[bitemeboat]

How does the dynaco st 70 compare to the new digital chip amps?

[dB Cooper]

I'm not sure how to answer that (and it doesn't seem like anybody else is either, apparently); they are radically different design approaches. But I did want to welcome you to AC.

[Phil A]

Welcome.  Really can't answer that either.  I did own an ST-70 many moons ago.  I think at the time I had Mirage SM-3 speakers.  I do have an digital integrated amp/DAC now (NuPrime IDA-8) in my office system that was recently acquired.

[WGH]

How does the dynaco st 70 compare to the new digital chip amps?

No comparison, the Dynaco is much more musical than a chip amp. But you need to update the Dynaco with Van Alstine's rebuild kit and then it will easily equal any $2000 amp.
http://www.avahifi.com/products/amplifier-rebuilds/ultimate-70-vacuum-tube-amplifier

I had a Hypex Ncore NC400 amp on loan for a month and it was clean, dynamic, absolutely quiet but no magic. We traded that amp around in different systems in different houses and no matter what we did it left us cold.

I forgot to mention a buddy has a Van Alstine rebuilt ST70 driving a pair of Nola KO speakers with excellent results so I am very familiar with both amps.

[mick wolfe]

How does the dynaco st 70 compare to the new digital chip amps?

For fairly efficient tube friendly speakers, I'll take a "modern" ST 70 every time as already mentioned.  For more inefficient difficult loads, a good digital amp may be a better fit.  I have 4 different sets of speakers currently in house. Three of the four sets fall in "tube friendly" category and I prefer listening to any of them with my Latino ST70. However the fourth pair fall in less than ideal category with impedance dips near 3 ohms. These speakers sound more at ease when using a Classdaudio SDS 254. ( 250wpc into 4 ohms)  FWIW, the 254 is used with a tube DAC/buffer. Bottom line, the answer to your question depends on many factors. The first one being what speaker are you trying to drive. From there... listening  levels, room size, etc.

[PeterCapo]

I've never heard a chip amp, but I can say the old Dynacos were very satisfying - provided they are functioning properly and then if their "sound" is in accordance with your taste, of course.

I should mention that, IMO, it really isn't necessary to drop a different circuit into a Dynaco.  From what I see, what often seems to happen is that someone will pick up a tired 30 to 50 year-old Dynaco, and after a little while drop in a different circuit from one of the several aftermarket vendors.  In such a case, of course it is going to sound "better" with the replacement circuit due to the fresh parts.

But, a 1:1 parts refreshing according to the original Dynaco circuit will also result in a really nice sounding amp that should hold its own against many other amplifiers.

[Tritium]

Dynaco ST-70 is still one of the finest amplifiers ever made.

You must live within the 35 wpc limitations, But they are hard to beat.

Just listened to a system using 4 Janszen electrostat panels per side a ST-70 for the top end.

Low end were Carbon Fiber 12"'s powered by a Modded Hafler DH-500.

I could easily live with that system, Clean airy top end and a deep accurate image.

Carbon 12's kicked like a mule. I think the crossover was 800hz.

[dB Cooper]

If you want to go ST-70 stock or near-stock, Van Alstine's old Audio Basics newsletter has a good article on simple mods to the stock circuit that improve performance (and what the shortcomings of the bone-stock circuit are).

The problem with staying stock is that many, if not all, of the original parts will have baked out of spec. PeterCapo is right that correcting this will improve the sound, but I disagree that there are no advantages to more modern circuits done with more modern parts and design/analysis techniques. Dynaco was a 'beer budget' brand that cut every corner that could be cut to meet price points while still providing quality audio performance. Their enduring popularity is largely due to the one place they didn't cut corners, namely the output transformers, which had a patented winding arrangement. This is in turn a big part of why they have been so popular for upgrading by Van Alstine et al.

[PeterCapo]

I think it is fair to say that, in general, the "modern" parts quality of the various Stereo 70 offshoots can likewise be applied to the original Dynaco circuit, e.g., increased capacitance in the power supply via low ESR electrolytics with polypropylene bypasses, polypropylene audio coupling caps, close tolerance resistors, fast or zero recovery diode for the bias supply, mil-spec bias pots, and other things.

