Hi,
As some of you may know, I have been working on an adjustable EQ as a sidekick to the Active filter two boards. I think I have found a way to make a real parametric EQ, with completely separately adjustable Gain, Q and fc. If anybody is interested I’m offering to create the artwork for this module also, and later there can be a group purchase.
Let me know what you think and what the options on the boards should be.
Thanks
\Jens
As some of you may know, I have been working on an adjustable EQ as a sidekick to the Active filter two boards. I think I have found a way to make a real parametric EQ, with completely separately adjustable Gain, Q and fc. If anybody is interested I’m offering to create the artwork for this module also, and later there can be a group purchase.
Let me know what you think and what the options on the boards should be.
Thanks
\Jens
My main reason for wanting a real parametric EQ – as opposed to the wery nice nodule posted by moamps – is that I consider the mox board along this EQ board as tools when developing active filters for speakers.
The problem – as I see it – with moamps EQ, is that I think it is difficult to find out what parameters the EQ has. This in turn makes it impossible to recreate the EQ on a smaller board for the final filter.
I have been trained at at place where they use the DP226 digital filter, and here you just set your parameters listen, tweak listen some more, and when you are happy with the overall sound from the speakers, you build your analogue filter according to the specs from the digital prototype.
This way, the first analouge filter is pretty close to what you want
I want to make an analogue DP226 to make sure that there is an easy transfer from listening prototype to final filter.
That said, I’m not an expert speaker builder – I’m a total newbie – but I know signal processing and hope to get the Loudspeaker guys to help out when it comes to all the acoustical questions I have
\Jens
The problem – as I see it – with moamps EQ, is that I think it is difficult to find out what parameters the EQ has. This in turn makes it impossible to recreate the EQ on a smaller board for the final filter.
I have been trained at at place where they use the DP226 digital filter, and here you just set your parameters listen, tweak listen some more, and when you are happy with the overall sound from the speakers, you build your analogue filter according to the specs from the digital prototype.
This way, the first analouge filter is pretty close to what you want
I want to make an analogue DP226 to make sure that there is an easy transfer from listening prototype to final filter.
That said, I’m not an expert speaker builder – I’m a total newbie – but I know signal processing and hope to get the Loudspeaker guys to help out when it comes to all the acoustical questions I have
\Jens
You are probably already very familiar with the common circuits out there (in fact it sounds like you already have designed something) - but the following may be of interest anyway (particularly the single stage shown as Figure 3):
http://www.ethanwiner.com/spectrum.html
Regards.
http://www.ethanwiner.com/spectrum.html
Regards.
Hello,
Netgeek:
Thanks for the link, in fact the circuit I have made is very similar to the one found in figure 3.
Ed:
I plan to make the EQ a module you can insert anywhere in the signal chain in your box of filters. The input will be gain, Feq and Q, all of witch will be 100% independent.
I hope to build a prototype on breadboard pretty soon when this is done I’ll post results.
In the mean time, please keep the ideas coming, as I’m not set on a design yet.
\Jens
Netgeek:
Thanks for the link, in fact the circuit I have made is very similar to the one found in figure 3.
Ed:
I plan to make the EQ a module you can insert anywhere in the signal chain in your box of filters. The input will be gain, Feq and Q, all of witch will be 100% independent.
I hope to build a prototype on breadboard pretty soon when this is done I’ll post results.
In the mean time, please keep the ideas coming, as I’m not set on a design yet.
\Jens
Bump. As long as there is as much space around the opamp pads as is on Jen's MOX boards, the discrete opamp would fit.
As usual, I think there are probably a lot of interested people who have absolutely nothing to say on the issue at the moment. (me included!) So we'll all look forward to more details as the prototype gets hashed out--it is much easier to offer (hopefully constructive) criticism than to come up with a design.
As usual, I think there are probably a lot of interested people who have absolutely nothing to say on the issue at the moment. (me included!) So we'll all look forward to more details as the prototype gets hashed out--it is much easier to offer (hopefully constructive) criticism than to come up with a design.
Hi Tyler, and the rest of you 
Im working on a proto single layer PCB to verify that everything is working as planned. I hope the have the layout ready in a few days, and post some measurements by the middle of next week.
But my speaker project is taking most of my spare time at the moment.
Ideas about configuration / schematics are still more than welcome
\Jens
Im working on a proto single layer PCB to verify that everything is working as planned. I hope the have the layout ready in a few days, and post some measurements by the middle of next week.
But my speaker project is taking most of my spare time at the moment.
Ideas about configuration / schematics are still more than welcome
\Jens
Hi,
Yes the circuit is still in the works. I have however had difficulties getting a layout and concept done that satisfies my need for simple adjustment using resistor ladders.
This has made me think along a different approach. I am wondering if a fully potentiometer controlled device would satisfy my needs. Choosing this approach would mean that the user would need to “reverse engineer” the settings by measuring the values of the potentiometers and inserting these values into some equations to determine Q and fc.
This is a rather clumsy way of adjustment control – comparing to the mox boards – but I have been unable to find a better way until now. Ideas are most welcome.
I have a working circuit – in the simulator - with potentiometers, but it needs to be tested I real life, and I don’t have the time right now.
