Dynaco ST-70 Series 3 Tube Amplifier Review

[Blumlein 88]

To be fair, the only thing this has in common with the original ST-70 is the brand name. The performance could be somewhat bettered if they had used something closer to the original topology, a high slope pentode and a high gm triode for the input stage. For the price, I'd expect better even for a tube circuit.

Exactly. The idea you are getting something like the Dyna ST 70 series 3 is a farce. At best it should have used the Dyna name with new model number. It was misdirection and false advertising. The company admitted they couldn't duplicate the transformers. They used a different circuit to work around not having 7199 tubes, and the case along with the power supply is different. The only thing in common with the Dynaco ST 70 is the name, and the fact it uses tubes and transformers. Well and both used EL34 output tubes.

 

[pseudoid]

Depends on the design goals and the rest of the circuit.

Hi, @SIY,
Would there me much improvement in the dashboard if the MAINS supply harmonics were not present?

I am not sure what this specific ST-70 clone uses for rectification (solid-state or tube?).
Some have said that since the inverting tube output provides for a cancellation effect to the supply harmonics of the positive swing, the -90db MAINS harmonics is about best to be expected.

 

[SIY]

Would there me much improvement in the dashboard if the MAINS supply harmonics were not present?

Not much; the log scale can be tricky. The THD+N is dominated by 2nd and 3rd harmonics. Just looking at 3rd, it's at -65dB. Converting that to percent, it's 0.056%. Second harmonic is similarly sized, so you can see that the power supply, radiative, and grounding imperfections aren't big contributors.

I am not sure what this specific ST-70 clone uses for rectification (solid-state or tube?).

Solid state.

Some have said that since the inverting tube output provides for a cancellation effect to the supply harmonics of the positive swing, the -90db MAINS harmonics is about best to be expected.

Ideally, there wouldn't be any 60Hz- the supply is running at a 120Hz fundamental. That's what the push-pull nature of the circuit rejects. The 60 comes from either grounding, transformer radiation, or coupling in the core of the power transformer and won't be much affected by the circuit's PSR.

 

[SIY]

Exactly. The idea you are getting something like the Dyna St 70 is a farce. At best it should have used the Dyna name with new model number. It was misdirection and false advertising.

This is unfortunately even common in the world of the tubes themselves. Type numbers became brands, so (for example) a 300B, 572B, 2A3, and even an EL34 will not conform to the specifications or ratings of those actual type numbers. In the case of the 572B, even the pinout is entirely different.

 

[anmpr1]

To be fair, the only thing this has in common with the original ST-70 is the brand name. The performance could be somewhat bettered if they had used something closer to the original topology, a high slope pentode and a high gm triode for the input stage. For the price, I'd expect better even for a tube circuit.

May have been posted earlier, but anyone looking for close to original Dynaco design language should probably look here for DIY

ST-70 KIT (120 VAC) - Dynakit Parts

Full kit package, less tubes and top vented cover. Kit requires user assembly of PC board. Choose either type: (A) original 7199 tube design or (B) our new 6GH8A tube design. Includes our new brown Polyimide circuit board! Note: The 7199…

www.dynakitparts.com

and here for prebuilt

GETDYNACO - ST-70 Tube Amp

DYNACO STEREO 70 (ST-70) Tube Amplifier SEE HOW TO BUY ONE where can I buy a new Dynaco or Dynakit Tube Amplifier. Get a new tube amp here. Factory wired

www.getdynaco.com

The most instructive and fun thing would be to build the kit version, but if you just want something to look at with a nostalgia angle in mind, the pre-built model probably represents good value, for that sort of thing.

FWIW, I built two MkIV kits from Dynakitparts (essentially single channel version of the ST-70) with good results. Very close to the original circuitry. Don't use them much anymore; maybe in winter time for extra radiant heat.

 

[Aperiodic]

Similar to LPs, I will never get the attraction beyond the nostalgia. I could not wait to get rid of LPs when CD came out.

