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[Art Welter]

Tom Reid wrote on Sun, 19 July 2009 00:46

Art Welter wrote on Sat, 18 July 2009 19:43 Tom Reid wrote on Sat, 18 July 2009 12:26 Try degaussing the drum. Tom, the disc that rotates in the drum is aluminum. It can't get magnetized. There is no magnetic storage, the system uses the oil and special rotating aluminum disc as a sort of capacitor storage. cool, Thanks, I get the technology behind the drum.  It's not making a good charge to read anymore.  Didn't know it was aluminum.     That would be the first place I'd look, the media.  Electronics work fine (since you've swapped out many parts), it's just the media won't imprint anymore.

Thinking about it, it could also be the "mudflap" neoprene like record head material changed over the course of time.

[John Roberts {JR}]

Art Welter wrote on Sun, 19 July 2009 13:12

Thinking about it, it could also be the "mudflap" neoprene like record head material changed over the course of time.

I have never messed with an oil can delay, and have little desire to, but I have wasted many years messing with CCDs so perhaps some common mechanisms apply.

The calculus for S/N in "charge storage" mechanisms are simple.

!- transfer efficiency in pumping charge into the storage device, or in this case storage media.
2- hold efficiency, or charge leakage losses between write and read.
3- read efficiency.

My uneducated guess is that the oil matters. The thickness of the oil film, spacing to electrodes, and perhaps even contamination in the oil.

Electronic charge storage devices electronically assist and manipulate the write and read cycles using substrate biases to force more complete charge transfer. I suspect a crude passive charge storage device will be lossy at both ends where the read is destructive, and the write is averaged with former charge state.

I find it remarkable that this approach ever worked at all, but assuming it did, yes the condition and orientation of the mudflap (electrode) should indeed matter. If the electrode is touching the metal drum that could shunt off charge.

If S/N changes with drum rotation speed that suggests mechanism #2, while I expect some deterioration with slower speed.

JR

PS: Does the aluminum drum need to be grounded? Or perhaps not grounded?

[Art Welter]

John Roberts  {JR} wrote on Sun, 19 July 2009 13:11

Art Welter wrote on Sun, 19 July 2009 13:12 Thinking about it, it could also be the "mudflap" neoprene like record head material changed over the course of time. My uneducated guess is that the oil matters. The thickness of the oil film, spacing to electrodes, and perhaps even contamination in the oil. I find it remarkable that this approach ever worked at all, but assuming it did, yes the condition and orientation of the mudflap (electrode) should indeed matter. PS: Does the aluminum drum need to be grounded? Or perhaps not grounded?

The oil can echo devices do work, though the high frequency response is severely limited, nothing much above 1K makes it through the process- and I don't think Dolby would help!
If you look at the picture posted in the original post, you can see the drum, which is just a common tin plated steel can like used for paint.

The aluminum disc inside is rotated by a motor similar to what is used in old turntables, erector sets, etc. Some units used belt drives, this unit uses shaft drive with a rubber idler drive wheel.

The disc is electrically isolated from the case, but the erase "head" is grounded to shunt off the echo charge, which I have counted around 18 repeats when it is disconnected.

And yes, the condition, type, and quantity of oil is crucial, the unit won't work at all with most types of oil. The reason most have gone to the scrap heap is because if not stored upright, the oil leaks right out of the bushings, then when started up and run dry, the special surface gets burnished off, and no amount of oil will fix it, just like when you run a transmission or engine low on oil.

I was flabbergasted in looking inside the unit the first time, it looks so simple: three mudflaps with wires coming off crimped holders, and a rotating disk.

But without the special etching and anodized process, and correct oil, the "simple" device would not work.

