Mackie "Perkins EQ" - the schematic

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cuelist

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From: http://www.mackie.com/technology/perkinseq.html

"The goal of Perkins EQ was to bring the classic EQ sound of British mixing consoles of the '60s and '70s and put it into a small-format mixer, for the first time ever. So Cal started with the Wien Bridge circuit topology--a very musical design made popular by mixing consoles from the hallowed 'British Invasion.'"

"To get past the tradeoffs of the Wien Bridge, he wrote 20 pages of equations describing the seemingly simple Wein Bridge circuit in complete detail. After solving the equations with calculus, Cal was able to specify capacitor and resistor values that would give Onyx mixers an extra 6dB of control (±15 dB) without excessively narrowing the "Q" or bandwidth of the filters. Next, Cal employed combining filters for minimum phase shift, making the entire EQ section as musical as possible.

Well here it is - looks like a bog standard wien-bridge implementation to me.

 

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JohnRoberts said:
Oh... he used calculus... is that magic?

Maybe it passes for magic at Mackie  ;D

The only difference I can see between this "magic" and that of say, most Soundcraft consoles (starting with the 1S back in 1979), is that the ratio between the two frequency defining capacitors is slightly larger; 2.6 versus the 2.2 of the Soundcraft circuit.

But 20 pages of calculus....   :eek:

 
I am still hopeful that one day engineers will stand up against the marketing crowd, and say "don't be fu*king ridicilous" on some press releases.
 
So the question is... does it sound any good? If not, Mr Perkins' calculus was in vain!

And what on earth is a '50KE' pot?
 
This type of arrangement of the Wien-bridge EQ is limited to 9.5dB boost/cut when using equal value caps.
There are two simple ways of increasing boost/cut.
One is to add a resistor from inverting input of the opamp to ground.
The other is to increase the capacitors ratio. This also increases the bandwidth (lower Q).
 
abbey road d enfer said:
The other is to increase the capacitors ratio. This also increases the bandwidth (lower Q).

It's probably that part that took'm 20 pages
 
abbey road d enfer said:
This type of arrangement of the Wien-bridge EQ is limited to 9.5dB boost/cut when using equal value caps.
There are two simple ways of increasing boost/cut.
One is to add a resistor from inverting input of the opamp to ground.
The other is to increase the capacitors ratio. This also increases the bandwidth (lower Q).

I did not think about the resistor from the inverting input - thanks!

I shall experiment...

 
sahib said:
I am still hopeful that one day engineers will stand up against the marketing crowd, and say "don't be fu*king ridicilous" on some press releases.

I consider myself a passable engineer who actually worked for several years in product management. So I not only got to write ad copy, but i was in the trenches competing against the subject organization so i will apologize in advance for my sour grapes.

The reality about advertising is that frequency matters. I won't waste time explaining all the reasons why but i witnessed an ocean change in the MI industry where the influence shifted from music store dealers advising walk in customers about what they should buy to satisfy a need, to those same customers being presold by magazine ads to request a specific model.

In the early days when they had only one mixer to sell, they were placing more ads for that one product, than I could to cover over a thousand SKUs. Needless to say I got my ass kicked as customers walked into dealerships demanding a mixer with PFL despite not knowing what it was or why they would need it on a 6 mic input mixer (they actually didn't on such a small mixer but it was a powerful way to differentiate their product).

Of course i was dealing with a different corporate culture that supported a strong dealer base vs. hard selling around dealers direct to consumers...  times change.

To respond to the above post, I was able to write honest ad copy and still be persuasive. Some readers even questioned my accurate claims  ;D,  so I had to be careful to not exceed market expectations (Peavey is only considered good for the money, like a cute blind date, never pretty.) but without the benefit of huge ad placement frequency I lost the market share horse race to the new self proclaimed pretty girl. The vast majority of customers are not capable of evaluating marketing claims like engineers, so they believe it when some me-too design is touted as some Edison-like second coming. I found it frustrating as an engineer (with one patent related to heat sink design) to see their power amp advertising program tout a clearly inferior thermal design, with pictures and arrows as somehow being superior... kind of like the big lie, repeated enough the market believes it.  I would appear weak and disingenuous if I publicly pointed out the shortcomings, in low frequency ads. There's an old saying in the newspaper industry, don't pick a fight with people who buy ink by the barrel. being right or wrong wouldn't matter if I picked a public fight...  those are just the realities of advertising.

