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VTA ST-70 Review (Stereo Tube Amplifier)

Rate this amplifier:

  • 1. Poor (headless panther)

    Votes: 123 64.7%
  • 2. Not terrible (postman panther)

    Votes: 45 23.7%
  • 3. Fine (happy panther)

    Votes: 16 8.4%
  • 4. Great (golfing panther)

    Votes: 6 3.2%

  • Total voters
    190

JP

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Showing some initiative would likely be of benefit.
 

theREALdotnet

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Wouldn’t it be really cool if there were some magic technology to scale down voltage levels?

It’s on my to-invent list. I think I’ll call it “The 10:1 Probe”…
 

MattHooper

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Showing some initiative would likely be of benefit.

Please remember what I had clarified early on:

"Just to be clear: The reason I asked you the original question is because this seems to get in to an interesting area of "what can be demonstrated, how, and at what point and by whom it would be considered 'demonstrated.'"

The point was this: If someone says "X had not been demonstrated" then the follow up question makes sense "what TO YOU, would demonstrate X?"

So the subject had turned to electronics like amplifiers altering soundstaging and imaging characteristics, about which there was reasonable skepticism. SIY had replied (presuming with respect to changes in imaging/soundstaging among amplifiers) "It makes no technical sense and indeed no one has ever demonstrated it."

That is why I was asking SIY specifically what WOULD constitute a demonstration of an amplifier altering soundstaging/imaging? I alluded to my own experience with changing tubes but also made clear it was just a handy example, in the specific context of asking what demonstration WOULD suffice for SIY?

I kept repeating that question to make the point of the discussion clear. While his answers - if he'd ever deigned to actually be anything other than vague or terse - MAY have been useful to me in doing my own blind test at some point.....the point of the conversation never required that I go out and actually test anything. It simply required SIY just laying out specifically what test would suffice to establish the claim and if he'd accept the results as demonstration of the claim.

These were the points he studiously avoided, unfortunately.

Since conversation hasn't been fruitful with SIY I wonder if you'd be interested in answering the question.

What test would you accept as having demonstrated that different amplifiers can alter soundstaging/imaging characteristics?

(You could choose any specific example you wish, e.g. the difference between a solid state and tube amplifier, difference between tube rolling...whatever).

Nobody needs to actually do this test. It's just a hypothetical question at this point. And no problem of course if you aren't interested. Thanks.
 

JSmith

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Vacuuming_Tube.jpg


ed0e3d36b342160431eebc883e97e8a1.jpg


... this amp seems quite distant from the goal of high fidelity audio reproduction.


JSmith
 

JP

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These were the points he studiously avoided, unfortunately.

He did answer, categorically, and clearly. You even quoted it above, in bold text.

What test would you accept as having demonstrated that different amplifiers can alter soundstaging/imaging characteristics?

I've given my .02: take some initiative. It's clear by the question that you don't understand what you're asking. The experimental shortcut @SIY recommended is probably your best, and easiest, path forward.
 

MattHooper

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He did answer, categorically, and clearly. You even quoted it above, in bold text.

??

The text I quote in bold from SIY: "It makes no technical sense and indeed no one has ever demonstrated it."

How in the world does that answer the question "Explain how one COULD demonstrate to you that different amps can alter soundstaging and imaging?"

That's like saying "That's not how you make authentic Italian pizza." "Ok, how DO you make authentic Italian pizza?" Reply: "Look, I just told you how!"

It's incoherent to suggest that bolded statement is an answer. So I don't know what you are talking about.



I've given my .02

You have not answered the point I've made in the conversation. I gave it to you clearly again and you've just avoided it.
No problem if you aren't interested, but please don't try to spin it as if you or SIY have answered the questions.


: take some initiative.

Like..asking people what they think when I want to know what they think?

Like taking a technical question to a member with technical knowledge?

Like having even taken the question to the tech crew of a pro audio shop?


It's clear by the question that you don't understand what you're asking.

I understand the point of my questions. If I'm still in the dark about some technical issues, it's not for lack of having asked the questions.

The experimental shortcut @SIY recommended is probably your best, and easiest, path forward.

Again...that still doesn't answer the point that I had clearly laid out. Neither you nor SIY has answered whether you would accept an individual (in this case me) passing such a blind test as confirmation of the proposed phenomenon. If you actually don't see why that is a pertinent question I will again spell out the reasons again if need be. Though I already have.

NOR, in the specific example of the tube amp test, has the question been answered of whether it actually makes sense to measure the way SIY seems to have suggested GIVEN that I've often read that tube amps can alter the sound given how they can react with a speaker load.

