ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
As probably you all know by now, is that the relay, which switches between 33rpm and 45 rpm, is not the most reliable version. Due to aging contacts are becoming oxidated and cleaning isn't the solution, and only temporarily.
As of the different switching behaviour of the relay, a replacement isn't easy to find. Modification with different relays needs some tinkering with probably an extra PCB.
So, my modifcation changes the original, but it works.
The target is to maintain a steady 33 rpm, which probably is used for 99% of the time, I think.
So I have done some recalculating for some resistors if I shortend the contacts for 33 rpm. Shorting the contacts for 33 rpm eliminates the failing contacts for 33 rpm. But it will give a problem with the speed at 45 rpm, when this speed is selected..
So I recalculated the resisitors R14 and R16. These resistors are becoming parallel to R15 and R17 (and 2R2) when the 45 rpm speed is selected.
To be short.
Change the R16 to 22K (calculated 27K) and R14 to 47K (calculated around 39K).
First adjust the speed for 33 rpm with R15, then next the speed for 45 rpm. with R16.
This mofication will avoid an unsteady, or even completely dead 33 rpm speed.
The downside is this. The 45 rpm speed adjuster at the top plate becomes nearly unusable. The 33 rpm adjuster stays in working order.
Here a picture where to shorten the relay.
Interesting but I would rather just get Beolover's drop in replacement relay. That way there is no change to the original circuit and the new relay is very reliable.-sonavor
I agree to stick with the original design. But the time-frame was very limited (it is going to be used as a part of demonstration this afternoon, with B&O biggest loudspeakers, who would have thought of that ), and these components can be bought at a local store.
There are pro's and con's about changing the original design. You might wonder why they didn't design this in the first place. A minimum steady current is flowing through the circuit, where at it's original design the current (at therefore the speed) is interrupted during switching.