? About Low Wattage Class A Amps

[stereo_luver]

I've been looking into some of the lower wattage class A amps lately but have several questions about them. I'm most baffled about the volume level with these 8 wpc amps. Most all of my tube amps are rated between 50 & 70 wpc. I often find that the "usable" power falls a little short of the volume I may want to CRANK it up to. I see at lower volumes that the sound is warm, clear and clean for the most part and I like this. Here are a few questions I'd like to ask. Any input would be greatly appreciated.

1. What should I look for in a purchase of a low watt class A amp?

2. Should I pay attention to speaker selection and what direction should I go?

3. Your thoughts and concerns with these type amps.

I hate to sound like a dumb a$$, but thats what I am when it comes to this subject.

Thanks in advance,
Chuck.

[madmax]

The main things to be concerned about are speaker efficiency and heat. Class A is running full all the time which uses a lot of energy and produces a lot of heat. An 8 watt amp can sound like a 500 watt amp if the speaker is efficient enough. Once you get into high efficiency speakers you have to start worrying about the queitness of the amp considering hiss and hum. Just thinking of getting into it myself.
madmax

[Face]

Start looking for efficient speakers.

[stereo_luver]

And a quality efficient speaker would be................................................ ................
BTW...I'm not opposed to buying older yet great quality.

[Face]

I'm a fan of Tannoy and currently own 9 of their speakers. :D Usually the larger the driver, the more efficient. Do some research though, sometimes a high current amp is recommended for some of the larger drivers. This is because some of the larger cones, such as the HPD-385's, are heavy and need a high current amp to control it.
Look into Klipsch and Altec also.

[GV#27]

My $.02
As others have mentioned speakers with high sensitivity are needed and the speaker needs has to present an easy load (8 ohms-ish).These low powered single ended tube amps are essentially distortion generators with high amounts of 2nd order THD.While this can give them a pleasing sound with the right speaker,it is far from accurate.

[Yashu]

Why would they distort more than, say, a typical push-pull or whatever type of design when you are not overloading them?

I would think that as long as you are not overloading the amp, it's not going to distort any more than any other would. It should distort less, considering there is far less in the signal path, and the amp circuit is very straightforward. Multi-output tubes would be more distorted because there is no way to perfectly match tubes, at least this is what common sense leads me to believe. SET amps should be fine given the proper speakers. That is the hard part... finding speakers that can fill your room on a few watts.

[GV#27]

Why would they distort more than, say, a typical push-pull or whatever type of design when you are not overloading them?

A push pull output stage will reduce(cancel) distortion.Also many of these low power single ended designs have low levels of negative feedback which can if applied reduce distortion.

[Yashu]

As I understand it, negative feedback actually increases several types of distortion while reducing only harmonic distortion. Harmonic distortion is not the only type.

SET amps seem to have the advantage on most types of distortion, with the con being harmonic distortion, but on orders that the brain finds pleasant. That is the amp... I don't like them because there just aren't that many speakers around that can use them well enough. Horns will amplify the shortcomings of more than just the amp.

[TroyD]

Look for a speaker at 90db 1w/1m with a reasonable impedance and you will be ok as long as you aren't looking to play at rock concert levels.


BDT

[mhardy6647]

If you have, for example, a pair of Klipschorns, you can get 107 dB at 1 meter (two 104 dB/W/m) speakers, stereo, with a 1 watt (more correctly, 2.83 VAC into 8 ohms) input.

[Yashu]

Yes... but be very very careful about what amp and source you use. For something like that, I suggest all tubes and vinyl. I can't imagine how bright those things would be on SS and modern upsampling CDPs.

[mhardy6647]

you are correct, sir.

[ben62670]

I like big powerful amps that run in class A for the first 10 or so watts before going A/B. Like the big Adcom's. GFA-565, GFA-585, GFA-5802, and GFA-5800. They have the class A power for low level listening, AND the power to keep going. I am not knocking nice class A's, but you can have your cake, and eat it too. To me it doesn't make a lot of sense to spend a bunch on efficient speakers that may compromise your taste, or wallet. I like the old monitors/SDA's that play nice with 10 watts, and can handle many more.

Ben

[stereo_luver]

I'm wondering how a pair of older Monitor 10's would sound? I've got a load of old Altec's, Jensen's & EV's somewhere and some horns and crossovers. I think I'm going to find some time to dig this stuff out and try and put together something just for fun. I knew I should hang onto that stuff for some reason.

