Awesome I have heard this called 'Baxandall tone controls' but whatever its name I understand it 100 times better than I did ! best walk through of this filter in the you tubes....cheers.
Yes, I believe that English engineer Peter Baxandall came up with this active tone control circuit back in the 1950s. Very simple and effective, the hallmarks of good design.
If you're asking about the max cut/boost level (currently just beyond +/-20 dB, around 11:30), you control that by the ratio of the pot to the associated feedback resistors (P2, R3, R4). Placing a resistor in parallel with C3 is generally not advisable.
@@ElectronicswithProfessorFiore No, please excuse my ignorance (and I haven't got to this in the text yet), I was wondering how we could make the frequency response curve shallower. That is roll-off to give more of a 'tilt' than a 'turn' over a larger range. So, 5kHz upwards a gentle rise rather than a sharp turn. You may have answered that by our choice in resistors but I was wondering.
@@simonyoungglostog I am not aware of a quick and dirty way to do that (like adding a resistor). The issue is that you're trying to get a slower roll-off than that of a single RC lag/lead network, so you'd need to have multiple networks that slightly cancel (or go to a completely different topology).
@@ElectronicswithProfessorFiore Just to let you know, I opened my lab for the first time and built some of these op amp circuits. All working as you suggest, I could get some good ringing on the triangle to square wave circuits when using small capacitors.
No, that's the TINA-TI simulator. Wrench has a DSP version of these bass and treble controls (with adjustable corner frequencies). It also has fully parametric EQ and graphic EQ. You can do spectral analysis of signals but it won't draw Bode plots like TINA-TI.
Would it be possible/advisable to make a 5 band graphic equalizer by taking 5 circuits as shown @4:13 but modify the capacitor of each one and summing their outputs?
You could, sort of, but if you're referring to a simple summing amplifier with this circuit (i.e., with 5 paths in parallel that lead to the summer), that has problems. Doing that, you can get some boost but you won't get much cut (those frequencies would be passed with unity gain through the other 4 sections). The bass-treble version shown at the end can be expanded with a mid section, and I've even seen 4 band versions, but they get unwieldy with a lot of interaction when you try to make a multi-band graphic EQ. For that, we use a different topology. The basic idea is to make a bunch of bandpass filters and then sum them together (kind of along the lines of what you were thinking).
@@ElectronicswithProfessorFiore Much thanks for the thoughtful reply. I'm in the process of making 7 cut/boost gyrator ckts and have a prototype working in breadboard layout. Lot's of connections and hook-up wire leading to a lot of noise. The ckt you presented looked so simple. I was hopeful it could cut-down the part and connection count. No worries. I shall proceed as planned. You know how it goes... Never pass-up the opportunity to build something that can be purchased at 1/4 the cost 😁
@@ElectronicswithProfessorFiore ... Anxiously awaiting a newly designed 5-band EQ circuit board. The output of each EQ band is summed with an inverted version of the original input. In theory, what's left behind is only a scaled version of the EQ'd signal. The 5 modified EQ bands are summed to create a penultimate output. Finally, the original (unaltered) signal is presented to a cut/boost circuit whose output is fed, along with the penultimate output, to a summing opamp. This gives the ability to fade-in (blend) the EQ'd bands with the original signal. On a simplified 2 band breadboard version (which did not allow adding back any of the original signal) either band could be modified (or completely removed) from the final output as-desired. -This is probably not novel but, it was for me and I had to design and build it. The summing can be done in different ways and in different points in the circuit. I had to try and observe them all. I’ve blown my time and money making something that already exists… -And this is why I call myself a hobbyist.
@@rayc1557 Not entirely clear on what you're doing but be careful with summing these signals. Remember, the outputs of the EQ circuits not only alter the signal amplitudes, they also alter the phase. If you're assuming that the outputs are perfectly 180 degrees out of phase, they won't be (the reactive elements introduce phase shifts). At some cut/boost setting you might be getting 150 degrees or 210 degrees (or whatever) instead of 180. That will mess with your summation. This is one place where simulation can be very handy as the manual calcs can be tedious.
@@ElectronicswithProfessorFiore I pondered that and did an experiment with a fully populated EQ board created a couple weeks ago. (BTW: The corresponding Class A amp and EQ board sound great - Much thanks to your refreshers on transistor circuits). The output of the EQ was simultaneously scoped/displayed alongside the original signal. After adjusting the volume to normalize the RMS levels of the 2 signals, I can identify the modification in amplitudes but, the zero-crossing of landmark signals are spot-on. I'm confused about this because of the very reason you cited. After a week of pencil & paper, I just decided to layout a board and give it a whirl. If it works, I'll send you my schematics. If it doesn't work, I'm out 72 bucks -but I'll learn a lot along the way. FWIW, I'm using a very unique circuit for the bandpass gyrators. I can send you links if you're curious.
Awesome I have heard this called 'Baxandall tone controls' but whatever its name I understand it 100 times better than I did ! best walk through of this filter in the you tubes....cheers.
