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-   -   Cello Palette Style EQ Design (was High End Tone Control)... (http://www.diyaudio.com/forums/analog-line-level/209644-cello-palette-style-eq-design-high-end-tone-control.html)

ThorstenL 27th March 2012 04:06 AM

Cello Palette Style EQ Design (was High End Tone Control)...
 
Folks,

At the other thread I noticed interest in what may be called a "functional clone" of the Cello palette. Please review the High End Tone Control thread for background information and the options discussed:

http://www.diyaudio.com/forums/analo...e-control.html

The Palette is best described as a Stereo Mastering EQ designed for easy and intuitive use by non-engineers (most EQ's need operators with at least two degrees and many years of experience to get suitable results). One way to describe the actions of the six controls of the Palette approximately is:

Bass [20Hz]
Drum [120Hz]
Lower Voice [500Hz]
Presence [2Khz]
Rasp [5KHz]
Air [20KHz]

Control ranges are 'weighted' so that any changes for a given rotation in for example the "presence" band are much smaller than the "bass" band, relating directly to the behaviour of the human hearing. The Palette has possibly more adjustment range than is beneficial and due to a number of factors a true clone is jut not a sensible option nor is it necessary.

Here the original:

http://farm4.static.flickr.com/3082/...962b6f0058.jpg

In principle we can realise something that follows most of the Palette design brief using any technology we care to apply, so much is established.

However "Vita brevis, ars longa" dictate that we cannot spend time, effort and money on making a Palette functional clone with each and every available technology and then to let everyone choose which design suits them best.

So for starters we set the following outline for the actual EQ function:

Centre frequencies:

20Hz +/- 12 ... 18dB
120Hz +/- 6 ... 9dB
500Hz +/- 3 ... 5.5dB
2KHz +/- 3 ... 5.5dB
5KHz +/- 6 ... 9dB
20KHz +/- 12 ... 18dB

We can make bands somewhat adjustable using switches if desired.

Adjustment range is open to some debate as well.

Controls should be able to use generally available potentiometers but can be implemented also with rotary switches.

If we limit ourselves to 24-Pole switches (actually 23 Poles usable) this gives us +/- 11 positions for boost/cut.

This suggests 0.4dB steps for the innermost bands (so +/- 4.4dB), 0.8dB steps for the intermediate bands (so +/- 8.8dB) and 1.2dB steps for the extreme bands (so +/- 13.2dB).

If these items are agreeable we can proceed to select the electronic circuitry, here is where the poll comes in. If you are interested in this analogue (re)mastering EQ project, please vote in the poll on the technology to be used. the poll is multi-choice to perhaps vote 1st & 2nd choice...

Ciao T

Gopher 27th March 2012 05:20 PM

Great idea Thorsten. This will probably be one of the best projects in diyaudio history.

ThorstenL 27th March 2012 05:22 PM

Hi,

Quote:

Originally Posted by Gopher (Post 2962343)
Great idea Thorsten, but what poll?

Top of this page?

Quote:

Originally Posted by Gopher (Post 2962343)
Let's not re-invent the wheel. I say optimised op-amps of the best sounding types available today used in Jung multi-loop configuration with separate high current buffers.

How about concrete suggestions?

Ciao T

mrkramer 27th March 2012 05:55 PM

What is an "East German EQ"?

Sounds somehow retro sylish to me!

MrKramer

ThorstenL 27th March 2012 06:51 PM

Hi,

Quote:

Originally Posted by mrkramer (Post 2962380)
What is an "East German EQ"?

Sounds somehow retro sylish to me!

Please see the first post and the link to the original tone-control thread.

It includes this schematic:

http://www.diyaudio.com/forums/attac...minimal-eq.jpg

I called it "East German EQ" because that is what it is. It was designed in East Germany in the late 70's and remains somewhat legendary for it's sound quality. It avoids the use of looped feedback, which similar western Pro-Audio design already used in massive amounts routinely. I can attest to the sonics of this type of EQ, I used it extensively.

This EQ shows the principles for what "ZenEQ" (Solid State) and the "HotEQ" (Tubed).

The circuit can be realised using only two N-Channel devices per channel, or if we want to very Zen, we can get away with one device (but must provide a tightly defined load).

The chokes in the filters can be replaced by Gyrators, using even single J-Fets. I would attempt to retain real chokes for as many bands as possible though.

It appears ZEQ/HEQ is currently ahead in the poll, the advantage is that that linear track pots may be used and few parts are required. The downside is that the active section must be designed in. So a Tube version would be a distinct Fork, the Fet version another.

Ciao T

Carl_Huff 27th March 2012 06:52 PM

ThorstenL,

The "East German EQ' uses good'ol inductors. Are you aware of a modern day source for them?

I like the old inductor EQs. In my experience the opamp gyrator equivalents just don't sound as good.

KSTR 27th March 2012 07:09 PM

Quote:

Originally Posted by Carl_Huff (Post 2962451)
The "East German EQ' uses good'ol inductors. Are you aware of a modern day source for them?

Slaughter a used DN27A :) ...a 27-band graphic EQ from Klark-Teknik, based around one single 5532 IIRC. Used to be a standard in FOH/monitor rigs, so one may get them cheaply in rotten condition (broken sliders etc). I sold the two I used to have, for lack of real applications for them.

Nrik 27th March 2012 07:09 PM

Please also read this thread

I can testify that the level-weighted soft-Q adjustments really can do what normal tonecontrols cannot.
The range on mine is similar to the original Audio palette, and eventhough it is rare that I use the full range it is sometimes needed (especially in the two lower bands). It is the case with some music mastered for the American market that you want to play with "European" sound.
So my advice: Don't choose to low a dB-range for the controls. With that many positions one can easily get satisfyingly small corrections when called for.

ThorstenL 27th March 2012 07:09 PM

Hi,

Quote:

Originally Posted by Carl_Huff (Post 2962451)
The "East German EQ' uses good'ol inductors. Are you aware of a modern day source for them?

I like the old inductor EQs. In my experience the opamp gyrator equivalents just don't sound as good.

The winding data for the east german EQ is included, sadly no direct info on the cores, however you can work that out indirectly, then adjust for available cores and wind your own... They where small so-called Pot-Cores.

I have some connections to custom inductors in modest quantities, so I am sure they could made available for a group-buy (PCB's too).

I think the LF bands (20 & 120Hz) sadly would have to use gyrators though.

Ciao T

jameshillj 27th March 2012 10:27 PM

As I understand this, the primary duty of the "Tone Stack/Control" is to correct recording anamolies but my speakers fall off pretty quickly below 34Hz, would it be better to move the lower 20Hz filter up to at least 34Hz for my system? And the next speakers I have in mind require the Link Transform eq (the B2 alignment, closed box design and would this conflict with this tone control design?

Having to work with a "Sea of Knobs" for years, it\'s not something I want to do at home - you just don\'t bother after a while.


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