Recent trashing of the VTA ST-70

[Idontknow]

Did anyone see Amir’s recent trashing of the Bob Latino Dynaco ST-70 on Audio Science Review’s YouTube channel? Thought the review was horribly done with several errors. I’ve had this amp for several years and it’s nothing like he describes. 

[MeloManiac]

8 minutes ago, Idontknow said:

Did anyone see Amir’s recent trashing of the Bob Latino Dynaco ST-70 on Audio Science Review’s YouTube channel? Thought the review was horribly done with several errors. I’ve had this amp for several years and it’s nothing like he describes. 

From his written review: "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." 

He's the kind of reviewer that looks at numbers only and excludes the human ears and brains. That's where the magic happens, in my opinion! 

Don't let the b*st*rds grind you down, enjoy the music! 

 

[captainbeefheart]

54 minutes ago, Idontknow said:

Did anyone see Amir’s recent trashing of the Bob Latino Dynaco ST-70 on Audio Science Review’s YouTube channel? Thought the review was horribly done with several errors. I’ve had this amp for several years and it’s nothing like he describes. 

 

Don't take what Amir says personally, he is objectively testing what an amplifier should do by definition, which is not add anything to the input of the amplifier. He basically uses SINAD as the test that determines how good an amplifier is, or it's purity if you will, which is what the definition of an amplifier should be from a technical standpoint. SINAD is noise and distortion in relation to the input signal, the more noise and distortion an amplifier has the worse it rates on the SINAD scale. These measurements tell us good information if you know how to interpret it. As long as you understand that you may actually like an amplifier with it's own "voice" which is not a pure amplifier, it's adding coloration, information that was not present in the original input signal. I am a stickler for noise, I truly think that should be as low as possible but not all distortion is created equal as I explained in the other thread. Amir is objectively testing how pure the amplifier is, not if it sounds good or not as that's subjective, as long as you remember this you can still use his tests to your advantage.

 

I may not be remembering the same test review but I think it scored poorly because the two channels were not balanced well which doesn't really say anything about the circuit, more that the particular specimen they had on hand was not functioning correctly and with the help of a good tech could get the two channels matched better. The fact the tube amp has more distortion and noise is why it rates so poorly on the SINAD scale. I have built and worked on far too many ST70's to care for, it's a decent amplifier but by no means is the best amplifier I have ever heard. The ST70 was remarkable in that it was an affordable piece of gear that gave good power and decent performance, it brought good quality music to many people which was great. It is a very simple circuit, nothing elegant or high tech but it did it's job well and when they are functioning as best as they can they are pretty good. They can reach around 1% THD at full output which is audible, I have measured them down to .3%THD when care was taken which I feel is getting to the point of questionably audible. More importantly is perspective, with efficient speakers I know I am well below 1 watt of power for my listening levels and 1 watt is actually quite loud. The ST70 has maybe .05%THD at 1 watt which should be inaudible and so it does a great job where it's being used at. Some may even argue the little bit of harmonic distortion at these levels isn't enough to cause major trouble but enough to sweeten the sound up, and now we are back to the argument of is an effects box, an amplifier with euphoric distortion considered "high fidelity" because it isn't a precise recreation of it's input. I believe you can have your cake and eat it too, I don't get hung up on low order harmonic distortion so long as it isn't up way past 1%, many SET amps that are afraid of feedback will easily show 5%THD at low power levels and these are effects boxes, adding information for pleasure to the signal so from a purist standpoint it may not be considered "high fidelity". I see many 300b amps that have 5% THD at just a few watts yet review well because they sound good, the distortion is pleasing and can introduce something positive to the mix.  Can we call them a bad amplifier? Depends on the definition of course, I'll agree okay it's not a great clean amplifier if that's what you are looking for but if it sounds good and you like it then it's a good amplifier for you and that's all that matters, just don't get angry if the amp you like tests poorly in an objective testing procedure where the goal is to measure the accuracy of the amplifier. I have come to the conclusion that lower order harmonic distortion can be up near 1% at full power and sound great, I won't call it an accurate amplifier but if it sounds good that's all that matters. With higher order harmonic content the level of distortion needs to be much lower or else it will have a negative impact on the amplifier and sound bad. I feel that the tube amps that have 5%THD at low power levels will cause some music, simple music to sound actually better because of the harmonies introduced but when complex music is involved these harmonics may not all sum to harmonious intervals and have a muddy effect, it's just not clean enough for some music. I feel there is a happy middle ground of not too pure and also not too distorted and these amps are the ones that seem to do everything well. But then again they will never objectively test accurate and so from a scientific standpoint they are not a pure and clean source of signal amplification but I am okay with that so long as it doesn't get to be too congested with coloration.

