PrimaLuna Dialogue Seven Tube Amp Review

[DanielT]

Unlikely. @levimax (for one) did the comparison using an old Dynaco ST-70 and couldn't distinguish it from a good solid state amp when it was done ears-only.

And such a Dynaco ST-70 I can definitely see someone who knows electronics tinkering with.
Something that Amir also noted when he tested it:

I love the simplicity of tube amps like this. There is just so little to them. If I were less busy, I wouldn't mind playing with one to get it to optimal performance.

Review and Measurements of Dynaco ST 70

This is a review and detailed measurements of the vintage Dynakit Dynaco Stereo 70. It is on kind loan from a member who bought it used online and repaired it. Previous owner hand upgraded it but could not get it working. Given that it is 60 years old, one can forgive the rust and dust...

audiosciencereview.com

With SINAD around 60 dB for a Dynaco ST-70 vs a solid state with SINAD around 90 dB, how can you hear the difference with a pair of speakers that have, for example, 40 dB distortion? The amp's distortion is then drowned out, or masked by the speakers' distortion, right? Maybe if we are more sensitive to higher order amp distortion than speaker distortion and can thus hear a difference between the amplifier and speaker mentioned in my example?
Given that both amplifiers have straight FR (or small but inaudible FR deviations), so you can discount that factor, that is.

 

[Biagiod]

Amir, thanks for revealing the Pandora's box of tube pre and amplifiers. Excellent review to be filed in the hystorical/vintage section of the forum to the benefit of posterity.
We came a long way indeed...

 

[Haskil]

Thank you Amir for this new test...

 

[fatoldgit]

strange...manufacture rates this as 70W in UL mode.

A Rogue M150 monoblock with 4 x KT88's (so the same config as above) gets twice this power in UL mode.

Official specs for M150 are:

SPECIFICATIONS
output power 150 WPC
frequency response 5Hz – 50 kHz ± 1dB
THD < 0.1% typ, < 1% at rated power
input sensitivity 1.0 V RMS
dimensions 14 ½” W x 19” D x 7” H
weight 55 pounds (25 Kg)
shipping weight 60 lbs (27 Kg)
power requirements 115/230V - 50/60Hz

 

[fatoldgit]

20 years old tube amp still with the original power tubes? Then this is normal, those tubes are worn out and should have been replaced long time ago as they age the most. With tubes that are in good shape this amp is not that noisy in my experience. I got the stereo version (Prologue 4) and with worn out tubes it makes audible noise, that is true...

But it's a tube amp, it will never be low noise. But this measurment should be done with relative new tubes that are tested and confirmed in spec, not with 20 years old tubes. Then you got the real numbers.

totally agree..unless this has a batch of fresh tubes... then its an invalid test.

Peter

 

[SIY]

With SINAD around 60 dB for a Dynaco ST-70 vs a solid state with SINAD around 90 dB, how can you hear the difference with a pair of speakers that have, for example, 40 dB distortion? The amp's distortion is then drowned out, or masked by the speakers' distortion, right? Maybe if we are more sensitive to higher order amp distortion than speaker distortion and can thus hear a difference between the amplifier and speaker mentioned in my example?
Given that both amplifiers have straight FR (or small but inaudible FR deviations), so you can discount that factor, that is.

Human ears are just not very sensitive to distortion. We are much more sensitive to frequency response.

 

[DSJR]

I will say what I already said at the time about tube amplifiers. Would any of you ever think of comparing a 19th century steam train with a modern magnetic levitation high-speed electric train? Does it make sense to compare speed, acceleration, fuel consumption? Of course not, but that doesn't devalue the steam locomotive as a glamorous vehicle. Tube amplifiers should not be considered as alternatives to modern solid state amplifiers, and it makes no sense to compare their performances, they are fascinating instruments, of an obsolete but very suggestive technology, I see nothing strange in an audiophile who wishes to own one and listening to him, just as it doesn't seem absurd to me that a train enthusiast enjoys a ride on an old steam locomotive.

Yes, but this amp isn't a good performer even amongst its valve-peers!

I'd be more interested in seeing how a now vintage E.A.R power amp does (509?) which deliberately used TV line-output valves to help the end user save money come replacement time, perhaps a Manley, Radford Revival or whatever.