[Face]

Monitor 10's would not do well with only a couple of watts.

[Yashu]

hehe, probably not. Sealed enclosure with large passive radiator... definitely needs some power there.

[TroyD]

There is a guy on here who runs a pair of RTA12's in an 8wpc tube amp.

I've run my Monitor 7a's on 15wpc.

If you are trying to play at rock concert levels, no, it doesn't work but at reasonable listening levels it's just fine. But, what would we know.

BDT

[Yashu]

Monitor 7s I can see on a 15w tube amp... I can see that sounding good. The tens are like two 7s in one big enclosure, and SET amps are much lower than 15w, so I am not sure it would work out so well.

A good push/pull tube poweramp that gives you around 65w, that can drive plenty enough speakers to build a great system. I have been looking at a tube amp that is about that, with a switch to a class A mode that is a fraction of that... That would be a great way to really test lower power, but still have the power you know that you need.

[TroyD]

No, there not. While I don't have the specs off hand, they aren't all that different. The efficiency and impedance curves are also similar...so, no, you aren't right.

A push/pull amp's power ratings depend on the circuits/tubes involved..it's not inherent to the design. I've owned a few. My current tube amps are ~25wpc and I've run some pretty big speakers on them and never run out of gas.

Again, experience sometimes has it's advantages.

BDT

[Yashu]

I know Troy... I wasn't trying to say all amps are like X. I was giving an example of a good place to start with tubes... have some power if you need it and ultralinear mode when you want to play with pure class A.

I am not sure you are right about the 10s though... it's double the active drivers and almost double the cabinet space. The tens clearly are asking for more power. I am sure there is some crossover work to keep the impedance from being cut an half, but I would say the 7s and the 5s would play better on lower power amps than the 10s. I can't see any way around that. Besides... don't the 7s image better anyway?

[mhardy6647]

10s are more efficient than the 7s. My own experience with 7s: they work reasonably well with a push-pull EL84 amp (ca. 14 wpc, an EICO HF-81 in my case) but did not sound good at all with a single-ended 2A3 amp (3.5 watt Bottlehead Paramour monoblocks, in my case).

EDIT: remember that the 10s are nominal 6 ohm speakers. Try them on both the 4 ohm and 8 ohm taps of a tube amp if possible; hard to say which'll sound better.

The early Polk Monitors were not designed for tube amps, and like many (but NOT all) speakers designed when solid state amplification was the norm, they really don't benefit much from tubes, IM (albeit somewhat limited) E and IMO.

[TroyD]

I've owned the 10's, I've owned the 7's. I've run them both on low powered amps (but not SET's). My experience is different from what you are saying.

So, you can 'think' something is true but I 'know' it not to be.

BDT

[mhardy6647]

Fair enough. What is your experience?

How satisfactory the pairing will be will also depend on type of music and volume level desired, of course. Just to clarify: I thought the 7s sounded OK but not life-changing on the HF-81. Conversely, a pair of ads L-710s I have were fabulous on the HF-81.

I have a pair of 10s now (original series) but haven't tried 'em on any tube amps at the house. Something like a push-pull 7591/7868 amp (e.g., Scott LK-72, Fisher 400/500 series receiver, ca. 25 wpc) would be well worth a try for a 7 or a 10... but I haven't actually tried it.

EDIT: oops you werent' talking to me, were you :-P sorry.

[TroyD]

Sorry about that, I was replying to Yashu.

Everyone's mileage will very, my point being that wattage isn't 'really' the issue.

BDT

[mhardy6647]

Yeah, I'm in space...


my point being that wattage isn't 'really' the issue
Absolutely true.

[Yashu]

Yes, I agree with that. The only way to know is to try.

[TroyD]

:rolleyes:

[Yashu]

It's true and you know it Troy ;)

I hear so many angles when it comes to tubes it isn't funny... some say tube watts are more robust than SS watts, some say the overdrive is what makes them sound so good, some say that watts are watts... some say it's the manufacturers that are misleading us by printing false measurements. Really... the only way to know is to try.

I know that, in my experience, double the drivers and the load is heavier, but twice the cabinet space and a properly tuned PR could offset that. You are dealing with surface area movement per watt, is really what it comes down to. If the 10s can move more air with less power then they are more sensitive. I do believe that there is a happy medium, and once over that, you are ending up in the low sensitivity range.

