Tilting Equalizer Design

Hello everyone!
I want to have a stab at designing my first ever piece of equipment. I always wanted a nice equalizer I could strip onto my 2 bus and after a lot of research I found this quite rare eq topology, tilting equalizer. I’m aware of the quad 34 pre and Tonelux and I wanted to do something a little bit different.
The things I’m looking for my design are:

• Balanced in/out (op amp or transformed balanced if possible)
  Tilting active eq with +- 6db of boost/cut
  Variable crossover frequency
  HP/LP

And also I was thinking about two different shelf curves or a switch between a shelf or a bell tilting eq (not sure yet if that would be a good/usable idea)

I would really like to focus on nice shelving/bell curves to make it as much universal as possible.

As I mentioned first this is my first attempt to designing a piece of equipment, and I’m a bit worried that it might be a bit too complicated but I treat this as a long term project and I can do it step by step slowly adding the features.

I’m attaching a copy of first draft of schematic I did for this, it includes a basic eq + balanced in and out, it doesn’t have any values though. Before I move along I want to see what you guys have to say about this idea.

I took most of the info from a great book called "Small Signal Audio Design"

Thanks for all your time and input!

I've played around with one knob tilt EQ for side-chain of noise gates to simply reduce or increase frequency sensitivity of the gate.  In this case panel space is dear so the one knob approach is desirable and you don't really care what the side chain sounds like.

To EQ full range signal I prefer something like parametric.  Are you confident you will like the result of tilt? Maybe breadboard one up and listen to it.

JR

What does A3 do that A2 can't do?

And there are better diff-inputs. The one shown DOES work in thousands of studios, but if you are building for yourself, I'd re-assign that 3rd opamp to a 2-amp input stage.

> breadboard one up and listen to it

+1. You can do just the one opamp (twice) and strap it into your stereo hi-fi.

Shameless plug: Our upcoming G23 "Ambler" is all this, plus some additional tricks...

Also Tubetech just released theit version https://www.gearslutz.com/board/high-end/944445-need-simple-stereo-eq.html

Detecting a trend?



Jakob E.

Aniol1349 said:

I’m attaching a copy of first draft of schematic I did for this, it includes a basic eq + balanced in and out, it doesn’t have any values though.

Click to expand...

The EQ section is adequate, the input section would work but could be improved, and the output section is flawed. It is the worst active balanced output structure, and, as drawn, wouldn't work at all.
I wouldn't advocate the use of input/output xfmrs; I would rather recommend the use of THAT 1206/1646.
Typical applications for a tilt EQ do not justify the added complexity of using higher-order filters.
There is some justification in using variable turnover frequency, though.
The frequency adjustment does not need a high resolution.
Switching capacitors with a rotary switch is the easiest solution.

PRR said:

What does A3 do that A2 can't do?

Click to expand...

The OP more or less copied circuits from one of Douglas Selfs book and put them in series.
The idea behind the A3 stage was that A2 doesn´t need to drive the output. Douglas Self designed the feedback path around A2 very low Z for noise reasons so that A2 couldn´t bear any more load, hence the buffer.

jensenmann said:

Douglas Self designed the feedback path around A2 very low Z for noise reasons so that A2 couldn´t bear any more load

Click to expand...

  Which is not obvious considering the absence of values on the schemo...

gyraf said:

Shameless plug: Our upcoming G23 "Ambler" is all this, plus some additional tricks...

Also Tubetech just released theit version https://www.gearslutz.com/board/high-end/944445-need-simple-stereo-eq.html

Detecting a trend?



Jakob E.

Click to expand...

I like how it has separate access to each shelf and then can offset the global setting with the tilt control. I never thought of that but it's the best of both worlds that way. Very clever.

On top of what's been said before, the proposed Tilt circuit does not do what it's supposed to do. It ends up being a simple LF shelf.

Basic tilt as above (from  Self - Small signal.. ) - measured response:

Jakob E.

gyraf said:

Basic tilt as above (from  Self - Small signal.. ) - measured response:

Jakob E.

