Dynaco ST-70 Series 3 Tube Amplifier Review

[rongon]

That's because it doesn't exist. People who insist it does, upon whom burden of proof rests, have failed utterly. I was one of them, couldn't tell the difference once levels were matched and I couldn't peek. I am also unable to find rigorous demonstrations of the existence of elves.

[SIZE=3]Petrushka[/SIZE]​

they have been put to well controlled double blind tests for decades,

There is no documentation of any tests like this, and if I did my own private test it would be discounted because the word is that those that say they can hear the difference between a tube and a solid state amp have failed to prove it in the past. But I can't find any documentation of an event where a person who claimed to be able to hear the difference was proved wrong, so how do we know that is the case? I mean... If a tree falls...?

If people have tested this, why is there no documentation of any of these tests?

The elves and ESP references are flippant and not helpful.
There are references to ESP not being real:

Neuroimaging fails to demonstrate ESP is real — Harvard Gazette

Psychologists at Harvard University have developed a new method to study extrasensory perception that, they argue, can resolve the century-old debate over its existence. According to the authors, their study…

news.harvard.edu

Daryl Bem Proved ESP Is Real. Which Means Science Is Broken.

The scientist couldn't have foreseen the crisis his research would touch off.

slate.com

But for being able to detect whether a tube or solid state amp is playing the music...

ABX Double Blind Test Results: Power Amps

Otherwise, all I could find was this kind of tiresome stuff about gear I'd never choose to use...

Finally -- So if I test this and find that I can hear the difference between Amp A and Amp B, nobody will believe me. That is why I'd like to see some evidence that somebody has done some kind of formal testing of this before me. That seems reasonable, at least it does to me.

 

[antcollinet]

I can see the harmonics even in the single 1Khz tone at 2k 3k etc and the noise at around 90db

You can see them in the measurements - yes - but even at these levels, you are probably not going to hear them in real world listening conditions. Even if you can, they are not likely to be significant.

which i would consider the real distortion

Noise and distortion are two different things.

 

[BDWoody]

There is no documentation of any tests like this, and if I did my own private test it would be discounted because the word is that those that say they can hear the difference between a tube and a solid state amp have failed to prove it in the past. But I can't find any documentation of an event where a person who claimed to be able to hear the difference was proved wrong, so how do we know that is the case? I mean... If a tree falls...?

If people have tested this, why is there no documentation of any of these tests?

The elves and ESP references are flippant and not helpful.
There are references to ESP not being real:

Neuroimaging fails to demonstrate ESP is real — Harvard Gazette

Psychologists at Harvard University have developed a new method to study extrasensory perception that, they argue, can resolve the century-old debate over its existence. According to the authors, their study…

news.harvard.edu

Daryl Bem Proved ESP Is Real. Which Means Science Is Broken.

The scientist couldn't have foreseen the crisis his research would touch off.

slate.com

But for being able to detect whether a tube or solid state amp is playing the music...

ABX Double Blind Test Results: Power Amps

Otherwise, all I could find was this kind of tiresome stuff about gear I'd never choose to use...

Finally -- So if I test this and find that I can hear the difference between Amp A and Amp B, nobody will believe me. That is why I'd like to see some evidence that somebody has done some kind of formal testing of this before me. That seems reasonable, at least it does to me.

Here's one a member did a few years ago. A place to start.

If "Tube Sound" Is a Myth, Why Tubes?

Okay, is the variable resistor connected to a series resistor or is that a variable output 20 k ohm pot? I can't tell from the picture. If it is a variable output pot it should be fine. Max output impedance would be 5 k ohm at -6 db. And you'll be using it at a lower setting with an even...

audiosciencereview.com

 

[Petrushka]

Bob Carver - Wikipedia

en.wikipedia.org

In 1985, Stereophile magazine challenged Bob to copy a Conrad-Johnson Premier Four (the make and model was not named then, but revealed later) amplifier at their offices in New Mexico within 48 hours. The Conrad Johnson amplifiers were one of the most highly regarded amplifiers of the day, costing in excess of $6,000 a pair.

