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What Makes a Good RIAA or Line Stage?

Hi Doug,

In a currently running thread on a certain RIAA / Line stage beginning with the letter "E", some very provocative comments were made that are of a general nature.

I fear that this conversation will be lost on the many individuals who have soured on the direction which that particular thread has taken. For the purpose of future searches of this archive, those interested in the "E" thread can click this link.

For the rest of us who are interested in some of the meta concepts involved in RIAA and Line Level circuits, I've kicked this thread off - rather than to hijack that other one. In that thread, you (Doug) mused about the differences between your Alap and Dan's Rhea/Calypso:

... the Alaap has the best power supplies I've heard in any tube preamp. This is (in my admittedly unqualified opinion) a major reason why it outplayed Dan's Rhea/Calypso, which sounded starved at dynamic peaks by comparison.

Knowing only a bit more than you, Doug, I too would bet the farm on Nick's p-s design being "better", but know here that "better" is a very open ended term. I'd love to hear Nick's comments (or Jim Hagerman's - who surfs this forum) on this topic, so I'll instigate a bit with some thoughts of my own. Perhaps we can gain some insight.

----

Power supplies are a lot like automobile engines - you have two basic categories:

1. The low revving, high torque variety, characteristic of the American muscle car and espoused by many s-s designers in the world of audio.

2. The high revving, low torque variety characteristic of double overhead cam, 4 valves per cylinder - typically espoused by the single-ended / horn crowd.

Now, just as in autos, each architecture has its own particular advantage, and we truly have a continuum from one extreme to the other..

Large, high-capacitance supplies (category 1) tend to go on forever, but when they run out of gas, it's a sorry sight. Smaller capacitance supplies (category 2) recharge more quickly - being more responsive to musical transients, but will run out of steam during extended, peak demands.

In my humble opinion, your Alap convinced Dan to get out his checkbook in part because of the balance that Nick struck between these two competing goals (an elegant balance), but also because of a design philosophy that actually took music into account.

Too many engineers lose sight of music.

Take this as one man's opinion and nothing more, but when I opened the lid on the dual mono p-s chassis of my friend's Aesthetix Io, my eyes popped out. I could scarcely believe the site of all of those 12AX7 tubes serving as voltage regulators - each one of them having their own 3-pin regulators (e.g. LM317, etc.) to run their filaments.

Please understand that my mention of the Aesthetix is anecdotal, as there are quite a few designs highly regarded designs which embody this approach. It's not my intent to single them out, but is rather a data point in the matrix of my experience.

I was fairly much an electronics design newbie at the time, and I was still piecing my reality together - specifically that design challenges become exponentially more difficult when you introduce too many variables (parts). Another thing I was in the process of learning is that you can over-filter a power supply.

Too much "muscle" in a power supply (as with people), means too little grace, speed, and flexibility.

If I had the skill that Jim Hagerman, Nick Doshi, or John Atwood have, then my design goal would be the athletic equivalent of a Bruce Lee - nimble, lightning quick and unfazed by any musical passage you could throw at it.

In contrast, many of the designs from the big boys remind me of offensive linemen in the National Football League. They do fine with heavy loads, and that's about it.

One has to wonder why someone would complicate matters to such an extent. Surely, they consider the results to be worth it, and many people whom I like and respect consider the results of designs espousing this philosophy of complexity to be an effort that achieves musical goals.

I would be the last person to dictate tastes in hi-fi - other than ask them to focus on the following two considerations:

1. Does this component give me insight into the musical intent of the performer? Does it help me make more "sense" out of things?

2. Will this component help me to enjoy EVERY SINGLE ONE of my recordings, and not just my audiophile recordings?

All other considerations are about sound effects and not music.

Cheers,
Thom @ Galibier
128x128thom_at_galibier_design
atmasphere's avatar
atmasphere
11,922 posts
 
Two of the main points I can't get around are:

(1) Whether or not a cartridge is a balanced or a floating single ended device. Floating single ended makes more sense to me.

and

(2) Since everyone more or less agrees that there isn't a 6dB noise advantage to running a cartridge in "balanced" mode, what might the advantages of running a cartridge in balanced mode be.

Hi Thom, since a cartridge is an inductive device, it has something in common with other inductive devices like audio transformers. Any output of an audio transformer can be used in the balanced mode, even if it is driven single-ended. All that is required is that neither side be at ground. Ground can be the chassis the transformer is on; in the case of a cartridge ground can be the tonearm/turntable.

BTW a 'floating single-ended' device will hum like the dickens. Single ended devices are always grounded.

I have a tube mixer I built that is single-ended for my keyboards and drives a single-ended output transformer that is designed for 600 ohms. The output of the transformer is tied to pin 2 and pin3 of the XLR; pin 1 is ground. It drives 600 ohm balanced lines effortlessly.

