REDD EQ, Helios 69 and Dick Swettenham

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ruffrecords

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I was recently asked if I could design an EQ that worked like the 'pop' and 'classic' EQ plug ins that used to be used in the REDD47 consoles and predecessors. Using the curves published in 'Recording The Beatles' I came up with a circuit based on a stripped down and modified Helios 69 EQ with a switch to selec 'pop' or 'classic'. I was then asked if I could not make it so both the the 'pop' and 'classic EQ curves were available at the same time. In doing this, a very strange thought occurred to me. The Helios treble EQ is virtually identical to the EMI 'classic' EQ curves (the frequency, step size and gain range are identical) as is the bass cut except for the frequency it works at. The bass boost is very nearly the same but tweaked from a shelf to a bell curve. The clincher is that the 'pop' 4.7KHz peaking EQ is a stepped version of one of the Helios 69 mid boost frequencies.

I then realised that Dick Swettenham, who designed the Helios 69 EQ, had previously worked at Abbey Road studios in the service and design departments so he must surely have had a deep understanding of the innards of the REDD EQ.

I am sure you can now see where I am going with this. Is the Helios 69 EQ simply a modified and expanded version of the REDD EQ?

I simulated a cut down version of the Helios 69 EQ (pic attached)  and it is surprisingly easy to get curves very close to those of the REDD EQ.

What do you think/know??

Cheers

Ian
 

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Dylan W

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Fascinating, Ian, had no idea Swettenham worked at Abbey Road. You know, I was just thinking about something yesterday.. I love the Abbey Road RS 127 plugin (a model of the outboard Brilliance Box, apparently used as an extension to the Pop/Classic board eq). It is a +/- 10dB boost/cut in 2dB steps, frequency selectable at 2.7K, 3.5K, and 10K. It's apparently another passive design. My Christmas copy of Recording the Beatles is still in the mail somewhere, so I don't know if the curves are in there, but it would be unbelievable to have a couple of these.

Dylan
 

Fablab

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To add the Brilliance in the circuit may be a great idea. I know the RS127 plugin and I find it amazing!
 

ruffrecords

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Funny you should mention the RS127 because as soon as I sent my outline design to the guy who asked about the REDD EQ, the first thing he said was could I add the RS127.

I'll look into it.

Cheers

Ian
 

ruffrecords

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I am in two minds about doing an RS127. One the one hand it is little more than three boost/cut frequencies on the Helios EQ, albeit with switched boost/cut on a single control so in that sense it is already available.  On the other hand, from reading Recording The Beatles, it seems the RS127 was used a lot as a passive balanced lossy stand alone outboard EQ so we could contemplate replicating that. Or we could do a brand new EQ which incorporates the REDD EQ and the RS127 in one.

Thoughts/preferences?

Cheers

Ian
 

ruffrecords

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Damn, that was quick AND decisive. I think we have a consensus!! OK, so my next EQ project is a REDD EQ with incorporated RS127.

The only real question is this. The RS127 had boost/cut  frequencies either side of the 4.7KHz 'pop' boost in the REDD EQ so it effectively just extended the range of frequencies the REDD had from one to four. In theory, with a REDD EQ followed by the RS127, you could boost at 4.7KHz with the REDD and boost/cut at another frequency with the RS127 at the same time. Do we want to be able to do that or can I incorporate the 4.7KHz in with the RS127 frequencies which means that although you can only boost/cut one frequency at a time you are not limited to just boosting at 4.7KHz?

I have a strong suspicion they selected a single frequency depending on the material and rarely if ever boosted at two frequencies simulataneously - but who knows?

Cheers

Ian
 

Fablab

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An option may be: 10khz control (High), 100 hz (bass) and to include the 5khz in the middle with the others values of the RS127 (2,7khz, 3,5khz, 5khz)

 

nille

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They talk about centre frequencies being shifted by the interfacing transformer on page 10 in the Abbey Road plugin manual.
Perhaps something to consider.
 

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Gearsix

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I know the RS127 is a passive circuit ... the REDD Eq is passive, too?
Anyway a passive circuit may be a good choice so each one can decide to put a tube or discrete makeup amp
I am building some REDD 47 preamplifiers and it may be amazing to have a complete channel strip of the REDD 51 Console
 

letterbeacon

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Yes, it would be great to use the REDD47 as the make up gain stage after the EQ and then there's also Ian's tube make up gain PCB to choose from too.
 

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