Shelf/bell topologies in SVF parametric EQs

[JohnRoberts]

You need to melt some solder to see how much clicking you get when switching between settings.

+1 to Abbeys point about having HPF and LPF around shelf filters. In an ideal world they would limit boost but not cut.

JR

 

[TwentyTrees]

I don't think this qualifies as a SVF. I may be wrong, but for me SVF involves the use of integrators.

Likely my misunderstanding!

 

[abbey road d enfer]

 

[atavacron]

IDK. I may have misunderstood your question...
Did you mean replacing a shelf EQ with a bell centered at the shelf's max boost/cut frequency?

Thanks for circling back. I’ll put it another way. Having established that a HP or LP resulting from a SVF tap or permutation can perform the same job as a buffered single pole (when fed into an inverting input of a cut or boost amp), I was saying that the next step was to evaluate the relative complexities and advantages of keeping the SVF for shelving, or swapping in a buffered single pole. The one condition being that the SVF Q has to be set the same as (or lower than) the single pole buffered Q.

 

[atavacron]

As JR mentioned, shelf EQ at high boost present risks of overload at frequencies outside the hearing range.
IMO, a big shelf boost needs to be complemented with a good HPF/LPF.

There is a real beauty and professionalism (I feel) in working without shelves entirely. You obv have to have a low Q setting, .4 or .5, available easily on the bell. In developing an all-round console parametric that will be fast, accessible, and function very similarly across mono and stereo/dual mono models, I’ve wrestled with whether to include shelves at all. It’s simpler not to - less parts. Harder to overload the low end, certainly. But the single biggest catch is that we’re all SO used to using shelves that a designer would be shooting themselves in the foot to not include them. Me, I like the straightforwardness of these designs, where the unit screams “that’s what the wide bandwidth setting is there for” instead of “here’s a shelf.”

 

[JohnRoberts]

I spent years in design trying to protect customers from themselves.

JR

 

[abbey road d enfer]

The one condition being that the SVF Q has to be set the same as (or lower than) the single pole buffered Q.

Not necessarily. There are some examples of 2nd-order shelf EQ.
You may want to check the K+H UE series. They are S & K based.
I used SVF HP and LP with variable "Q" for an extra control of the global response.

 

[atavacron]

Amek 2500, ISA 430, referenced by Jakob upthread. ISA 430 Hi/Lo are switched Bax, looks like, so I didn’t screencap, but the PDF is in Tech Docs.

 

[atavacron]

@abbey road d enfer I'm not finding a Neve 83022 (or 88032 for that matter). Is that SKU right? I see there’s a modern 8803. I did reference the DBX905, which I know is handy for its frequency control scheme, but I find the drawing itself confusing.

 

[nille]

Neve 83022
https://groupdiy.com/threads/neve.44877/post-1066777

 

[Brian Roth]

Remember that the Net EQ, for correct operation, must use the center-tapped pots. Failure to do that results in unpredictable interaction between bands. Since shelves have usually a wider BW than bells, this interaction may be more noticeable.

My life has been crazy, so I'm just catching up with this thread. Re-read it several times.

I'm probably exhausted but I think the NetEQ is based on an old article Porter wrote. He claims"no interaction" and doesn't use a CT pot. See attached.

Bri

 

[atavacron]

Neve 83022

Wow, comprehensive low impedance design in both the cascade and SVF sections; I like that. 1981 is pretty early for this sort of approach, pushing the 5532 and 5534 down to their drive limits… Anybody got a frontpanel pic? Looks like a strip’s dynamics/eq section.

 

[atavacron]

My life has been crazy, so I'm just catching up with this thread. Re-read it several times.

Glad to have ya.

I'm probably exhausted but I think the NetEQ is based on an old article Porter wrote. He claims"no interaction" and doesn't use a CT pot. See attached.

Bri

Yeah that’s the same NetEQ mix topology. Cool circuit, all killer no filler. Maybe the wide separation between the bands helps with the no interaction aspect.

 

[atavacron]

Shoot, which Neumann Danner cassette was it that’s just three bells and hi/lo cuts, but the bell Qs are labeled 3 / 1 / 1/3 octave and are done with SP3T toggles? I wanted to drop a pic here and ask if anyone’s used it or something similar, and if only having Qs of .4 / 1.4 / 4.3 felt limiting for finer bus work or mastering.

 

[Brian Roth]

IIRC the Porter design as in the Net EQ used a center tapped EQ boost/cut pot to ensure the center point was indeed flat.

Maybe I'm missing something.

Bri

 

[Brian Roth]

Looking at Porter's claims in the mini article I posted.....

hmmmm.. Well, a classical Bax is a mess is a mess of interacting/"moving parts", so Porter's claim of "no interaction" was accurate.

So, do we use multiplies of cascaded stages for an usable EQ???? Like I mentioned, I'm tired and worn out these days from multiple family issues, so I am not always asking correct questions.

I saved Porter's ancient article for decades....hmmm...he mentioned 5534 and 5532 opamps which dates into the 1980-ish era.

lol.... shrug

Bri

 

[richiyobs]

Hi folks
I builded Barry P. Simple Bax eq and it s great!
Yes center click pot for gains are important.... At beginning used log standard one and you can imagine how difficult was to find the flat condition without analyzer...
Also tried Steve Dove type and also this one funny and good results
Best

 

[atavacron]

So, do we use multiplies of cascaded stages for an usable EQ????

Paul Gold of Salt Mastering (who’s on here somewhere but I don’t know his user name) was talking for a while in the mid-teens about developing an all-shelving eq, two lows and two highs. That sort of reinforced my idea of using a four-band Net EQ topology and having the two lows and two highs both shelve. I’m sure it’s been done before. The EQ Olympics would be if one switch changed all four bands from bell to shelf, with no opportunity to change just one.

Check this out though, people, around the nine minute mark. Seems like a mix amp combined outputs and lived to tell the tale. Also, four shelves.

 

[Brian Roth]

Never tried an EQ with two adjustable single pole filters each for LF or HF that were built as a variant of Porter's "summing" design. lol it may be MAGIC!

Bri

 

[abbey road d enfer]

I'm probably exhausted but I think the NetEQ is based on an old article Porter wrote. He claims"no interaction"

You're right. My mistake. I stand corrected.

and doesn't use a CT pot.

As someone else said, it's for a positive center point.