Cello Audio Palette

Hi DSP_Geek, now that you have clarified that you will also use this in a recording chain your modifications make a lot of sense to me. :D

We live in an imperfect world and I still have quite a lot to learn. I am learning to equalize my CDs properly for the small space I use them in, and in the face of major hardware changes.. I'm a long way from the 30 something guy who listened to the Palette all those decades ago.

The fact that we are talking about this design more than 30 years on I think is a testament to the concept and execution of the Palette. I turned down the opportunity to get one many, many years ago - given what I now know I sometimes regret that decision.
 
Recording chain? Oh no no no, this is for my home system. The tunable parms are based on my experience in live sound, is all. To get the original Palette all you gotta do is set the controls for the heart of the sun, er, default frequencies and you're good to go. Anything else is gravy.

And, yes, Burwen moved the needle a damn sight when he designed the Palette.
 
Somewhat over 30 years ago I had the opportunity to work with Dick Burwen for a time at Copley Controls, and got the full basement system demo which of course included what was probably the original prototype of the Audio Palette. He explained that the center frequencies and boost/cut values were very carefully determined through listening tests, etc.

I do remember that part of the demo involved playing a piece of music where panning certain controls on the Palette resulted in quite a change in the placement of certain instruments in the sound stage. I was extremely surprised to say the least. I don't remember a lot of details this long after the fact. Just wanted to mention that there was nothing arbitrary at all about the philosophy behind the design.

I was a purist (call that naive?) and didn't believe in any EQ or tone control use at the time. These days I use a MiniDSP SHD and Dirac3 for room/system EQ, somewhere along the way I changed my mind.. LOL
I also had an opportunity to work with Dick and Copley Controls. In 1983, my Diasonics 10 kW per axis Class G Gradient power project was canned and replaced by 3 racks of Crown 2 kW Class ABs. I can't believe none were ever stolen. Artifact-free MRI images required RTI noise and spectral purity as good as high end audio at the time. The Crowns were great, but in the application, were power sucking hogs. Plus, the racks were too fragile for mobile MRI applications.

While we were trying to bootleg a solution, along came Dick with his "Sine Wave Class D Antenna Rotor" array-configurable motor drivers - my first experience with 10 kW per axis Class D, or any Class D, for that matter. In those days, IC designers hadn't solved the issue of Class D modulator linearity. Delta Sigma modulators were still telephone quality.

Dick's class D design was exceptional. We bought ~ 1,000 of Copley's compact, efficient, light weight, exceptionally low THD devices. He literally saved our mobile MRI business.

Dick's a fan of equalizers. For years I'd complained that the "spectral purists" of the CD Standards group and their abhorrence of RIAA or NAB-like equalization, created some noisy CD player preamps for those of us who were studio headset users.

Don't let anyone try to convince listeners that properly-used equalization causes "distortion". Distortion is the creation of harmonic terms that aren't in the original material - the genie out of the bottle. Equalization can be done and undone and a boon to recording/playback.
 
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Cello Palette preamp

Here is a version done with state variable filters. The problem with other designs presented is that the 'Q' did not match that of the Cello. This one is a subtle variation on the Barry Porter studio parametric EQ, a well known classic circuit. I have built this circuit before and was really happy with the results. Unfortunately a stereo version contains lots of opamps. You would want to use quiet ones such as the LM4562. I have a stereo version using all thru hole parts in the works. The PCB is out for fab now. The PCB for both channels fits into a 1U chassis.

The schematic for one channel is here: Dropbox - Barry Cello Parametric EQ_00.jpg - Simplify your life

It is a huge jpeg.

I think this design has one cut/boost setting for the four inner bands and another for the lowest and highest ones. The palette has different cut/boost for each band. Is that correct?

I notice that you changed the centers of the lowest and highest filters from 15->20Hz and 25kHz->20kHz. What's the reason for this?

http://www.celloseattle.com/ctdocs/prodserve/peripherals/audiopalette.html
Frequency Adjustment Controls:
25 kHz control: +/- 24 dB in 1.00 dB increments
5 kHz control: +/- 12 dB in 0.50 dB increments
2 kHz control: +/- 6 dB in 0.25 dB increments
500 Hz control: +/- 6 dB in 0.25 dB increments
120 Hz control: +/- 14.5 dB in 0.50 dB increments
15 Hz control: +/- 29 dB in 1.00 dB increments

If I built one of these, I'd use digitally-controlled devices for the pots. Then the palette can go in the rack and be controlled remotely.

My passive LCDuino-based preamp uses an R-2R type relay-controlled log attenuator board for volume. The resistors on these attenuator boards could be calculated so the stereo attenuator log boards become linear pots. I'd have to write new code for the control software and add controls for the palette to my remote control.

I looked at many digital pots such as the Microchip MCP42xxx a few years back and dismissed them because the "pot" sections in these devices aren't purely passive resistive devices, but chains of transistor and resistors configured to give the desired pot-like behavior. They have high-ish distortion and mostly poor tolerances and many require biasing the audio signal or otherwise dealing with an A/C signal feeding a device with voltages limited to 0-Vcc. Does anyone know of some chip more suitable for audio that would be cheaper, simpler, and smaller than my LCDuino R-2R solution?
 

Jaytor

Member
2019-10-11 8:33 pm
Oregon
If I built one of these, I'd use digitally-controlled devices for the pots. Then the palette can go in the rack and be controlled remotely.

