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Can 10 watts of Class A really drive speakers?

doucanoe said:
I have come close to picking up a single or a pair of the Monarchy SM-70 or SM-70 Pro's for the last few years.


One thing that has been holding me back has been a nagging reports of these amplifiers producing a audible amount of hum when used with moderately high to high sensitivity speakers. While I have hear that this can be remedied with some circuit mods or a trip back to Monarchy for an attitude adjustment, it seems to be prevalent enough that I have been a little spooked off. I even spoke with C.C. Poon about it (some time ago now) and that conversation did little to elevate my concern.

I have spoke with a few on A-gon that had these for sale and asked them pointedly about it. Only one claimed no audible hum what-so-ever but they were using speakers @92-93 dB sensitivity. The others claimed that they could hear hum from their horns speakers but you needed to be within 1-2 foot from the horn mouth to pick up on it. Seeing as how I'm in a small room and typically using speakers 100 dB @ 1w/m or more sensitivity, I've been reluctant to roll the dice and buy. Maybe some or all of this issue has been addressed with later versions of the amp and Monarchy's new offerings.

I have heard nothing but great reports about the SM-70/SM-70 PRO beyond the potential for hum with certain speakers deal. I'd more than likely be a buyer if I could audition first to make sure I had no problematic hum with what I am running here.


RC
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I have two of them and no hum here what so ever. I have heard if amps hum, to go to a double plug with no ground. This seems to be a problem with alot of sub plate amps. The speakers my Monarchy's power are 94 and 96 db/1watt.
 
luddite said:
Wow. This is confusing to me. Is there a tech paper out there explaining this subject? I had a 17 watt/channel amp and when I got a 30 it sounded louder and the 75 is too much louder to go past 12 o'clock. So how do these 3 and 5 and 10 watt/channel class A amps do it?
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Well, you certainly don't want even more too much louderest, do you! If you want the dial past 12 o'clock without the louderest-ness, I suggest that you turn it up counter clockwise.

The answer to the second part of your post is that they don't do it, it just seems that way.

Best Regards,
TerryO
 
luddite said:
Not all that helpful, there... so as usual I've had to resort to answering my own question using Google.
This, in my ignorance, is my chosen answer:
http://sound.westhost.com/class-a.htm
But, is it correct? I have no idea. Makes sense to me (knowing nothing).
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Yes, Rod Elliot is a 1st class engineer and his information can usually be taken without reservation.

I believe that if you're really interested, that you'll find Bob Cordell's new book "Designing Audio Power Amplifiers" to be quite good, but it may be a bit advanced for anyone just starting out.

Also, one of the amateur amp builder's best sources of hi-tech information is Nelson Pass of Pass Labs. He's practically a God among diy amp builders and he writes in easily understood terms about his SOTA explorations into advanced design. He's one of a kind, so don't miss out!

Best Regards,
TerryO
 
luddite said:
Sold.
The guy reminds me of Edgar Villchur.
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There you go!

Another very interesting and extremely bright guy is Prof. Keith Johnson of multi-faceted Audio fame. The "legend" is:

"While he was in grade school, Ampex Corporation awarded him a scholarship and training program for his three-channel recorder and microphone project. He developed photolithography construction of magnetic heads at Stanford University in the sixties, consulted with Sherman Fairchild and applied his proprietary Focused Gap technology to master recorders and later to high-speed tape duplicators when he co-founded Gauss Electrophysics."
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The "Westhost" white papers always pop up on Google searches and they're generally quite good.

In terms of the discussion in recent posts to this thread, it feels like folks may be confusing (preamp and/or voltage amplifier) gain with power amplifier power output. How loud a given amplifier or receiver plays as a function of the volume control setting has fundamentally nothing to do with the amp's power output capabilities (except, of course, at its very upper limit) - it does reflect the gain (or attenuation of the signal) being delivered between the source and the power amp's output devices
 
I've used The "Westhost" white papers to satisfy my own courisity and find them informative. The parts I am interested in are common knowledge all he did was put it together where I could find it. I have a different opion about the high power reqirements and SPL required for a stereo system however. My own 88 db/w speakers sound great with nothing more than 10 watts on my peak meters of the 100+ I have avaliable and go plenty loud. Even those 10 wpc Tube amps would sound great with these speakers.

If it's concert level sound I wanted then I'd have pick up a pair of Altec Lansing Model 19's (My favorite Rock speakers) for sale on the other side of town and connected up my 100 wpc Bryston amp for something like 115 db at my chair in my 30' rec room. I won't lie to you, I'd love to hear it for a few song's. But for the most part I never listen to my current system anywhere near full power so that part of the artical doesn't make any sense. The fact that many audiophiles with far less power and spl he's suggesting throughly enjoy their systems bring's into serious doubt his conclusions in that regard.
 
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I have a set of homebrew speakers, seen in my avatar, that I estimate to be around ~98db/1Watt efficient. I have a set of SEP 6BQ5 Roberts/Akai Monoblocks that will drive them to respectable volumes. Connected to my 200wpc Mac MA6900, the meters rarely exceed the 2 watt (average) mark, at 10 watts they are very loud, at 50+ watts---painfull.

Dave
 
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