[jjptkd]

1 hour ago, Idontknow said:

Thought the review was horribly done with several errors. I’ve had this amp for several years and it’s nothing like he describes. 

 

 They trashed the Carver 275 as well although admittedly there were some pretty legitimate complaints about build quality, safety and not hitting rated spec's they never listened to the amp which is a shame as its one of the best sounding amps I've ever had the pleasure to own.

 

I think its a little amusing that the Carver 275 is their second "worst" rated amp and I replaced it with their second "best" rated amplifier the Topping PA5 and while its a fraction of the price and decent in its own right it is no where near the sound quality (IMO) of the Carver-- just proves to me that those type of reviews are meaningless in terms of listenability. 

[captainbeefheart]

54 minutes ago, jjptkd said:

 

 They trashed the Carver 275 as well although admittedly there were some pretty legitimate complaints about build quality, safety and not hitting rated spec's they never listened to the amp which is a shame as its one of the best sounding amps I've ever had the pleasure to own.

 

I think its a little amusing that the Carver 275 is their second "worst" rated amp and I replaced it with their second "best" rated amplifier the Topping PA5 and while its a fraction of the price and decent in its own right it is no where near the sound quality (IMO) of the Carver-- just proves to me that those type of reviews are meaningless in terms of listenability. 

 

Yes possibly meaningless in terms of subjective listenability but I don't really think I have ever heard Amir say anything about the stuff he tests as "sounding bad" and more so that it "tests bad".  Test data is objective data, that's it and most of us should know that certain tests like SINAD  are not the last word in if something sounds good or not, only how it performs. Would you agree this is an accurate assumption? As I explained in my last post, we have certain definitions for technical equipment, the equipment in theory should pass the input off to the output as unchanged in content only changed in amplitude, basically a wire with gain. These tests tell us how the equipment performs objectively but doesn't tell us how it sounds subjectively, we need to correlate the objective data with the subjective listening experience and draw a conclusion to what matters and to what degree does things matter.

 

For example the Carver 275, forget the bloated specs and look at it's performance, it clearly is not a good amplifier in terms of accuracy but subjectively it sounds good. So we need to correlate why it sounds good and measure badly. What I like about Amirs tests is things like channel balance, that's something where subjective distortion arguments don't matter because it's obvious you want both channels in a stereo amplifier to match as close as possible. If the two channels do not match well you know the device isn't designed well and there needs to be a quality control issue rectified to improve upon the product.

 

I feel the engineer side of the coin needs to make these correlations better, to sit back and say okay well this amp does produce 1% distortion at 50 watts but it's distortion is benign at 1 watt where most of our amps live their life at. Take into consideration the distortion from the loudspeakers at these sound levels, they will be a magnitude higher than any poor testing amplifier, seriously 30% at low frequencies so why are we losing sleep on an amp that has .5%THD at 50 watts? So some perspective needs to be had by many. Loudspeaker distortion grossly out weighs any other distortion in the chain. If you understand how sound propagation works it's extremely non-linear so lots of second order harmonic distortion will be added between the transducer and your ear. The math behind fluid dynamics is how sound propagates, the equations are nonlinear, our hearing is single ended in nature. The equations show high energy peaks moving faster than the low energy troughs, this is what makes sound propagation through air non-linear and so it's not pure. I truly believe our brains are so used to evolving with this harmonic distortion content (second harmonic dominant) that it sounds natural to us, so in conclusion to the amplifier not being pure and passing an accurate depiction of the input, it's presenting the information in a natural manner to how we are used to hearing things in nature and so we just say "yup this amp just sounds right" yet it has high distortion compared to what we can achieve. I believe the true masters of amplifier design understand these concepts, they are not objectively trying to make a pure and accurate amplifier, they are cooks in a kitchen adding harmonic spices into the stew to voice the amplifier in likable way. One can argue it's not "high fidelity" but the better question is do we want high fidelity? Maybe a little natural harmonics is what triggers the "it sounds good" button in our minds. It's a fascinating topic, we should do less arguing and do more research to come to some conclusions where the objective world can be correlated into the subjective world.

