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[Viitalahde]

I finally took a good look at the schematic, and understood why I completely dismissed it. I always thought this was a basic state variable circuit with the filters in series. Now I'm interested.

There's going to be a new parametric in my rack someday, and I'm anyway moving away from cloning to public domain and open concepts, I just like the idea.

So Brad.. How's the midrange, 600Hz-1200Hz? This is the area my current EQ kills anything I've heard, but especially in the upper mids it could be better even if the high end is brilliant.

[dcollins]

Viitalahde wrote on Fri, 07 March 2008 11:40

I finally took a good look at the schematic, and understood why I completely dismissed it. I always thought this was a basic state variable circuit with the filters in series. Now I'm interested.

There are a number of interesting aspects to that design, which is why I brought it to peoples attention in the first place!


DC

[zmix]

I think an interesting way to implement this EQ would be to run the output of each filter to a rotaty switched resistive ladder attenuator feeding a SPDT center-off switch.  The center lug of the SPDT/CO switch would be connected to the attenuator following the filter's output. The outer lugs of the SPDT/CO would feed Pins 2 and 6 of U2.  

This way you would have a three position switch determining whether each band was going to "Cut" or Boost" or, in the center position, be "out".

This also effectively doubles the number of positions available on the attenuator.


EDIT:  I see that Mike Pecchio had a similar idea here.

[Viitalahde]

zmix wrote on Tue, 11 March 2008 15:50

This also effectively doubles the number of positions available on the attenuator.

Yay, that's exactly what I do with my current EQ. No "out" though, don't know why I never implemented that. It'll be there in the next EQ, which is probably going to be this one if I like it after prototyping.

Cut/boost -switch is cool, I've been happy a couple of times that I actually have the possibility for more cut/boost than, say, 6dB. Right now I have 12dB max.. and I think I've once done 7,5dB somewhere in the high end. Argh.

[T. Mueller]

zmix wrote on Tue, 11 March 2008 10:50

I think an interesting way to implement this EQ would be to run the output of each filter to a rotaty switched resistive ladder attenuator feeding a SPDT center-off switch.  The center lug of the SPDT/CO switch would be connected to the attenuator following the filter's output. The outer lugs of the SPDT/CO would feed Pins 2 and 6 of U2.   This way you would have a three position switch determining whether each band was going to "Cut" or Boost" or, in the center position, be "out". This also effectively doubles the number of positions available on the attenuator. EDIT:  I see that Mike Pecchio had a similar idea here.

PLEASE pardon my lack of understanding; still learning.  Am I reading this right in that you're describing a way to implement attentuation with more precision/resolution to the filters?  I read Mike's post; sounds like a fun project.

[zmix]

T. Mueller wrote on Tue, 11 March 2008 14:34

zmix wrote on Tue, 11 March 2008 10:50 I think an interesting way to implement this EQ would be to run the output of each filter to a rotaty switched resistive ladder attenuator feeding a SPDT center-off switch.  The center lug of the SPDT/CO switch would be connected to the attenuator following the filter's output. The outer lugs of the SPDT/CO would feed Pins 2 and 6 of U2.   This way you would have a three position switch determining whether each band was going to "Cut" or Boost" or, in the center position, be "out". This also effectively doubles the number of positions available on the attenuator. EDIT:  I see that Mike Pecchio had a similar idea here. PLEASE pardon my lack of understanding; still learning.  Am I reading this right in that you're describing a way to implement attentuation with more precision/resolution to the filters?  I read Mike's post; sounds like a fun project.

.

My suggestion is probably simpler than you think it is..

Basically in this EQ, as in most active EQ circuits, the input signal is split off into two paths, one straight through to the output amp and one through an EQ filter, either a shelf or a bell (peaking) filter.

If you combine these two paths at the output amp, you will get an additive effect at the frequency of the filter.

If you invert the polarity of the filter 180˚ you will have a subtractive effect at that frequency.

In the stock circuit, each filter's "cut/boost" control is essentially a pan pot which directs the output of the filter to either the inverting input of the output amp (for cutting) or the non-inverting input (for boosting).

If you use a toggle switch (after the filter's ouput attenuator) to direct the filter's output to either the inverting or the non-inverting port in the output amp, you can use the entire travel of the "cut/boost" pot or alternately all of the positions of the rotary "cut/boost" switch towards your desired result.


To simplify it further, suppose you have an 11 position switch for the cut/boost function.

In the original schematic this will give you 5 cut positions and 5 boost positions and the middle postion is 'flat'.

In version I suggested you will have 11 positions of cut or boost and you don't waste one position to have a 'flat' setting (since the cut/boost selector toggle has an 'out' position).

[T. Mueller]

Quote:

In version I suggested you will have 11 positions of cut or boost and you don't waste one position to have a 'flat' setting (since the cut/boost selector toggle has an 'out' position).

Yup.  This is what I meant by "precision/resolution"--I meant amplitude.  Sweet.

[Greg Reierson]

After a long hot summer I finally got the BP up and running. I'm still getting a feel for it but so far it's rockin! I built mine as a ganged stereo unit (like the Gyraf XIV). I don't have an actual image but here's the art file for the front panel.
Any other brave souls with a story to share?


GR

[mastertone]

Beautiful!
Damn i want to do this one...

[hnewman]

Here's mine in action.

[dcollins]

hnewman wrote on Tue, 11 November 2008 09:44

Here's mine in action.

I'm so glad to see this design, and Barry Porters name, get some exposure.

I think it will beat the revered Sontec, and does not use any un-obtainium parts.

DC

[bblackwood]

I certainly love mine!

[TotalSonic]

hnewman wrote on Tue, 11 November 2008 12:44

Here's mine in action.

It looks excellent Harris!  You definitely have got some fine goodies in those racks now.

btw - what are the 4 controls in the center of it? - gain, hpf & lpf, shelves?

Best regards,
Steve Berson  

[TotalSonic]

dcollins wrote on Tue, 11 November 2008 19:26

I think it will beat the revered Sontec, and does not use any un-obtainium parts. DC

Seems Harris has got the Sontec part covered as well - from the studio shots there's a modded "new" MEP250EX in the rack on the left.

Best regards,
Steve Berson    

[hnewman]

The 4 center pots are HP and LP filters.  I use it in tandem with the 250EX all the time (which Burgess assured me has the "same sound" as the bigger brother mastering EQ's, which I find unlikely considering what a rough handling beast it is), and they are fantastic compliments but very different animals.  The BP is huge and clean, whereas the Sontec gets real dirty real fast, and has hardly any headroom.  I wouldn't part with either under any circumstances.