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    Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

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    metlmrk

    Posts : 9
    Join date : 2011-06-23

    Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by metlmrk on Thu Jun 23, 2011 9:17 am

    Greetings everyone,

    It’s probably obvious but I'm new here. I am hoping to solicit some opinions about the ST-70 and MK-II or III Power Amps. I have a PAS II and two ST-70 power amps. I just picked up the second ST-70 recently. I am running them bridged for the 70watt output to each speaker. I am now wondering if a pair of the Mark III 60 watt amps would sound better/cleaner than the bridged ST-70. I have never had the opportunity to listen to a MK-III so I thought I would pick the “Collective brain” here in hopes that someone or many someone’s had or has both for a comparison. Any advice would be appreciated.

    Thanks in advance! Mark

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by j4570 on Thu Jun 23, 2011 9:32 am

    If I were buying monoblocks, I'd buy Bob's M-125's!

    metlmrk

    Posts : 9
    Join date : 2011-06-23

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by metlmrk on Thu Jun 23, 2011 9:40 am

    Thanks for taking the time to reply. sunny My personal preference for tube equipment is for Vintage unmodified units. Thanks again!

    j4570

    Posts : 141
    Join date : 2010-08-30

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by j4570 on Thu Jun 23, 2011 10:41 am

    Well, if it's vintage, then you are back to the MK III I guess. While I have not compared bridged ST70's vs. MK III's, every bridgeable amp I ever owned sounded better to me unbridged. I'm interested too if anyone has done an actual comparision.


    GP49

    Posts : 733
    Join date : 2009-04-30
    Location : East of the sun and west of the moon

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by GP49 on Thu Jun 23, 2011 6:02 pm

    By "bridged" do you mean the Dynaco-design parallel connection of the inputs, driving both amplifiers simultaneously with identical signals and paralleling the outputs? If so, that is an inferior method that works poorly because...among other reasons...it mixes together the feedback signals that are supposed to correct each channel's "errors" separately; so that it corrects NEITHER channel.

    It also does not result in a doubling of output power as one might think, because the power supply of the ST-70 is not sufficient to support that high a combined output. Compared to this, a Mark III or Mark II would be preferable. I actually prefer a conventional single ST-70 with its nominal 35 watts per channel, to two of them connected in this parallel-connected so-called 70-watt hookup. More is lost by this mode of operation than is gained by the added output power.

    Does this mean I think Dynaco was wrong to provide this form of mono operation on the ST-70? YES!

    A PROPERLY "bridged" operation of a stereo amplifier involves inverting the phase of one channel and taking the output across the two "hot" speaker outputs, with no connections to or between the "common" output terminals. It is most often found on car stereos where it permits a higher output power than would be available from a conventional amplifier on a 12 volt power supply. Some audiophile-grade amplifiers have used it successfully, too. Either way, to get the best results, you need a phase inverter stage for one of the stereo amp's inputs, and it must obviously be of superior quality.

    Jules Saint 70

    Posts : 3
    Join date : 2011-12-09

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by Jules Saint 70 on Fri Dec 09, 2011 8:47 pm

    Thank you GP49 for your information on this subject. I have been wondering about this also.

    Blitzen

    Posts : 47
    Join date : 2009-07-10

    Biamp!

    Post by Blitzen on Fri Dec 09, 2011 9:38 pm

    Can you possibly bi-amp your speakers? Use one amp per speaker- one channel for bass, the other treble (or mid & treble). Some speakers have the two sets brought out on the back (and then tied together, which can be taken off), making it easy. That would be the better way to go.
    Come to think about it, that's what I should be doing with that other amp...hmmmmmm.

    j beede

    Posts : 328
    Join date : 2011-02-07
    Location : California

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by j beede on Fri Dec 09, 2011 11:11 pm

    I have never listened to a pair of "mono" ST-70s. I have owned many stock ST-70, several ARC ST-70-C3 and currently own a pair of Mark IIIs that I have rebuilt from the ground up. Driving Quads, Martin-Logan CLS, Magnepans, and NHT "one"... the Mark IIIs easily get my vote. The Mark IIIs produce a more controlled, more extended range. I hear more depth and stereo effect with the Mark IIIs. The combination of the Mark IIIs with the (homely) PAS2 has produced some of the best music I have heard in my home.

