Thank you Brian - you confirmed what I feared. 

Caveat emptor.  The seller is the former Van denHul repair guy in Germany -  Detlev Brod.  He offered a new SPU mono, at a price too good to be true.  I specified the GM25, and when I contacted him to inform him of the error, he told me that it doesn't matter - they are both monos!!!!!

since these are conical styli, is there any downside to retipping with a "non-Ortofon" stylus.  Assuming the retipping is done properly?  Does supension, compliance, output, or something else change?

scott

skushino wrote:

Thank you Brian - you confirmed what I feared.Caveat emptor. The seller is the former Van denHul repair guy in Germany - Detlev Brod. He offered a new SPU mono, at a price too good to be true. I specified the GM25, and when I contacted him to inform him of the error, he told me that it doesn't matter - they are both monos!!!!!

Since these are conical styli, is there any downside to retipping with a "non-Ortofon" stylus.Assuming the retipping is done properly? Does supension, compliance, output, or something else change?

Brian Clark wrote:

Perhaps Zyx will come out with a mono cart one day soon since they are now fashionable. Brian.

Sorry to be responding to an old post but ZYX has just released a mono cart which costs less than 400 dollars in Japan.
I found out when I was recently lectured on how all stereo MCs are flawed in channel balance because ZYX has got the patents on the remedy. They all lack “real stereo” which leads to compromised stereo imaging and S/N ratio.

Now, Romy has taught us to think about what is missing or wrong with the sound first before we upgrade, and I think that is very good advice. I am therefore rather skeptical and am in no rush to dump my Ikeda and Koetsu.

But, I was told that this phenomenon is very easily verifiable by playing left and right speakers separately and noticing big imbalance for non-ZYX carts.

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.

Brian Clark wrote:

My stereo corrector (834P with air-vane caps) has a shorting switch across the two channels at the input. I suggest you incorporate the same. With it out of circuit I did indeed get that hum you refer to with the SPU Mono. Switching to short eliminated it.

I see, it is exactly what I thought. So, you short the “hot” between two channels at the input? It is already shorted on the cartridge side but you shorting it locally (on the corrector side) kill the loop across the cable. The same effect might be archived if we drive signal from SPU via one cable and then split it on the phonostage side via a switch or having a switch on outside of the corrector feeding right and left cable. It looks like your solution is less painful… Oh, well, not I need a switch and to drill a hole… I will need to learn to disengage the mono switch. I wonder if other options are available… for instance to shunt the RCAs on the cable that feed signal from SPU. Then it will be still bridge locally and the loop will be not 120cm but a few millimeters.

Brian Clark wrote:

What form has your new corrector taken?

Something similar to what you have, mine is combined with ET2 transformer.

http://www.goodsoundclub.com/LatestPosts.aspx?ThreadID=5856

Romy the Cat wrote:

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….

Well, it is resoled and it is resoled remarkably simple and effective. Now both stereo and mono cartridges with max out gain of my playback have noise of a CD player. Furthermore the geometry of the cables became to be irrelevant for ground loops. A magic solution? You bet, at least in my case.

I spoke today with Dima and he noted that what I am complaining about should not take please. As one of the possible solution he proposed to decouple the grounding of the transformer primary from ground with a pair of small 50R-100R resistor. I did exactly that: I removed the direct short and I put instead 100R resistor on each channel from ET2’s primary to ground.  It works like a champ. Dima, spent a long time explain to me why it will be immaterial for stereo and work one in mono… and it works!!!