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In Reply to: Need suggestions to tweak SFS40 posted by SeanC on July 31, 2002 at 17:03:00:
Sean, don't expect the SFS-40 to do a very good job with your MG-12's unless you listen at pretty quiet levels in a small room. At roughly 35 watts a channel, the SF doesn't have the balls to push the Maggies full tilt in a larger room. Choice of music will also be a big factor. Note also, the older SF products were not noted for being a "warm" amplifier; many have called them SS amps disguising as tubes. Apparently the designers were more interested in good measurements than good sound.That said, there are some things you can do to improve the sound. Room setup and speaker placement will be critical to achieve a balanced sound. The amp itself, while built like a truck, would benefit from some different parts in the signal path. Riken resistors, Holco and Auricaps will give you more of a tube sound, and there's lots of others you can try. Regular old carbon comp resistors are also better at providing a more tubelike sound where you can use them.
Choice of driver and output tubes will also affect the sound. The Holland EL-34s sound great in this amp using Bugle Boy ECC88s as drivers, but you'll have even less power. You might want to go with Bugle Boys for drivers and Ei KT-90s for output. Your amp has the current swing to drive the KT-90s pretty hot, which they need to sound good. Make sure the Bugle Boys are not noisy/microphonic and are well balanced between tube sections. Tung Sol 6550 is another good choice, but don't bias them above the recommended 50 ma.
Make sure your speaker wire is not highly resistive, and hopefully has fairly low capacitance and reactance to boot. Kimber 8TC works very well with this amp.
If your funds allow it, use the KT-90 on the bass speaker of your Maggies with the KT-90s. You'll get some of the most accurate and deepest bass you've ever heard, better than what I've heard from any SS amp as yet. Pick up a Dynaco ST-70 or a Sound Valves STA-70i and use this amp to power the panels on your speakers. This would involve horizontal bi-wiring from both amps. All these amps are close enough in output that you should have pretty balanced sound without doing anything else, but if you need to attenuate one amp, adding an active crossover with attenuator before the amps will open up the sound even more. This is probably the only way you're going to achieve the degree of tube "lushness" that you appear to be looking for.
If you have a tubed preamp you might want to consider a good SS amp to drive the Maggies; most of the "tube warmth" you're looking for will be provided by the preamp anyway. If you're CD only, try the Bottlehead Foreplay, if you don't mind a little soldering, or an ASL for a few bucks more, into a Plinius SS amp. This is a good combination as well. If you want to stay all tube, the Foreplay/Dyna ST-70/SFS-40 combination into your Maggies will knock your socks off.
Good luck; enjoy the music.
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Follow Ups
- Suggestions - foolno1@blazenet.net 03:36:58 08/01/02 (3)
- Re: Suggestions - SeanC 10:10:43 08/01/02 (2)
- Revised suggestions - foolno1@blazenet.net 15:43:50 08/01/02 (1)
- Have you heard of the ZEROs autoformer? - SeanC 17:15:58 08/01/02 (0)