Same here.As a veteran of the ‘heyday’ of vinyl, I can tell you I don't miss it much if at all.

I once attehded a talk at Capital Audio Fest given by Klaus, the owner of Odyssey Audio. First, everyone in the group agreed unanimously that transducers were the biggest problem in most audio systems as far as fidelity goes. Next, the same group of people agreed virtually unanimously that vinyl sounds better than digital. Well, guess what phono cartridges and record cutting lathes (both part of your vinyl signal chain) are? Some people are committed to a delivery format that literally can be traced directly back to Thomas Edison. To each his own, I guess. Have at it.

 

[rongon]

Maybe a bad tube? Or one that is not firmly seated? (Visual inspection didn't show such through the grill.)

A tube amp will require more aggressive intervention to troubleshoot. To know if a tube is firmly seated, you'd have to 1) turn off the amp and let it cool, 2) take off the grill, 3) remove and reinsert the tubes to make sure they're firmly seated straight into their sockets. That's basic 'old radio guy' stuff. Tubes are not and never were 'user friendly'.

 

[WillBrink]

Same here.As a veteran of the ‘heyday’ of vinyl, I can tell you I don't miss it much if at all.

I once went to a talk at capital audio fest given by Klaus, the owner of Odyssey Audio. First everyone in the group agreed that transducers were a big problem as far as fidelity goes. Next, the same group of people agreed virtually unanimously that vinyl sounds better than digital. Well, guess what pho cartridges and record cutting lathes (both part of your vinyl signal chain) are? Which some people are committed to a delivery format that literally can be traced directly back to Thomas Edison. To each his own, I guess.

I think for some they genuinely do, something something about how some people like distortion and the artifacts LPs offer. I don't dismiss them out of hand per se for their preferences, I just don't "get" why/how they have them. I also think nostalgia has a far greater impact on their bias than they realize or understand. I have warm and fuzzy memories of listening to my 8 tracks in my old player, but I don't mistake it for quality audio. I also thought the boom box I owned was the height of audio.

 

[Aperiodic]

To be fair, the only thing this has in common with the original ST-70 is the brand name. The performance could be somewhat bettered if they had used something closer to the original topology, a high slope pentode and a high gm triode for the input stage. For the price, I'd expect better even for a tube circuit.

Absolutely, the main thing they are were selling here is name recognition and some fancy casework (and a few pieces of 'sppropriated' circuit design work.) They disappeared as a result,

 

[rongon]

There is a high-pass filter with two settings:

Good thinking as this amp is not capable of producing much clean power at the lowest range (see measurement below).

That's actually a very good thing in a medium powered tube power amp. The reason the amp can't deliver undistorted power at very low frequencies is that all output transformers have limited primary inductance, which limits the amount of power that can be transferred efficiently from the (high impedance) power output tubes to the (low impedance) speakers. At low frequencies, the output transformer's limited inductance causes power to be burned off by the output tubes as (useless) heat rather than being transferred from the tubes to the speaker (load). It's one of the limitations of tube power amps. Removing frequencies at the amp input that the speaker is not going to play anyway makes the feedback loop more capable of keeping the output impedance and distortion low(er), rather than trying to correct for giant gulps of infrasonic booms caused by the output transformer's inability to efficiently drive large 20Hz signals into the speaker load.

Generally, people who like tube amps do not require the kind of bass response avid home theater and super-objectivist listeners demand of their setups. Some people use tube amps to drive their midrange/tweeter speakers and use a solid state amp to drive their woofers, to try to get the subjectively smooth mids and highs of tube amps along with authoritative bass from their systems. That does require the additional complication of an external crossover, possibly operating at line level, but some people have made that work. Many speakers come with bi-wiring capability, so you can use two different amps to drive the tweeter separately from woofer. There's some sense to that. The tube amp will operate with much lower distortion if it's not required to drive very low frequencies into the load.