[OO1]

2 hours ago, jjptkd said:

 the Topping PA5 and while its a fraction of the price and decent in its own right it is no where near the sound quality

 the Topping PA5 is also this new generation of non-repairable amps as the Chips  Fail on the main-board  .

 

any  problem after the warranty is out ,   you throw it in the trash or you order a new Board , while on the other hand , you can fix a Carver 275   with  available parts .

[captainbeefheart]

12 minutes ago, RandyH said:

 the Topping PA5 is also this new generation of non-repairable amps as the Chips  Fail on the main-board  .

 

any  problem after the warranty is out ,   you throw it in the trash or you order a new Board , while on the other hand , you can fix a Carver 275   with  available parts .

 

Perfectly said, there are trade offs for everything. So we use all this technology at our disposal and can make a Class D amplifier with literally no distortion with some of these new chips out on the market yet is that worth the fact it is going to go into the landfill after 5 years? I personally hate throwing things away and am not from the throwaway generations. I'll gladly take some benign or possibly pleasing distortion and know my amplifier will last as long as I will and if there ever needs to be repaired can easily be done. This is why I stick with linear power supplies and linear amplifiers, especially tubes because they are more robust than transistors. One wrong move with a transistor and half the circuit gets destroyed which requires a lot of work. Tube amps for the most part just check many boxes for me so that's what I prefer, but if a SS amp checks enough boxes also I don't mind either. But an amp where the chips go south and it's done, to the landfill and you're back on the market having to make another amplifier purchase. Another perspective is friends and family not into this hobby, they don't care so long as it sounds good and many will never be able to pick certain amps out in a blind test, they don't even think of the equipment they just enjoy the music. I have relaxed more into this mindset now, I don't try and listen to my gear, I just enjoy the music without worrying "can it be better?". So if my system sounds great and my amp can be easily repaired and last another 30 years I think that is better for the world then people throwing away so much electronics, it's very wasteful. One could even argue that the electrical efficiency of the class D technology balances out in the long run due to how much waste is produced, not to mention resources being wasted. The tube amp that needs a cap job and tubes every 20 years may just have a smaller carbon footprint, especially if we are talking nuclear reactor power which is clean then the well built discrete amp wins because of much less waste in the long run.

[Idontknow]

3 hours ago, captainbeefheart said:

 

Don't take what Amir says personally, he is objectively testing what an amplifier should do by definition, which is not add anything to the input of the amplifier. He basically uses SINAD as the test that determines how good an amplifier is, or it's purity if you will, which is what the definition of an amplifier should be from a technical standpoint. SINAD is noise and distortion in relation to the input signal, the more noise and distortion an amplifier has the worse it rates on the SINAD scale. These measurements tell us good information if you know how to interpret it. As long as you understand that you may actually like an amplifier with it's own "voice" which is not a pure amplifier, it's adding coloration, information that was not present in the original input signal. I am a stickler for noise, I truly think that should be as low as possible but not all distortion is created equal as I explained in the other thread. Amir is objectively testing how pure the amplifier is, not if it sounds good or not as that's subjective, as long as you remember this you can still use his tests to your advantage.

 

