Interesting quote on 1970s EQ design

[Guest]

From Barry Porter (Trident, Cadac,Raindirk ) - now sadly deceased

Old quote - but useful...
"The EQ of 70's stuff was invariably based on standard tone control
techniques for the HF and LF, and coils for the MF, all wrapped around a
two or three transistor amplifier. Distortion was high, but as there was
plenty of 2nd harmonic, it sounded pretty good. In the late 70's, when
people were moving to single transistor gyrators, I developed a system
based on a dual inverter main signal path with state variable filters
for the peaking sections and single pole high and low pass for the HF
and LF shelving sections.
This design, which I initially used in a rack mounting EQ sold by Audio+Design, was first used in a Cadac console.
It was then "borrowed" (or stolen - take your pick) by several UK console
manufacturers, leading to a rather nasty argument between myself and
Soundcraft.
I resolved this by publishing the circuit in Wireless World
magazine for all to use.
Most applications of it have been awful, caused mainly by the use of TL072 op-amps and the like, and the refusal of others to bother to find a source of centre-tapped pots, which are essential to stop interaction between the sections and to maintain a constant Q characteristic.
"

Just out of interest - here is the the link for Barry's Net EQ
http://www.wavefront.mcmail.com/neteq.pdf
http://www.wavefront.mcmail.com/readmeeq.pdf

 

[Guest]

Putting more info and quotes from Barry here (all available on web sites - but very interesting non the less)
Unfortunately since his death - Barrys web site is no more...

What I don't yet know how to do is control the input gain of all six amps in a 5.1 Mixer using a single potentiometer.
Had the same problem when I designed the Cadac C Series 5.1 recording console. VCA's were the obvious answer, as none of the digital pots will handle a decent signal level, but although VCA's from That Corporation would meet most of the customers requirements, they were eventually rejected on the grounds of noise and distortion.
The final answer was a Penny + Giles 6 gang pot - at around 160UKP each!

How much is the attenuation of the pan pots on your mixing console??
Back in the 1970's, I was Technical Director of Trident Audio
Developments, and we had this continual argument about how much
attenuation to put into our pan pots. Some people said 3dB whereas
others said 6dB. Given a bit of thought, it becomes obvious that the
amount of reflections in the control room will have a considerable
effect.
In the end, we did some tests in the Trident Studios control
room, and after much time, came to the conclusion that the correct
amount was 4.6dB (Nothing like being accurate)
At around the same time, Clive Green at Cadac was also doing tests aty
Lansdowne Studios, and he came to the conclusion that 4.5dB was
correct.
From that day, Cadac consoles (which I now do the basic design) have
been 4.5dB down in the centre, and as far as I am aware, there has
never been a single complaint.

 

[NewYorkDave]

An interesting fellow, indeed. When I received word of his death, I promptly saved his entire website to my hard-drive for future reference.

 

[Guest]

[quote author="NewYorkDave"]An interesting fellow, indeed. When I received word of his death, I promptly saved his entire website to my hard-drive for future reference.[/quote]
ah.....
any chance of sharing... I can't find head nor tail of any of his stuff