[trebejo]

So I have this TVC as a preamp. It is a naturally balanced circuit. It wants to use those xlr outputs.

I have this very nice amp. Really, the nicest amp you could ever want. It has tubes in the input stage. It's really nice! And... it only has RCA inputs.

Supposedly, after doing a little unorthodox interconnecting, there is an additional 6 db of gain. Maybe a lower noise floor. Who knows. If nothing is going to blow up, it would be fun to give it a try...

Soooo... if I take a cable that has an xlr plug on the TVC preamp output end, and an RCA plug on the amplifier input end, and the "+" plug of the xlr is connected to the "+" plug of the RCA, and the "-" plug of the xlr is connected to the "-/ground" plug of the RCA, and the "ground" plug of the xlr is not connected to anything in particular... will the wonderful FV Ultra 550 amp be unhappy with this arrangement? Will there be smoke and firemen?!

btw this TVC is a a very passive little fellow, who doesn't even use a power cord. There is a DAC feeding the TVC, but that's supposed to be buffered from the amp by the transformer...

[avahifi]

I think you will either get nothing out at all as the plus and minus signals will cancel each other, or you will get lots of hum because of no ground connection, or maybe both.

Not enough kauphy this morning to think clearly about this.  Need help. 

Frank

[turkey]

It should work, although there's a good chance of getting hum too. It's easy enough to solder up a pair of cables, so give it a shot.

[Wayner]

or



Wayner 

[turkey]

or



Wayner 

I've done similar cables to go from balanced to unbalanced. If I remember, sometimes you had to connect the shield only at the XLR end to avoid a ground loop.

It never worked as well as using a transformer or an active circuit to do the conversion. I preferred transformers because they worked in both directions, isolated the two sides (less chance of grounding problems), and didn't have batteries to go dead at 3A when no stores were open.

[Wayner]

Agreed. Start here and see where it goes. Just remember that pin 2 is suppose to be hot, tho I remember some manufacturers within there own equipment lines swaped 3 and 2,,,,,, I remember reading this somewhere. I also recall this as the converter cable for microphones from XLR to 1/4".

The standard is:

Pin 1 is Shield.
Pin 2 is Hot
Pin 3 is Neutral.

Wayner

[gjs_cds]

Hey Wayner---How exactly is this a "win"?  It looks like a conversion for convenience more than anything else.  I fail to see how this could contribute to better sound?

[Occam]

So I have this TVC as a preamp. It is a naturally balanced circuit. It wants to use those xlr outputs.
.....
Supposedly, after doing a little unorthodox interconnecting, there is an additional 6 db of gain. Maybe a lower noise floor. Who knows. If nothing is going to blow up, it would be fun to give it a try...
....

The above implies that the secondary of the TVC has a center tap that is connected to signal ground. By moving the ground to the bottom of the secondary, rather than the center tap, leaving that unconnected, you would get that additional 6db gain.

You need to verify (or divine the actual) configuration. Use an ohmmeter. Measure the resistance between pin 3 of the input and pin 3 of the output XLRs (same channel). If the inputs to your TVC do the same measurement, but between the signal ground (outer shell of the input RCA, and Pin 3 of the same channel's output.
Measure the resistance between pin 1 & 3 of an output XLR. Measure the resistance between pin 2 & 3 of the output XLR.
Post your results. Those measurements will tell you how to configure your TVC for your application.

Hasn't anyone hereabouts heard that old adage applicable to both audiophiles as well as carpenters.
Measure twice, cut once
Heck, I'd settle for measuring once.

It seems that all the responders believe you TVC output is floating (unreferenced to ground), which would be quite unusual.

EDIT:Given the equipment, and a willingness to spend $10 at Radio Shack for the cheapest of multimeters, you'd have to work awfully hard to get ground loop hum.

FWIW,
Paul

[trebejo]

Thank you guys!

A buddy is mailing me a couple of cables to try and see which way works best (if at all). Wayner, your diagram is one of 'em!

Alas, I do not own the most obvious and helpful measuring device, an ammeter/ohmmeter/etc.

I own another measuring device though--a camera.  I'm going to take a photo of the innards and post it tomorrow. From memory, the RCA outputs of the TVC were "+" and then "-/ground" joined together.

La gran clue is that Nicholas@promitheus is pretty certain that there'll be 6db of gain.

As for how is this a win, well, that's one of the things I aim to find out! The most immediate "win" is that I'd get to bring down the volume knob by three clicks and, who knows, maybe try to find out what the amp sounds like when it is doing some actual clipping--er, no, I mean, lower the output impedance of the preamp and perhaps get a lower noise floor and whatever that means in terms of what a pair of tin ears like mine can hear.

Or, to put it bluntly, "because it's there". 

[Wayner]

Hey Wayner---How exactly is this a "win"?  It looks like a conversion for convenience more than anything else.  I fail to see how this could contribute to better sound?

This, as the post implies, is a compromise. The solution offered is something that may "work". It has no implication to be a "win" senerio and I have no idea where that came from in the first place.

Just trying ty help a guy convert from XLR to RCA.

Wayner