Review - New Dynaco ST-70 Series 3

Discussion in 'Audio Hardware' started by BIGGER Dave, Feb 6, 2019.

  1. wrat

    wrat Forum Resident

    Damn dynaco resurrected again?? I had a dynaco by Panor preamp i was pretty damn good wish I still had it
    sushimaster likes this.
  2. Socalguy

    Socalguy Forum Resident

    ^ This ^
    loudinny and rebellovw like this.
  3. captwillard

    captwillard Forum Resident

    Yeah, I can’t type today.
  4. chervokas

    chervokas Forum Resident

    Besides the potential for heat damage (and, speaking of Dynaco ST-70, nothing was likely as bad as the old phenolic boards in the originals), there can be mechanical stress causing intermittent connections or even solder breaks in cases where tube sockets are mounted on circuit boards and tubes are frequently removed and reinserted.
    loudinny likes this.
  5. BIGGER Dave

    BIGGER Dave Forum Resident Thread Starter

    I haven't dissembled it, however it appears the power tube sockets are bolted to the chassis which would suggest flying leads. The preamp tubes however appear to be soldered to the PCB. I need to open her up to confirm...
  6. arley

    arley Forum Resident

    I imagine that the circuit, even if 'improved', has to be close to the original. Some years ago I built a VTA ST-70 and have been very pleased with its performance. I also have a vintage Dynaco ST-70 which has gotten a little flakey; I'm going to put the VTA board in it.

    That pretty much sums up the ST-70. For its price point, it really does deliver the sonic goods with detail, imaging, soundstage, etc.
    Last edited: Feb 8, 2019
  7. chervokas

    chervokas Forum Resident

    The link provided earlier suggests more substantial differences relative to most upgrades in that it uses a different output transformer design than the original. Most of the upgrades use the same Dynaco output iron or Dynaco output iron design, not this one apparently.

    Most updates beef up the power transformer and filter capacitance, which is done here; often they replace the tube rectifier with solid state, which is done here (although there are a number of different ways that might be implemented); and there are any number of different driver circuits that upgraders have used in place of the original. This also has a new driver circuit. Some also have regulated power supplies, I don't think that's the case here. This one, unusually, has a switchable high pass filter to roll off bass at two fixed in front of the input. Not sure how that is implemented.

    So, updated ST70s abound, and yeah, this is another one, each is a little different from the other, but with different OTs, this one is even a little more different still it would seem. Not that I know exactly what's different with the OTs.
    JackG likes this.
  8. arley

    arley Forum Resident

  9. allied333

    allied333 TUBE AMPLIFIER REBUILDER - inquire

    A Scott 299C is a good sounding amp. You believe the Dynaco is better so that says a lot about the sonic quality of the Dynaco. Thanks.
  10. TarnishedEars

    TarnishedEars Forum Resident

    Seattle, WA
    I read the development speil by the chief engineer on the project. He touches on the new OTs. According to him all of the aftermarket ST70 transformers available on the market today may look like original dynaco transformers, but none of them perform like dynaco transformers. All of the current units ones supposedly ring like crazy. It was not clear to me as to the reasons why this would be true, but one thing that I know for a fact is true today is that many of the materials used in vintage OTs are simply not available anymore today. The exact types of steels, and the insulating materials for the originals are all obsolete or have been deemed environmentally hazardous and simply can't be sourced anymore. So they supposedly tweaked the output transformers design a bit until they were able to replicate the rise-time and lack of ringing in the originals stereo 70 transformers. To me, this actually sounds like a better approach than just trying to knock-off a stereo 70 transformer exactly using modern materials, but while ignoring the performance differences. Everybody has long acknowledged that the Dynaco iron was always Dyanaco's biggest claim to fame. And if the story is to be believed, then it sounds like this iron is truer to the performance of the original iron than are any of the stereo 70 knock-offs out there.

    As an engineer myself, I was actually much more impressed with what I read about this project than I had expected to be. And frankly, dumping the original 7199 input/driver design in favor of what sounds-like it is probably a full williamson design implementation really should be great news as the 7199 was one of the major design compromises in the original design IMO.

    I'd love to get my hands one an original stereo 70 transformer and a couple of different modern copies to compare their performance myself on my test bench to verify his story. Unfortunately I'm not quite curious enough to spend the money required to source the parts, or I'd run the tests myself to verify his claims.
    Last edited: Feb 10, 2019
    Ghostworld, JackG and sushimaster like this.
  11. BIGGER Dave

    BIGGER Dave Forum Resident Thread Starter

    The Dynaco Cheif Engineer claiming his new Dynaco transformers surpass all other current Dynaco transformer clones may be based in some truth, or it just may be marketing spin. I’ve never heard a current Dynaco ST-70 clone so I can’t say either way. The only thing I can say is I’m very pleased with this amp.
    33na3rd likes this.
  12. juno6000

    juno6000 Forum Resident

    Pembroke Pines, FL
    Does it sound good at low volume levels?
    scoutbb likes this.
  13. indy mike

    indy mike Forum Pest

    I have a vintage pair of Dynakit/Dynaco MK IV amps and have run GE 6L6GC pairs with no problem - the build manual mentions that you can run 5881s or KT-66s by adjusting the bias. I checked over at the Dynaco Tube Audio Forum and Roy Mottram (who owns/runs amp maker Tubes 4 Hi-Fi) and he reaffirmed what the manual said - 6L6GCs work fine in vintage Dyna amps, drop the bias down to 1.25 volts and you're good to go (I also bias my EL34s at 1.25 volts). No mix and matching different tube types - use either sets of EL34s or sets of 6L6GCs. The 6L6GC is good for around 30 watts, the EL-34 is pushing around 40 watts in the MK IV.