I had some speakers a while back, they were very sensitive yet huge, no horns or anything, just big 12" woofer and such. They were my first real set of speakers, they were from 1980. My amp was low power as far as SS goes, yet I could not turn the volume up past 12 o clock... now, fast forward to today, I still have that old amp, and I can turn the volume all the way around to full and not reach the DB levels with my bookshelves and small towers that I was able to get from those big vintage monsters.

Air displacement per "watt". If the 10s can displace more air per watt than others then that is reasonable... I am just saying that there will be a point where the 10s will stop scaling at a point smaller speakers wouldn't on fleapower amps.

I don't know... I still don't think we should even be considering <100db speakers for these little SET amps. It is different in the nearfield where you are closer to the speaker, but inverse square law applies to farfield.

[TroyD]

I agree the only way to 'know' is to try. That's my whole point, I have and you haven't.
You can suppose all you want but if you don't have any experience with it, at a certain point, it's just hot air.

A simple 'huh, I wouldn't have thought that. Perhaps I may be mistaken' would do nicely.

BDT

[Davidpsalt]

agreed

[tonyb]

Yashu......blow up any speakers in your lifetime?
Seeing that you like to turn the volume up past noon and all the way around....
Distortion must be musical to you....:eek::confused:

[Yashu]

I have tried SET amps and various speakers, Troy... don't pretend to peep through my windows man, that's creepy.

Haha... the old amp thing... hell that was more than 15 years ago. It never clipped, I just wasn't expecting my new speaks to have such lower sensitivity. I was used to speakers with a very high sensitivity, so the modern stuff threw me off at first.

I have more than enough power now, hell, I even adjust the gain on my pre out so I can use more than 1/5 of the volume control. With a separates system it actually makes sense to use the most of your pre's volume, especially if you have an all class A pre, like most good ones are. That way, you are getting the most out of the class A gain stage, and also if you have an AB amp, it helps keep it biased towards A for a longer swath of DB.

Those old speakers are long gone, and the old amp is in the closet. It used to be my garage amp for a while when I had a garage. Mated nice to some vintage JBL 2500s.

[TroyD]

I form my opinions based on the fact that you don't seem to know a hell of a lot about tube amps.

Somehow, I think you inherited liv4fam's big bag of nothing.

BDT

[Yashu]

There you go again... don't make accusations Troy, unless you are peeping through my window... which, again, would be kindof creepy.

There is nothing I have said that is incorrect about tube amps so far, so perhaps you are also predicting future or alternate events? Peeping tom with ESP, that is... a not a comforting thought there, but since you may have ESP, you, perhaps, already knew what I was thinking?

I hope that you do not start another macho man war in audiophile land, I was kindof glad when the last one ended, and was hoping that you would keep your word, and you know... not instigate one?

Not that you can't disagree with what I have to say about SET amps, as if I expected you to actually agree with ME on anything! I could say the sky is blue and you would accuse me of having no knowledge of the sky, when what should be happening is you just stating that you think it is pink and then letting the conversation move on like intended. That is what a forum is for... discussion and debate.

[TroyD]

I'm not looking to start anything with you...in fact, if you go back, I never started anything with you in the first place. In point of REAL fact, I asked you SEVERAL times to not reply to me. So, at least get your facts correct.

Second, your point about a low powered tube amp being able to run a pair of Monitor 10's is horse****, which causes me to wonder if you have experience with either lower powered amps and/or the Monitor 10's as what I and others have experienced doesn't square with what you are saying. In other words, we've looked into your big bag and there was nothing there.

BDT

[Yashu]

No offense, but you just aren't going to get much from a 2w SET amp on the 10s. The music might sound fine at lower volumes... most volumes even, but that is for the midrange and treble, the bass on the otherhand... anyway, SET amps are great, I don't mind the warm fuzzy sound of the pleasant harmonic distortion, I just wouldn't try to crank it, is all I am sayin', unless you have a 300B 9w per channel, then I can see most listening levels sounding wonderful, even taming the SL2000 a bit if you have one. When I say crank it, I don't mean concert level, I mean the level at which the sound envelopes you completely.

I do a lot of low volume listening (with tubes! imagine that), but it doesn't beat the dynamics of listening at a level where the sound... it just surrounds you almost. This is not ear deafening, but it is something I would desire in my system, and you would not quite get there with a little 2w SET amp on the monitor 10s, unless... you sat close enough I suppose.

Maybe we are thinking of different amps... There are 2w common SET (EL84? I know there is a less than 2w tube as well, don't remember...) amps, 6w EL34 amps, 9w 300b, all the way up to a 30w (which really WOULD power about anything within reason.)

