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    Bridged ST-70 or ST-120 Amps?

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    hamrhed97

    Posts: 2
    Join date: 2010-01-09

    Bridged ST-70 or ST-120 Amps?

    Post by hamrhed97 on Sat Jan 09, 2010 8:56 am

    Is it possible to run the Bob Latino ST-70 or ST-120 amps in a bridged mode? Has anyone done this? Any general comments?

    Thanks.

    hamrhed97

    Posts: 2
    Join date: 2010-01-09

    Re: Bridged ST-70 or ST-120 Amps?

    Post by hamrhed97 on Sat Jan 09, 2010 4:05 pm

    Bob,

    Thanks for the reply. Are there any limitations or trade-offs to wiring the amps as monoblocks as opposed to a bi-wire set up with a pair of stereo amps?

    Thanks.

    Bob Latino
    Admin

    Posts: 1910
    Join date: 2008-11-27
    Location: Massachusetts

    Re: Bridged ST-70 or ST-120 Amps?

    Post by Bob Latino on Sat Jan 09, 2010 5:05 pm

    hamrhed97 wrote:Bob,

    Thanks for the reply. Are there any limitations or trade-offs to wiring the amps as monoblocks as opposed to a bi-wire set up with a pair of stereo amps?

    Thanks.

    Hi,

    If your speakers have two inputs I would go the bi-wire route. From connecting speakers with these amps both ways, I think (for some reason) these amps sound better biwired than to make the dual channel amp a monoblock. It may have something to do with separating the woofer and tweeter sections of the speakers and giving them their own amp. It could also be that when the amp is wired as a monoblock you have two output transformers wired together and slight differences between the two transformers can cause subtle out of phase (negative) effects. I might add here that the difference between the two methods is very small and also that this is really IMHO.

    The trade off is that to truly run the amp as a monoblock you can't just wire up the stereo/mono switch, flip the switch to mono and connect your speaker. If you do that you wind up with two 35 watt amps carrying the same signal. When you connect your speaker to either speaker terminal it is still going to look at just 35 watts. To really make the amp a monoblock you also have to run a wire from the 16 ohm speaker terminal on one channel to the 16 ohm speaker terminal on the other channel IF you have 8 ohm speakers. The 70 watts would then be available at either speaker terminal. If you have 4 ohm speakers you would run a wire from the 8 ohm terminal to the other 8 ohm terminal and again the 70 watts would be available on either speaker terminal. Simply put, it takes more effort to truly make the amp a monoblock ...

    Bob

    pgsvensk

    Posts: 3
    Join date: 2012-04-22

    Re: Bridged ST-70 or ST-120 Amps?

    Post by pgsvensk on Sat Apr 21, 2012 8:27 pm

    I'm a newbie here, so please be gentle. I've acquired a Dahlquist DQ-1W sub, and a Dynaco ST-120. How would I bridge the amp to drive that sub? I would likely have to pay someone to do any mods. Any helpful information would be most appreciated. Thanks!

    hawaii.ken

    Posts: 157
    Join date: 2012-01-31

    Re: Bridged ST-70 or ST-120 Amps?

    Post by hawaii.ken on Sat Apr 21, 2012 9:00 pm

    @pgsvensk
    I think it would be helpful if you would give some details of your whole system.

    GP49

    Posts: 489
    Join date: 2009-04-30

    Re: Bridged ST-70 or ST-120 Amps?

    Post by GP49 on Sat Apr 21, 2012 9:03 pm

    The only proper way is to invert the phase of one channel and take the output across the HOT outputs. The Dynaco method of operating the Stereo 70 in mono by paralleling the channels does not work well; it causes high distortion and does NOT double the output power as claimed.

    Whatever means you use to invert the phase of one channel, generally an inverting amplifier stage, must be of as good quality as the rest of the amp, otherwise it will degrade the performance.

    pgsvensk

    Posts: 3
    Join date: 2012-04-22

    Re: Bridged ST-70 or ST-120 Amps?

    Post by pgsvensk on Sat Apr 21, 2012 9:43 pm

    @hawaii.ken: Oops, here you go: Tandberg 3006A power amplifier, Tandberg 3008a control amplifier (both in excellent condition), and 2 M&K Bookshelf 75 speakers on original M&K stands, Sony BDP-S480 Blu-Ray player, and an attached computer full of lossless FLAC files. This is essentially my music-only system for my home office, there's a multi-channel A/V system upstairs.

    hawaii.ken

    Posts: 157
    Join date: 2012-01-31

    Re: Bridged ST-70 or ST-120 Amps?

    Post by hawaii.ken on Sun Apr 22, 2012 12:51 am

    @pgsvensk This is only a recommendation:

    Use your ST-120 to drive your M&K Bookshelf 75 speakers. Use one channel of your Tandberg 3006A power amplifier to drive your Dahlquist DQ-1W sub.

    Passive line level crossover:
    http://store.hlabs.com/pk4/store.pl?view_product=25

    You may have to get some of the attenuators to match the levels between the ST-120 and the Tandberg 3006A.

    ruffian

    Posts: 43
    Join date: 2010-02-26

    Re: Bridged ST-70 or ST-120 Amps?

    Post by ruffian on Mon Apr 23, 2012 11:18 pm

    pgsvensk wrote:I'm a newbie here, so please be gentle. I've acquired a Dahlquist DQ-1W sub, and a Dynaco ST-120. How would I bridge the amp to drive that sub? I would likely have to pay someone to do any mods. Any helpful information would be most appreciated. Thanks!

    Do you have one of the solid state 'Dynaco ST-120' amps? When you say ST-120 here people think you are refering to the tube amp sold by tubes4hifi/Bob Latino. They are entirely different beasts.

    pgsvensk

    Posts: 3
    Join date: 2012-04-22

    Re: Bridged ST-70 or ST-120 Amps?

    Post by pgsvensk on Tue Apr 24, 2012 12:25 am

    @ruffian, ah yes, I have the solid state ST-120.

    Bob Latino
    Admin

    Posts: 1910
    Join date: 2008-11-27
    Location: Massachusetts

    Re: Bridged ST-70 or ST-120 Amps?

    Post by Bob Latino on Tue Apr 24, 2012 8:17 am

    The VTA ST-120 is TUBE amp and the the original Dynaco solid state amp was called the "Stereo 120" not the "ST-120". Apparently, enough people call this original Dynaco solid state amp the "ST-120" that confusion has set in between the original Dynaco amp and the VTA ST-120. Probably in hindsight, I should have named the VTA ST-120 the "VTA ST-125" to avoid the confusion.

    As a side note, back in the mid 1960's I heard the original Dynaco Stereo 120 solid state amp. It was probably (at least in its stock form) the WORST sounding amplifier that I ever heard. Yeah - It "measured good" but sounded bad. Hard, brittle, flat etc. and when pushed hard to the point of distortion the top end of this amp would make your "ears bleed". I though at the time > "This is the future of hi-fi?". There is a fellow on Ebay who (at least he used to?) sell upgrade kits for the original Dynaco Stereo 120 that would make the amp sound noticeably better. I guess we can forgive Dynaco for the original Dynaco Stereo 120. Many of the original solid state designs of the 1960's (by todays standards) were not very reliable and were, in general, poor sounding amps.

    Bob

      Current date/time is Wed Sep 03, 2014 1:58 am