Why not try the newest iteration? http://www.dynaco.com/st70.php Back when I was modding these(1980s), Joe Curcio providing numerous tips that helped me maximize their performance. ie: much more capacitance in the power supply(two 5AR4s wouldn’t have hurt, but- would have required, at least, another filament trans). http://www.curcioaudio.com/st7upg_3.htm When the original went out of production, some 350,000 had been sold. Certainly, a major feather in David Hafler’s hat, if not the most popular stereo amp, in audio history.
ST 70 best sounding version?
Thanks for reading and for your input. I am thinking of acquiring another tube amp to use in a secondary system and there are so many versions of the Dynaco ST70 available (will Vincent, latino, van alstine, etc). Has anybody heard several and any feedback would be greatly appreciated....Ralph/Atma too! Cheers!
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I'm partial to Bob Latino's version but the only other one I've heard is the original and I'm going from memory there. I have built a pair of Mark IIIs from the Triode Electronics kit and the power supply upgrades are nice but the chassis is more utilitarian than Bob's. There's enough stuff out there you could build any kind of 70 you want. |
I was searching for the link that rodman provided. I have not heard the new series 3, but it is selling for $1,500 when its price when it was introduced just a couple of years ago was $3,000, so it was obviously not too popular. So bear in mind I have not heard it or any of the modded ones, but it is the one I would purchase. I do have the original ST70 with the desirable cloth lead transformers (I think that what they were referred to as), an original with the Japanese sourced transformers and a series 2 made by the Panor corporation. I just purchased another amp and will be putting these up for sale when I get around to it since I don’t need them all. |
And while bdp24 is surely right about design flaws, I love mentioning that the ST-70 is the greatest selling amplifier of all time. I will sheepishly mention that mine are in storage at this time. Per the Absolute Sound article titled - The Ten Most Significant Amplifiers of All Time - "Along with Avery Fisher’s 500c, David Hafler’s ST-70 put high performance audio in the American home. Introduced in 1959, the ST-70 is the world’s most prolific stand alone amplifier with over 300,000 units manufactured. Amazingly, its clear, three-dimensional sound is comparable to many amplifiers made today." |
I've had a couple of stock Dynaco ST70's, and there have been some mods or even redesigns which addressed the flaws in that very historically-important and influential amp. Some of Bill Johnson's early ARC designs were variations on those of David Hafler (particularly the SP-3 pre amp)---even at the time of the SP-3/D75/D51, Johnson was selling modded ST70's, and Frank Van Alstine at one time offered an extensive mod which eliminated the ST70's major flaws. In contrast, Roger Modjeski started with a blank slate for the RM-10, creating a completely new design, not an updated version of a design from the 1950's. Why anyone would want an ST70---old or new, stock or modified---rather than an RM-10 is a mystery to me, especially when an RM-10 can be had for the same price as an ST70. What if a Porsche cost the same as a VW? ;-) To view the historical significance and number of Dynaco ST70's sold as a reason to consider it worthy of consideration today is akin to doing the same for the Acoustic Research 3a in the field of loudspeakers. Good for it's time, but far surpassed today. I regularly see pairs of AR 3a'a offered on Audiogon at a price that can also buy one a pair of Vandersteen 2c's. Which loudspeaker would you rather own? |
FYI: Bob Latino sells his wares on http://www.tubes4hifi.com/, along with Roy Mottram who sells pre-amp kits and customizations to original Dynaco 70s. Regarding recitfer tube vs SS, Bob’s amp can run either without issue. In addition, there are a lot more upgrades to the amp beyond the power supply (output transformers, better caps, upgraded chokes, high precision resistors, driver circuit changes, a fully modern tube compliment, upgraded chassis, to name but a few). So IMHO Bob’s amps are really just modeled after the Dynaco ST70--his VTA 120 is a fully modern amp that is much closer to the Rouge Magnum and other modern tube amps that can run KT88s and KT120s (and now even includes an auto-bias board option.....) Full disclosure--I own Bob’s VTA 120--super product with super support (something you might want to consider). Great supporting community as well. |
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I have two Stereo 70s as well as Adcom 5802s and Sonic Frontier amplifiers. Both Stereo 70s have been updated. One has the original stock circuit with all caps and resistors replaced with modern polypropylene caps and metal film resistors. The updated stock amp sounds very nice. Sonically it has a lush midrange with a deep soundstage. The midrange is sweet sounding, bass is OK but not tight and the highs are pleasant. The Curcio designed mod has both boards (4 6DJ8s). Sonically the amp is excellent, if the 6DJ8s are in good shape. The amp has a very open, clean sound, a deep and wide sound stage and tighter bass than the stock unit. Sonically it's not sweet sounding but seems accurate. The Adcom 5802s by comparison (bi-amped) are Nelson Pass designs (3 gain stages). The amps produce very tight bass, a wide and deep soundstage, very low noise, and a smooth and pleasant high end with excellent reproduction of spacial cues (when they exist). The Sonic Frontiers sound similar to the Curcio design with a bit more punch likely due to the larger power transformer and output transformers. |
Triode Electronics of Chicago offers a new power transformer for the ST-70 that has increased current for the rectifier circuit. This allow you to run dual 5AR4s in parallel rather than one- thus fixing the biggest single weakness of the original amp (which had distortion low enough that it rivals the classic Marantz 8B), which is that it eats rectifier tubes. You can reduce distortion in the amp by replacing the 7199 driver tube with a 6GH8A, by using an inexpensive adapter for the conversion available on eBay. 6GH8s are a lot cheaper and easier to find than 7199s! Finally, a set of ODAM V-Caps work out very nicely as the main coupling caps in the ST-70- better sounding and better performance. Of course the stock filter caps should be replaced, along with the selenium rectifier used in the bias circuit. The filter cap to use is a 4-section part made by JJ, available from CE Distribution. Its small enough it can be mounted beneath the chassis, allowing the 2nd 5AR4 to be located where the old filter can was. Out of spec resistors should be replaced. I don't like the speaker terminals but without chopping up the chassis there's not much for it. |
I needed some music in the room I have placed my treadmill. I hooked up my all original Dynaco ST70 to an even older Heathkit AA141 tube preamplifier that a friend gave me years ago. Tubes used in the Dynaco are old stock Mullard el34s and rectifier along with RCA or Amperex 7199’s (I can’t remember). I threw some inexpensive Chinese 12ax7s that I had laying around in the Heathkit.. Hooked up to a Yamaha T85 tuner and B&W DM110 speakers, this antique system is surprisingly pleasant. So bottom line, the Dynaco ST70 in its original configuration can sound OK. |