low frequencies are going to get delayed more than your high frequencies. In terms of audio, this means that your bass will get delayed enough to be not only audible, but highly annoying!
It still would be cool to take a look at the phase plots for the filter section, but I don't feel like simulating it :).
Quote from: Cliff Schecht on April 18, 2009, 12:04:37 AM
Quote from: MohiZ on April 17, 2009, 05:12:55 PM
I'm one of those who tend to ignore the phase plots. But seriously, what does it matter? I thought the human ear can't hear a difference in phase anyway. I get it that phase differences can be used to advantage in phasers, etc. but in a distortion circuit such as this one, is there a difference anywhere else than the screen of the scope?
The human ear CAN hear the difference from phasing, even in distortion circuits. It causes all kinds of problems like smeared bass, nasally sound, ringing, even oscillation! Look up Barkhausen Stability Criterion, understanding it can help you understand why your distortion is self-oscillating. In a fuzz circuit, phase misalignment can cause those nice square waves to become ringy, although this typically isn't a problem with passive filters. With active filters, you sometimes get humps in the group delay that can reveal problems as well. For example, with a Butterworth filter type, you have a slight hump in the bass frequencies - this means that your high frequencies are going to get delayed more than your low frequencies are going to get delayed more than your high frequencies. In terms of audio, this means that your bass will get delayed enough to be not only audible, but highly annoying!
It still would be cool to take a look at the phase plots for the filter section, but I don't feel like simulating it :).
Phase has more meaning/effect if it is referenced to something. The phasing of the harmonics is more meaningful if you run the waveform through a phaseshift network that doesn't attenuate. A filter, on the other hand, attenuates the harmonics significantly therefore significantly reducing the effect their phase will have on the resulting waveform. Also, the phase change through a tone control circuit is static, therefore you never really notice what it is doing. It all gets lumped into the 'character' of the various ways of implementing tone controls.
This is a pretty interesting read:
http://silvertone.princeton.edu/~john/monauralphaseexperiments.htm
--john
Quote from: Cliff Schecht on April 18, 2009, 12:04:37 AM
Look up Barkhausen Stability Criterion, understanding it can help you understand why your distortion is self-oscillating.
http://web.mit.edu/klund/www/weblatex/node4.html
hmmmm. Someone from MIT seems to think there's a problem with good ol' mister Barkhausen. :icon_wink:
Quote from: johngreene on April 18, 2009, 12:00:06 AM
Quote from: earthtonesaudio on April 17, 2009, 10:31:06 PM
The thing that most bugs me about the post-clipping EQ in the TS is that it really seems like overkill. A passive high-cut followed by a buffer could replace maybe a dozen parts and still work basically the same.
I think it is pretty elegant. The passive high cut rolls off the harsh overtones at just the right spot. Then the buffer with the tone control goes from additional cut to boost. The TS808 had several designs before it with different EQs. So it wasn't exactly the first try...
There is no boost. When the tone control is maxed the opamp stage merely counteracts the cut that was made by the earlier passive high cut. The tone knob just goes from mild treble cut to extreme roll off. I have to agree with earthtonesaudio that it seems rather overkill. I don't know anyone who uses the tone knob on any setting less than about 60%. It's a waste. For what it is though, I'll agree that it's tuned rather well. I wasn't happy with any of the other cap combinations I tried, but I'm still tempted to scrap the whole tone control circuit and try something different.
Quote from: johngreene on April 18, 2009, 12:24:45 AM
Quote from: Cliff Schecht on April 18, 2009, 12:04:37 AM
Quote from: MohiZ on April 17, 2009, 05:12:55 PM
I'm one of those who tend to ignore the phase plots. But seriously, what does it matter? I thought the human ear can't hear a difference in phase anyway. I get it that phase differences can be used to advantage in phasers, etc. but in a distortion circuit such as this one, is there a difference anywhere else than the screen of the scope?
The human ear CAN hear the difference from phasing, even in distortion circuits. It causes all kinds of problems like smeared bass, nasally sound, ringing, even oscillation! Look up Barkhausen Stability Criterion, understanding it can help you understand why your distortion is self-oscillating. In a fuzz circuit, phase misalignment can cause those nice square waves to become ringy, although this typically isn't a problem with passive filters. With active filters, you sometimes get humps in the group delay that can reveal problems as well. For example, with a Butterworth filter type, you have a slight hump in the bass frequencies - this means that your high frequencies are going to get delayed more than your low frequencies are going to get delayed more than your high frequencies. In terms of audio, this means that your bass will get delayed enough to be not only audible, but highly annoying!
It still would be cool to take a look at the phase plots for the filter section, but I don't feel like simulating it :).