I may not be remembering the same test review but I think it scored poorly because the two channels were not balanced well which doesn't really say anything about the circuit, more that the particular specimen they had on hand was not functioning correctly and with the help of a good tech could get the two channels matched better. The fact the tube amp has more distortion and noise is why it rates so poorly on the SINAD scale. I have built and worked on far too many ST70's to care for, it's a decent amplifier but by no means is the best amplifier I have ever heard. The ST70 was remarkable in that it was an affordable piece of gear that gave good power and decent performance, it brought good quality music to many people which was great. It is a very simple circuit, nothing elegant or high tech but it did it's job well and when they are functioning as best as they can they are pretty good. They can reach around 1% THD at full output which is audible, I have measured them down to .3%THD when care was taken which I feel is getting to the point of questionably audible. More importantly is perspective, with efficient speakers I know I am well below 1 watt of power for my listening levels and 1 watt is actually quite loud. The ST70 has maybe .05%THD at 1 watt which should be inaudible and so it does a great job where it's being used at. Some may even argue the little bit of harmonic distortion at these levels isn't enough to cause major trouble but enough to sweeten the sound up, and now we are back to the argument of is an effects box, an amplifier with euphoric distortion considered "high fidelity" because it isn't a precise recreation of it's input. I believe you can have your cake and eat it too, I don't get hung up on low order harmonic distortion so long as it isn't up way past 1%, many SET amps that are afraid of feedback will easily show 5%THD at low power levels and these are effects boxes, adding information for pleasure to the signal so from a purist standpoint it may not be considered "high fidelity". I see many 300b amps that have 5% THD at just a few watts yet review well because they sound good, the distortion is pleasing and can introduce something positive to the mix.  Can we call them a bad amplifier? Depends on the definition of course, I'll agree okay it's not a great clean amplifier if that's what you are looking for but if it sounds good and you like it then it's a good amplifier for you and that's all that matters, just don't get angry if the amp you like tests poorly in an objective testing procedure where the goal is to measure the accuracy of the amplifier. I have come to the conclusion that lower order harmonic distortion can be up near 1% at full power and sound great, I won't call it an accurate amplifier but if it sounds good that's all that matters. With higher order harmonic content the level of distortion needs to be much lower or else it will have a negative impact on the amplifier and sound bad. I feel that the tube amps that have 5%THD at low power levels will cause some music, simple music to sound actually better because of the harmonies introduced but when complex music is involved these harmonics may not all sum to harmonious intervals and have a muddy effect, it's just not clean enough for some music. I feel there is a happy middle ground of not too pure and also not too distorted and these amps are the ones that seem to do everything well. But then again they will never objectively test accurate and so from a scientific standpoint they are not a pure and clean source of signal amplification but I am okay with that so long as it doesn't get to be too congested with coloration.

 

Really appreciate your detailed explanation here. I gotta print your responses up. I really respect what you are saying and although I don’t quite understand these technical aspects anywhere close to your level, I am starting to appreciate it more because you seem level headed on both sides as a listener and a tech. That’s the best of both worlds. Your experience far exceeds mine as I am more a listener but I’m definitely going to be listening to you as well haha! 

[Idontknow]

3 hours ago, jjptkd said:

 

 They trashed the Carver 275 as well although admittedly there were some pretty legitimate complaints about build quality, safety and not hitting rated spec's they never listened to the amp which is a shame as its one of the best sounding amps I've ever had the pleasure to own.

 

I think its a little amusing that the Carver 275 is their second "worst" rated amp and I replaced it with their second "best" rated amplifier the Topping PA5 and while its a fraction of the price and decent in its own right it is no where near the sound quality (IMO) of the Carver-- just proves to me that those type of reviews are meaningless in terms of listenability. 

 

That’s what’s interesting about your comments. Even though things can measure badly, they may still sound good but I think in the end as captainbeefheart said, if it sounds good to us that’s what matters.

[captainbeefheart]

51 minutes ago, Idontknow said:

 

Really appreciate your detailed explanation here. I gotta print your responses up. I really respect what you are saying and although I don’t quite understand these technical aspects anywhere close to your level, I am starting to appreciate it more because you seem level headed on both sides as a listener and a tech. That’s the best of both worlds. Your experience far exceeds mine as I am more a listener but I’m definitely going to be listening to you as well haha! 

 

Thank you for your kind words, I write here in hopes to give the community fact based information about our hobby and how to improve our own experience. The passion is music, for some they lose sight of that but it boils down to enjoying music. We want to experience the magic of music right in our own homes whenever we choose.

 

Okay enough about that, let's do a thought experiment shall we?

 

