Studer Motor hum

[Linnovice]

Morning all. I have a late model Studer A807 MkII machine. It functions perfectly but has an annoying motor hum when in play mode. Nothing in ff or fr only in play. It’s not at mains hum frequency (50kcs), if there is any frequency it’s around 1.5 seconds cycle. At normal/louder passages it’s inaudible but on quiet passages it can be quite intrusive. I don’t think it’s binding brakes or anything straightforwardly mechanical as it sounds electrical.
Would any of you knowledgable guys/girls have an idea what this could be?
I would appreciate any guidance with this as I’m completely flummoxed.
Mike

[Radio Wrangler]

Not sure of the 807, but studer/revox used a milled series of slots in the bell of the Papst outer rotor capstan motor, along with a variable reluctance sensor to read the passage of the slots. The permanent magnet in the sensor applies a little force to the bell which varies as the slots pass and this creates a quiet characteristic whine. Different pitch for different tape speeds.

At mains freq, it could be from a motor winding or the pinch wheel engagement solenoid.

David

[Ted Kendall]

The 807 capstan motor is DC, has a capacitive tach head and doesn't produce the classic "Studer whine". This could be a cyclic load variation, or perhaps the capstan motor needs lubricating. Is there audible wow or flutter?

[Linnovice]

Hi Ted,
It’s a late model capstan motor. There is no audible wow and flutter, I also lubricated it (with the correct oil) earlier this year. The sound is not so much a whine, more of a drone.

[Linnovice]

Hi all. I'm in the process of servicing my Studer A807 MkII. All is well except I think I have created a problem for myself.
When it comes to the capstan motor the service manual quotes three variants. The first requires a specific oil which should be applied every six months, the second is similar except that you apply a specific liquid grease once a year and is identified by a red label, the third does not require oiling at all as it has ball race bearings and no label.
So, I checked mine before starting and found a red label but it's in a position where it is not possible to read. I ordered the correct grease as per the manual and then applied it. I then found that when I spin the capstan by hand its started making a noise so I removed the top circle and bell washers to investigate only to find it's a ball race version. I fear some of the liquid grease has got into the bearing (although they are sealed) and diluted the existing grease.
What can I do? Can I just change the bearing as in the spooling motors or is it a very specific bearing? Is it possible to remove the liquid grease by forcing another high melting point grease into the bearing? Does anyone have any suggestions?

[John Caswell]

Have a look at the Nagravox Australia site. he carries all sorts of spares and may be able to offer advice/help/suggestions

John

[Linnovice]

Hi all, the answer to my question is yes, you can change the bearings. It’s a straightforward procedure and replacement races are readily available. Easiest option is not to oil them in the first place though ;-).