Phono Pre-amp with XLR

quote]However making a balanced amp is more expensive since you will need almost twice the components.[/quote]

It is more expensive but you do not need twice the components. Maybe 50% more if you are talking tubes, maybe not even that if you are talking solid state.

While I do think that true balanced phono amps are a good thing. This because with MC the signal is very low and you can use all the help you can get in amplifying the signal with getting increasing the noise level. However making a balanced amp is more expensive since you will need almost twice the components.

Also in pro audio almost no equipment is truly balanced they just use a RCA/XLR conversion at the in and outputs of amps. This is done so they can use longer cables.

In home audio you will often see the same. XLR inputs the an IC that converts the signal into non balanced. To me this is pointless since almost no one uses long cables in home audio. If a non balanced amp has XLR inputs I think it should say this in the manual. Otherwise people might think that any amp with XLR inputs is also balanced.

Tdaudio, if the preamp is differential, but you only drive one input, perhaps the non-inverting input (with the other input being tied to ground, where the minus output of the cartridge is also tied), the gain will be exactly the same as if you were driving both inputs, assuming the source to be the same cartridge in both cases. What you loose is the cable immunity (tonal neutrality) and rejection of noise in the cable.

What would be more frightening is if you encounter another male dressed as a female XLR. That would be decidedly unbalanced.

I'm wearing an XLR costume for halloween just to frighten people. Male.

Tdaudio, If you read Ralph's (Atma-sphere) post and then read mine from yesterday, you will find a remarkable confluence. I have been using an MP1 for about 14 years now. I think some balanced phono stages offer RCA phono inputs because, as Ralph indicated, the world has not beaten a path to his door. Some other manufacturers fear that offering XLR inputs will frighten off persons who have typical RCA-terminated phono cables. I like that Ralph is a man of principle and won't compromise his design by offering an inferior connection to a balanced circuit.

Atmasphere, nice explanation of the cable and connector issues.

And I agree that using RCA connectors with a balanced input is to be avoided.

Lets assume a phono pre has RCAs with the inverting lead grounded and only the noninverting signal feeding the balanced diff amp. What does that mean to the bal diff amp vs having both the noninverting and the inverting signals in a proper xlr configuration.

Going beyond CMR and such, it seems like there might be some difference in feeding half of the diff amp vs feeding both inputs. But maybe not. Still the same gain?

Thanks again, TD

RCA jacks can be used as an input to a balanced preamp. How it works is that the RCA jack is isolated from the chassis ground, so that the 'ground' connection of the RCA can function as the inverting input to the balanced preamp.

There are some problems with this approach- you still have to use a ground post, perhaps no problem if the ground connection is supplied. However, the interconnect between the tonearm and the preamp **must not use the minus (-) output of the cartridge as a shield for the plus (+) side!** This would result in hum.

Now assuming that such a cable issue is dealt with, you still have the problem of the fact that at the RCA connection itself, the 'minus' (inverting) connection is shielding the 'plus' (non-inverting) connection. This damages the overall Common Mode Rejection Ratio of the system; IOW, it makes it susceptible to hum.

You can set up the RCA so only one of the inputs of the preamp is driven and the other side is at ground, but again the CMRR of the preamp is not available to the user, although you don't have some of the hum susceptibility of the scenario in the prior paragraph.

So, on a very practical basis, the XLR is a superior connector. Any use of the RCA for a balanced connection is a sort of kludge approach.

Atmasphere, with a true balanced phono pre amp, does it make a significant sonic difference if the pre amp is designed with RCA inputs where the inverting signal from the cartdrige is grounded at the RCA jack leaving only the noninverting signal going into the balanced diff amp?

Thanks, TD

Prochk3, I looked at the phono pre ad and saw it claimed the unit was fully balanced input to output. But it has RCA instead of xlr inputs.

If the RCA is grounded as it usually is, the noninverting or plus signal is still going to the noninverting input of the balanced differential phono amps circutry. Its called a dif amp because it ampliflies the difference between the noninverting and the inverting inpts. So even if the inverting input is grounded you still get a signal at the output because of how the diff amp works. Thus you have a the xlr for the output of the balanced phono pre.

Now the outside of the RCA input jacks may be floating, not grounded, and thus the inverting signal from the cart still makes it to the iverting input of the bal diff amp.