As I said, I presented SIY's suggestion to the amp techies who work on amps for a living, for the purposes proposed, and they said the suggestion didn't make sense (including for the reason above). Again...they may be wrong, and I am admittedly ignorant of whatever engineering fact I'm missing....but someone who actually wanted to be helpful or engage in the conversation would explain the answers to these questions rather than just say "I've given my 2 cents" (which haven't explained them) or just ignore them.

You don't have to want to engage the questions I've raised, which is perfectly fine. But at least try to avoid suggesting you've answered the questions and placing all the blame on me for being puzzled. That comes off as disingenuous.

(But, then again, you'll have to talk slow with me: I "always miss the important parts"... )
 
Last edited:

MakeMineVinyl

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Please remember what I had clarified early on:

"Just to be clear: The reason I asked you the original question is because this seems to get in to an interesting area of "what can be demonstrated, how, and at what point and by whom it would be considered 'demonstrated.'"

The point was this: If someone says "X had not been demonstrated" then the follow up question makes sense "what TO YOU, would demonstrate X?"
If there is a difference in imaging or any other parameter which is tagged in a listening session, I'd stop right there and take the before and after conditions and subject them to electronic measurements to see if something electrical has changed. A null test might also be helpful. Chances are that anything which is enough of a change to be heard can then be measured with existing instrumentation (like an AP).

On that thought, I'm astounded that an audible change in things like imaging etc hasn't ever happened (apparently) at the same time there also existed in the room (or could be easily fetched) the electronic measuring gear to try to quantify what changes, if any, have taken place.

Doesn't that sound a bit fishy that audible changes have 'never' happened where there was instrumentation available to measure the change? Or if there was in fact instrumentation available, the people involved were so intellectually lazy as to not try to figure out what is going on? :eek:
 

theREALdotnet

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I understand the point of my questions. If I'm still in the dark about some technical issues, it's not for lack of having asked the questions.

It is a question I would love an answer to (or at least a discussion about), as well. In my view, stereo imaging and soundstage depth are illusions conjured up by the brain, in response to stimuli from the physical world, sound pressure waves in this case. But while they are illusions they are nevertheless real (not placebos or perception biases), in that the same illusion will be produced by most people in response to the same stimulus. Much like the stereo phantom centre – it is a product of our brain, but everybody’s brain seems to produce it under the same circumstances.

It should therefore be possible to characterise the stimulus, and determine which properties it must or mustn’t have in order to produce the illusion of soundstage depth and imaging. Analysis of artificial head (with shoulders!) recordings would likely be the start.

From reading and hearing between the lines of various presentations and interviews I get the impression that this is a fairly well-researched field, but that most of the results are proprietary and closely guarded by the likes of DBX and Dolby Labs.
 

JP

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When I cook something on my stove using propane supplied from two different tanks, the aroma and flavor of the food are different depending which tank is used.

??

The text I quote in bold from SIY: "It makes no technical sense and indeed no one has ever demonstrated it."

How in the world does that answer the question "Explain how one COULD demonstrate to you that different amps can alter soundstaging and imaging?"

That's like saying "That's not how you make authentic Italian pizza." "Ok, how DO you make authentic Italian pizza?" Reply: "Look, I just told you how!"

It's incoherent to suggest that bolded statement is an answer. So I don't know what you are talking about.

Explain how one could demonstrate to you that the propane tank used can alter the aroma and flavor of what is cooked on the stove it supplies?


Like..asking people what they think when I want to know what they think?

Like taking a technical question to a member with technical knowledge?

Like having even taken the question to the tech crew of a pro audio shop?

Which one of those includes you doing some independent research/study/etc.? You're burdening others to do work for you without making any effort to independently understand the topic.


I understand the point of my questions. If I'm still in the dark about some technical issues, it's not for lack of having asked the questions.



Again...that still doesn't answer the point that I had clearly laid out. Neither you nor SIY has answered whether you would accept an individual (in this case me) passing such a blind test as confirmation of the proposed phenomenon. If you actually don't see why that is a pertinent question I will again spell out the reasons again if need be. Though I already have.

If I equally divided a can of soup and reheated both portions on the stove in the exact same way, but using two different propane tanks, and could pass a double-blind test that the two portions smelled and tasted differently, would you accept that as confirmation of my proposed phenomenon?


NOR, in the specific example of the tube amp test, has the question been answered of whether it actually makes sense to measure the way SIY seems to have suggested GIVEN that I've often read that tube amps can alter the sound given how they can react with a speaker load.

