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    Dynaco ST-70 mono bridged

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    KeywestJimmy

    Posts : 2
    Join date : 2013-03-22

    Dynaco ST-70 mono bridged

    Post by KeywestJimmy on Fri Mar 22, 2013 3:21 pm

    The consensus seems to be that the Dynaco ST-70 does not lend itself for operation as a mono-block. I have seen the posts on this forum and others that go into the details why this is so. However, with the switch on the front practically begging to be run in mono, I gave it a shot. Low and behold--wow! It sounds much better in mono. Both ST-70s I'm using are stock.

    Now, I'm trying to reconcile the bad reputation it has as a mono-block with what I'm hearing. I'm hooking up the ST-70 using two Y-adapters, one for each channel, utilizing both of the front RCA plugs. (I've seen instructions that say to use only one, however, this does not seem to work at all.) I strap the commons together on back and strap the 16 ohm taps too. I'm running vintage electrostatics speakers.

    Anybody else prefer to use the ST-70 in mono?

    hawaii.ken

    Posts : 157
    Join date : 2012-01-31

    Re: Dynaco ST-70 mono bridged

    Post by hawaii.ken on Fri Mar 22, 2013 4:18 pm

    Hmmm.... interesting. What "vintage electrostatics speakers" are you using?

    stewdan

    Posts : 160
    Join date : 2010-03-07
    Age : 78
    Location : Houston Texas

    Re: Dynaco ST-70 mono bridged

    Post by stewdan on Fri Mar 22, 2013 4:28 pm

    IMHO -- I think the monoblock bias that you are talking about comes from the fact that the stock ST70 is at best a 25-30 WPC amplifier and when you use it as a monoblock, it is in the 50 to 60 Watt range. Mark IIIs are 60 Watt Monoblocks and I think the prevalent thought was that two Mark IIIs were more powerfull and better sounding that two ST70s treated as MonoBlocks.

    There was some info on the Web 10 or 15 years back about how the Monoblock ST70 would/could not sound good because of the NFB that the Stock Circuit uses.

    In the mid 1990s there was ST70 replacement board called the PAD70 (Purist Audio Design 70) which Glass Audio Reviewed. It used 12AX7s instead of the 7199, had individual biasing of the Output Tubes and did not use the NFB from the output Transformers and could be easily wired (strapped) into a MonoBlock. I had one ST70 and bought two their boards thinking that if it sounded good as Monoblock I would buy another ST70. Well it sounded ok but I switched back to a Stereo Amp which I like the sound of better and I have been using it that way ever since. A stereo amp definitely sounded better to me than a single Monoblock. (Again, all this is IMHO)

    By the way, at that time I was using a pair of AR2As and a pair of Dynaco A-25s





    KeywestJimmy

    Posts : 2
    Join date : 2013-03-22

    Re: Dynaco ST-70 mono bridged

    Post by KeywestJimmy on Fri Mar 22, 2013 10:52 pm

    Dennesen 180s

    peterh

    Posts : 643
    Join date : 2012-12-25
    Location : gothenburg, sweden

    Re: Dynaco ST-70 mono bridged

    Post by peterh on Sat Mar 23, 2013 4:51 am

    KeywestJimmy wrote:The consensus seems to be that the Dynaco ST-70 does not lend itself for operation as a mono-block. I have seen the posts on this forum and others that go into the details why this is so. However, with the switch on the front practically begging to be run in mono, I gave it a shot. Low and behold--wow! It sounds much better in mono. Both ST-70s I'm using are stock.

    Now, I'm trying to reconcile the bad reputation it has as a mono-block with what I'm hearing. I'm hooking up the ST-70 using two Y-adapters, one for each channel, utilizing both of the front RCA plugs. (I've seen instructions that say to use only one, however, this does not seem to work at all.) I strap the commons together on back and strap the 16 ohm taps too. I'm running vintage electrostatics speakers.

    Anybody else prefer to use the ST-70 in mono?
    parallelling 2 amps that might have slightly different gain would lead to one amp acts as load instead
    of power source.
    What should be done is bridge-coupling where one is at opposit phase with the other.

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