Yes, I believe that English engineer Peter Baxandall came up with this active tone control circuit back in the 1950s. Very simple and effective, the hallmarks of good design.
This was very helpful, thanks!
Finalyi understand how Baxandall works! Thanks!
thank you ! 🙌
Excellent. Thank you. If we add a resistor parallel to C3, would that make the treble curve shallower?
If you're asking about the max cut/boost level (currently just beyond +/-20 dB, around 11:30), you control that by the ratio of the pot to the associated feedback resistors (P2, R3, R4). Placing a resistor in parallel with C3 is generally not advisable.
@@ElectronicswithProfessorFiore No, please excuse my ignorance (and I haven't got to this in the text yet), I was wondering how we could make the frequency response curve shallower. That is roll-off to give more of a 'tilt' than a 'turn' over a larger range. So, 5kHz upwards a gentle rise rather than a sharp turn. You may have answered that by our choice in resistors but I was wondering.
@@simonyoungglostog I am not aware of a quick and dirty way to do that (like adding a resistor). The issue is that you're trying to get a slower roll-off than that of a single RC lag/lead network, so you'd need to have multiple networks that slightly cancel (or go to a completely different topology).
@@ElectronicswithProfessorFiore Thank you. That makes sense.
@@ElectronicswithProfessorFiore Just to let you know, I opened my lab for the first time and built some of these op amp circuits. All working as you suggest, I could get some good ringing on the triangle to square wave circuits when using small capacitors.
are you using "Wrench" to analyze
No, that's the TINA-TI simulator. Wrench has a DSP version of these bass and treble controls (with adjustable corner frequencies). It also has fully parametric EQ and graphic EQ. You can do spectral analysis of signals but it won't draw Bode plots like TINA-TI.
Thanks for the prompt reply
Thank you so much!!!
Would it be possible/advisable to make a 5 band graphic equalizer by taking 5 circuits as shown @4:13 but modify the capacitor of each one and summing their outputs?
You could, sort of, but if you're referring to a simple summing amplifier with this circuit (i.e., with 5 paths in parallel that lead to the summer), that has problems. Doing that, you can get some boost but you won't get much cut (those frequencies would be passed with unity gain through the other 4 sections).
The bass-treble version shown at the end can be expanded with a mid section, and I've even seen 4 band versions, but they get unwieldy with a lot of interaction when you try to make a multi-band graphic EQ. For that, we use a different topology. The basic idea is to make a bunch of bandpass filters and then sum them together (kind of along the lines of what you were thinking).
@@ElectronicswithProfessorFiore Much thanks for the thoughtful reply. I'm in the process of making 7 cut/boost gyrator ckts and have a prototype working in breadboard layout. Lot's of connections and hook-up wire leading to a lot of noise. The ckt you presented looked so simple. I was hopeful it could cut-down the part and connection count. No worries. I shall proceed as planned. You know how it goes... Never pass-up the opportunity to build something that can be purchased at 1/4 the cost 😁
@@ElectronicswithProfessorFiore ... Anxiously awaiting a newly designed 5-band EQ circuit board. The output of each EQ band is summed with an inverted version of the original input. In theory, what's left behind is only a scaled version of the EQ'd signal. The 5 modified EQ bands are summed to create a penultimate output. Finally, the original (unaltered) signal is presented to a cut/boost circuit whose output is fed, along with the penultimate output, to a summing opamp. This gives the ability to fade-in (blend) the EQ'd bands with the original signal. On a simplified 2 band breadboard version (which did not allow adding back any of the original signal) either band could be modified (or completely removed) from the final output as-desired. -This is probably not novel but, it was for me and I had to design and build it. The summing can be done in different ways and in different points in the circuit. I had to try and observe them all. I’ve blown my time and money making something that already exists… -And this is why I call myself a hobbyist.
@@rayc1557 Not entirely clear on what you're doing but be careful with summing these signals. Remember, the outputs of the EQ circuits not only alter the signal amplitudes, they also alter the phase. If you're assuming that the outputs are perfectly 180 degrees out of phase, they won't be (the reactive elements introduce phase shifts). At some cut/boost setting you might be getting 150 degrees or 210 degrees (or whatever) instead of 180. That will mess with your summation. This is one place where simulation can be very handy as the manual calcs can be tedious.
@@ElectronicswithProfessorFiore I pondered that and did an experiment with a fully populated EQ board created a couple weeks ago. (BTW: The corresponding Class A amp and EQ board sound great - Much thanks to your refreshers on transistor circuits). The output of the EQ was simultaneously scoped/displayed alongside the original signal. After adjusting the volume to normalize the RMS levels of the 2 signals, I can identify the modification in amplitudes but, the zero-crossing of landmark signals are spot-on. I'm confused about this because of the very reason you cited. After a week of pencil & paper, I just decided to layout a board and give it a whirl. If it works, I'll send you my schematics. If it doesn't work, I'm out 72 bucks -but I'll learn a lot along the way. FWIW, I'm using a very unique circuit for the bandpass gyrators. I can send you links if you're curious.