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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
jmaldonado
57 posts
 
"RIAA eq deviation no more than 0.05 dB... Why?"

Five reasons:

1. Because the technology exists
2. We can use this technology without any detrimental effect on the audio quality
3. It adds a negligible cost to the product
4. It automatically results in basically perfect channel balance throughout the full audio band
5. It'd be a tribute to Dr. S. Lipshitz (of RIAA eq. fame)

Of course, RIAA eq. is only one of many parameters affecting the reproduction of LP records. I support that. As for channel matching, please see point 4 above.

"What's next? +/- 0.00005 dB equalization?"

That's impossible!
jcarr
382 posts
 
The magnitude of RIAA error is not particularly useful unless we also consider the range of frequencies that are affected by the error. in practice, a 1dB deviation that only hits one note is not going to be very noticeable, but a 0.1dB error that spans an octave or more can be quite noticeable. In fact, the manner of musical presentation changes when this happens. That said, I do think that the less total deviation there is from the RIAA curve, the better. True, LP recordings and mastering systems have their own deviations, but they can deviate in any direction, and as long as we keep as close to the standard curve as we can, the frequency deviations in one's LP collection should average out. At least we won't be favoring certain recordings over others, which would certainly be the case with an RIAA playback network that wasn't right.

I don't think that speaker colorations are an acceptable excuse to tolerate RIAA deviations. Admittedly it is next to impossible to exactly duplicate electronic colorations in the speaker and vice versa so that they can be truly compared, but at least in my experience, it has seemed that electronic colorations are much more noticeable and less forgivable than speaker colorations. I think that this is because acoustic colorations in the environment are part of everyday life, and compensating for this is a constant, subconscious process.

Regarding when balanced phono amps were introduced, I have on my bench a schematic for a discrete FET balanced phono amp from the Japanese audio magazine M&J which is dated January 1985, and I am pretty sure that there are earlier examples (especially from the tube guys).

I don't think that complexity in a design is necessarily a bad thing, because a major goal of this approach should be to get smaller "modules" with more well-defined tasks/behaviour/environment. This makes it easier to design, understand and debug the functions and can lead to better performance, even if the overall complexity becomes greater. A simple circuit can lead to a wider, less clearly defined range of responsibilities being assigned to fewer parts, and this can result in lower performance.

IME, NFB is just another tool, neither good nor bad by itself. The results of using NFB have a lot more to do with the capabilities and sensibiities of the designer than NFB per se. I usually dial in the amount of NFB by ear as well as by measurement, and sometimes I'm at 0dB of NFB, sometimes 50dB.

Although I fully agree with the "holistic" approach, I think it is possible to achieve a good-sounding line or phono amp using a variety of technologies, circuits and approaches. However, topologies and components by themselves don't know what they are supposed to sound like. Good sound, bad sound, they don't know any better. The most important component of all is the designer, and the final sound extracted from the topologies and components is only as good as the designer allows.

regards, jonathan carr
ndoshi's avatar
ndoshi
19 posts
 
Interesting reading, a bit heavy on methodology but the editorial notes and Dr Toole's response will give some background on what is actually possible and why we hear things the way we do.
This post started out as an attempt to educate ourselves to why and what are the things that matter to us humans and therefore must be attended to in design...

http://www.audioholics.com/techtips/roomacoustics/HumanHearingAmplitude.php
thom_at_galibier_design's avatar
thom_at_galibier_design OP
729 posts
 
Thanks ever so much for visiting this thread, Jonathan.

You make a very provocative point about varying sensitivity to different distortions (mechanical / speaker vs. electronic) which most definitely fits into the overall design process.

I have great respect for someone who has the courage to take on a complex design. It is a daunting task and one can easily get lost.

We need the electronic equivalent of the "Alpha Male" to push the collective envelope. Yes, some of them will suffer the electronic equivalent of the ill-fated Donner Party, but it's a choice they knowingly make, and we all benefit from the few successes along the way.

Cheers,
Thom @ Galibier
atmasphere's avatar
atmasphere
11,793 posts
 
Hi Thom, having been in the business of balanced phono production longer than anyone else (since 1989- all the prior balanced phono circuit art were not *production* circuits) I can safely tell you that there is a lot of misconception brought out in the links you provided. I wish I had seen them when they were current!

The advantage of a balanced differential phono section is not that the cartridge will somehow act differently, it is the fact that the cable and the electronics act differently! To take advantage of the improved behaviors, we need to hook up the cartridge itself in balanced mode. This is easy as cartridges take quite naturally to this.

The result is lower noise throughout the phono system. In our case this allowed us to eliminate a stage of gain. That made the preamp more transparent, as it now makes less noise and distortion with wider bandwidth. IOW the signal path is actually simpler, not more complex, quite the opposite of the usual drone of balanced circuits being more complex!
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