All of the above assumes you believe there is a difference in *subjective* sound quality between a tube amp (of whatever kind) and a well implemented solid state amp. I know that's a contentious subject around here, so I ain't gonna touch that...

 

[Aperiodic]

I think for some they genuinely do, something something about how some people like distortion and the artifacts LPs offer. I don't dismiss them out of hand per se for their preferences, I just don't "get" why/how they have them. I also think nostalgia has a far greater impact on their bias than they realize or understand. I have warm and fuzzy memories of listening to my 8 tracks in my old player, but I don't mistake it for quality audio. I also thought the boom box I owned was the height of audio.

Agree with all of the above. I will even concede to vinyl boosters that on a really good TT setup (not necessarily uber-xpensive) vinyl can sound better than it has a right to, given the medium's myriad technical and performance shortcomings. But to me, good digital just crushes all but the absolute best that analog can muster. A lot of people's outlooks were affected by crappy roll-the-tape transfers from the early days of the CD. I think a lot of the resistance has to do with that,

 

[rongon]

I think for some they genuinely do, something something about how some people like distortion and the artifacts LPs offer. I don't dismiss them out of hand per se for their preferences, I just don't "get" why/how they have them. I also think nostalgia has a far greater impact on their bias than they realize or understand. I have warm and fuzzy memories of listening to my 8 tracks in my old player, but I don't mistake it for quality audio. I also thought the boom box I owned was the height of audio.

It's not just nostalgia. I think there's a subjectively softer edge to the playback that makes some setups easier to listen to for purely musical (aesthetically speaking) enjoyment, rather than for pure accuracy (faithful reproduction of the source material). This is not a better/worse thing. It's more of a subjective thing, an "I like this kind of sound" rather than "this is better than that".

For my hi-fi/musical enjoyment, I've vacillated back and forth between objectivist vs. subjectivist leanings, all my adult life. I currently have a modest 'objectivist' kind of setup, which I enjoy for its dynamics, relatively low levels of distortion and noise, etc. But then I spin an LP and find I really enjoy that sound too. I also added an old tube preamp I'd built years ago and immediately heard the 'tubiness' (extra low order harmonic distortion) immediately. Playing small scale music (i.e., small jazz groups, string quartets, etc.) it made things sound more present and in-the-room, and most importantly for me, less 'electronic sounding'. But of course it becomes a muddy mess with a well recorded large scale symphonic work from a high quality digital file.

Comparing why people like the sound of a tube amp to nostalgia for a 1980s boom-box is really not fair. Perhaps folks here have never heard the kind of vinyl and tube amp setup I'm thinking of. They are really fun to listen to, even if they are not nearly as accurate, low noise, low distortion as a Topping DAC > Fosi amp > Revel speakers kind of setup. That's fun to listen to, enjoyable, not better.

EDIT TO ADD:
I'll bet not a single person here has ever heard a well produced early 1950s 78rpm record (in good condition) played on a truly 'transcription quality' 78rpm playback setup (a truly top-end radio station turntable such as Garrard 301 or similar) the correct type of cartridge/stylus, phono preamp with correct EQ for the record, etc. It's simply amazing how ridiculously good a pristine 78 can sound. Most of the music we get to hear from 78s is in digital formats (CD, files) remastered with heavy-handed use of noise reduction from analog tape transcriptions which were themselves heavily re-equalized to reduce noise and may have deteriorated over time. To get the real sound of an original 78, you need to get your hands on an original 78 and play it back with the correct playback equipment (which is all obsolete and hard to find). But once you do get that together, you'll be simply stunned at how good that can sound. I heard "Just Friends" from the original 78 pressing of "Bird With Strings", from around 1950. I've heard that all my life on LP, CD and now digital file transfers. None of those modern remasters sound anywhere near as musically satisfying as that original 78. That there was an object lesson in how difficult it is to talk about whether this or that technology 'sounds better' than any other. Does "Bird With Strings" sound better playing from a DAC into a pair of JBL M2 speakers? Or does it sound better from the original 78 played through the period-correct state of the art setup? So. which is 'better' if the music I want to hear is Bird With Strings?

