I don't know the answer, but that is an interesting feature.
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I know I can buy the XLR junction box. But I think these are highly over priced. At least for a VPI Scout they are. But then I would need a XLR-RCA cable and I would perfer a RCA-RCA cable.
From what I understood is that if I disconnect the ground from the plus in the RCA junction box I can use it balanced.
There is another way to do it as well.
Since your box has a ground post is why you can do this. The signal is actually balanced all the way to the box. All that happens in the box is that the RCAs are connected. The RCAs are insulated from ground.
If the barrel connection of the RCA is not treated as the shield connection (which is the ground post) then you can set up a true balanced line. The only issue you may have is if someone touches the sleeve connection of the RCA while its playing- you may get a buzz at that point.
But otherwise this can be a totally balanced setup. BTW, we offered the first balanced line preamp (MP-1) back in 1989, and this has been one means of making the balanced connection to the phono that we have used since that time. The complete scenario is in our preamp owner's manual, which can be downloaded from our site; click on 'Support'.
Ground post = shield of **both** channels, pin 1 on both XLRs.
Center pin of RCA = pin 2 of XLR
ground sleeve of RCA (which is insulated from the ground of the box BTW) = pin 3 of the XLR.
The connections for pin 2 and pin 3 are a twisted pair within the shield of the cable.
The advantage of doing this is that the phono cable will cease to have an effect on the sound (worth doing IOW).
The Phono stage has only RCA inputs. There is a diagram in the manual describing how to wire an RCA interconnect to go from RCA phono box to the RCA input. As I interpret it:
The cable needs to have two wires and an external shield.
One wire is for the +ve (Middle pin), the other for the -ve (Barrel)
The shield is not terminated to the barrel.
The shield is terminated for both interconnects to the ground wire at the source end only. The ground wire to the junction box.
Imagine something like Belden 1800F, where instead of using XLR's you use RCA's.
Here is a link to vinyl engine that has a post on this:
Brf, Since Mordante uses a RCA to RCA cable with a separate wire for earth ground, I think Ralph is saying the opposite, that Mordante CAN use his RCA cable and still effect a balanced connection to his preamp. But at the preamp, we need to know what that switch really does, to be sure one way or the other. Further, and even more important, we need to know whether the phono stage itself is a truly balanced device, internally. The presence of the XLR input jack is not proof of that. If the circuit is not balanced, then there is little to be gained by doing anything.
Mordonte, contact the mfg and find out what that switch does. I used a balanced Ayre phono pre amp with both RCA and XLR inputs. The single ended / balanced switch simply grounded the inverting (or negative) signal. So leaving it in the balanced position even while using the RCA inputs gave me connection to both inputs of the phono pre diff amp inputs. Its not the ideal way to do it but electrically it was sound. There was a clear difference in the sound with the switch in balanced vs the single in favor of the balanced. You might be able to tell just by experimenting.
As was said above, having a seperate ground wire is required.
BTW I have a VPI XLR junction box that I got for my
Aries II that I never used if it would work for you should you want to go that way.
Thank you all for the advice. If I use a special RCA to RCA cable. I would need to modify the junction box. Maybe I will do this inthe future.
For now I will just enjoy the music. My girlfriend would not be amused if right now I would start about buing cables. But maybe in the future I will keep an eye open for the Nordost Blue heaven leif RCA-RCA phono cable.
I am no expert, but here is what I understand. Sorry if this is too obvious and too long. Much of it is just repeating what has been said above. But, here goes anyway.
A cartridge has a + and a - lead, with no ground. My guess on the VPI is that the + goes to the center of the RCA output jack and the - goes to the sleeve of the RCA output jack. My guess is that the switch on RCA input on your phonostage simply lets the sleeve float (balanced) or ties it to ground (unbalanced). In that case, a standard RCA should work for balanced, with Atmasphere's cavity that the shield of the wire is now carrying a signal so can be sensitive to noise.
A wire with 2 conductors and an outside shield is a better option. It sounds like you may already have that type of cable, since you say you have a separate clamp for ground on the cable. If that is the case, you may be all set. Just connect the grounds on your cable to the grounds on the VPI and RCM and you may be all set. But you cable may also just have 1 conductor and shield with an extra clamp to connect the ground screw to the shield. You can check with a multi-meter (see below).
To be sure, I would call VPI and ask them specifically how the RCA outputs are wired. I would contact RCM and ask them what the switch does.
If you can use a multi-meter, you can test what the switch on the RCM does. Just check for continuity from the ground post to the outer sleeve of the RCA input with the switch in both positions, with the unit unpluged and nothing connected to the RCA of course. If it just connects the outer sleeve to ground when in unbalanced mode , there should be continuity.
You can also use the meter to check the wiring of your interlink and be sure that the center, sleeve and clamp are all independent.
You can get a continuity test or cheap multi-meter for 10 bucks if you do not have one.
I have read that you should be careful with a multi-meter on the VPI side, since the current from the meter may damage the cartridge. I have no idea if this is true or not, but I would err on the side of caution. If you disconnect the cartridge leads, then you could test how the leads on the shell connect to the RCAs.
My nexts steps would be to contact VPI and RCM and also check to see how your cable is wired.
My guess is your are all set, but I would check with VPI and RCM just to be sure.
The Ayre phonostage manual gives a good description of connecting a RCA to a XLR. You are not using an XLR, but the diagrams are good for understand the wiring. At least I found them useful when trying to figure this out originally.
Brf - I think the issue is how the VPI junction box is wired. I think the negative lead from the cartridge may go to the sleeve of the RCA, but am not sure. If it is, then there is a solution in just wiring the cable correctly. If the negative goes to ground or is not connected to the sleeve of the RCA in the junction box, then the junction box needs to be re-wired.
I checked my Scout junction box. The sleeve of the RCA output is not tied to the ground nut. So, I believe the negative sides of R & L of the cartridge are connected to the corresponding sleeves of the RCAs, as I suspected. It seeems that the configuration is, although I did not check the continuity from the headshell to the RCAs.
L + Center Pin L RCA
L - Sleeve L RCA
R + Center Pin R RCA
R - Sleeve R RCA
Chassis to grounding nut on junction box.
This is the situation that AtmaSphere described above and is described in his manual.
The RCM manual clearly shows that the switch on it simply connects the sleeve of the RCA either to ground or to the minus input of the phonostage.
So, a standard RCA should work for balanced mode, with the caveat that the shield on the RCA cable is the negative balanced signal, not a ground.
The best solution would be a 2 conductor cable with a ground shield. Again, it is not clear what configuration your cable is, but it may be the appropriate cable.
Again, I am not an expert, but that is what I have found out. Since it corresponds to what AtmaSphere said, it might be right. He actually knows what he is talking about.
Hope it helps.
Brf - I understand the RCM schematics. However, you also need to understand the VPI configurations to be sure everything works in balanced mode.
I am simply trying to provide a view of the connections on the VPI side. Fortunately, I think the VPI provides both the appropriate positive and negative signals to the RCA connections that will allow the RCM to function with balanced inputs, with the proper cabling
To be overly blunt, just looking at the RCM configuration is not sufficient to be sure the whole system will work correctly. You need to look at the VPI side also, which I think I have done.
Fortunately, I think the VPI and RCM configurations will work to provide the appropriate balanced connections needed, with the proper cabling.