Click to expand...

Interesting. Looking at the schemo,  my simulation seems correct and your measurements not.
So the schemo above must be wrong. What is yours?

Tilt according to Self (but I scaled the values, res ca. x10, caps ca. /10):

Thanks guys for all your replies,

As I said before this is my first "design" attempt so I have a long way before I can do something useful with.

It's a long term project for me and as someone have noticed I copied D. Self design from his book as a starting point.

I apologize for the lack of the values on my  schematic I guess my question with this was if the balanced I/O would work in that configuration  and if the phase would be correct between the I/O.

I'm now revising this first draft  more seriously, I have breadboarded a mono channel of the basic eq and now I want to focus on the shelves, maybe try gentle resonant shelves with  variable turnover frequency in the tilt topology, Also possibly I will reduce the range of high shelf by half of the lo shelf.
I'm still not sure how I could make this idea usable for processing stereo material in a pleasing way, so any suggestions are more than welcome.
Maybe it will never become something usable but it will definitely improve my understanding and knowledge of basic design.

I will keep posting my progress with this project, meanwhile thank you all for the replies!

gyraf said:

Tilt according to Self (but I scaled the values, res ca. x10, caps ca. /10):

Click to expand...

That's interesting.
For it to work properly, resistors R3 & 4 must be smaller than R1 & 2. When they are equal, only the low shelf can be seen.

Aniol1349 said:

I guess my question with this was if the balanced I/O would work in that configuration  and if the phase would be correct between the I/O.

Click to expand...

It is not on your posted schemo. You note the first stage as inverting, which it is not.
You must cross either the input or output connections.
And as I mentioned earlier it wouldn't work because you need galvanic connection of the non-inverting input of A3, which can be done by either replacing the capacitor by a direct connection, or adding a resistor to ground (10 to 100 kohm).

Aniol1349 said:

I'm still not sure how I could make this idea usable for processing stereo material in a pleasing way, so any suggestions are more than welcome.
Maybe it will never become something usable but it will definitely improve my understanding and knowledge of basic design.

Click to expand...

Could I suggest refining your goal using a software plug in first?  As a mastering engineer I've always been fascinated by the idea of tilt eqs but based on the experimentation I've done using the best digital plug in EQ I know (DMG Equilibrium) I've found them to be much less useful than I expected.

I do find separate 6dB/Oct shelves to be far more useful and if I was building a simple stereo hardware EQ (which I am) I would focus on that based on my needs.

I did sim a 3dB/Oct tilt a little while back which I thought could be useful, my main issue with regular tilt topologies for stereo bus use is around the turnover frequency. 

ruairioflaherty said:

Aniol1349 said:

I'm still not sure how I could make this idea usable for processing stereo material in a pleasing way, so any suggestions are more than welcome.
Maybe it will never become something usable but it will definitely improve my understanding and knowledge of basic design.

Click to expand...

Could I suggest refining your goal using a software plug in first?  As a mastering engineer I've always been fascinated by the idea of tilt eqs but based on the experimentation I've done using the best digital plug in EQ I know (DMG Equilibrium) I've found them to be much less useful than I expected.

I do find separate 6dB/Oct shelves to be far more useful and if I was building a simple stereo hardware EQ (which I am) I would focus on that based on my needs.

I did sim a 3dB/Oct tilt a little while back which I thought could be useful, my main issue with regular tilt topologies for stereo bus use is around the turnover frequency.

Click to expand...

Agreed. The way analog tilt EQ's work, they don't produce a real tilt, they actually change the balance of the contents above and below the pivot frequency. What most users want in a tilt EQ, is applying a gradual slope to the frequency response. In that case, defining a pivot is not pertinent.
Making an analog filter that does it is not very difficult, making it variable is not easy.
Easy task for DSP, though.
Everytime I feel the need for such action, I always end up using a combination of wide parametrics.