Picture in your mind the grooves of a vinyl record, this squiggly line pressed into the material holds all the information in the material we listen to. Think about that for a second, all the subtle nuances, the bow sliding across a violin string, the air passing by a singers vocal chord as they inhale a breath between vocalization, the splashy goodness of cymbals, everything is embedded information contained within that one squiggly line. Now ask yourself how is this possible? If you want to understand more you need to delve into some higher math, and it's called the Fourier transform. Every signal imaginable, any squiggly line you can draw is nothing more than the sum of multiple sine waves of different frequencies. For simplicity lets think now of a band, first we have a singer, then add in a guitar player, then a bass player, etc..... The total sound we hear is the sum of it's parts. So that's how we analyze an amplifier. We input a sine wave, and perform a Fourier analysis of the output and if the original sine wave has changed in shape it will break it down into individual sine waves of different frequencies. So we can say okay we input a pure 1kHz sine wave and the waveform shape changed a little so now at the output we not only have 1kHz but also 2kHz at -60db down. It's information embedded into a transfer function. I can only go so far explaining it, you must take the journey further yourselves and study the mathematics which will give you much better insight into why this is. Math is a construct that helps us explain things and it can do it very well. Some people argue math was always there regardless if humans never existed but I do not agree, math is nothing more than human concept, a construct we made to help us do things and understand the world around us. This is why people that do not understand the deeper mathematics will never grasp these concepts, snake oil theories are then constructed and myths are spread and the world is a worse place. Once you have the Fourier transform down it is a smaller part of the Laplace transform which is just mind boggling and amazing at the same time. It shows how math can explain such beauty in the complex nature of the physical world around us. Sorry but math is a major part of the gig, if someone claims to be an expert in audio, say Paul McGowan from PS Audio but has a very rudimentary understanding of mathematics then you can be certain that he is going to be a bad source to learn about audio and music. You'd be much better off learning about audio and audio devices from a physicist or a mathematician. That's just how it is, using math and concepts to understand complex things is the only way to go to learn this stuff at a deeper level.

[Idontknow]

What I didn’t understand about the review was when Amir started to explain his listening impressions. Why with as much knowledge as he should have does he make 9 watts sound as if it’s nothing when in fact it takes just a few watts to run various types of efficient speakers and just explain that to the audience so they understand properly and aren’t mislead?  The other issue is he didn’t explain which infinity speakers he was using. I asked him and he wouldn’t say. I did research and found out they were 6 ohm speakers with 88 dB efficiency called the Infinity R253. In the video, he explains that the amp needs to be used with efficient speakers, yet why does he act disappointed when he listens to it himself without matching his own speakers correctly in the first place? It just gave me the impression that he wanted to bash the product to make it match how it measured. That’s the impression I got from that, but maybe I’m wrong. So, what I can’t understand is why he would rate the  floppiness of the bass at louder listening levels without matching the correct set of speakers himself? 

 

Also those speakers he was he was using are about $400 speakers. I’m okay if people enjoy inexpensive speakers, but shouldn’t he be using something nicer in order to help discern the differences of the gear he is comparing?

[Idontknow]

captainbeefheart , I was curious what you like as a listening system yourself. You are obviously a mountain of knowledge. Do you normally listen to solid state amps and/or tubes? What speakers and what music do you generally listen to? Curious how a person with your knowledge selects gear.  btw, now you know why my avatar says idontknow. Thanks

[billybob]

Yes, ...

[billybob]

When you start running down the competition, you are likely in trouble.

[captainbeefheart]

2 hours ago, Idontknow said:

What I didn’t understand about the review was when Amir started to explain his listening impressions. Why with as much knowledge as he should have does he make 9 watts sound as if it’s nothing when in fact it takes just a few watts to run various types of efficient speakers and just explain that to the audience so they understand properly and aren’t mislead?  The other issue is he didn’t explain which infinity speakers he was using. I asked him and he wouldn’t say. I did research and found out they were 6 ohm speakers with 88 dB efficiency called the Infinity R253. In the video, he explains that the amp needs to be used with efficient speakers, yet why does he act disappointed when he listens to it himself without matching his own speakers correctly in the first place? It just gave me the impression that he wanted to bash the product to make it match how it measured. That’s the impression I got from that, but maybe I’m wrong. So, what I can’t understand is why he would rate the  floppiness of the bass at louder listening levels without matching the correct set of speakers himself? 

 

 

I agree, Amir seems like a relatively smart guy so he should be a bit more open minded to things and look into them but I feel although he has very nice test equipment and is pretty good with it he is not an engineer. I believe his outlook on amplifiers is that it should drive modern less efficient speakers so he isn't going to go out of his way to find something that makes the amplifier shine. So it can be viewed actually both ways, some people could claim he is only choosing easy to drive speakers for his tests which isn't realistic for the real world which lets be honest is probably full of speakers that are not very efficient. The argument in that a good amplifier will drive any speaker, this to me is just silly and "for the masses" thinking. When you design to be good at a lot of things, you will not reach greatness at any one thing. To a point I can see how it makes things easier for consumers if they didn't need to research things in order to see if they will pair well together but hey this is a complex and dynamic subject and market so it will never be that simple. Which leads me to how I choose my stuff.