Phase has more meaning/effect if it is referenced to something. The phasing of the harmonics is more meaningful if you run the waveform through a phaseshift network that doesn't attenuate. A filter, on the other hand, attenuates the harmonics significantly therefore significantly reducing the effect their phase will have on the resulting waveform. Also, the phase change through a tone control circuit is static, therefore you never really notice what it is doing. It all gets lumped into the 'character' of the various ways of implementing tone controls.
This is a pretty interesting read:
http://silvertone.princeton.edu/~john/monauralphaseexperiments.htm
--john
Very interesting read! I was actually looking for an article about that exact thing - I've run experiments myself in the lab and have noticed the same effects on timbre from phasing. A great example of phasing is running two out of phase square waves at very close frequencies. The effect you hear is the harmonics going in and out of phase and it really adds a lot to the sound. I guess the point I was trying to make earlier is that phase has a big effect in certain places. I agree that a typical tonestack (nth order passive RC filters) isn't going to have much of a noticeable effect too, my example was specifically for active filters. We really don't see a lot of active filters in guitar distortions, but phase distortion can sound cool too! Best example I can think of is a fuzz type effect (think square waves) with a nearly self-resonant filter, that would sound gnarly!
Quote from: Projectile on April 18, 2009, 01:24:16 AM
[
There is no boost. When the tone control is maxed the opamp stage merely counteracts the cut that was made by the earlier passive high cut. The tone knob just goes from mild treble cut to extreme roll off. I have to agree with earthtonesaudio that it seems rather overkill. I don't know anyone who uses the tone knob on any setting less than about 60%. It's a waste. For what it is though, I'll agree that it's tuned rather well. I wasn't happy with any of the other cap combinations I tried, but I'm still tempted to scrap the whole tone control circuit and try something different.
i really think it depends on your view of the function of the tone knob. some people view/hear 12 Noon as the "Voice" of the pedal, in which case, the Tone Knob can Boost Highs or Cut more. Some view Full as Zero Cut. It all depends on the view/ear of the user and not so much as the other factors as long as you don't care to see how the design was intended to work.
IMHO, seeing as full noon can be quite harsh, I think the pedal had an intended voice some where between 40% and 60%. For the record, I can use a TS with low tone settings for smooth lead tones with single coils. Not unusable, just not-optimal IMO.
I can HIGHLY suggest trying a W-Taper 20K replacement. It events out the sweep much better than stock. I just did this mod in my Route 66/TS9 Clone and it is miles above the regular tone control.
Quote from: Projectile on April 18, 2009, 01:24:16 AM
Quote from: johngreene on April 18, 2009, 12:00:06 AM
Quote from: earthtonesaudio on April 17, 2009, 10:31:06 PM
The thing that most bugs me about the post-clipping EQ in the TS is that it really seems like overkill. A passive high-cut followed by a buffer could replace maybe a dozen parts and still work basically the same.
I think it is pretty elegant. The passive high cut rolls off the harsh overtones at just the right spot. Then the buffer with the tone control goes from additional cut to boost. The TS808 had several designs before it with different EQs. So it wasn't exactly the first try...
There is no boost. When the tone control is maxed the opamp stage merely counteracts the cut that was made by the earlier passive high cut. The tone knob just goes from mild treble cut to extreme roll off. I have to agree with earthtonesaudio that it seems rather overkill. I don't know anyone who uses the tone knob on any setting less than about 60%. It's a waste. For what it is though, I'll agree that it's tuned rather well. I wasn't happy with any of the other cap combinations I tried, but I'm still tempted to scrap the whole tone control circuit and try something different.
I was talking about the tone control circuit -after- the cut. It definitely has boost. Although the entire circuit together actually does provide some boost, but it is mostly in the mid range (because of the passive cut).
Thats really useful.
Thing I notice with spice is that it ignores the efects of clipping (by measureing the output amplitude of the input frequency), which as we know adds lots of high end. It confused me for a while when i was studing the TS schematic, thinking why does it cut so much of the highs, forgetting that the clipping will have added alot of harmonic content that needs to be tamed. I think perhaps the designers were making the tone knob cut so much because if it recived a very high input level and the gain was set high, you would need extra cut to remove some of the highs.
Quote from: owenjames on April 18, 2009, 12:18:46 PM
Thats really useful.
Thing I notice with spice is that it ignores the efects of clipping (by measureing the output amplitude of the input frequency), which as we know adds lots of high end. It confused me for a while when i was studing the TS schematic, thinking why does it cut so much of the highs, forgetting that the clipping will have added alot of harmonic content that needs to be tamed. I think perhaps the designers were making the tone knob cut so much because if it recived a very high input level and the gain was set high, you would need extra cut to remove some of the highs.
i noticed that too, but its important to leave the diodes in the simulations because they also limit level.
