Need help with DIN to RCA phono cable troubleshooting

I don’t think this is optimal in a signal ended system. The fifth pin grounds the arm. You run the risk that if someone connects the shield to the RCA at the preamp end then an earth loop is created.

You are correct, however the comment was made in response was to this:

Nandric - for all phono both balanced and unbalanced the arm earth ( 5th pin ) should be a separate wire which you connect to preamp chassis. This simply grounds the arm itself and has nothing to do with the cartridge signal.

Which in the case of balanced operation is false. In a balanced setup, the tone arm ground is pin 1 no if ands or buts. You might want to take a look at how the balanced standard operates- AES file 48 defines it.

(FWIW, we were the first to recognize that the phono cartridge is an inherently balanced source and began using it that way in 1988. If there was a ground loop problem I'm sure we would have run into it by now, but if you understand how balanced works- the ground is **ignored** by the input of the phono preamp. This could be done by an SUT, which would have its primary connected to pins 2 and 3 of the XLR which is the cartridge connection, and no connection whatsoever to pin 1, which is the tone arm ground.)

If I read your post correctly you are grounding the floating signal shields at the sending end ( tonearm ) via the arm ground wire to the preamp chassis, whereas I ground the floating signal shields at the preamp end separately to the preamp grounding post. Since all three shields are floating and only connected at one end they cannot create an earth loop.

No, I don't think you read it correctly. I think it also possible I did not understand your post either.

In a single-ended system the cartridge is **never** at any point grounded to the tone arm, its grounding wire or the chassis. If the (single ended, with RCA input connection) preamp is wired correctly (and many are not) the circuit ground will not be the same as the chassis ground (if it is, a ground loop occurs). Usually the circuit ground is referenced to the chassis by some means that prevents any significant ground loop current. So the signal "ground" (which is arbitrary as the source is balanced), which is really the 'minus' or inverting output of the cartridge, is tied only to the circuit ground and not the chassis. Meanwhile the tone arm ground is tied to chassis and not the circuit ground. No ground loop is possible.

Again, what I actually said was that in a cable that has a conventional twisted pair plus shield construct that I prefer to disconnect the floating shield from the RCA and connect the floating shield ( not the -ve signal from the cartridge ) to the preamp chassis via drain wires. In my experience that arrangement has lowered the noise floor.

If such a wiring situation were to exist, this would be the proper practice (if this is what you meant the first time 'round, IMO you stated it much better this time!). However this is unusual in a single-ended connection (although in this case it is easier to see how the cartridge is in fact a balanced source).

atmasphere

... FWIW, we were the first to recognize that the phono cartridge is an inherently balanced source and began using it that way in 1988.

Ralph, you are mistaken. Broadcasters used balanced phono connections way back in the '60s and '70s, and maybe even earlier. Back then, LPs and 45s were common in radio studios, even where the station also used broadcast carts.

^^ Actually except for the balanced thing, Dover and I were on the same page. I thought I had made that clear in my last post.

I do feel I should clarify some things in **your** post however :)  (please note that I am not quarreling)

First, if an XLR appears on a preamp the expectation should be that it supports the AES file 48: the balanced line standard. However in practice you are correct in that buyer beware- in high end audio, the XLR connector is often there in appearance only.

I feel the term 'balanced' is the more common word but I like 'symmetrical' as that might be more descriptive when used to describe the preamp.

The reason to go balanced with a phono setup is not simply because the cartridge is a balanced source! There are two advantages- the one most people know about is the possibility of lower noise, particularly if the preamp is fully differential from input to output. Any noise imposed on the cable cannot get amplified. BTW, if a step up transformer is used, all transformers have the ability to operate balanced and even if the output is single-ended, the ability to reject noise in the cable is maintained.

The second benefit of balanced line is less understood by audiophiles, but was actually the intention of balanced line from its inception- and that is to reduce or eliminate any artifacts that come from the interconnect cable itself. For anyone that has been considering a large sum of money to buy an expensive single-ended phono cable this should be welcome news. The fact is that if the interconnect cable is built correctly (twisted pair within a shield, pin 1 of the XLRs being tied to the shield and no need for a separate ground wire) it will not need to be expensive and will compete easily with cables costing thousands of dollars.

IOW it will sound better.

Now you see debate in high end audio all the time about whether balanced is better or not! Some people say its only better if long lengths are employed. While it does excel at long lengths, even if its only 6 inches its still going to work better. But quite often the debate arises simply because the high end audio equipment used didn't support the balanced standard and as a consequently the result are variable!

That standard is there for a reason (which is to eliminate cable artifact).

I know this sounds a bit circular, but frankly I don't understand why a manufacturer would present an expensive product that does not do what it should. This is distressingly common in high end audio!

Here are the elements of balanced operation. If you follow these, the cable will have far less artifact and so will sound better:

1) pin 1 is ground, pins 2 and 3 carry the signal.
2) ground is ignored. It is for shielding only and at no point carries any signal current!
3) the cable will be a twisted pair within a shield.
4) the output of the balanced connection will drive a low impedance if possible, which will appear between pins 2 and 3.

In the case of a LOMC, point 4 is very easy, since many LOMCs are loaded at only 100 ohms. For this reason the interconnect cable should not impose any sonic artifact whatsoever.

FWIW, most high end audio manufacturers get messed up on 2) above. Quite often if they have a balanced product, they design it such that the output of pin 2 is with respect to ground and the output of pin 3 is with respect to ground. This is a mistake- the output of pin 2 should be with respect to pin 3!

@cleeds , Thanks for pointing that out. I have worked on a lot of broadcast gear over the years and have yet to see see any balanced phono sections and so conflated that to thinking that no-one had sorted out that phono cartridges are a balanced source. I do know for a fact though that our MP-1 was the first balanced line preamp ever offered in consumer audio and that its phono section was the first fully differential phono section ever made.