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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
hagtech
175 posts
 
Whoah, Thom! Look what you started here.

I have to disagree with the assertion that a cartridge is balanced. It isn't. It's floating single-ended. To have true balanced, you need 3 signals. A reference level (return), positive polarity, and negative polarity. A cartridge obviously has only 2 pins per channel.

However! You can turn force it into balanced mode by creating the reference (middle point) for it externally. This is most easily done using a step-up transformer that has a center tap on its primary. You ground the center tap and connect the cart across the entire primary. Ralph, I assume this is what you do? I hooked up a Trumpet phono once this way through XLR inputs. Works great.

The other alternative is to use an opamp type differential stage. Also called instrumentation amps. The drawback with this technique is a relatively weak dc impedance on the reference (permitting hum), unless you also drive it actively.

jh
jmaldonado
57 posts
 
A Line or RIAA stage could be characterized as "good" if it complies with its primary objective: To amplify the music signal with enough gain to be listened comfortably at the proper volume level, and do it without introducing obvious anomalies not present in the original recording. I think many of today's products could fit in that description.

Do you want more than merely "good"? First, the device should be accurate, transmitting all aspects of the reproduction with completeness and neutrality. With accuracy I'm not implying a clinical, analytic or sterile sound. This is not accuracy, is just, well, sterility. It also should be able to process even the most dynamic signals without any trace of compression or congestion. Every nuance, every detail, every "emotion" should come out in the right proportions. Nothing should be added or removed. The device should be "transparent" in the sense that listening to it would give you the feeling of being closer to the original event, not processed through electronic circuits.

As for the circuit details, there are probably as many different opinions as there are designers out there, but some general desirable characteristics could be extracted. It should have as extended a bandwidth as possible, both ABOVE and BELOW the audio band (officially 20 Hz to 20 kHz). Low noise is absolutely fundamental. A low distortion is highly desirable, because a high amount of it can be easily discernable as an added "gloss" in the instruments. Feedback can improve the measured specs, but if not properly done it will also rob life from the music (causing that sterile sound). In the RIAA department, it should provide clean gain for your cartridge (some of them needing up to 70 dB), and be able to manage input signals of at least 10 times without overloading. It should decode the RIAA curve with the minimum error possible, or it will show up as a permanent color of your sound. Finally, the unit should be reliable, stable, and have a fast warm-up time.

We now have the technology to satisfy all of these requirements simultaneously. If a unit aptly does that, there is a good chance that you will experiment all that "emotion" trapped in your recordings.
dan_ed
2,451 posts
 
Jose, or anyone else, have you correlated RIAA error to colorations? As in, error of x amount or of y type leads to a z coloration.

Is that a clear question? :)
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rauliruegas
13,052 posts
 
Dear Dan: Absolutely and José and I already tested about, the colorations/distortions/degradation are differents depending where in the frequency range are those inverse RIAA eq deviations.
Almost all phonolinepreamps have its own " colorations " other than the RIAA eq but the ones in the RIAA are more " be present at " because any single frequency deviation affects almost three octaves and this three octaves deviation we noted like a coloration, this special coloration is really a degradation to the cartridge signal because those frequency deviation does not exist in the cartridge signal.

One of the first critical and important task in any phonolinepreamp ( is one of the reasons why they exist ) is to mimic in accurate way the RIAA eq, this inverse RIAA eq must be that " mimic/accurate " to be ( at least in this stage ) truer to the recording .

A good phonolinepreamp IMHO has to have a inverse RIAA eq. deviation no more than 0.05db from 20 to 20kHz.

Our Phonolinepreamp RIAA eq deviation spec is: 0.015db but normally we are below that figure. Obviously that this spec not tell us how the audio device will sound, José already explain other very important subjects to have a good quality performance in a Phonolinepreamp device.

Hagtech, I agree with you about the misunderstood when we name " balanced " to a phono cartridge, it is not, our design is fully differential input to output and the connection is " floating ".

Regards and enjoy the music.
Raul.
hagtech
175 posts
 
>>RIAA eq deviation no more than 0.05db<<

Why?

Just how many cutting lathes in the 50's and 60's were built to this specification? And let's put this into perspective by comparing to the average speaker response. Why are speakers allowed 100x more error? Does that make sense?

The key here is that the stereo channels be matched. They need to be very tight. The relative matching is what preserves the spatial cues, soundsage, focus, etc. An absolute error of even 1dB can be reasonable as long as the channels are equal.

Hey, I've been promoting accurate RIAA eq for years, but let's not go off the deep end like the 70's chase for lower THD. What's next? +/-0.00005dB equalization? This is looking to me like its all about marketing.

jh
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