Stereo 70 with SDA 1B's?

Bigerik

Hey folks.
Wondering if anyone has run a Dynaco Stereo 70 with SDA 1B's? Have a chance to try one out, but just not sure if it has the balls to drive the SDA's. My room is small and I usually don't push them too hard.
Admittedly, it is a modern Stereo 70, with bigger iron and the ability to run nigh onto any tube.
Any thoughts?

Face

Hey Erik!

Sorry, I can't give you a definitive answer, but as long as your ST-70 is common ground it should work for your application.

F1nut

I have a friend that ran a 70 with SDA's, 2B's if I recall. You should be fine.

george daniel

I have a friend who is running his 2B's with a stereo 70 and he extremely happy with the results.Let us know your impression--have fun.

Bigerik

Thanks guys.
Really appreciate the support I have always received over here.

Kind of an exciting prospect, if it has enough balls. Just love that big, warm midrange.

Schurkey

When these speakers were NEW, Polk claimed they were an easy load to drive; other than needing a common-ground amp (in most cases) and having somewhat lower impedance.

Why after twenty-something years does everyone think they're difficult to drive? What changed?

Any amp that can't drive a 4-ohm (nominal) load at moderate volume isn't much of an amp.

First Guess: That Stereo 70 will be MORE than enough (depending on the volume level and size of room, of course.)

nadams

Schurkey wrote: »

When these speakers were NEW, Polk claimed they were an easy load to drive; other than needing a common-ground amp (in most cases) and having somewhat lower impedance.

Why after twenty-something years does everyone think they're difficult to drive? What changed?

100 watts then is not 100 watts now. The ratings system changed. People started using HT receivers instead of dedicated amps.

I'd say that a 100 watt receiver is not enough to drive my SDA 2's. But, my Adcom GFA-545 is more than enough. I think the problem would come from someone like myself, who could boldly claim "100watts isn't enough!!!" if I didn't know better than to do such a thing...

Schurkey

nadams wrote: »

100 watts then is not 100 watts now. The ratings system changed. People started using HT receivers instead of dedicated amps.

Did the rating system change; or is it a matter of the rating system NEVER WAS adequate? The FTC does indeed need a hearty ****-kicking; I'd just like to be sure they get it for the right reason. You're right--a proper full-range amplifier spec should require a 20-20K (or wider) bandwidth, a reasonable distortion figure (i.e. NOT the TEN PERCENT thd + noise that I saw on a "700 Watt" HTIB receiver at Scum's Club) and a reasonable impedance/resistance load--preferably a published, advertised spec at 8 ohm, AND 4 ohm, AND 2 ohm. The test should be done with ALL CHANNELS DRIVEN instead of one or two driven out of the 5 or 8 loaded into the receiver, AND the power rating advertised should represent ONE channel--not all of 'em added together.

Of course, the load will be purely resistive since no-one is going to agree on a "standard" capacitance/inductance for testing purposes. Still, a man can dream...

Separate amps never were as popular as receivers. Your point about HT receivers is taken; I've seen the sort of mass-market JUNK that's being passed-off as legitimate product in the stores. But there NEVER was a time where bottom-feeder equipment wasn't available.

Even a Chinese HT receiver/amp (that is rated for a 4-ohm nominal load) should be able to drive Polk speakers. The primary issue is that cheap-junk receivers AREN'T rated for a 4-ohm load--and that doesn't make Polk speakers hard to drive, it means that the amp manufacturer is cutting corners.

inspiredsports

One major design parameter that changed in most newer receivers is that they do not employ heavy, high-current power supplies. My 1987 NAD 7600 Receiver is rated at 170W RMS X 2 at 8 ohms and it can sustain up to 5db headroom bursts for nearly a second (it takes a LOT of reserve current to be able to do this). It is rated for up to 400 WPC peaks (and 600WPC peaks into the 4 ohm load SDA SRS 2's I'm driving)

It weighs something like 38 lbs. A new lightweight power supply based amp would need to be rated at perhaps 300 WPC X 2 to emulate the performance of this old beast.

Look at the huge transformers on tube gear. The rule of thumb is that large reserve of current effectively allows you to double the RMS rating of tube gear when considering speaker loads. The 80 WPC rated Dynaco Stereo 70 would perform like at least a high quality 160 WPC solid state amp with peaks I'm sure equal to the SS example above.

The NAD 7600 coasts driving my SDA-2B's, so I'd be willing to bet a nicely restored Stereo 70 would do an even better job. I'm negotiating with a guy for Stereo 70 right now that will hopefully be this winter's restoration project.

snow

Most older tube amps have 8 and 4 ohm taps amd I have used a Scott 299 with my SDA's with great success I see no reason why a Dynaco ST-70 wouldndt be plenty in most applications with your SDA-1B's unless you need ear splitting sound levels. tube wpc is in most cases equal to 4 x SS watts has been my experience.

Let your ears be the judge



REGARDS SNOW