Balanced vs RCA preamps

My preamp has both, XLR   Lundahl balanced inputs transformers, since most Digital front ends are balanced ,then on the outputs RCA Because of Linear Tube Audio,originally Designed by David Berning with his unique Micro-Z-OTL  output stage ,which the Vacuum tubes run much more efficient ,lower noise ,The team at LTA  found over a few years to make it even better a Gen 2 Version , and use the Rays Select  6SN7 vacuum tubes , detailed a bit warmer , and  the other tubes 12AT7  or 12AU7  which I am using with some Very rare Medical grade Telefunken tubes  a great combo , + using 2 Hifi tuning Supreme CU-  Copper Gold -  4 amp 20 mm slow blow fuses on back ,which VH Audio Carry.

and as a good option ,and not too expensive  a Hifi tuning Supreme Silver gold 20 mm 3.1 amp Fast blow on the main board 

with a AQ Tornado Source  power cord ,Exceptional results and a who who of Excellent top notch parts quality which I know very well ,having 40+ years in Audio ,beating preamps at 2x the price $6350 Retail ,Mike at Audio Archon was very helpful , and fair-in  pricing.

Where did you get this from? Have you done your homework before taking 10 seconds to write this? Let me do some homework for you, and you can do the rest to see if you can find anything to support your false statement.

DAC	XLR	RCA
Topping Pre90	40	21.5
Schiit Freya+ F / Kara	600	75
Audio Research LS17 SE	600	300
Audio Research 6 SE	600	300

 

 

@lanx0003  It is a fact in high end audio though that most producers of balanced line products pay no attention to AES48 (the balanced line standard), or the use of dBm levels (more later). That is part of the reason there is a balanced vs RCA debate.

You have to be careful about things you read like the specs above! I own the two of the Topping DACs; The 40 Ohm value is actually the two 20 Ohm output impedances put in series when really they should be in parallel, which would be about 10 Ohms.

WRT to the ARC stuff they are doing the same thing. FWIW ARC preamps in general tend to have high output impedances.

IOW this is a nomenclature issue, not an output impedance issue.

The standard for balanced line studio line level input impedance is 600 Ohms. Common accepted good design practice is that the circuit driving a load like that will have an output impedance about 1/10th of the load impedance. So we can assume that the source impedance will be 60 Ohms or less. That's a lot lower than most single-ended preamps...

Balanced line levels are usually expressed in dBm. dBm is the VU reading you would get on a VU (Volume Unit) meter when the meter is across a 600 Ohm resistor. So its a measure of power; that requires the output impedance to be even lower. There are two levels that are standards in use: -4dBm and +10dBm; 0dBm is one milliwatt dissipated into a 600 Ohm load.

My Neumann U67 microphones are designed to drive a 150 Ohm load. That implies an output impedance of 15 Ohms.

Our MP-1 preamp can drive 600 Ohms directly at +10dBm despite using a vacuum tube output. This also suggests a low impedance and in fact they will drive 32 Ohm headphones.

My old Ampex 351 studio tape machine was designed to drive 600 Ohms and also supported +10dBm.

Most tube preamps will fall flat on their face trying to drive loads like that. In fact most solid state RCA preamps will too.

My Otari MX70 1" tape machine has 600 Ohm inputs which expect at least -4dBm. You need a low impedance output to drive that.

I designed the first balanced line preamp offered to high end audio back in the 1980s so yes, I researched this quite a lot prior to saying what I did , and yes, balanced outputs generally are usually lower output impedance unless the manufacturer had no intention of supporting common balanced line practices.

atmasphere

It is a fact in high end audio though that most producers of balanced line products pay no attention to AES48 (the balanced line standard) ... That is part of the reason there is a balanced vs RCA debate.

Not really, the benefits of balanced designs are pretty well known. Designing to the AES spec is just one approach to balanced design.

...the Topping DACs; The 40 Ohm value is actually the two 20 Ohm output impedances put in series when really they should be in parallel, which would be about 10 Ohms. WRT to the ARC stuff they are doing the same thing.

The Topping and Audio Research schemes are different than your designs. That doesn’t make your design right or "proper" any more than it makes the ARC design "improper," as you’ve claimed. They each take a different approach to balanced amplification, either method offers improved CMRR. (Similarly, some speaker designers use sealed boxes, some use ported boxes and some use no boxes at all. Each approach can be valid and its success will depend on implementation.)

The standard for balanced line studio line level input impedance is 600 Ohms ... Our MP-1 preamp can drive 600 Ohms directly ... Most tube preamps will fall flat on their face trying to drive loads like that. In fact most solid state RCA preamps will too.

Most home users have no need to drive 600 ohm loads.

You have to be careful about things you read like the specs above! I own the two of the Topping DACs; The 40 Ohm value is actually the two 20 Ohm output impedances put in series when really they should be in parallel, which would be about 10 Ohms.

@atmasphere  One should be very careful when interpreting the impedance of a true balanced XLR cable. The two conductors (pin 2 and pin 3) carry both positive and negative signals from the source to the load simultaneously, behaving like a parallel connection. However, because they are of opposite polarity, the signals travel in differential (v.s. common) mode. The resulting voltage is the so-called differential voltage, which is twice the amount of the individual phase voltage.  This explains why the voltage from an XLR port is twice that of its RCA counterpart.

Similarly, the resulting impedance, known as differential impedance, is also twice the impedance per phase.  The manufactural reports either impedance per phase or the differential impedance.  Hope this helps.