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In the Forum: Analog Playback
In the Thread: Tell me about more about Ortofone SPU Sound.
Post Subject: The Mono cartridges ground loop syndromePosted by Romy the Cat on: 6/3/2008
 Brian Clark wrote:
Per Winfeld confirmed to me that the coil former assembly is rotated 45% compared to the regular SPU such that only lateral motion is sensed. Unfortunately I did not think to ask him how the coil/coils was/were wound. Since the quoted DCR is significantly higher than for the SPU GM - 100ohms vs 6 ohms - I can only speculate that (a) there are more turns on the the former and (b) there are two coils are connected in series and the two outputs are taken in parallel.

My SPU Mono is currently with Expert Stylus for re-tipping and I have just rung them but unfortunately Mr Hodgson Snr, who had a long working relationship with Winfeld until the latter's retirement, was not in. Hopefully I should be able to establish the facts with him tomorrow.

Brian.
Yes, Brian,

I understand about the SPU construction in term of vertical motion absence, thanks,  but my interest was about electrical construction. SPU is by nature are Stereo Pickups and your speculation that they use two coils are connected in series with parallel out sounds like pleasure. What I observe confirm this speculation. Thos types of the cartridges are inclined to ground loops. I just finished my new phonostage with different grounding schema and it deals way better with the mono cartridges ground loop syndrome. It is still not completely defeats it as I feel it might not defeatable. In my old configuration I used a dedicated mono phonostage where it was no problem but with the new phonocorrector I would like to use stereo and mono needles in the same way – I am not sure that it is possible. Both right and left primaries of my transformer have referent to ground and with mono cartridges with stereo parallel leads they ALSO connected on the cartridge side – here is where the loop take place. Each individual mono lead – right or left are dead silent but as soon the second channels is connect to primary I got the loop. It is not too strong but it is there. I think I need to put a switch that would disconnect the right and left primary in case the Mono SPU is used. I ‘m still thinking about a more elegant solution….

Rgs, The caT

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