My passive LCDuino-based preamp uses an R-2R type relay-controlled log attenuator board for volume. The resistors on these attenuator boards could be calculated so the stereo attenuator log boards become linear pots. I'd have to write new code for the control software and add controls for the palette to my remote control.
I had the same thought. I owned one of the original Cello Audio Palette's in the late 80's/early 90's and absolutely loved it. At the time, I had a custom listening room with a cable conduit in the concrete floor so I could mount the Palette in a custom coffee table in front of the listening position. After moving a couple times and having no easy way to use the Palette, I ended up selling it. Probably the one piece of gear that I regret selling the most.

I am currently using the AMB attenuator boards in a balanced tube-buffered preamp I am close to finishing up. I wrote my own control software since I wanted to add some extra features and use a TFT display (couple photos below), but I think using Arduino-controlled relay attenuators for the band adjustments would be fairly straightforward. Depending on the band, 0.25, 0.5, or 1db steps would make sense. I'd probably make a custom rechargeable remote with six rotary encoders connected using wifi or bluetooth to the base unit (instead of trying to use optical which I think might be a bit slow and cumbersome).

This project is definitely in my "queue" but I've got another tube amp project I've started working on that I want to build first.

PRE3_Build18.jpg
PRE3_Build8.jpg
 
I am currently using the AMB attenuator boards in a balanced tube-buffered preamp I am close to finishing up. I wrote my own control software since I wanted to add some extra features and use a TFT display (couple photos below), but I think using Arduino-controlled relay attenuators for the band adjustments would be fairly straightforward. Depending on the band, 0.25, 0.5, or 1db steps would make sense. I'd probably make a custom rechargeable remote with six rotary encoders connected using wifi or bluetooth to the base unit (instead of trying to use optical which I think might be a bit slow and cumbersome).

My custom rechargeable remote is in the middle of the photo. It's part of another project which controls an ABX switchbox and other relay-based boards and is programmed to do blind ABX testing as well as just switching relays. I plan on integrating this code with the LDCunio code after re-architecting the system to run on on embedded Pi or similar in the preamp. This is about eight year old tech, using xbee radios. The new system would be service-based on the Pi and eventually controlled by an app over wifi.

Controlling the palette from this would be my highest priority if there was a clear path to building one.


custom-rechargable-remote.png
 
Late 90's, I saw 5 or 6 Audio Palettes were piled up on the floor of the hallway of Sterling Sound, a famous mastering studio in NYC (Now NJ). They all looked like heavily used, so I guess they were also used as professional mastering processors in 90's.

Before internet age, mastering was an esoteric and secret process, so this is probably not something that a lot of people know...
 
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Ten years ago I was working for DTS. At that time there were maybe 12 dedicated Mastering Studios left in the Hollywood area. I was told that there were three times that only a few years before. At the time they were all being faced with having to make major investments so that they might handle DTS:X, Dolby Atmos and Auro-3D. It represented a huge investment. Last I knew their number had all but disappeared and they are doing video and their audio tracks. I expect the pure music houses are mostly small bedroom and office operations these days.
 
Its all about money. The unwashed won’t pay for music if they can avoid it, pop stars and their groups are professionally managed to maximize profits as soon as possible, before the shine wears off. I assume this means there is less incentive to encourage any real artistry in the mixing end, just apply a formula on a computer to suit well researched music tastes, thus maximize short term appeal for better sales. Is this too cynical? I don’t know the industry, I hope it’s not like this. We need more like Chesky.
 
Its all about money. The unwashed won’t pay for music if they can avoid it, pop stars and their groups are professionally managed to maximize profits as soon as possible, before the shine wears off. I assume this means there is less incentive to encourage any real artistry in the mixing end, just apply a formula on a computer to suit well researched music tastes, thus maximize short term appeal for better sales. Is this too cynical? I don’t know the industry, I hope it’s not like this. We need more like Chesky.
Dear Bigun,

We're all too critical and cynical.

Speaking of the Great Unwashed, my aging, presbycusic ears still can't tolerate mp3s. For uncompressed audio, I carry a CD player, very-well-hidden in my backpack, hard-wired to my headset. Took me almost 10 years before I bought my first CD Discman. I was hacked when my 2016 RAV4 eliminated the CD player.

Spent the last few years of my career, professionally testing ANC headsets in an anechoic chamber. The result - it took me 5 years of side-by-side testing to decide which brand to buy for my personal use.

Nothing has changed - when I bought our first color TV, I had 3 side-by-side in our living room.

Designing A/V gear has destroyed my senses of hearing and vision. Designing medical scanners has made me a Royal PITA whenever I'm being scanned.

Remember, a) it was the CD that turned many of the masses into semi-audiophiles and b) porn has always been a major driver of photo, video and memory development.

ron
 
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Ten years ago I was working for DTS. At that time there were maybe 12 dedicated Mastering Studios left in the Hollywood area. I was told that there were three times that only a few years before. At the time they were all being faced with having to make major investments so that they might handle DTS:X, Dolby Atmos and Auro-3D. It represented a huge investment. Last I knew their number had all but disappeared and they are doing video and their audio tracks. I expect the pure music houses are mostly small bedroom and office operations these days.
It broke my heart after I 'd left National. Each bench in the Audio labs had several Audio Precision 2700 Analyzers and Tek Curve Tracers. When they closed Bldg C in Santa Clara, they sold them, surplus. Today, I could use at least one of each. First, my garage lab is too cluttered. Second, I'm too cheap to buy them and Third, my wife would kill me, or worse.