Please comment on the circuit posted by netgeek here
http://www.ethanwiner.com/spectrum.html figure 3
\Jens
Yes the circuit is still in the works. I have however had difficulties getting a layout and concept done that satisfies my need for simple adjustment using resistor ladders.
This has made me think along a different approach. I am wondering if a fully potentiometer controlled device would satisfy my needs. Choosing this approach would mean that the user would need to “reverse engineer” the settings by measuring the values of the potentiometers and inserting these values into some equations to determine Q and fc.
This is a rather clumsy way of adjustment control – comparing to the mox boards – but I have been unable to find a better way until now. Ideas are most welcome.
I have a working circuit – in the simulator - with potentiometers, but it needs to be tested I real life, and I don’t have the time right now.
Please comment on the circuit posted by netgeek here
http://www.ethanwiner.com/spectrum.html figure 3
\Jens
HI,
I have been attempting a similar project with little luck. I want a 3-band parametric EQ, and want adjustable Q, gain, and freq. The problem lies in the fact that I want to adjust all of these parameter via digital potentiometer. It is very difficult for *me* to find the solution to this problem, while retaining signal quality.
We need more than 6dB roll-off for sure, which necessitates a 2-pole filter, only complicating my quest for adjustability. I am aiming for a 3-pole with 18dB roll-off, while retaining the adjustable parameters. I have looked into the state-variable concept, which provides the adjustable Q and gain that I am seeking...along with the center frequency. Those are all easily adjustable, but the problem lies in the flat 6dB roll-off curve.
In order to have a sharper drop and less adjacent band interactance, I would have to add filters which greatly increases the difficulty of controlling the units based on resistance values only.
Perhaps one of you guys has created a "digital capacitor?"
How are you managing parameter control?
-Matt
I have been attempting a similar project with little luck. I want a 3-band parametric EQ, and want adjustable Q, gain, and freq. The problem lies in the fact that I want to adjust all of these parameter via digital potentiometer. It is very difficult for *me* to find the solution to this problem, while retaining signal quality.
We need more than 6dB roll-off for sure, which necessitates a 2-pole filter, only complicating my quest for adjustability. I am aiming for a 3-pole with 18dB roll-off, while retaining the adjustable parameters. I have looked into the state-variable concept, which provides the adjustable Q and gain that I am seeking...along with the center frequency. Those are all easily adjustable, but the problem lies in the flat 6dB roll-off curve.
In order to have a sharper drop and less adjacent band interactance, I would have to add filters which greatly increases the difficulty of controlling the units based on resistance values only.
Perhaps one of you guys has created a "digital capacitor?"
How are you managing parameter control?
-Matt
Member
Joined 2003
I am interested to know how your project is going Jens. I am going to be designing and building a parametric equalizer for my thesis project in school, and am interested to know how other people have designed such a device so that I have some reference if I get lost while designing mine. Thank-you for that excellent link to the Ethan Winer website, I think that information will come in very handy. Is your equalizer very similar to the schematic on that website? For example, are you using the same TL074 op-amps?
As it is only the beginning of the school year, I am just getting started on this project, and am just done some preliminary research so far.
As it is only the beginning of the school year, I am just getting started on this project, and am just done some preliminary research so far.
Hello,
I have not had time to do much work on this. The project is however still active and the design is in the works.
First tests using a circuit similar to that of Ethans are successful, put the adjustment are rather clumsy and until I’m satisfied I will not publish the result.
DcibeL if you find any smart ways of making resistor ladders work simply in your project, please let us know.
\Jens
I have not had time to do much work on this. The project is however still active and the design is in the works.
First tests using a circuit similar to that of Ethans are successful, put the adjustment are rather clumsy and until I’m satisfied I will not publish the result.
DcibeL if you find any smart ways of making resistor ladders work simply in your project, please let us know.
\Jens
Member
Joined 2003
I have now had the opportunity to discuss my project with my advisor, and he would like to see my parametric equalizer be built using a programmable IC, which will be controlled by a PIC microcontroller preferrably using I2C protocol, and of cource have a nice LCD display. My task now is to try see if such an IC exists and if not, then I will have to modify my project to make it more interesting.
Member
Joined 2003
Thank-you very much for informing me of that IC. I had looked the other day and found a few chips, but none of them did exactly what I wanted them to. I am not familiar with the TSSOP package so I will have to check (1) If the pins are spaced large enough that they can be soldered by hand and (2) If our PCB machine can make tracks for surface mount devices. I am almost certain that I won't be able to use this IC, but I will investigate.
I had a visit with my project advisor today, and we are almost set on a design for this thing. As of right now, we are back to a complete op-amp controlled circuit, using a PIC and digital pots to control it. This way, it can have an LCD displaying the values, and buttons that don't wear out to control it, rather then analog pots that do wear out. I am actually quite exited about this design, hopefully I can make it work.
I had a visit with my project advisor today, and we are almost set on a design for this thing. As of right now, we are back to a complete op-amp controlled circuit, using a PIC and digital pots to control it. This way, it can have an LCD displaying the values, and buttons that don't wear out to control it, rather then analog pots that do wear out. I am actually quite exited about this design, hopefully I can make it work.
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