In both cases, the challenging amplifier could only be treated as a “black box” and could not even have its lid removed. Nevertheless, Carver, used null difference testing, (null difference testing consists of driving two different amplifiers with identical signal sources and exact levels, but out of phase by exactly 180 degrees. If the amplifiers were 100% identical, no sound would be heard. If sound was heard, the audio amps had different properties). Bob Carver used "distortion pots" to introduce amplifier characteristics, fine-tuned to null-out any sound differences. His modified amplifier sound was so similar, Stereophile Magazine editors could not tell the difference between his amplifier and one costing more than $6,000.[5] This amplifier was marketed as the M1.0t for about $400.00. Carver successfully copied the sound of the target amplifier and won the challenge. The Stereophileemployees failed to tell the difference in their own listening room.[5] He marketed “t” versions of his amplifiers incorporating the sound of the Mark Levinson and Conrad Johnson designs which caused him some criticism. In light of this criticism, Carver went on to design the Silver Seven, the most expensive and esoteric conventional amplifier up to that time and duplicated its sound in his M 4.0t and later models which sold for some 1/40th the price (around $600–$1500).

 

[Blumlein 88]

I've heard or for friends shown there were audible differences. It was due to frequency response from the output impedance interacting with speaker impedance to alter the resulting sound.

 

[rongon]

Which is highly likely if you try to drive a little beast like Sonus Faber Concerto with a Dynaco Stereo 70.

If "Tube Sound" Is a Myth, Why Tubes?

Okay, is the variable resistor connected to a series resistor or is that a variable output 20 k ohm pot? I can't tell from the picture. If it is a variable output pot it should be fine. Max output impedance would be 5 k ohm at -6 db. And you'll be using it at a lower setting with an even...

www.audiosciencereview.com

I have a pair of Sonus Faber Concerto speakers. That is not an easy load at all. Driving it with a little TPA3116 amp makes it sound dark and sleepy. The Concerto perks up quite a bit if driven by a Behringer A800 amp. Not only does it need a low Zout, it seems to require a fair bit of power (current) sunk into the load.

 

[DonH56]

I've heard or for friends shown there were audible differences. It was due to frequency response from the output impedance interacting with speaker impedance to alter the resulting sound.

This is what has typically led to distinguishing tube from SS amps IME, along with tube amps often having higher noise floor (more hiss). Which means it is very dependent upon the speakers used for testing, of course. I was able to instantly distinguish a SS vs. tube amp driving a pair of B&W 802D's, somewhat to my own surprise as well as that of the salesman and friend I was with, but on a different set of speakers (not sure if Magnepan or something else, 10+ years ago) the differences went away.

Again IME, the biggest issue with comparing amplifiers is level matching, which needs to be a lot tighter (0.1 dB or better) and more rigorously controlled for proper testing than usually happens. Switching between amps with different gains, or a salesman with his hand on the volume control, makes it all to easy to favor one amp over another.

 

[GXAlan]

I wanted to rate this thing, but I didn't see a choice labeled "Probably as good as you're going to get with tubes."

Sonic Frontiers SFS-80 Review (Vintage Tube Amplifier)

Sonic Frontiers SFS-80 Tube Amplifier: A "new" benchmark to beat from 1992 Up next on testing gear that would be impossible to ship safely... the Sonic Frontiers SFS-80 tube amplifier. 70 lbs, all concentrated in the transformers. Believe it or not, Sonic Frontiers is a company we all know...

www.audiosciencereview.com

 

[SIY]

Sonic Frontiers SFS-80 Review (Vintage Tube Amplifier)

Sonic Frontiers SFS-80 Tube Amplifier: A "new" benchmark to beat from 1992 Up next on testing gear that would be impossible to ship safely... the Sonic Frontiers SFS-80 tube amplifier. 70 lbs, all concentrated in the transformers. Believe it or not, Sonic Frontiers is a company we all know...

www.audiosciencereview.com

If memory serves, they used a Curcio circuit for input/driver, differential cascode of ECC88.

 

[Blumlein 88]

This is what has typically led to distinguishing tube from SS amps IME, along with tube amps often having higher noise floor (more hiss). Which means it is very dependent upon the speakers used for testing, of course. I was able to instantly distinguish a SS vs. tube amp driving a pair of B&W 802D's, somewhat to my own surprise as well as that of the salesman and friend I was with, but on a different set of speakers (not sure if Magnepan or something else, 10+ years ago) the differences went away.