As far as modern circuits and modern design analysis, I have noted that some of the drop-in PCB replacements either break-out the 7199 into discrete voltage gain and phase inverter tubes or just go to a different topology like the popular long tailed pair.  What’s particularly modern about that?  Breaking out the integrated 7199 into separate tubes gives you basically the same circuit, and the long-tailed phase inverter, to the best of my knowledge, has been around for decades like the cathodyne phase inverter of the original Stereo 70.

My impression is that Ed Laurent and David Hafler were consummate engineers.  IMO, the original Dynacos are not audio pablum suited primarily for newbies to cut their teeth on.  They continue to be a serious expression of hi-fi.

IMO, "shortcomings" of the original Dynaco circuit have been greatly overstated over time, which only makes sense given a cottage industry seeking our business.   For those interested who may have not yet seen it, here is a landmark technical study of the original bone stock Stereo 70 that corroborates its fine qualities, dispels some myths, and takes a sensible view of the variety of supposed "improvements" available: http://www.audioregenesis.com/documents/ST-70%20Base%20Line%20Testing.pdf

[dB Cooper]

I think it is fair to say that, in general, the "modern" parts quality of the various Stereo 70 offshoots can likewise be applied to the original Dynaco circuit, e.g., increased capacitance in the power supply via low ESR electrolytics with polypropylene bypasses, polypropylene audio coupling caps, close tolerance resistors, fast or zero recovery diode for the bias supply, mil-spec bias pots, and other things.

I think you would find the discussion of the stock circiuit in the Audio Basics 1982 newsletter very interesting as it discusses these and other issues from an engineering standpoint. Starts on p.15. Happy to send you pdf if you want.

No question, Dyna was very good stuff and great value; that's why it's still sought after today.

[PeterCapo]

Thank you for your offer.  I have long been aware of the article to which you refer, about the low frequency issue with the coupling capacitors and the feedback loop.  I think it also recommends a low pass filter as well as a high pass filter, at the inputs, and I think it talks about some other things, too.

The issue I have with it is that most recorded music probably does not have low enough frequency content for the high pass filter to be needed.  As far as the low pass filter, the high frequency response and distortion of the original Stereo 70 are fine, and it sounds great.  At the end of the day, what matters most is how it sounds.


*Reason for edit: eliminate redundancy.

[dB Cooper]

Thanks for sharing that. As Van Alstine pointed out though, cartridge mistracking and subsonic artifacts are part and parcel of vinyl playback, which was the only option for most listeners at the time aside from the far-less-common open reel decks. I'm not an electrical engineer so my understanding is left behind a a certain point.

[PeterCapo]

Yes, that is an excellent point.  I haven’t had my turntable set up in a while.  But, when I went looking for a phono preamp, I made sure it had a subsonic filter.  A number of vintage preamp sections from the time of the original Dynacos had low filters, but they tended to cut out too much of the music.  I think subsonic filters became more prevalent in the late 1970s/early 1980s, and I remember demos where woofer excursion was significantly reduced without really affecting the sonics.  I’d say a subsonic filter is a really good idea ahead of any amplifier.

[dB Cooper]

Yes, that is an excellent point.  I haven’t had my turntable set up in a while.  But, when I went looking for a phono preamp, I made sure it had a subsonic filter.  A number of vintage preamp sections from the time of the original Dynacos had low filters, but they tended to cut out too much of the music.  I think subsonic filters became more prevalent in the late 1970s/early 1980s, and I remember demos where woofer excursion was significantly reduced without really affecting the sonics.  I’d say a subsonic filter is a really good idea ahead of any amplifier.

Yeah, the Dyna 'rumble' filters were smooth slope (forget the specs) that started well into the upper bass range; not really 'subsonic' filters as we think of those today.