Art Welter

[Alex Schultz]

Art Welter wrote on Sat, 18 July 2009 19:57

John Petrucelli wrote on Sat, 18 July 2009 17:49 Art, The circuits are fairly typical tube amplifier stages, so no, they are not doing anything special beyond that. If you've tried a number of different amplifying circuits with no improvement, maybe the disc itself is faulty and can no longer hold an electric charge? I think Bob L offered some spare parts? JP If there is no special impedance match in the circuit, you are probably right, the disc may be shot, so not worth any more experimentation. As Bob also said, (and I knew) oil can echos are low-fi at best. The people that are most fond of them are really liking the extra tube preamp stage the unit adds, the echo is just nostalgic. It may have been run dry long enough that the "magic" disc etching is just not thick enough to hold enough of the special oil to get a decent S/N anymore, though the surface does look unusual, almost like a compact disc. Thanks for the insight. Art Welter

Maybe mount the disk in a drill press and give the disk a new "etching" with 1200 grit - or finer - emory paper? Ya never know.........

[Tom Reid]

Quote:

I was flabbergasted in looking inside the unit the first time, it looks so simple: three mudflaps with wires coming off crimped holders, and a rotating disk.

JR mentioned CCDs.  
I was amazed by the some of the movie players of that age.
Later villified when they perfomed as anticipated.

[Tom Reid]

Alex Schultz wrote on Sun, 19 July 2009 17:58

Art Welter wrote on Sat, 18 July 2009 19:57 John Petrucelli wrote on Sat, 18 July 2009 17:49 Art, The circuits are fairly typical tube amplifier stages, so no, they are not doing anything special beyond that. If you've tried a number of different amplifying circuits with no improvement, maybe the disc itself is faulty and can no longer hold an electric charge? I think Bob L offered some spare parts? JP If there is no special impedance match in the circuit, you are probably right, the disc may be shot, so not worth any more experimentation. As Bob also said, (and I knew) oil can echos are low-fi at best. The people that are most fond of them are really liking the extra tube preamp stage the unit adds, the echo is just nostalgic. It may have been run dry long enough that the "magic" disc etching is just not thick enough to hold enough of the special oil to get a decent S/N anymore, though the surface does look unusual, almost like a compact disc. Thanks for the insight. Art Welter Maybe mount the disk in a drill press and give the disk a new "etching" with 1200 grit - or finer - emory paper? Ya never know.........

The equivalent of formatting the drive?

[David Buckley]

John Roberts  {JR} wrote on Mon, 20 July 2009 07:11

I find it remarkable that this approach ever worked at all

+1

I'm sure the OP has yet to try high voltage drive from a valve stage and I suspect that may be important.  The more signal one can get on in the first place, the lower should be the S/N.  

[Art Welter]

David Buckley wrote on Sun, 19 July 2009 21:02

John Roberts  {JR} wrote on Mon, 20 July 2009 07:11 I find it remarkable that this approach ever worked at all +1 I'm sure the OP has yet to try high voltage drive from a valve stage and I suspect that may be important.  The more signal one can get on in the first place, the lower should be the S/N.

As the OP (me) stated in the OP:
I have tried using pre-amps, small power amps, various input and output transformers, and can get lots of echos from it, but the signal to noise  ratio is about 1/1, actually more noise than signal.

To elaborate, I have used several watts (from a tube/valve amp) straight in and through many different transformer types to see if the problem was impedance or power related.

Higher drive levels were only marginally better than pre-amp levels.

Art Welter

[SteveKirby]

The historical links imply that the oil is just to help limit leakage.  It would seem that there would need to be some sort of dielectric coating or rim on the disk to hold the charge through the next few rotations.

[Mac Kerr]

SteveKirby wrote on Mon, 20 July 2009 13:52

The historical links imply that the oil is just to help limit leakage.  It would seem that there would need to be some sort of dielectric coating or rim on the disk to hold the charge through the next few rotations.

In the patent application I thought I read that the recording media, the rubber belt, was used because the charge was a "static" charge and needed a non-conductive medium so it didn't stray. The oil was to reduce leakage back to the air. I would think S/N would be influenced by both the level of charge on the belt from the record head, and the depth of erasure provided by the erase head. I would expect to need very high voltage in the record head to impart a significant "static" charge, and good contact and grounding to erase it. The oil also seems to need to be non-conductive and to provide a good seal against outside air.

This seems like a fun project to play around with if you know about tubes (I don't), but it might be easier to renovate an Echoplex for that type of effect, or use modern electronic FX, but where's the fun in that?

Mac