 

[fpitas]

Does anyone have a schematic? It would be interesting to see where they went wrong.

But if you (re-)designed it properly, it would no longer be audiophile.

 

[kchap]

Some of these amps Amir is testing are very old. Have owners checked the plate currents on the output stage. It's important to avoid a net DC current in the output stage.

 

[fpitas]

Some of these amps Amir is testing are very old. Have owners checked the plate currents on the output stage. It's important to avoid a net DC current in the output stage.

Unbalanced idle current is bad, but this thing has tons of odd-order distortion as well as even-order.

 

[FrantzM]

And that, for $2800.oo..

Peace.

 

[SIY]

Unbalanced idle current is bad, but this thing has tons of odd-order distortion as well as even-order.

I'm guessing that it's an input stage/phase splitter topology issue. Love to see a schematic, but lacking that, I'm guessing that they did something fashionably silly and used what they thought was an SRPP but isn't (a remarkably common design error).

 

[fpitas]

I'm guessing that it's an input stage/phase splitter topology issue. Love to see a schematic, but lacking that, I'm guessing that they did something fashionably silly and used what they thought was an SRPP but isn't (a remarkably common design error).

I would like to think someone purposely added distortion in pursuit of tube sound. But yeah, it's probably sheer incompetence.

 

[kchap]

I'm guessing that it's an input stage/phase splitter topology issue. Love to see a schematic, but lacking that, I'm guessing that they did something fashionably silly and used what they thought was an SRPP but isn't (a remarkably common design error).

I had to look that one up.

 

[misureaudio]

Never been able to keep a tube power amp for more than a one day listening in my systems, in the last 45 yrs.

 

[FrantzM]

I would like to think someone purposely added distortion in pursuit of tube sound. But yeah, it's probably sheer incompetence.

I hope I am not being mean to Prima Luna the company. I have lived for a long time among subjective audiophile and was one not too long ago. I spent most of my audiophile life as a subjectivist, somewhat tubophile ... I know that they (we? ) believe, intently with a fervor that could be compared to that of religion. They, the subjectivists, are a market, with substantial buying power or my term substantial buying willingness, thus commercial concerns target them. The cookbooks for tube design are public domain. The rest is a (not simple) matter of execution, i-e: marketing, manufacturing, distribution, etc... This not as easy as many would think, but doable...
This particular company founds its niche, that of not-yet (sometimes, NOT.. period) well-heeled audiophiles but who have drunk the subjectivist, "tubist" kool-aid, to desire tube things. They buy those things, dreaming at the time when they can afford more expensive, thus in their mind better, tubes equipment

and

let's admit that these :

Look Koooooler , than

that:

Peace

 

[fpitas]

Never been able to keep a tube power amp for more than a one day listening in my systems, in the last 45 yrs.

I've heard good ones. They sounded just like good SS, though.

 

[JSmith]

Gosh, what a mess really... the other PrimaLuna was much better. Spend more get less?

Nice to see the results though, cheers @amirm.

Let's have a look under the hood;

The amp kept improving its performance as I left it on. I waited a half hour and it kept going:

Half an hour seems like a very long "slowly"!

Furthermore, the PrimaLuna is equipped with SoftStart™, which brings the amplifier on line slowly to prolong the life of internal components, including the tubes. This makes the PrimaLuna a joy to own and operate.

Hmm... the test data in this thread and here does not correlate to this claim below;

Exclusive to PrimaLuna, this circuit monitors and smoothly adjusts bias constantly and instantly. The genius of this design is that the Adaptive AutoBias™ actually improves the overall sound quality and performance of the amp. Between 12 and 30 Watts, measured distortion levels drop by over 40%. In addition, tubes do not have to be matched, and there is no bias (re-)adjustments needed, ever.

JSmith

 

[Steve Dallas]

Looks heavy for a distortion pedal.

 

[calugg]

Amir, thank you! I'm a life member of the bad-back club. So, as Class D amps get better and better, I'm skipping the tube stuff. I can't lift anything over 25 pounds. So, small subwoofers, bookshelf speakers that are under 25 lbs, and the like. It's just not worth the 3 months of PT if I over lift.