As I said, I presented SIY's suggestion to the amp techies who work on amps for a living, for the purposes proposed, and they said the suggestion didn't make sense (including for the reason above). Again...they may be wrong, and I am admittedly ignorant of whatever engineering fact I'm missing....but someone who actually wanted to be helpful or engage in the conversation would explain the answers to these questions rather than just say "I've given my 2 cents" (which haven't explained them) or just ignore them.

You don't have to want to engage the questions I've raised, which is perfectly fine. But at least try to avoid suggesting you've answered the questions and placing all the blame on me for being puzzled. That comes off as disingenuous.

(But, then again, you'll have to talk slow with me: I "always miss the important parts"... )

SIY said to use an ADC to capture the signal at the speakers. At the speakers.

I felt it clear, but my two cents were not to answer any of your questions - the use of the colon was rather intentional. I'm not going down the rabbit hole on a nonsense hypothetical, especially with someone who hasn't demonstrated an interest in gaining any knowledge surrounding the topic.
 

Head_Unit

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I'm often tempted to get a tube amp just for the excellent, classic cosmetics... then I'd tell listeners we're running it real hard and this is how music is supposed to sound ("you can hear the tube warmth!" etc) when really a tiny silver box housing NC252MPs hidden in the corner is what's actually running everything
To make that scheme complete, though, you need to set up A/B versus a "solid state amp" which would actually be a hidden tube amp. See what people prefer!
 

confucius_zero

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Measurements like these make me wonder how Extra Low Dynamic Range sound is a preferred attribute in the "audio enthusiast" realm as the "meat" of the musical elements of sound is emphasized and therefore sounds "more rounded"?
 

drDE

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This is a review and detailed measurements of the Bob Latino's take on Dyna ST-70 stereo tube amplifier. I believe (the kit?) costs US $1,430. This unit was bought used for around US $900.
View attachment 196345

The polished stainless steal case looks very nice. The three transformers give it substantial weight. As you see, the front-end/bias is a new design:

View attachment 196346
The indicated bias voltages are from original Dyna design and don't hold for this configuration. Per Bob, the right DC bias voltage for the EL34 tubes is 0.4 volt which is what I adjusted them to. There is fair amount of interaction between the four pots so I had to go back and forth half a dozen times to get it adjusted so.

There is a switch for operation in triode in addition to pentode. Most of my testing was done in Pentode mode but I also ran a dashboard in triode mode.

Tubes that are included are: NOS Mullard EL-34's and a NOS Brimar CV4003/12AU7 and new production Prima Luna 12AU7s.

The RCA connector was loose as was the ground terminal in one channel. Neither seemed to impact operation unless you really tugged on the RCA connector the wrong way.

Back panel is modified as well with inclusion of modern binding posts:
View attachment 196347

The taps are 4 and 8 ohm (labels are old and don't apply). New power cord is included.

VTA ST-70 Measurements
I let the unit warm up good deal before setting the bias. As such, output was quite stable with time:
View attachment 196348

Here is our dashboard in pentode mode:
View attachment 196349

I could not impact the power supply spikes with any grounding scheme. They are inherent to the design of the unit. Worst offender though is the third harmonic which peaks to nearly -50 dB and sets SINAD accordingly. With median SINAD score of all amps tested at 78 dB, this is copious amount of distortion of course. But it betters the Carver Crimson 275 amplifier by a few dBs (46 dB SINAD).

Then again, distortion is up by some 10 dB relative to the true vintage Dynaco ST-70 amplifier. That unit achieved a SINAD of 63 dB in good channel.

There has been some discussion in their forum about the correct bias voltage so I also tested the unit by setting it to 0.45 volt. That helped the weak channel gain about 2 dB in SINAD and also brought its gain closer to the other channel. Not sure what the impact on longevity of the unit is to operate it at that level.

Triode mode costs you more performance in the form of increased distortion:
View attachment 196350

As noted, watch out for difference in volume as you AB because the gain goes down in Triode mode. Continuing with 0.4 volt bias and pentode mode we get reasonable SNR values for a tube amp:

View attachment 196351

Again, this betters the Carver to the tune of 7 dB.

Frequency response was fine in one channel but had an odd notch in the other:

View attachment 196352

Fortunately it is outside of the audible band so just a curiosity (although lack of gain/level matching remains a small issue).

Crosstalk was surprisingly good:
View attachment 196353

Multitone shows the effect of all the distortion/intermodulation products (and power supply noise):

View attachment 196354

Let's sweep for power:
View attachment 196355

So we get 10 more watts than Carver 275 before clipping. The distortion rise is more steep though, resulting in much less power if we limit distortion to just 1%:
View attachment 196356

Using the 8 ohm tap we get the same power as 4 ohm:
View attachment 196357

I was hoping to listen to the amp but forgot and took it all apart for the review. When I get a chance, I will give it a listen.

