Tape Project Forum

General Category => General Discussion => Topic started by: ironbut on June 30, 2008, 05:43:06 PM

Title: Image for Stellavox
Post by: ironbut on June 30, 2008, 05:43:06 PM
(http://img247.imageshack.us/img247/7719/picture1sh7.th.png) (http://img247.imageshack.us/my.php?image=picture1sh7.png)
Title: Cello Audio Suite Tape Input Module
Post by: stellavox on July 01, 2008, 04:14:59 AM
You are looking at the Cello P603 tape head playback module from their Audio Suite sitting on a folder containing the design drawings and performance measurements.  I picked this and a bunch of other Cello modules/parts/drawings/etc. from the person who bought the inventory at auction early this decade, where they?d been sitting ever since.

As far as I know, Tom Colangelo designed the P603 in the mid 80?s, and it descended from the Levinson ML5 tape electronics he designed in the mid 70?s. All the input modules in the Audio Suite (B100/101 - phono, B200/201 ? high level) had the same ?architecture?; with each channel consisting of a plug-in ?front end? and ?output? op-amplifier board constructed using discreet transistors.  The differences between modules had to do with feedback and input loading configurations.  The Audio Suite was powered by an outboard ?Master? power supply which furnished regulated +/- 30 VDC to the main chassis via an umbilical cord.  These voltages were further regulated down to +/-25VDC by additional plug-in regulators in each module ? one per channel.

Each module could be mounted in a custom 19? rack-type enclosure, holding up to 10 modules depending on their individual width ? the P603 takes up 3 module widths. The modules bolted into a rear-mounted busbar assembly consisting of 10, quarter-inch (cross-section) copper buses running the width of the chassis; two for ground, two for +/- voltage, three for left/right ?main? output (including signal ground) and three for left/right ?monitor? output.  The P301 Output Module has a switch to select either the ?main? or ?monitor? bus.  Each input module accepts balanced inputs via rear-mounted Fischer connectors or unbalanced inputs via RCA jacks.

The P603?s front panel has three 10-turn potentiometers per channel, offering adjustable equalization at 31.5hz, 1Khz and 10Khz.  It also has a tape speed switch for each channel to allow for different tape head loading at 15 or 30 ips.  The module originally cost $5000!  Heck, I guess a fully ?loaded? Audio Suite cost around $20K.

I?ve verified that it functions correctly but now have to go back to the ?graveyard? to see if I can find any sheet metal parts to put together a chassis.  The original was composed of separate panels and brackets.  Hopefully a few still exist ? don?t want to think of having to fabricate a new one.  I was lucky to also get a phono and output module but no high level input modules seemed to be there. The Audio Suite was not configured with tape recording electronics but if I can come across a few high level input modules I may try to modify them for record.
 
An Audio Suite configured for tape playback was apparently sold along with the Cello Palette, a five-frequency variable equalizer, to a number of recording studios and record companies.  I was also able to pick up two sets of Palette Preamplifier assembled PC boards.  The Palette Preamplifier differs from the original Palette in that it uses IC op amps versus discreet parts and variable pots for the equalization adjustments versus special stepped attenuators in the original ? otherwise they look pretty much the same.

I found it interesting that Mark Levinson chose the Palette?s six EQ bands and ranges after considerable listening/experimenting: 15hz [+/-29dB in 1dB increments}; 120hz [+/-14.5dB in ? dB increments]; 500hz [+/-6dB in ? dB increments]; 2Khz [+/- 6dB in ? db increments]; 5Khz [+/- 12dB in 1/2db increments] and 25khz [+/- 24db in 1 dB increments.  All those who have been lucky to hear it ?in action? have been QUITE impressed.

To be continued?

Thanks Steve for loading the picture for me!

Title: Re: Image for Stellavox
Post by: Studer Fool on July 01, 2008, 02:49:53 PM
Fascinating!  I look forward to your continuation Charles!
You state:
Quote
The P603?s front panel has three 10-turn potentiometers per channel, offering adjustable equalization at 31.5hz, 1Khz and 10Khz.
Do you know what the plus/minus db range was for each frequency was?
Presumably the tape eq was NAB? and at what speeds?  Do you have the schematics?

cdw
Title: Re: Image for Stellavox
Post by: ironbut on July 01, 2008, 05:39:42 PM
There was a review in Stereophile of the Pallette and I seem to recall it was in the same issue that had an extensive article on Pope Records who used the Pallette to eq somewhere in their recording chain. I threw out most of my old issues a while back. But at the time (1986?) it inspired me to hunt one down and spend a little time with it. It was miles ahead of anything I'd ever tried at the time, but who knows. Those sonic memories have a tendency to grow more golden with the passing of each year.
Title: Re: Image for Stellavox
Post by: stellavox on July 02, 2008, 06:20:04 AM
Chris,

Ready for that Buffalo to Albany, Erie Canal bike ride - How many miles total is it again?

without hooking the module up and playing back a tape with "reference" test tones, I can't opine what the range of the EQ adjustments might be, but its probably pretty wide - and is supposed to allow for IEC as well as NAB compensation (the material I have doesn't say).  As far as speeds are concerned, the existing speed switch simply inserts a loading resistor for each and I'd opine again that there should be plenty of adjustment for speeds down to 7 1/2.