 

One thing that annoys me about Amir is he always jumps for the 4 ohm load even if the tube amp doesn't have a 4 ohm tap. He does this quite a lot and I don't think he understands that with a transformer output and tubes the load is reflective and tubes work best if you keep them in their linear region like with many things.

 

2 hours ago, Idontknow said:

captainbeefheart , I was curious what you like as a listening system yourself. You are obviously a mountain of knowledge. Do you normally listen to solid state amps and/or tubes? What speakers and what music do you generally listen to? Curious how a person with your knowledge selects gear.  btw, now you know why my avatar says idontknow. Thanks

 

I would be crazy not to have learned about all sorts of types of amplification topologies and listen to them or even design them myself. I'll cut to present time which has me making amplifiers that suit my speakers. I have enough data to know how much power I require with all my speakers. I do have a vintage transistor receiver with my RB-81 mkII speakers but my 1982 La Scala's and 1975 Heresy's use tubes. The heritage series is what I like to design amps around. They are easy in regard to needing low power but besides power they are anything but an easy load, an easy load would be a constant purely resistive load. So low power is good because then we can have a relatively pure signal path without needing to parallel a bunch of devices together. The low power thing is huge because we can now use class A single devices (single ended) especially triodes which are very linear to begin with so they require less external error correction. To be fair feedback is feedback though so long as it's done well. As for the lumpy load I like the addition of current feedback from the output load, this means the amp reacts to current through the speaker, I make this adjustable where you can dial in the low frequency resonance to get the best damping possible. I test with reactive loads in order to make sure stability is maintained via adequate phase margin.  This can all be done with transistors also and to great results, I just prefer tubes. Although single ended Class A is the least efficient giving them low output power and higher distortion vs push pull or complimentary output stages I still just like the sound. So I guess I like a little second harmonic distortion.

[jjptkd]

6 hours ago, captainbeefheart said:

I believe the true masters of amplifier design understand these concepts, they are not objectively trying to make a pure and accurate amplifier, they are cooks in a kitchen adding harmonic spices into the stew to voice the amplifier in likable way. 

 

I think you're spot on here, this is from Bob Carver's reply to the ASR review of the 275:

 

"The 275 is a powerful, easy to listen to amplifier. I am happy with its design. In fact, this is one of the best designs I have produced. The general reception of the 275 to date has been that of a high quality design, one that does not disappoint in any respect. The performance as it was measured by Amir does not do justice to the sound engineering practices that the 275 represents.

 

I am not going to explain or attempt to refute the reasoning behind each criticism Amir has made, the product speaks for itself and stands on its long history of satisfaction. These amplifiers were not designed to be “world beaters” in measurement domain, but instead, they were designed to sound the best and to do so at an affordable price in relation to other products they might be fairly compared to. It is unfortunate for this type of bad press to make such an impression on people not directly familiar with the amplifier, or the design and its goals.

 

In conclusion, if someone were to come to an audio show and criticize the sound in a room with music playing through a 275, it would be much harder to make the argument that it’s in any way a deficient product or design. I stand by that. The character of this amplifier is exactly what I wanted it to sound like."

[henry4841]

7 hours ago, captainbeefheart said:

The heritage series is what I like to design amps around. They are easy in regard to needing low power but besides power they are anything but an easy load, an easy load would be a constant purely resistive load. So low power is good because then we can have a relatively pure signal path without needing to parallel a bunch of devices together. The low power thing is huge because we can now use class A single devices (single ended) especially triodes which are very linear to begin with so they require less external error correction. To be fair feedback is feedback though so long as it's done well. As for the lumpy load I like the addition of current feedback from the output load, this means the amp reacts to current through the speaker, I make this adjustable where you can dial in the low frequency resonance to get the best damping possible. I test with reactive loads in order to make sure stability is maintained via adequate phase margin.  This can all be done with transistors also and to great results, I just prefer tubes. Although single ended Class A is the least efficient giving them low output power and higher distortion vs push pull or complimentary output stages I still just like the sound. So I guess I like a little second harmonic distortion.

I am in your camp. Heritage loves tubes. 

[Schu]

Tests great... sounds terrible.

Or, in this case

Tests terrible... sounds great.

