Cello Palette Style EQ Design (was High End Tone Control)... - Page 3 - diyAudio
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View Poll Results: If you where to build a Cello Palette functional clone, what technology do you want?
I want a Software Palette, Analogue EQ is SO 20th Century 8 16.67%
I want a purely passive EQ to which I want to add my own input buffer and output amplifier (MPPJBTS) 9 18.75%
I want a Minimalist discrete EQ using Tubes (ZenEQ derived from the "East German EQ") 15 31.25%
I want a Minimalist discrete EQ using Solid State (ZenEQ derived from the "East German EQ") 22 45.83%
I want Op-Amp's with parallel and summed bands (e.g. NitePro EQ3D) 5 10.42%
I want Baxandall Sections with Op-Amp's connected in series (e.g. Carl_Huff) 3 6.25%
Multiple Choice Poll. Voters: 48. You may not vote on this poll

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Old 28th March 2012, 09:37 PM   #21
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Thorsten, I think you've done an amazingly well with culling the options. The result is something that has been generally unavailable to many of us. Thank you.

As for myself and for budgetary reasons, I think that I need the lower 3 controls run by gyrator, and some ideas on where to locate 39mh, 15mh and 820uh small signal inductors, since I'm not accustomed to procuring them.
So, when you get the time, I'd sure like to see this project succeed.

Because I do not know, I wanted to ask if the BC560C okay with the 40v rails shown. There is a Fairchild BC556C, Fairchild KSA992 and Toshiba 2SA970-BL, which are all slightly different but have higher voltage spec if you happen to need it. Indeed, the decision is yours and I very much appreciate what you have done so far.
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Old 29th March 2012, 01:42 AM   #22
Bonsai is offline Bonsai  Taiwan
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"I refuse "to lead" and to be the one who lays the down guru style on how it can only "one way, this way and no other". I'd rather people find THEIR way. "

Really?
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Old 29th March 2012, 05:23 AM   #23
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by Carl_Huff View Post
Please continue working up your FET & inductor solution. I've got a stash of suitable inductors leftover from the old days when I had an Auditronics 36 Grand mixing console. The EQ in that console was the reason that I kept it so long. I still have a stash of parts hoarded away. I have stash of FETs as well. If you complete the design I will be sure to build it.
Well, not much else to add really. I don't think I have time to create a PCB and to get further on parts selection.

Attached the version with gyrators for the two LF bands where mouser does not stock suitable inductors.

Click the image to open in full size.

Mouser Stock Numbers for the other four bands are included as an example and as help for those too lazy to even do a quick search there, however they are not necessarily the best choices, just what I could find and which looked okay. The circuit is adjusted to account for the inductor DCR for the items listed.

As these inductors do not have closed core they have a tendency to pick up stray fields. Custom made units on a pot core may be better and one could certainly make the whole set.

The Curves and other performance remains essentially unchanged, as before I have included the Tina-Ti simulation file... The use of Op-Amp's for the Gyrators is necessary (if undesirable), in the simulator at least, as using the same compound Fet/BJT leads to an overall level boost and wrong Q.

The OPA2604 shown here is really just a stand-in, use whatever works for you. The Op-Amp's need more current capability than anything else... Video Op-Amp's are probably a good choice, but can be problematic to stabilise. Adjust rail voltages as needed for the Op-Amp's of choice.

Ciao T
Attached Images
File Type: gif ZenEQ-Gyrators.gif (21.3 KB, 832 views)
Attached Files
File Type: zip ZenEQ-Gyrators.zip (21.0 KB, 48 views)
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Old 29th March 2012, 06:09 AM   #24
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by ThorstenL View Post
Well, not much else to add really.
Checked a few more things.

Using a CCS (ideal) for the output follower tail increases THD mildly by increasing H2, but reduces higher order content, this is more pronounced with loads far greater than 10K.

The Resistor between base and Emitter of the BJT in our Inverted Fetlington shows also some sensitive re. HD. Increasing the value 3.3K shows a minimum of higher order HD at the cost of 6dB more H2.