I have not heard a 30w SET amp, I am sure it costs more than my car, but I have heard some of the lower watt SETs and various tubes, and various speakers, incl. vintage Polk. Did you know there was a huge audio community group here where I am living that meets every month..? I have heard all sorts of goodies, plenty to fill a bag.

Anyway, the OP said low wattage class A amps, and it doesn't get much lower than a 2w SET amp, so that became my example.

[TroyD]

The original conversation had NOTHING to DO with SET amps.

We were talking about lower powered amps, in general. YOU are the one that brought up the whole SET amp thing.


I've been looking into some of the lower wattage class A amps lately but have several questions about them. I'm most baffled about the volume level with these 8 wpc amps.

I, and other members, have run speakers like the Monitor 10's (and other similar speakers) to quite satisfying levels on amps between 8-15wpc. That's it. End of the story. Got anything else to add other than a derail? NO? Thanks for playing.

Back on the bozo list.

BDT

[mhardy6647]

Do I need to drag my 10s and my Paramours upstairs and put this to rest? :-)

I can tell y'all that 10s on an EICO HF-81 (14-ish wpc, PP EL84) sound just fine with all types of music I've tried. The 10s are actually fairly efficient; remember that they are in essence ported speakers (albeit with a somewhat bizarre LF impedance curve due to the PR). I probably already said all this before though...

sorry to intrude

[TroyD]

I'm whipped on the subject as well....

Those that don't know...well, they just don't know.

BDT

[hypertone]

I'm wondering how a pair of older Monitor 10's would sound? I've got a load of old Altec's, Jensen's & EV's somewhere and some horns and crossovers. I think I'm going to find some time to dig this stuff out and try and put together something just for fun. I knew I should hang onto that stuff for some reason.

I'm running 11W RMS into some Monitor 10's. Although I never listen at rockin' loud levels because I live in an apartment, I never feel I am lacking power. When I first got the monitor 10's, I was actually suprised at how well my amp (Tripath 2024C based) drove these speakers.

[beardog03]

are 8 ohm speaks better to use than 4 ?

[treitz3]

are 8 ohm speaks better to use than 4 ?
That's a broad question.

[beardog03]

Would I get more from my tubes with 8 ?

I have gotten the impression that 8 ohms is easier to push

[treitz3]

Oh it's easier to push, but in my limited experience, it seems that tube amps don't have as much of a problem with lower impedances as with SS amps. Allow me to step back out of the conversation and let someone who is more knowledgeable/experienced with tubes chime in.

[mhardy6647]

You make better use of the output transformer's secondary winding using the higher-impedance taps. Thus, in the (first!) tube era, many loudspeakers were 16 ohm loads. My Valencias are 16 ohm speakers, and I use the 16 ohm tap for 'em with fine results.

The 10s are 6 ohms; whether the 8 or 4 ohm tap will sound better should be determined empirically :-)

An impedance mismatch of "up to 100 percent" (i.e., 4 ohm speakers on an 8 ohm tap, or vice versa) won't do any harm, although it will have some "tone control" effect on the frequency response (sort of like high-$$$ speaker cables and interconnects).

I'm ducking now! :-)

[ohskigod]

for note, I have heard Fireman32's setup with 8 watts push pull on RTA12b's (would make sense, since Dave's my friend and I sold him the gear :D )

I know the RTA 12's are above 90 in efficiency, but not sure ofthe exact figure.

you'd be very surprised how clean they sound, and downright stunned how the bass loaded up in his small livingroom at the time (he has since moved since I heard them)

sounded good. damn good. good enough to make his next serious purchase a turntable and NOT an amp or speaker upgrade.

Troy calls it right, youre not getting concert level volume, but it's loud and clean enough to move you, thats for sure.

[Yashu]

90+ sensitivity and 8+ watts and you should be ok for most listening. I mean... how often do audiophiles crank the volume anyway..? half of you guys don't even have a remote.

[stereo_luver]

I got a remote....wheres the damn remote?

[TroyD]

90+ sensitivity and 8+ watts and you should be ok for most listening. I mean... how often do audiophiles crank the volume anyway..? half of you guys don't even have a remote.


That's what we've been saying all along. :rolleyes:

BDT

[Yashu]

Then why were you arguing with me! hehe... if we have been agreeing all along?

At least we agree, so I am looking at the bright side.

[TroyD]

You must be exhausted at the end of the day from switching feet so often.

BDT