Whenever I go to audio shows, I see evidence of subsonics, sometimes major subsonics,  in almost every room running vinyl. I remember one room running a all tube chain (I think it was ARC or C-J) into Joseph Audio monitors. The woofers were flopping like a freshly boated fish. I asked the exhibitor about it and he brushed it off with "These woofers can handle it". Maybe, but my question (to him and about the ST-70) was more related to what else was happening in the preamp and amp as they were puking their guts out trying to play back high-amplitude 4-5 Hz record warps. The preamp did have a subsonic filter switch, and I considered flipping it as an experiment, but I decided if he didn't care what his demo was doing, why should I.

[JerryM]

There's very few folks on the planet who understand the Dynaco St-70 as much as Frank VanAlstine. The names are nearly synonymous.

Here is an Enjoy the Music re-print of Frank's 1982 Audio Basics article regarding tube amps and the St-70 more specifically. http://www.enjoythemusic.com/magazine/manufacture/0902/index.html. Clearly, he's stayed on top of the game to this date.

In any case, just call Frank. His number is posted on his website. He typically answers the phone. He's a great guy. Just give him a call and ask the things you want to know. 

Have fun,

Jerry

[dB Cooper]

This thread has gone from a discussion of the ST70 vs chip amps to an ST70 thread. To get back to that, I've never really listened to a chip amp although they are cheap and some like the Akitika have good reputations. Hard to imagine they'd really be competitive with a good-running 70 though.

[charmerci]

... and he brushed it off with "These woofers can handle it". Maybe, but my question (to him and about the ST-70) was more related to what else was happening in the preamp and amp as they were puking their guts out trying to play back high-amplitude 4-5 Hz record warps. The preamp did have a subsonic filter switch, and I considered flipping it as an experiment, but I decided if he didn't care what his demo was doing, why should I.

[avahifi]

I am glad to see the reference and link to our original Dyna 70 discussion.  The info is as valid now as it was back 35 years ago.  Click on the link above in JerryM’s post and learn something more than just opinions.

We still support the Dyna 70 with our Ultimate 70 rebuild, available either as a do it yourself kit or as a factory rebuild.  The complete kit manual is available free of charge.  Email me at frank@avahifi.com to request it.

The Ultimate 70 includes a new mother board with audio and power supply circuits that follow the rules we identify in the 1982 paper kindly linked by JerryM above.

Of course, the Ultravalve goes much further, including four regulated power supplies. It has none of the limitations of a stock 70, even one with all new parts, because new parts alone do not correct the original design limitations.

Frank

[bluemeanies]

DILLY, DILLY!

[PeterCapo]

I am glad to see the reference and link to our original Dyna 70 discussion.  The info is as valid now as it was back 35 years ago.  Click on the link above in JerryM’s post and learn something more than just opinions. ... Of course, the Ultravalve goes much further, including four regulated power supplies. It has none of the limitations of a stock 70, even one with all new parts, because new parts alone do not correct the original design limitations. Frank

DILLY, DILLY!

Is any amplifier perfect?  An engineer could probably find something to "improve" in just about any amplifier.  Do modifications that improve certain things on a test bench assure increased subjective listening satisfaction?  I think it's fair to say that any number of audiophiles would not think so.

Just the same, the original Dynaco Stereo 70 circuit has long since been vetted by different, independent lab tests, for instance the former Stereo Review / Hirsch-Houck Labs and others. 
The more recent lab test posted over at Audio Regenesis renews our perspective: http://www.audioregenesis.com/documents/ST-70%20Base%20Line%20Testing.pdf   
And, just recently, The Absolute Sound magazine made comments to the effect that the original Stereo 70 still sounds good today - scroll down here: https://www.theabsolutesound.com/articles/the-12-most-significant-power-amplifiers-of-all-time/ ...note this TAS article may not even be referring to a completely restored sample - a very important point to keep in mind whenever evaluating an original.

So, while math is hard to argue with, it neither necessarily invalidates nor necessarily correlates actual listening experience.  It's a loss to the audio community that a cottage industry of modifiers - more than one - have convinced folks that the only way to get an original Stereo 70 to sound truly good, or truly high end, is to change the circuit.  I can't help but think about all the listening enjoyment [of the original] that has been missed because of this.

-Peter

PS: I have no business interests or affiliation with anyone.