 

[Robin L]

Agree with all of the above. I will even concede to vinyl boosters that on a really good TT setup (not necessarily uber-xpensive) vinyl can sound better than it has a right to, given the medium's myriad technical and performance shortcomings. But to me, good digital just crushes all but the absolute best that analog can muster. A lot of people's outlooks were affected by crappy roll-the-tape transfers from the early days of the CD. I think a lot of the resistance has to do with that,

I also think early CD players had issues with a lack of focus. Of course, that's my subjective opinion from nearly 40 years back, and it's possible that I simply got used to the sound over time. But my subjective sense when I got a t.c. electronics M2000 to use as a DAC in the mid 1990s was that resolution increased to a marked degree. Note that the CD players I was using from the late 1980s through the mid 1990s were budget models and the turntables I was using were not. A lot of the CDs I was listening to were brand spanking new DDD productions from well-regarded engineers. I listen to the same CDs these days and, as you say, they simply crush all but the best analog.

 

[rongon]

I am never going to argue that LP playback is in any way 'better' than or 'superior' to digital sources. However, I wonder what kind of cartridge/tonearm/turntable/RIAA preamp setups folks here were using back in the day?

The reason I ask is that LP playback is not very good until you get into crazy tweak-geek/obsessed hobbyist territory. (These days, cost is also not a very good predictor of playback quality in this field.) A Technics SL1200mk2 with a Shure V15 is just not in the same class -subjectively- as a completely rebuilt Garrard 301 with a Schroeder tonearm and a current Audio Technica 740ML MM cartridge (assuming all are properly set up, which is a big ask!). The SL1200 may have lower wow and flutter, steadier lock on the speed, and even lower rumble, but... Remember, all of these things are highly imperfect transducers, with countless flaws compared to our digital stuff. How an LP playback setup sounds is very much the result of purposeful tailoring of compromises between desired features and unavoidable imperfections. It even matters what the capacitance of the tonearm cable is, with frequency response changing with cable length. Tweak, tweak, tweak, every last thing is a compromise between this and that.

Incidentally, I thoroughly enjoy my Raspberry Pi-Moode player > Topping D10 > Behringer A800 > JBL Studio 530 setup. It doesn't do everything I want (it is a budget setup, after all) but it's really pretty darn good, I think, and wonderfully maintenance-free. An RPi-Allo Boss-Moode setup retired the Pioneer PD-D6-J I'd been using from 2009 to 2016. The D10 later retired the Boss DAC.

 

[WillBrink]

Agree with all of the above. I will even concede to vinyl boosters that on a really good TT setup (not necessarily uber-xpensive) vinyl can sound better than it has a right to, given the medium's myriad technical and performance shortcomings. But to me, good digital just crushes all but the absolute best that analog can muster. A lot of people's outlooks were affected by crappy roll-the-tape transfers from the early days of the CD. I think a lot of the resistance has to do with that,

At a fraction of the $ no less. That part drives me bonkers, but it's their money, so what ever makes them happy I guess.

 

[rongon]

At a fraction of the $ no less. That part drives me bonkers, but it's their money, so what ever makes them happy I guess.

If you measure time and effort as part of 'cost' then I completely agree. Digital playback and Class D amplification are far more cost-effective. No question.

However, if you're a hobbyist and are willing to spend the time to hunt down a classic top-of-the-line piece from the golden age of American hi-fi (ca. 1960), refurbish that and outfit it with a good tonearm, which includes the skill and patience to install that tonearm correctly, then you can still put together a really good record player for under $1000. But if you factor in $15 an hour for your time and effort, the costs go through the roof.

If you're like me and have a wall unit full of LPs from decades of record buying, then playing records can be a really nice way to spend a rainy Sunday. Replacing that collection with digital copies would cost a fortune, and take a lot of time and effort.

