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St-70 running Magnapan speakers, Will this hurt the amp??
Posted:
Mon Oct 19, 2009 7:20 pmby Tanner
I just got a ST-70 about a month ago, I went thought it replaced the board with a VTA, Replaced the tubes (all of them) I'm running Magnapan speakers with it and the sound is breathtaking. Will this hurt the amp to run a planer speaker? I do not play it LOUD maybe 30-40 percent at the loudest. Will I be ok?
Posted:
Mon Oct 19, 2009 7:24 pmby Ty_Bower
No problems at all. Whenever he doesn't have the Ampzillas hooked up, I'd imagine Skidave runs his MG 1.6 on his Stereo 70. They sound real good either way. I'm sure he will chime in here shortly...
Posted:
Mon Oct 19, 2009 7:49 pmby Tanner
There rated @ 5ohm should I use the 4 ohm tap or the 8 ohm one??
Posted:
Mon Oct 19, 2009 8:06 pmby Ty_Bower
Let me see... maybe I can reason this one out.
Pentodes mustn't be operated with a load that crosses past the left of the "knee" in their curve. All other things being equal, the line of a higher reflected load will have a flatter slope. I'd think that might bring you closer to the region that should be avoided.
The A470 is specified with a 4.3K ohm primary impedance. On the 4 ohm secondary tap, that's an impedance ratio of 1075:1. The 8 ohm tap would be 538:1. That would mean a 5 ohm load would reflect 5375 ohms if connected to the 4 ohm tap, and 2688 ohms if connected to the 8 ohm tap.
I suppose the 8 ohm tap connection is technically the "safer" connection, as it keeps you far away from the kink in the curve. In this case, it's quite a ways from the designed load. You might be able to extract more power at such a low load, but certainly distortion will suffer. I'd use the 4 ohm tap myself. I can't imagine there'd be any problem with that. Speaker impedance ratings usually lie anyway - they're always lower than they say.
You're almost certainly safe to try them both, and see which one sounds better to your ears. The 8 ohm tap should seem louder (at the same setting of the volume knob) than the 4 ohm tap, but it should clip much earlier.
Posted:
Mon Oct 19, 2009 8:12 pmby Tanner
Thanks, I had them on the 8 ohm tap for the last 3 weeks. I will try the 4 ohm and see how it sounds
Posted:
Tue Oct 20, 2009 1:46 pmby skidave
Use the 4 ohm tap. You did not specify which Magneplanars...but you will hear the different distortions...tube amp distortion Vs panel distortion. I like my ST-70 with my Magneplanars (1.6QR).
You will learn to really enjoy the sound of tubes with Maggies. See a recent discussion here:
http://www.diytube.com/phpBB2/viewtopic.php?t=3700
Dave