The schematic, considering the op amps as gain "blocks" is pretty simple.  I'll try to take a 'jpeg of it and if legible could send it to Steve for posting. 

Charles

Forgot to mention - a number of years back, I built a tubed equalizer to mimic the Palette.  Came out pretty nice.  Tried posting some info and pictures here but couldn't.  Again, if Steve wants to be really   nice I could send the 'jepgs to him. Waddyathink Steve???
Title: Re: Image for Stellavox
Post by: Studer Fool on July 02, 2008, 03:56:47 PM
Charles,
You asked:
"Ready for that Buffalo to Albany, Erie Canal bike ride - How many miles total is it again?"

It's a 400 mile ride in 8 days.  You can see what it's all about here:http://www.ptny.org/canaltour/index.shtml (http://www.ptny.org/canaltour/index.shtml) 
I'll be riding my Easy Racers "Gold Rush" Replica, a fabulous recumbent bicycle.  http://www.easyracers.com/04-gold_rush.htm (http://www.easyracers.com/04-gold_rush.htm)

But to move back on topic, that is quite an archaeological audio dig you have going on there Charles.  Thanks for the alignment eq frequencies as this is something I have been contemplating in view of doing outboard playback electronics, hence my curiosity in db range deemed needed/useful.  Do you recall what machine Cello was using for the transport, was it the Studer A80/RC like at Levinson?  Only having a switchable input loading resistor when switching speeds is interesting as that alone would be enough only for NAB at 71/2 and 15 ips which are both 50 Hz, 3150 Hz (3150 us, 50 us) unless of course they used their own tape eq standard.  IEC/CCIR for 71/2 to 15 ips changes from 2240 to 4500 Hz (70us to 35 us) .  Having a 1KHz control alone it seems difficult going from NAB to CCIR/IEC without something more.  Perhaps there's support documentation that would clarify the expected use.  Or much more likely only NAB was expected of course!

cdw

Here below is an experiment trying to place and do a table on tape eq's.  Preview won't work for me so I apologize if it ends up gobbledygook:

TAPE SPEED
Professional
Commercial Tape Records
and Home Recorders
IEC, RIAA, & EIA
Open-Reel
Broadcast Cartridge
IEC & NAB
IEC1 (IEC) IEC2 ( NAB)
95 mm/s 3.75 in/s
Not Used
Professionally
[NAB only]
50 Hz, 1800 Hz
(3150 s, 90 s)
[Commercial-not std]
[50 Hz, 1800 Hz]
[(3150 s, 90 s)]
50 Hz, 1800 Hz
(3150 s, 90 s)
190 mm/s 7.5 in/s
0 Hz, 2240 Hz
(, 70 s)
50 Hz, 3150 Hz
(3150 s, 50 s)
0 Hz, 3150 Hz
(, 50 s)
50 Hz, 3150 Hz
(3150 s, 50 s)
380 mm/s 15 in/s
0 Hz, 4500 Hz
(, 35 s)
50 Hz, 3150 Hz
(3150 s, 50 s)
[Commercial-not std]
[0 Hz, 6300 Hz]
[(, 25 s)]
Not Used
for Tape Records
and Home Recorders
760 mm/s 30 in/s
[IEC1 is obsolete]
[0 Hz, 4500 Hz]
[(, 35 s)]
AES-1971 (no NAB)
0 Hz, 9000 Hz
(, 17.5 s)
Not Used
in Cartridge
Not Used
for Tape Records
and Home Recorders
Title: Re: Image for Stellavox
Post by: ironbut on July 02, 2008, 05:24:20 PM
Quote from: stellavox on July 02, 2008, 06:20:04 AM
Chris,

Ready for that Buffalo to Albany, Erie Canal bike ride - How many miles total is it again?

Hey you guys,.. I used to live in a little town (village) called Lancaster NY. Looking at those pictures along the canal really brought back some great memories. It's great to see that the folks back there have preserved and restored some of the beautiful villages around there. When I was in Lancaster, I used to bike to East Aurora all the time. It's a great area for fossil hunting too.

The schematic, considering the op amps as gain "blocks" is pretty simple.  I'll try to take a 'jpeg of it and if legible could send it to Steve for posting. 

Charles

Forgot to mention - a number of years back, I built a tubed equalizer to mimic the Palette.  Came out pretty nice.  Tried posting some info and pictures here but couldn't.  Again, if Steve wants to be really   nice I could send the 'jepgs to him. Waddyathink Steve???

Hey, bring it on Stellavox. I'd love to see that stuff too!