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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
dan_ed
2,451 posts
 
Thanks to you designers for posting your thoughts. Good one, Thom!

In my mind the next logical question would concern the RIAA curve itself. I'm sure we'd all agree that following the curve as close as possible is a good thing, but just how close does the implementation (not the design) have to be before the listener begins to have doubts about what he or she is hearing?
atmasphere's avatar
atmasphere
11,841 posts
 
The idea that power supplies somehow compare to engines falls apart fairly easily. What if you have large capacitances *and* tight regulation for example?

In addition to excellent power supplies, a good RIAA section will be low noise with as few stages of gain as possible, to minimize distortion. In addition, the best of them will be tube, and passive EQ. Passive EQ allows one to avoid negative feedback, which puts an unnatural 'sheen' on top. Expect first-rate components throughout- handpicked to meet the RIAA curve and for low noise, etc. If on a PCB the material will be something other than FR4 to minimize dielectric effects of the board. Layout will include star grounding for low noise, and attention to RF suppression and improving stability by providing grid stop resistances and local power supply bypass.

I am also of the opinion that since the LP is recorded in balanced mode, and since the cartridge is balanced, that the phono section ought to be balanced too and to that effect we created the first balanced phono preamps in 1989.

The line stage ought to have similar characteristics- simple signal path, zero feedback, quality components, etc. A little understood issue is that the line section is supposed to control the interconnect cable to the point that the cable drops out of the system equation- IOW the cable between the amp and preamp will make little difference. If this is not the case for you your line section lacks this ability.

The volume control will be manual multi-position switch, or if it is remote, a motor drive operating a multi-position switch which is the only way to build up a decent volume control.

Power supplies will be outboard to minimize noise, and locally bypassed for the same reason. I can go on and on...
whart's avatar
whart
3,047 posts
 
I cannot contribute to a technical discussion here, but can explain, anecdotally, what I have experienced in preamps and phonostages I have lived with since the early 1970's. My first serious foray into separates involved an old solid state MacIntosh preamp (I think it was a C-22) and a Dynaco 400 power amp. The amp had oodles of power at the time for driving dynamic speakers, but the preamp sounded compressed. I transitioned to a more modern solid state preamp by a 'fringe' company- Quintessence- which was more dynamic and quieter than the Mac, but had nowhere near the bloom or aliveness of the ARC SP-3, which I then switched to, along with tube amps and Quad ESLs. (Remember, we are still circa about 1974-75).
When the Sp-10 preamp was introduced, I eventually gave up my SP-3. Differences? Less euphonic, at least by comparision to the SP-10, and far more dynamic. Downsides- noise, tube anomalies, very sweet phono stage, and whatever bass or upper range limitations the preamp suffered were not readily apparent on the limited bandwidth system I was running.

Currently using a Steelhead with a Lamm L2. The Steelhead is dead quiet and hugely dynamic, but sounds a bit threadbare- I also am using the MM input rather than the transformer. With the Lamm linestage in the chain, the proceedings take on a richer, more involving, but less powerful presentation at the frequency extremes. I am probably willing to trade off some of the bandwidth for the extra life and body that the Lamm brings to the table.
With horn type speakers, I am also obviously less willing to tolerate noise.
One of the common things to both the SP-10 and the Lamm is a tubed-based power supply. I don't know if that contributes to the liveliness I like.
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.
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