JP
Major Contributor
Showing some initiative would likely be of benefit.
Wouldn’t it be really cool if there were some magic technology to scale down voltage levels?
Showing some initiative would likely be of benefit.
These were the points he studiously avoided, unfortunately.
What test would you accept as having demonstrated that different amplifiers can alter soundstaging/imaging characteristics?
He did answer, categorically, and clearly. You even quoted it above, in bold text.
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.
Like, say... a voltage divider?Wouldn’t it be really cool if there were some magic technology to scale down voltage levels?
... this amp seems quite distant from the goal of high fidelity audio reproduction.
JSmith
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).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?"
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 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.
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?
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.
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"... )
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!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
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.
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Great review @Amir, I’m going to use this as reference to not buy valve gear…..ever!
Jimi Hendrix made a living off of distortion.
I know enough to know this amp is being misrepresented. Have you even spent time with the amp yourself with different speakers.?
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.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.
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.