Conclusions
Other than the unique look of the unit, I am the wrong guy to ask about the appeal of these tube amps. :) There is little to hang your hat on as far as fidelity merit. That aside, comparing to the Carver Crimson 275, performance is better in most areas. Sadly distortion is much worse than the original ST-70. Not sure if this is planned or artifact of not measuring the performance of all these mods.

Anyway, this is not for me but some of you have different priorities than me. :)

-----------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Amir, I appreciate that you took the time to make this review. I don’t mean to sound rude or disrespectful, however, there are some matters you didn’t address that I’d like to share. Things that measure negatively doesn’t necessarily mean things will sound bad and you made that review appear as if it necessarily makes it sound bad. I also have issues regarding the context in which you presented the YouTube review.

It amazes me that a man of your experience didn’t explain this. To the best of my knowledge, you didn’t even explain the speakers you used in the review other than briefly eluding to some Infinity speakers. What speakers does Infinity make that are efficient? You mentioned that the bass was flabby and also expressed the lack of power output the amplifier had. All you did was briefly elude that a person would need efficient speakers. If so, the why didn’t you do that yourself?

Anyone with experience knows you have to match the proper speakers with the amp being used, so of course you’re going to get flabby bass if you’re using inefficient speakers. You then talk about 9 watts as if it’s nothing. I can run an efficient pair of speakers with just 3 watts and it can sound extremely powerful and loud, yet you didn’t even address either of these facts in your YouTube video. I’d appreciate hearing your thoughts on what I’ve mentioned and if there’s something I overlooked, then I apologize. Thank you, drDE
 

drDE

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Great review @Amir, I’m going to use this as reference to not buy valve gear…..ever!

Amazes me how the context of the way a review is presented can so easily throw nearly an entire audience off key without even realizing it. Amir’s review has many mistakes you guys are overlooking and most people who have been fooled by this have obviously never even listened to this amp in the first place. Doesn’t anybody listen to music anymore? Jimi Hendrix made a living off of distortion.
 

BDWoody

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Jimi Hendrix made a living off of distortion.

He made amps?

You don't get the difference between the creation of music and the reproduction of it?
 

drDE

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I know enough to know this amp is being misrepresented. Have you even spent time with the amp yourself with different speakers.?
 

BDWoody

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I know enough to know this amp is being misrepresented. Have you even spent time with the amp yourself with different speakers.?

Misrepresented?

You believe his measured results are wrong, or you just believe that because you like it, everyone else should?

I wouldn't have a reason to spend time with this amp. My preference is for what comes out of an amp to simply be at a higher volume that what goes in, not for it to add a generous helping of Jimmy Hendrix style distortion to everything that goes through it.

Maybe you are used to reviews that are actually sales pitches.

I'm sure that under some conditions it can sound lovely, like most amps, but it's objective performance really isn't inspiring me to want to dirty up my music like that.
 

rebbiputzmaker

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Misrepresented?

You believe his measured results are wrong, or you just believe that because you like it, everyone else should?

I wouldn't have a reason to spend time with this amp. My preference is for what comes out of an amp to simply be at a higher volume that what goes in, not for it to add a generous helping of Jimmy Hendrix style distortion to everything that goes through it.

Maybe you are used to reviews that are actually sales pitches.

I'm sure that under some conditions it can sound lovely, like most amps, but it's objective performance really isn't inspiring me to want to dirty up my music like that.
You really cannot understand why people might have concerns when it comes to some of the reviews. The facts are the facts, the numbers the numbers but it’s the assumptions and the misinterpretations and the lack of proper application which concerns people. If you want to be fact orientated then opinions should be left out of the equation. If what you really want is opinion, then this is not objective this is just subjective interpretation with some numbers to justify the opinion.
 

BDWoody

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If you want to be fact orientated then opinions should be left out of the equation. If what you really want is opinion, then this is not objective this is just subjective interpretation with some numbers to justify the opinion.

In the same way that a doctor expresses his opinion of my overall health based on a bunch of objective measurements and tests, I have no problem with a knowledgeable, experienced electrical engineer expressing his opinions based on what he finds after an examination of a box of electronics. That doesn't mean that my doctor can't be wrong, nor does it mean our host is infallible, but it does mean he starts with a level of credibility that few reviewers have, and to say he should just be a measurement bot is a bit silly.

I do understand that a lot of people don't like it when their special gear is made out to be less special than they believe it should be.
 
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