[captainbeefheart]

13 hours ago, jjptkd said:

 

I think you're spot on here, this is from Bob Carver's reply to the ASR review of the 275:

 

"The 275 is a powerful, easy to listen to amplifier. I am happy with its design. In fact, this is one of the best designs I have produced. The general reception of the 275 to date has been that of a high quality design, one that does not disappoint in any respect. The performance as it was measured by Amir does not do justice to the sound engineering practices that the 275 represents.

 

I am not going to explain or attempt to refute the reasoning behind each criticism Amir has made, the product speaks for itself and stands on its long history of satisfaction. These amplifiers were not designed to be “world beaters” in measurement domain, but instead, they were designed to sound the best and to do so at an affordable price in relation to other products they might be fairly compared to. It is unfortunate for this type of bad press to make such an impression on people not directly familiar with the amplifier, or the design and its goals.

 

In conclusion, if someone were to come to an audio show and criticize the sound in a room with music playing through a 275, it would be much harder to make the argument that it’s in any way a deficient product or design. I stand by that. The character of this amplifier is exactly what I wanted it to sound like."

 

People love a good drama filled controversy. The audio market is filled with so many false claims and bloated specs to sell things I think when a large player like a Carver was caught being misleading with their specs it just opened up the floodgates. I don't remember if Amir even listened to the amp or not but his shtick is to do specification testing to see if products of forum members meet them. As an amplifier engineer and builder myself I would never use a 15 watt output transformer for a supposed 75 watt amplifier, it's just unethical. The way the specs were presented was it could do 20Hz-20kHz with less than 1% THD at 75 watts RMS. Since the testing showed the amp was way off from these specs the actual sound of the amp wasn't really ever considered which is sad but understandable. If it was marketed truthfully, in that it is a 17 watt RMS amplifier but has the ability to provide large peak power for short periods which extends the headroom for music playback it would have been much less controversial and people would move past the specs and actually listen to the amplifier. I read a good amount of the threads on ASR and I don't think the sound of the amp was in question, only the rated specs, build quality, and safety concerns which nobody could look past. It's certainly a strange duck, using KT120 tubes with a 15 watt transformer and B+ and loading to push high power but the transformer was always going to be the limiting factor. Many just question why didn't they just use a properly rated output transformer? So to many it looked like the company was trying to purposely deceive the consumer which is always going to be bad press once the cats out of the bag. I can see both sides of the argument.

[captainbeefheart]

My first post was in regard to Amirs testing of the vintage unit he tested and not the Bob Latino version so I watched the correct review today. It still had a slight channel mismatch as the original and the same noise problems bleeding into the signal but what I thought was interesting was the original performed better than the Bob Latino version. So in my other post when talking about distortion reading was incorrect and the Bob Latino is a lot worse. I suppose it's no surprise because for whatever reason Bob decided to change the front end and reduce the amount of feedback which easily shows in the measurements. The ST70 should not have 1% THD at only 10 watts! The best part of the ST70 was the design in that was simple and yet had reasonable performance where Bob's front end board is more complex than the original yet performs worse. The advantage of triode mode is to have less distortion and it was very odd to have more distortion at 5 watts output in triode mode vs pentode mode, my guess again is since open loop gain drops so does feedback, but still you can get pretty low distortion with no feedback with triode outputs so this version of the ST70 is just odd. I am not familiar with the Bob Latino version, only the original one. Then there was that sharp roll-off at 30kHz on one channel, my guess is that channel was unstable and so they added a pole in to reduce bandwidth to get it to behave. Instead if you take the time to work out proper compensation networks you will have a happy amplifier, especially with such low amount of feedback being used something is most likely off in the layout making one channel worse. This probably accounts for why the channels don't match well either.

 

I don't know why these modern tube amp designers do not take advantage of all the tools we have at our disposal, first is the power supply noise that bleeds into the signal, the power supply should be improved upon first and foremost. I won't lose sleep over low amounts of low harmonic distortion but the Bob version should perform much better, I cannot believe the made the ST70 worse instead of better. You want at least 16 bit performance so there is resolution with music, especially complex music as the multi-burst tone showed just a bunch of "grass" which can lose low level detail. I would be okay with 1% at 40 watts but at 10 watts that was very surprising to see.

 

There it is, my actual take on the Bob Latino version and not the original that I was talking about in my earlier posts. I was thinking with upgraded front end Bob was improving upon the original design but it appears that is not the case. I will have to look into the schematic of the Bob Latino version if I can find one online as I am very curious what is going on with these amps.