Quote from: Projectile on April 17, 2009, 05:39:19 AM
...
That discovery is what led me to start this thread (http://www.diystompboxes.com/smfforum/index.php?topic=75576.0) where I calimed that the GeoFX article on the Tubescreamer must be wrong. The arguments on that thread were what led to Aziltz conduct his spice analysis which cleared everything up, and I thank him for that. Apparently nobody was following my original post, which is okay, because most of it is just a lot of pointless arguing and mis-communications. I was wrong about some of my initial assumptions anyway, which were just my noob explanations for what I was seeing on frequency plots that directly contradicted what I was reading. If anyone is more curious about the details, I would suggest just skipping to the 3rd page of that thread.
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Actually that thread was exactly what I was looking for. I posted to the end of it a similar paradox (in my mind) and wonder if you or anyone would like to help clear that up as well?
Hi
my 2c regarding phase....
One could argue about humans hearing or not hearing phase, but I know that if a pedal with gain doesn't shift phase, or shifts 180 degrees, you can get mountains of feedback (expecially with simple old valve amps). e.g. the Fuzzface with its 2 simple inverting stages. Feedback is often quite audible ( :icon_wink:).
Of course, depending on what you want to achieve, stacks of feedback can be a good or bad thing. Jimi did very well with it.
cheers
Quote from: aziltz on April 17, 2009, 09:28:26 AM
Here's what happens when you increase C4. Stock, 2x and 3x. (Same values as the BYOC Mods). It seems to pull the mid hump down a bit, into the 400Hz range.
(http://i132.photobucket.com/albums/q18/aziltz/Tube%20Screamer%20TS9%20Simulation/MidHump-C4.jpg)
Bump for a good thread. Azilitz, thank you for confirming what I'm hearing. I got two TS builds but one with the .1 cap instead of the .047 was louder. Now with the graphs you posted, I see why along with less mid-hump, it's also louder. Just saved me the trouble of tinkering with the 'stock' build (I built the modded TS first), second-guessing myself if I put it together right. ;)
I'm glad it was helpful!
Also, for someone using the TS to boost, IMO you want the sharp mid-hump to cut into a mix. Seeing how the controls vary the freqs, I think the charts give a good idea of how to move that hump around when other instruments occupy the same sonic space. But I bet those who use the TS to full effect already know. ;D It starts with the tone control, then with the gain knob to compensate for the dB's gained or lost. For that, I think the tubescreamer is a really nice design, even with stock components. :)
I really like this thread thanks to the OP for all the work and documentation :icon_cool:
Gave me some better idea of what mods I want to try,ect
FWIW my TS clone has the W taper tone control,which I like better than an A or B taper.
Still I use it with the tone maxed and the gain maxed,and it has a 1M gain pot in place of 500K
While I like the tone control for taming the highs on single coils(like previously mentioned),with HBs it stays on max rotation.
I often wonder if it would be better with another tonecontrol,or even a TMB but then it wouldnt really be a TS anymore.
*Necro-bump*
Finding this thread a couple months ago gave me something to do with my dusty old TS-5. As predicted, replacing C4 with 0.15uF and C5 with 0.1uF worked to extend the frequency response in both directions, making the pedal sound a little more natural/neutral. Replacing the 51k resistor (R3) with a 33k reduced the extra gain from that mod. (I do like being able to achieve a clean tone at the bottom end of the gain control on overdrives.)
One thing I really dig about my Blackstone is that I don't need to turn down a tone control at higher gain settings to keep the treble in check. The Tube Screamer's 51pF feedback cap (C3, 47pF in my pedal) is too small to do much except quell oscillation, so it strikes me as a wasted opportunity to do that sort of thing. I bumped mine up to 150pF, and it's nearly perfect at allowing clear low-gain sounds and smooth high-gain sounds. It became a goal to be able to leave the tone control at noon, but 1 o'clock still sounded best. So I replaced R6 with 900Ω to extend the high-end corner frequency a tiny bit more, and now that goal is achieved.
So thank you @aziltz, wherever you are. It was a fun sequence of mods, and I actually like this pedal a lot more now. :icon_cool:
(http://i.imgur.com/p3JFtqc.jpg) (https://imgur.com/p3JFtqc)
glad to read that mods worked out well, i always like success stories.
i really want to buy a real Ibanez ts-9 or other version in an original green box which says 'tube screamer', and then mod the circuit to become a Swedish chainsaw. [insert evil laughter]
cheers