Anyway, I think the cost thing is well understood. What is not understood is why LP playback can sound actually really good, even though it is measurably horrible by any objective standard.

And to stay on topic -- Some tube amps sound really good too. Not nearly as accurate as the latest Class D stuff. Definitely with more transformer-induced hum (usually not correctable by additional PSU ripple filtering/decoupling or voltage regulation). The Stereo 70 variant under test here probably sounds pretty good. It measures well for a commercial tube amp. But I'm not going to tell anyone it's 'better' than a Fosi Audio V3 amp or similar. One may like one more than the other, but that is not at all the same thing.

 

[rongon]

I also think early CD players had issues with a lack of focus. Of course, that's my subjective opinion from nearly 40 years back, and it's possible that I simply got used to the sound over time. But my subjective sense when I got a t.c. electronics M2000 to use as a DAC in the mid 1990s was that resolution increased to a marked degree. Note that the CD players I was using from the late 1980s through the mid 1990s were budget models and the turntables I was using were not. A lot of the CDs I was listening to were brand spanking new DDD productions from well-regarded engineers. I listen to the same CDs these days and, as you say, they simply crush all but the best analog.

I used to get into arguments over whether anyone could hear the difference between 16-bit/44.1kHz PCM and 24-bit/96kHz PCM. I used to record jazz groups on an ADAT with 20-bit ADCs, which I'd save as 24-bit/48kHz PCM tracks. I used Sonar to mix and master those recordings, keeping all tracks in 24/48k (which was not easy back in 2002). I used WaveLab to master the resulting 24/48k stereo master files down to 16/44.1k for CD. I always noticed a sort of vague 'grayness' to the CD-quality stereo tracks compared to my 24/48k master tracks. It's impossible to put into words that convey what I heard, but it was not confirmation bias. I'd go back and I'd hear it. Not super easily, but if listened closely, I could tell which was which.

I firmly believe in the idea of 'headroom'. If a machine is capable of handling X amount of workload and you make it handle all of that X amount of workload, the machine is working at its full capacity, and failures will become more likely. If a machine is capable of handling X(4) amount of workload and you only ask it to handle X(1) amount of workload, that machine will be less likely to introduce errors or unwanted output. The Topping D10 is capable of working with 32-bit/384kHz PCM, as are many other DACs these days. Processing 16-bit/44.1kHz PCM is a light task for these machines. Wouldn't you expect they would 'sound better' handling this task? Maybe that's too simplistic. I don't know.

 

[WillBrink]

If you measure time and effort as part of 'cost' then I completely agree. Digital playback and Class D amplification are far more cost-effective. No question.

However, if you're a hobbyist and are willing to spend the time to hunt down a classic top-of-the-line piece from the golden age of American hi-fi (ca. 1960), refurbish that and outfit it with a good tonearm, which includes the skill and patience to install that tonearm correctly, then you can still put together a really good record player for under $1000. But if you factor in $15 an hour for your time and effort, the costs go through the roof.

If you're like me and have a wall unit full of LPs from decades of record buying, then playing records can be a really nice way to spend a rainy Sunday. Replacing that collection with digital copies would cost a fortune, and take a lot of time and effort.

Anyway, I think the cost thing is well understood. What is not understood is why LP playback can sound actually really good, even though it is measurably horrible by any objective standard.

And to stay on topic -- Some tube amps sound really good too. Not nearly as accurate as the latest Class D stuff. Definitely with more transformer-induced hum (usually not correctable by additional PSU ripple filtering/decoupling or voltage regulation). The Stereo 70 variant under test here probably sounds pretty good. It measures well for a commercial tube amp. But I'm not going to tell anyone it's 'better' than a Fosi Audio V3 amp or similar. One may like one more than the other, but that is not at all the same thing.

