300b lovers

lynn_olson

... On paper, op-amps can do an amazing job driving a cable, in practice, not so much ...

That’s a quite confounding claim. What components using op-amps do you find objectionable?

There are many excellent differentially balanced components that use op amp circuits, including all of the ARC Ref series preamps and amplifiers. Many people consider that a better approach than transformer-coupled circuits.

Due to package heat-dissipation limitations, most op-amps operate in Class AB. Now, they have a stupendous amount of feedback, and it takes a difficult load to excite the AB transition, but it’s still there. Speed is the friend of op-amps, so the high slew rate versions (more than 20V/uSec) often sound cleaner and smoother than the slower versions.

It is difficult to build a discrete solid-state circuit with distortion specs that exceed an integrated circuit, but it can be done, and they are often seen in the pro recording studio world. These do operate in Class A, and that is always mentioned in the sales literature.

I'm a bit surprised that ARC uses op-amps in their "Reference" series. Why not just buy Topping or SMSL and get even better performance, or if you insist on made-in-America, Benchmark, who live up to their name in performance standards?

Why buy an high-end audiophile component, with audiophile pricing, made from off-the-shelf $5 parts. What's the point? I don't see the value proposition. Now, if there are a zillion discrete transistors, and it does 1000V/uSec and delivers 500mA mA into a 300 pF load, that's insane, but still in the realm of engineering possibility.

Tube gear costs a lot because transformers and vacuum tubes are inherently labor-intensive, and the parts are not inserted on circuit boards with pick-and-place machines. I'm one of those madmen who think zero-feedback circuits are interesting, and I like tubes. Nelson Pass is your man if you like zero-feedback JFET/bipolar transistor circuits.

If you are more sensible, read ASR reviews, ignore the comments section, ignore the single-dimension SINAD number, and look at the noise floor of the multitone IM distortion graphs. That is the true wideband IM distortion, and multitone is the most severe test of the entire circuit. The Shenzen group of manufacturers have some really good engineers, and it shows in the IM distortion measurement. From what I can see, Bruno Putzey and the Shenzen guys are at the top of the game, if specs are at top of the list. They also know how to "tune" a power supply to get a subjective result.

I guess the micro-rant above is about audiophile components where the case costs more than the parts in the audio circuit. It doesn’t make sense to have a $500 case housing $50 worth of parts (in the audio circuit), unless the look is the main reason to buy the product.

I didn’t mean to imply any connection between Bruno Putzey and the Shenzen group. Bruno works in Europe, and designs top-class DACs and Class D amplifiers, which are inherently complex and very hard to get right.

The Shenzen engineers have slowly but surely improved their game, and the Chinese have been quietly building complete OEM products for high-end European and American famous-name manufacturers. Many deluxe and high-end raw parts are built right there in China, so they don’t have to go far to design and build their own high-end components, Whether you love or hate ASR, they have uncovered some terrific Chinese products.

On the international scene, a lot of truly remarkable products are coming out of Eastern Europe these days. Some real talent there.

This is where my good friend Lynn and I disagree:)   I have heard my Lampi Pacific in the same system as the May (which Lynn doesn't favor).  I have heard various tube based DACs, the Schiit Yggy and a few others for SS, and the Pacific is in a different universe to my ear than any of the others.  I have not heard the Bruno Putzey DAC except briefly in the Songer/Whammerdyne room.  I liked the sound, but I need to hear things in a known system.  That DAC was over $10K though.  I will bet money that in a blindfold test I will prefer the Pacific or perhaps the expensive SS DAC over the $1000 Chinese dac du jour on ASR.   Of course the rest of the system has to be totally transparent for such differences to be heard.  My 2 cents and others will disagree.  Of course the law of diminishing returns kicks in very hard somewhere about $1000-2000.  The Pacific and others of that class live and breathe in a way that even the May cannot (to my ear).

Why buy an high-end audiophile component, with audiophile pricing, made from off-the-shelf $5 parts.

@lynn_olson

It might be because those parts work...

Tube gear costs a lot because transformers and vacuum tubes are inherently labor-intensive, and the parts are not inserted on circuit boards with pick-and-place machines. I’m one of those madmen who think zero-feedback circuits are interesting, and I like tubes. Nelson Pass is your man if you like zero-feedback JFET/bipolar transistor circuits.

If you are more sensible, read ASR reviews, ignore the comments section, ignore the single-dimension SINAD number, and look at the noise floor of the multitone IM distortion graphs. That is the true wideband IM distortion, and multitone is the most severe test of the entire circuit.

FWIW, we use surface mount parts in the module we designed for our class D amp. We assemble them to the board by hand (no machines). You use different tools for that- a different soldering station, and special reader’s glasses so you can see what you’re doing.

You missed one of the more vital measurements: distortion vs frequency. Why this is important is that it can show you if the amp is going to make more distortion (and audible, annoying distortion) than the specs would otherwise show.

Zero feedback amplifiers have a ruler flat line across the audio band in this regard. Beyond that the distortion spectra must allow the distortion to be innocuous. That’s why SETs sound they way they do.

When the amp has feedback, that’s when you can have troubles with distortion rising with frequency. This happens because the design, whether tube or solid state, has insufficient Gain Bandwidth Product (and also points to poor engineering; feedback is control theory, which is a field that is well understood elsewhere in the electronics industry). For those that do not know this term, GBP is the frequency where the gain of the circuit has fallen to a value of 1 (unity gain) and so is the highest frequency where a sine wave can be relatively undistorted. Obviously an amp with a gain of one is not useful- 25 to 30dB is more useful so a preamp can drive the amp in a conventional manner (SETs don’t need quite so much gain, but since they don’t usually use feedback they aren’t part of this discussion).

For example if the amp has a GBP of 1 MHz and we are looking for 30dB of gain (a gain of 1000) out of the design, you divide 1MHz by 1000 and you get 1KHz. That is the frequency where the feedback will fall off on a slope (starting at 6dB/octave, but as frequency is increased, falling off faster)- and the distortion will rise on a converse slope.

This is why a simple THD value can hide dirt under the carpet; the fact that distortion will be much higher at 7KHz than it is at 100Hz. Its why most solid state amps can play bass just fine, but sound bright and harsh- you’re getting more of the audible annoying kinds of distortion at higher frequencies than the specs otherwise show! This has been one of the bigger disconnects between the spec sheets and what we hear over the years and has given rise to the myth that there are things we can hear that we can’t measure and explains why amps that ’measure poorly’ can sound so good.

It is recently become possible to build solid state amps that have so much GBP (we have 20MHz in our class D) that the distortion vs frequency is a ruler flat line, just like in an SET (but of course, overall much lower distortion, so greater detail is audible since distortion can obscure detail); IOW the feedback employed in such amps is supported across the entire audio band. That is why its now possible to build solid state amps that sound for all the world like the best tube amps.

FWIW ASR does on occasion graph distortion vs frequency on their site, but its apparent to me that they don’t understand its significance: the line that exists between that graph and what the amp actually sounds like. If you have all the measurements you can know that!