Again IME, the biggest issue with comparing amplifiers is level matching, which needs to be a lot tighter (0.1 dB or better) and more rigorously controlled for proper testing than usually happens. Switching between amps with different gains, or a salesman with his hand on the volume control, makes it all to easy to favor one amp over another.

Not surprising as Maggies have a nearly resistive impedance that almost does not change over frequency.

 

[GXAlan]

If memory serves, they used a Curcio circuit for input/driver, differential cascode of ECC88.

Yes, it’s definitely a Curcio circuit. The other details were apparently higher spec capacitors and stuff like that.

In that same thread, one of the engineers for Sonic Frontiers talks about their balanced differential design that was a successor.

 

[DonH56]

Not surprising as Maggies have a nearly resistive impedance that almost does not change over frequency.

I'm aware, but am thinking it was not my Maggies but another speaker (conventional) in the store, just can't recall which one. But no doubt one with less impedance excursion than the B&W.

 

[dzerig]

Don't think I'll ever understand wanting this tech

I absolutely love my monoblock tube amps. I first bought tubes to see if it took the edge of solid state gear.

Are they the better sounding than my solid state, recommended measuring Jot 2? For some headphones, yes. For others, no. Having 3 impedances headphone outputs wired directly to the txformer (instead of cheating with resistors) is probably what is producing the sound I love -- at least more so than the tubes themselves. I suspect the Dynaco st70 'sound' that people love is due to the txformer which is a 'special' design. Version 3 is not the same build, but they tried their best they say.

This seems a little pricey for what it is, but if the transformer is as high quality as they say, it's probably a fair price. More than I would pay for what it is however.

 

[Art of sound]

You can see them in the measurements - yes - but even at these levels, you are probably not going to hear them in real world listening conditions. Even if you can, they are not likely to be significant.


Noise and distortion are two different things.

Sure. i don't want to conflate noise and distortion. on the topic of distortion, not all distortion sounds the same. measuring focal headphones drivers from last generation i believe have great dynamics that almost everyone who reviewed them had praises to sing despite the soundstage being narrow show distortion at higher volumes that almost no one complained about. If having higher distortion at 1k-5k for example 85db should make it bad for dynamic range then why does the subjective review opposite of that.

 

[SIY]

I suspect the Dynaco st70 'sound' that people love is due to the txformer which is a 'special' design.

What specifically is the ST-70 sound and where has it been demonstrated to exist?

 

[Rottmannash]

But Harley Davidson's actually put out good audio and have much better torque.

hope you don't want to take a corner at speed...

 

[motorstereo]

hope you don't want to take a corner at speed...

Why not? What would happen?

 

[tubesguy]

Why not? What would happen?

It doesn't take much lean to cause the floorboards/foot rests to scrape. That can be unpleasant.

 

[levimax]

I've heard or for friends shown there were audible differences. It was due to frequency response from the output impedance interacting with speaker impedance to alter the resulting sound.

I agree FR variations due to higher output impedance has the biggest potential for audibility. When I did a level matched blind test between an original ST-70 and a Neurochrome Mod 86 I could tell no difference but while I had everything set up I also measured the FR of the 2 amps and then added 0.9 Ohm resistance to the Neurochrome at which point the FR matched almost perfectly. See measurements below. For a push pull Hi-Fi tube amp like the original ST-70 the internal resistance is about 0.7 Ohms and even though it measurably changed the FR it was not audible to me (but may be to someone). A SET tube amp on the other hand can have ~5 ohms of internal resistance which rather than causing a fraction of a dB FR difference could cause 1 or 2 dB of FR difference which can be clearly audible in some cases depending of course on the speaker's impedance curve. Tube amps are not practical or cost effective (especially for higher power) but a Hi-Fi tube amp sounds fine. Many tube amps today are not Hi-Fi by today's standards or even by 1950's standards (They are effects boxes) which I think causes a lot of confusion. Rather than mess around with expensive tube amps or DSP tube emulators if you want to find out what your system would sound like with a "Hi-Fi" tube amp put a 1 Ohm resistor in series with the speakers to see what a SET would sound like use a 5 ohm resistor.

 

[motorstereo]

It doesn't take much lean to cause the floorboards/foot rests to scrape. That can be unpleasant.

Yeah; and that's part of riding a big cruiser. Scraping the footboard feelers is not the least bit unpleasant if one has basic riding skills.
Now what about grass clippings blown into the road? Is that considered dangerous to?