    As for the version of the ST-70 amp this thread was started for, I'd check the manual or contact the manufacturer about trying out sets of 6L6GCs - don't do something that might void your warranty.
  14. rebellovw

    rebellovw Forum Resident

    Sounds like marketing - I know Bob Latino (VTA ST70, ST120, M125) - uses extremely high quality US built transformers - I believe Hayboer - which have an exceptional reputation. I'm sure they are awesome though. My amps are 70lbs back breakers - dead silent - and man dependable. I'd love to see some pictures man!
  15. TarnishedEars

    TarnishedEars Forum Resident

    Seattle, WA
    Yes, they will work. But the operation will be far from optimal if you should try it. The screen tape % for running a 6L6 variant tube in UL mode is very different than it is for running an EL34 in UL mode. So while the amp will certainly work if you bias it to use 6L6s, you are not actually running in UL mode when you do so.
    Last edited: Feb 10, 2019
  16. BIGGER Dave

    BIGGER Dave Forum Resident Thread Starter

    Not interested in running anything other than EL34’s. I have so many NOS EL34 tubes; Mullard XF2, RFT/Siemens, even some Amperex XF1 metal base!
  17. indy mike

    indy mike Forum Pest

    I like to think of it as having a different flavor of ice cream just to shake things up - right now I've got xF2 Mullards under the hood, last swap was for the GE 6L6GCs...
  18. Benzion

    Benzion "Cogito, ergo sum" Forum Resident

    Brooklyn, NY
    For some reason I thought it was an integrated.

    EDIT: In fact, I could have sworn they started with an integrated for around $3K. I think I even had a thread here about it, trying to gather opinions. Now it's not even shown on their website, how strange.

    EDIT EDIT: Found my old thread, to refresh my memory. Apparently, the integrated was a prototype called ST-1, unveiled at Munich in 2016. It appears to never have lifted off the ground, as it's not being offered by Dynaco now.

    What's interesting, is that this ST-70 discussed here was originally coming out with an MSRP of $2,999.00 - basically twice its current price. And, at the time of my old thread, another iteration of the Dynaco design - the Van Alstine Ultra Valve was mentioned as a possibility, for $1,600.00.

    I wonder now how Dynaco managed to lower its price by half (what did they have to sacrifice on the inside?), and if it was done to directly compete with the Van Alstine unit..
    Last edited: Feb 10, 2019
  19. BIGGER Dave

    BIGGER Dave Forum Resident Thread Starter

    I don’t know if they made sacrifices internally, or if they realized they weren’t going to sell at $3K. On this website ( Dynaco ST70 ), it states “In celebration of our award*, we are offering a limited number of units at a very special promotional price” ($1,499 instead of the previous $2,999). Time will tell if they will keep the price permanently at $1,499. I can tell you I ordered mine on JAN 7, however it didn’t arrive until FEB 5 due to it being backordered.

    * 2018 The Absolute Sound Product of the Year Award

    Or, it could be they put the $3K price out there to test the waters and found no one was interested at $3K. I know I wasn’t! But at $1,499 I took a chance and I’m happy with the results.
  20. BIGGER Dave

    BIGGER Dave Forum Resident Thread Starter

    Well, that Forum is run by Bob Latino who sells ST-70 kits and completed amps. The forum members that post there are dedicated to Bob and his livelihood so there is some bias there. Bob’s amps and kits are certainly of very high quality. Having several choices is always a good thing!
    juno6000 likes this.
  21. JackG

    JackG Forum Resident

    That's what I thought upon seeing the lower price. I lost interest in this when I saw the original $3000 price a few years ago, but this seems more reasonable. Then again, you can pay way more than this for a Chinese amp.
  22. rjpjnk

    rjpjnk Active Member

    Bolder CO
    BIGGER Dave,

    Are you still liking the Series 3 ST-70?
    I just ordered one and they say it will ship in two days.

    I am eager to compare it to my Bob Latino VTA ST-70. I've read so many posts on various forums where people are comparing the new Dynaco product to the VTA and AVA products, but so far I haven't come across any reviews by somebody who actually has them both on hand for evaluation. Have you heard of any?

    Naturally any ST-70 like amp is going to get compared to these two established options, and now that they are all about the same price it gets even more interesting. I hope to be able to provide some listening and test data in the near future.
    TarnishedEars likes this.
  23. samurai

    samurai Call Security!

    Curious, switchable to mono?
  24. BIGGER Dave

    BIGGER Dave Forum Resident Thread Starter

    No. This is strictly a two-channel amp.

    I’m still digging the new Series 3 ! I swapped the JJ 12AU7/ecc82 tubes for NOS Mullard, but left the JJ EL34 in there for now. I’m going direct (no Preamp) from my Sony X800/Gungnir MB into the Dynaco (then out to Harbeth M30.1), and using the level controls on the front of the Dynaco to adjust the volume. Depending on the CD, I usually have enough volume for my preferred listening levels (I don’t listen as loudly as I did when I was younger). I am thinking of getting a Preamp so I can raise the volume to higher levels when the mood strikes, and have the ability to adjust the volume remotely. I’ve been looking at the Schiit Freya, but haven’t made a decision yet.

    (I have a McIntosh C712 preamp I could try however that’s currently part of my vinyl rig in a seperate room.).
  25. loudinny

    loudinny Forum Resident

    Heat and boards = not great, tube sockets mounted to boards = not great. PTP wiring is easily repaired, when boards go bad you’re generally SOL.

    Boards increase affordability, PTP is labor intensive and therefore much more expensive.

    Both function. Just a preference I tend to favor the old school PTP design with tube amps and leave the boards for solid state designs.
    Last edited: Mar 19, 2019
    Ghostworld likes this.

Share This Page