I would be reluctant to trust a simulator implicitly on small details like that, so the circuit would have to be build and measured to confirm the sim and I suspect optimum values will be quite a bit different.

Ciao T
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Old 29th March 2012, 10:30 AM   #25
EUVL is offline EUVL  Europe
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Those who would like a detailed explanation of how this circuit basically works, or how an opamp version would look like, could have a look at this excellent site :

Bandcut and Bandboost - Series LCR and Pot
Bandcut and Bandboost
Bandcut and Bandboost
http://www.ecircuitcenter.com/Circui..._boost_cut.htm

Some, however, swear by a pure passive approach, even though it is cut only.
Google e.g. White Instruments Model 4420.


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Old 29th March 2012, 10:52 AM   #26
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by EUVL View Post
Some, however, swear by a pure passive approach, even though it is cut only. Google e.g. White Instruments Model 4420.
The White 4420 was meant to EQ resonances, feedback etc. in PA systems, hence it is deigned cut only.

However technically speaking a pure passive EQ can offer boost, the old Langevin Model 252A for example was a purely passive 7-Band Graphic EQ that could offer boost.

However, the penalty you incur is static attenuation.

My original idea was to actually just make a passive EQ (not exactly Langevin Style, but related) and let everyone add their favourite buffers (input) and Gainstages (output), however this is only a distant third.

Once we have finalised the Filters the circuit can indeed be applied with a wide range of electronics, Op-Amp's, discrete Op-Amp's, Tube Op-Amp's, discrete solid state (as shown) or Tubes set as analog's to the Fets.

Ciao T
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Old 29th March 2012, 10:53 AM   #27
EUVL is offline EUVL  Europe
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BTW could it be that C10 should be swapped with R21, and C12 with R20 ?

See Fig. 7 of :
Audio Designs With Opamps


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Old 29th March 2012, 10:54 AM   #28
EUVL is offline EUVL  Europe
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> My original idea was to actually just make a passive EQ (not exactly Langevin Style, but related) ....

So what exactly do you have in mind ?


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Old 29th March 2012, 11:01 AM   #29
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by EUVL View Post
BTW could it be that C10 should be swapped with R21, and C12 with R20 ?

See Fig. 7 of :
Audio Designs With Opamps
No, of course not. What RE shows as usual is not 100% correct (that comes from copying others). The circuit using what is basically a Sallen Key Filter does not behave correctly like a "virtual inductor". It "kind of works", but is not a correct alternate to using an inductor.

Ciao T
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Old 29th March 2012, 03:15 PM   #30
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by EUVL View Post
So what exactly do you have in mind ?
Not much really. I looked.

What I was thinking originally was that there was no way to get sensible agreement on "Op-Amp's" vs. "Discrete" vs. "Fet" vs. "Bjt" vs. "Tube".

One Man's "best sound ever" seems anothers "worst sound ever"'.

I was thinking it more constructive to bypass all of this tosh and instead have a pure passive tone control, with the kind of attenuation that comes as price of having "Passive Boost", the kind I called MPPJBTS in the original thread. This allows everyone to pick their own poison and use whatever they want as input buffer and as output "re-gain" amp.

Manley's "massive passive" EQ for example uses an Op-Amp as input buffer and a tube circuit as re-gain amplifier and for output buffering.

So really, for the active side anything goes...

Anything Goes
Click the image to open in full size.

But it seems that expecting today's DIY'ers to work out (or select from the existing body of work) a buffer and an around 20dB - 30dB linear Amp in their favourite technology (or to type xxxmH into the search at mouser or digikey) is asking too much.

So this ended up being the "ZEQ" (ZenEQ) instead, which is pretty much close to a buildable project (add powersupplies - Salas-Shunts anyone?).

Substituting the Fet's with tubes and scaling impedances by a factor 10 would turn this into the "HEQ" (HotEQ) with a 10dB noise penalty...

Ciao T
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