All makes perfect sense to me that some simply prefer the LP sound regardless of objective measurements. I also think the the longer we do the hobby the more we realize the master matters more than the medium. The first CDs I got sounded terrible. I like to listen to some recordings from 50's such as Peggy Lee, and they sound incredible. I don't know how they sound on LP and good tube set up, but the transfer to digital was clearly done right as it's jaw dropping recording quality when streamed.

 

[rongon]

I like to listen to some recordings from 50's such as Peggy Lee, and they sound incredible.

It's worth pointing out that 1) these were originally recorded to analog magnetic tape, 65 or so years ago. When you get a 2015 'from the original master' remaster of a recording made in 1955, that tape has been deteriorating for nearly 70 years. Think about what the tape sounded like in 1965 vs. today. 2) That analog tape was objectively far inferior to digital recording media from the beginning, with tape hiss, etc. that digital recording does not have, and 3) all the signal processing like dynamics limiting/compression, equalization, reverb and other effects were done using analog gear such as optical compressors which used the equivalent of a light bulb to control the analog audio voltage! Look up what a spring reverb tank is. I mean, talk about primitive. Yet, many of today's recordings sound harsh, flat, just plain nasty, and they're using objectively far superior tools at every step of the recording chain. Why would that 1950s recording sound so great, while a recent recording in a similar style (perhaps Tony Bennett & Lady Gaga for example) doesn't sound like that?

We distill our thinking down to 'Digital Superior to Analog' without thinking about the enormous number of things-that-can-go-wrong in the process of recording music and then getting that to the consumer. This is an art form, after all. For many musicians, the recording studio itself is another musical instrument.

I used to completely agree with the 'hi-fi system as sonic Xerox machine' ideal. The playback system should give you an ideal copy of what's in the source material. The problem is that through the years, I've heard many super-clean systems that don't sound like a joyful noise. Yet I've heard some playback systems that very obviously color the sound that were great fun for listening to music. I don't pretend to understand what makes music sound interesting or not. I'm just reporting what I've heard and felt over 50+ years of checking out music playback systems. Eh, but it's probably all a waste of time anyway. Live music played by human beings sounds waaaaaaay better.

 

[WillBrink]

It's worth pointing out that 1) these were originally recorded to analog magnetic tape, 65 or so years ago. When you get a 2015 'from the original master' remaster of a recording made in 1955, that tape has been deteriorating for nearly 70 years. Think about what the tape sounded like in 1965 vs. today. 2) That analog tape was objectively far inferior to digital recording media from the beginning, with tape hiss, etc. that digital recording does not have, and 3) all the signal processing like dynamics limiting/compression, equalization, reverb and other effects were done using analog gear such as optical compressors which used the equivalent of a light bulb to control the analog audio voltage! Look up what a spring reverb tank is. I mean, talk about primitive. Yet, many of today's recordings sound harsh, flat, just plain nasty, and they're using objectively far superior tools at every step of the recording chain. Why would that 1950s recording sound so great, while a recent recording in a similar style (perhaps Tony Bennett & Lady Gaga for example) doesn't sound like that?

We distill our thinking down to 'Digital Superior to Analog' without thinking about the enormous number of things-that-can-go-wrong in the process of recording music and then getting that to the consumer. This is an art form, after all. For many musicians, the recording studio itself is another musical instrument.

I used to completely agree with the 'hi-fi system as sonic Xerox machine' ideal. The playback system should give you an ideal copy of what's in the source material. The problem is that through the years, I've heard many super-clean systems that don't sound like a joyful noise. Yet I've heard some playback systems that very obviously color the sound that were great fun for listening to music. I don't pretend to understand what makes music sound interesting or not. I'm just reporting what I've heard and felt over 50+ years of checking out music playback systems. Eh, but it's probably all a waste of time anyway. Live music played by human beings sounds waaaaaaay better.

That was sort of the point I was getting at. "On paper" digital should be superior, but there's clearly more to it then that. Realizing some of the best sounding recordings I have heard on my system were recorded/made all in the analog domain, I decided to needed to soften my position some. The master matters more than the medium all things being equal was my conclusion.