I actually worked to ramp up my advertising budget funded by product sales, and my program was starting to work but that product targeted budget got grabbed by a new advertising director before i could prove decisively to upper management that increased advertising works. I was stereotyped as an engineer who couldn't possibly understand marketing so I lost that battle and  moved out of marketing..

JR
 
JohnRoberts said:
The reality about advertising is that frequency matters.

Another reality is that reality has very little to do with marketing and advertising.

I base this on 25+ years in the A/V industry, most recently as product manager in a couple large, multinational corporations. The truth (!) is - everybody lies and nobody cares. Competitor A exaggerates his figures by 25% so you're told to do the same otherwise you'll look inferior. Customers, at least the ones who's been around the block a few times, knows this and discount by the same amount. Less experienced customers just takes it on face value.

Ridiculous, yes, but nevertheless true. Is anyone ever caught out doing this? Nope, no one ever really checks and magazines have long stopped doing tests. Most of them are happy editing press releases into "reviews" and taking advertising money.

I remember when Mackie introduced their "XDR" series preamps, about 10 years ago. Lots of hyperbole - here's a 'sound bite':

"No other company in the world has spent the sheer number of research hours and $250,000 in R&D costs on a single mic preamp design that we just did. Greg Mackie believed it was worth it because a new vastly-improved design could be used on so many different mixer models – and thus could be used by far more people than any expensive esoteric outboard preamp. We started with blank paper, concerned only with matching or exceeding the performance of $1000 to $2000-per-channel esoteric outboard preamps. By the time we were finished, we ended up re-engineering far more than just Mackie's core preamp technology."

More here if anyone wants to read the propaganda piece:  http://www.mackie.com/technology/XDR.html

I will say that they are pretty good at what they do, Mackie's PR department. For example, who'd have thought of describing a simple common mode chokes as: "...bifilar wound DC pulse transformers with high permeability cores..."

The XDR amps are not bad but again, like the "Perkins" eq, it's just about as 'industry standard' as it gets. Where the $250.000 went I don't know.



 
Don't take me seriously. I have been married to a marketing executive for over 20 years. ;D

In terms of Mackie's 10 year old press release, I don't believe they spent that amount of money on a frigging mic-amp either, but even if they did, then they were and are probably the only company in the world because no other company would be stupid enought to do that. 
 
It is entirely possible that they spent that much money on total engineering budget for their next generation mixer, probably including a chunk of Greg and Rick Chen's salary (if he was still there then).  Peavey could claim they spent 40 years perfecting their mic preamp and not be lying.

The big lie is that there are huge differences between mic preamps as most are approaching theoretical noise floors, etc.

I can't speak about other industries but I don't find that everybody lies in the sound industry while I have found several well respected companies guilty of exaggerating the significance of some selected specifications when it serves their interest. For example, one well respected power amp company invested a lot of their advertising dollars into touting their numerically high damping factor numbers while the real world difference between a damping factor of 300 and 3 million (at the amp terminals) is not audible.

We (Peavey) even caught companies lying, or at least making erroneous claims, in ads where they published direct product performance comparisons. They cancelled the ad as soon as we put them on notice, but I suspect the people who saw the ads believed the false claims. I'd love to see them rerun the ad with the correct numbers but that wouldn't help them sell their product.

There is a large gray area in how loudspeakers are specified where advertisers often must sink to meet the sleaziest competitor to not lose in such distorted comparisons.  The shift to direct selling, or pre selling consumers from magazine ads compels advertisers to stretch to differentiate their products any way they can, as customers often make up their mind to buy from a causal reading of specs without really understanding what they mean. 

Caveat emptor. Advertisers can distort the truth without actually lying.

JR
 
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