    JunkyJan

    Posts : 103
    Join date : 2008-12-09
    Location : BC, Canada

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by JunkyJan on Sun Dec 18, 2011 7:38 am

    j beede wrote:... the Mark IIIs easily get my vote. The Mark IIIs produce a more controlled, more extended range. I hear more depth and stereo effect with the Mark IIIs. The combination of the Mark IIIs with the (homely) PAS2 has produced some of the best music I have heard in my home.
    Agreed - I have an ST-70, (Bob's kit), as well as a pair of Mk IIIs fitted with VTA boards... If I were to only have one amp for the rest of my life, I'd go with a pair of Mark IIIs.

    -- JJ

    klctubes

    Posts : 2
    Join date : 2011-10-13

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by klctubes on Mon Dec 19, 2011 7:38 am

    Go with MK 111's

    Bob Latino
    Admin

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    Location : Massachusetts

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by Bob Latino on Mon Dec 19, 2011 9:07 am

    Blitzen wrote:Can you possibly bi-amp your speakers? Use one amp per speaker- one channel for bass, the other treble (or mid & treble). Some speakers have the two sets brought out on the back (and then tied together, which can be taken off), making it easy. That would be the better way to go.
    Come to think about it, that's what I should be doing with that other amp...hmmmmmm.

    If you are going to use TWO ST-70's on a two channel stereo system it is much better to BIAMP rather than run the ST-70's in mono. The reasons not to use an ST-70 in MONO are listed quite accurately by GP49 in his post above. In the VTA ST-70 and ST-120 amps the stereo mono switch is not even used.

    You can BIAMP with two ST-70's on a stereo system if you have two separate inputs on your two speakers. Most modern speakers have two separate inputs for the woofer and tweeter sections which are connected by two metal straps. You remove the two straps and now you have two separate inputs. Now you can either HORIZONTALLY biamp or VERTICALLY BIAMP. Horizontally biamping is having one ST-70 on the two woofer sections and one ST-70 on the two tweeter sections. Vertically biamping is having one ST-70 one each stereo channel. Over the years I have tried biamping both ways and (at least with the ST-70) VERTICAL biamping IMHO has always sounded best. Why ?

    1. Greater signal isolation. Vertical biamping keeps each stereo channel's signal on ONE amp. This usually translates into a more spacious and accurate sound stage.

    2. Better power handling. Loud bass notes take more out of the amp's power supply. If you were to horizontally biamp and have just one amp on both woofer sections, then just ONE quad cap on ONE amp would have to deal with the bass for both channels. If you, however, vertically biamp then two quad caps (one on each amp) can share the bass load.

    I know of perhaps a dozen VTA ST-70/ST-120 users that biamp with two amps on their music system.

    Bob

    Jules Saint 70

    Posts : 3
    Join date : 2011-12-09

    ST-70 12AU7 conversion

    Post by Jules Saint 70 on Wed Dec 21, 2011 8:33 pm

    I am considering the tubes for hi- fi kit which replaces the 7199 board with a 12AU7 board-Can someone comment on this? Is there a better way to go?

    tubes4hifi
    Admin

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    Join date : 2008-11-30

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by tubes4hifi on Wed Dec 21, 2011 11:42 pm

    are you kidding? Probably over 1000 people who would tell you there's nothing better.
    About 900 people on this forum alone, let alone AudioAsylum and all the others.
    But of course there are probably 3 or 4 people somewhere who might claim that something else is better . . . Rolling Eyes

    Jules Saint 70

    Posts : 3
    Join date : 2011-12-09

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by Jules Saint 70 on Thu Dec 22, 2011 1:28 am

    Of course you could be a little "biased" , If you'll pardon the expression on a tube site....

    scott6058

    Posts : 37
    Join date : 2009-01-21

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by scott6058 on Thu Dec 22, 2011 7:07 pm

    If you were to consider The MKIII's you won't be happy with them until you use Bob's VTA upgrades. Trust us they really sound wonderful.
    Yes they are not original but they are also not for sale.

    tubes4hifi
    Admin

    Posts : 1286
    Join date : 2008-11-30

    Re: Choosing a Power Amp ST-70 or a pair of MK-III (Or MK-II)

    Post by tubes4hifi on Fri Dec 23, 2011 3:22 pm

    Scott, . . . .what's not for sale?
    tubes4hifi web page

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