Cartridges work the same way. It may not have been the intention of a cartridge manufacturer to make a balanced source out of it, but that is in fact how they behave since neither side of the cartridge is 'grounded', i.e. tied to its metal body. In fact many cartridges don't have a metal body! So really the question is more like: how in the hell can this thing be single-ended?" When looked at that way, you suddenly see why there have to be special grounding considerations (ex.: the third grounding wire) that you would not normally expect to see on your typical single-ended output (like from a tuner).

One obvious advantage of operating a cartridge balanced is the interconnect cable itself, which is less likely to have the usual interconnect cable colorations and less propensity for hum/noise pickup. Although the *output* of the cartridge is going to be the same regardless of balanced or single-ended, there is in fact a noise advantage to the input amplifier, simply because it is differential and makes less noise than a single-ended input amplifier.

IOW there is little advantage insofar as the cartridge itself is concerned, but plenty of advantage from everything that you use with it: the cable and the preamp itself.
hagtech
175 posts
 
>>since a cartridge is an inductive device<<

Being inductive should have nothing to do with balance. The transducer could be capacitive (touch sensor) or resistive (thermistor). It's just a two-terminal device.

>>there is in fact a noise advantage to the input amplifier, simply because it is differential and makes less noise than a single-ended input amplifier<<

I don't believe this is true. You get double the gain, but same SNR.

>>there is little advantage insofar as the cartridge itself is concerned, but plenty of advantage from everything that you use with it: the cable and the preamp itself<<

Yes, this is where we agree!

jh
jmaldonado
57 posts
 
Cartridges work the same way. It may not have been the intention of a cartridge manufacturer to make a balanced source out of it, but that is in fact how they behave since neither side of the cartridge is 'grounded', i.e. tied to its metal body. In fact many cartridges don't have a metal body! So really the question is more like: how in the hell can this thing be single-ended?" When looked at that way, you suddenly see why there have to be special grounding considerations (ex.: the third grounding wire) that you would not normally expect to see on your typical single-ended output (like from a tuner).
That's correct. I just wish every audio designer got an obligatory course on noise theory and balanced systems. There would be much less misinterpretation and mythology about this important advancement. Balanced is one of the greatest ideas in audio history.

Although the *output* of the cartridge is going to be the same regardless of balanced or single-ended, there is in fact a noise advantage to the input amplifier, simply because it is differential and makes less noise than a single-ended input amplifier.
Correct again, provided you are talking about RFI, hum and other sorts of external EMI entering through the input cable as a common mode signal. In MC cartidges, hum rarely disappears completely, but a balanced system will dramatically reduce it compared to a single-ended system. If you mean thermal noise (hiss), the right answer is: It depends of the design of the preamplifier. You can design a balanced circuitry with much less noise than a single ended one. It just depends on your skill and the technology you are using.

Being inductive should have nothing to do with balance. The transducer could be capacitive (touch sensor) or resistive (thermistor). It's just a two-terminal device.
Correct. Strain gauges, which are resistive elements, also work by using the differential principle.

>>there is in fact a noise advantage to the input amplifier, simply because it is differential and makes less noise than a single-ended input amplifier<<

I don't believe this is true. You get double the gain, but same SNR.
Incorrect. Strictly speaking, a balanced circuit will have two input gain cells operating in differential mode. This circuit would produce 3 dB [20log(sqrt(2))] more noise than a single gain cell operating in identical conditions. With double the gain (6 dB), the result would be a net loss of 3 dB in SNR. However, as said above, it depends on the designer's skill and the technology used. There's no limit on how noiseless a circuit can be (balanced or not), except that imposed by nature.

Regards,
hagtech
175 posts
 
This circuit would produce 3 dB [20log(sqrt(2))] more noise than a single gain cell operating in identical conditions

Except the signal is split between the two inputs! This is not the same as two amplifiers operating in parallel, whereupon you would get the 3dB SNR advantage.

jh
mothra
110 posts
 
raul,

the vast majority of recording engineers to not like uncolored recording equipment in my experience. The ubiquitous sound of the proximity effect on a neumann u-47 up close that bumps in the high midrange and rolls off steeply in the higher freq.is evidence of this. Especially today, accuracy is not the name of the game. heavy editing and the close mic'ing of soloists in classical music, changing the sound stage has taken some of the natural quality that remained in classical music recording longer than some forms, out of it.

The very idea of multiple microphones really changes what the ear would hear "live". And yes, you can out you ears when the mics are, but how the mics are mixed together and their on and off axis response are just two factors of many that make recording an art as much as a science. Sometimes microphones with poor freq response measurably, have more of a "you are there" feeling than people would imagine. Sort of the like quad 57 speaker can be very musical. The famous rca living stereo string sound is wonderful but far wider than an actual orchestral image.

I tend to be digressive in these discussions and I apologize, but given your post on this, I wanted to point out that these things are carefully designed often for the colorations they bring to music. Reproducing equipment hopefully is trying for less coloration and more neutrality in that it gives the recording its intended sound. But recordings themselves are all over the map. Engineers, sadly are moving even further away from reality as they have been doing since the 70's when heavy isolation came into vogue.
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