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!