That is not the ideal way to handle a balanced signal but the positive/negative signal from the cartdrige does make it to noninverting/inverting input of the bal diff amp.

I do not know if there is a significant difference sonically.

Atmasphere, what is your take?

Phono preamps can be misleading because some are single ended but add an extra balanced circut at the end. That is undesireable if you want to keep gain stages to a minmum.

TD

I guess with some things (many amp designers), single ended equals "less is more" in the sense that no transformers are needed to deal with low impedance/balanced conversion, and that's fine for short run cables I suppose...I found through many years as an electric guitar player how much you lose with long, unbalanced cables, especially when you add up the distance the signal travels through a pedal board heap. I deal with that by putting a small "micro amp" at the end of the chain to "unload" the signal to the guitar amp...even the genius Les Paul tried to promote "low z" technology for guitars and it just never went anywhere. An attractive feature of my Dacmagic are the balanced outs, as are the balanced ins/outs of my Kavent preamp and old, trusty, Forte' power amp. I realize that sticking a pair of XLRs on the back of a turntable would be heresy to some, but really...come on designers! You could put the table 47 feet away from the preamp...

Wolf_garcia, surprisingly (to me anyway), no, 'we' collectively don't seem to know that, even though that is the fact of the matter.

I say this because when we introduced the MP-1 22 years ago, it was the first balanced line preamp made. The fact that it is balanced line and not single-ended has been its biggest marketing problem: audiophiles and dealers alike have had problems with the idea that balanced lines are inherently superior in every way. One of the biggest superiorities, IMO, is the simple fact that if you do the balanced line properly, the cable no longer has to be expensive (that is why you will find me recommending Mogami Neglex cables in other threads).

We (rather innocently and also rather naively) assumed that audiophiles would be very interested in a technology that offered immunity to cables such that a $0.10/foot cable could sound as good as one that is $1000.00/foot. Boy were we wrong. Many audiophiles buy expensive cables for reasons that have nothing to do with audio: http://en.wikipedia.org/wiki/Veblen_effect

Yeah...I guess I meant, or it should have been obvious that I meant, we need more balanced XLR input/output stuff to limit the loss in micro signals in cables...like all the pro gear and recording stuff I've been using seemingly forever. But I guess we all know that, right?

Wolf_garcia ALL phono cartridges *are* balanced, and any MC is also considered low impedance. But you knew that, right?

Shouldn't ALL phono cartridges be balanced/low inmpedence? It seems like all TTs should have balanced/"low z" outs as the signal is so tiny from the cartridge it could assuage the loss issue...and issue assuaging is good. I want to live in a balanced, low impedence world...is that so wrong? ASSUAGE I SAY!

Thanx for the responses everyone

Grinnell - I checked out the unit you mentioned and am a little confused as to how to wire this up - it appears to only have a total of 2 XLR jacks - I would have assumed that you would need two sets one for in from the phono and one for out to the pre/pro.

What am I missing - this is the source of my confusion for a number of phon stages I have seen

Thanx again

Try one of the BAT tube phonostages. I have used both (run balanced in and out) with the balanced junction box on a SSM signature. Great sound, super quiet.

As long as you understand that the type of input or output jack (RCA vs XLR) makes very little difference per se. What I think you want is a balanced phono stage that truly processes the phono signal in balanced mode. Such a preamp will typically provide XLRs in and out, but some of them also provide RCA inputs, for tonearms that have only RCA terminations and customers who are not competent to change over from RCA to XLR. A single-ended phono stage will almost never have XLR inputs but might have XLR outputs as an option. Sometimes XLR outputs on an SE stage actually sound less good than the native RCA outputs, because to generate the balanced output signal, the phono output has to be processed one more time, either by going thru a transformer or thru a buffer of some kind. Maybe you know all this, and if so, I apologize for the pedantry.

right here

http://cgi.audiogon.com/cgi-bin/auc.pl?preaphon&1320714940&auc

I am using a VPI Superscoutmaster/rim drive with a balanced XLR junction box to an Ayre preamp. The result is an absolute quiet background and clear, clean signal. My LP's are as quiet as CD's. No hiss, hum, - nothing even with the volume control raised.

Depending on your budget you should have a look at either Blue amp or the BMC phono amps. Both brands are non tube though. As far as I know both of these brands make true balanced phono amps. Many brands do give the option of XLR in/out but often the amp it self operates non balanced.