OT: Use of LOW POWER Amps

[mah]

Low power amps considered for driving loudspeakers are often somewhat expensive. Auditioning one on your own loudspeakers in your own listening situation is advised.

Here is an easy to read article that covers the subject reasonably well: Speaker Sensitivity, Dynamic Range, and Amplifier Output | Confessions of a Part-Time Audiophile

The SPL Calculator referred to in the text: Pro-Audio and lighting Calculators. Calculator page de dBs, plus some others that are generally handy.

Adjustment can be made to accommodate the sensitivity of your speaker and its SPL at a selected distortion level in order to arrive at a result for your particular situation.

[alancohen]

I was very surprised at the jump in sound when I got my Heathkits. Prior I was using a 95dB sensitivity full-range speaker with a 3W steady state amp and could achieve 97db with the volume control halfway. Plenty for me. But the Heathkits at around 102dB? made a huge difference. I then jumped to a 15W OTL and have even more headroom.

I like what he mentions about amp speed. How fast an amp and speaker can go from 0-95dB makes a big difference in dynamics and listening pleasure for me, especially with good old-fashioned non-compressed music. I don't need volume to hear detail. It's just there, which makes it feel more fulfilling.

[cradeldorf]

Shouldn't a speaker determine how fast an amp sounds? The higher the Fs the quicker they sound?

[mah]

It mostly comes down to F=Ma

F= Fd(drive force) minus Fr(resisting force), of the system

M = effective mass being driven

a= resulting acceleration of the moving parts.

The inertia of the system and the EFFECTIVE driving force determines the time response to any input force.

Resisting forces are from from suspension stiffness, back EMF. cabinet air springiness, etc.

For a transient to be reproduced faithfully, the effective force and moving mass relationship must be such that an appropriate acceleraton response of the system is achieved.

Lots of other factors come into play but the main ones are above.

For a given system there will be an F= Ma relationship for a given level of reproduction accuracy.

Because the main parameter that can usually be chosen is POWER(giving Fd), selection of an amplifier of adeqaute power is essential. If you can live with a lower dynamic range(lower than average listening level) and less dynamic response then a lower-power amplifier may suffice but you will have to live with higher distortion.

Raising the LF cut-off frequency reduces the power requirement.

[mah]

Altec Best, feel free to add OT to the title. My oversight.

[alancohen]

I think F=Ma is a bit of an oversimplification. Power, in and of itself, will not yield more dynamic range. Sure more horse power in a car will get you from 0-100mph faster, but it will not stop you any faster and maybe have the opposite effect. All the extra hardware you need to get going maybe prevent you from stopping quickly.

Getting from 0-95dB quickly is important, but getting back from 95 to 0 is equally important for a satisfying dynamic range.

Not all Fd is created equal. My 65W Onkyo amplifier sounded like crap compared to my little 3W cathode follower. I'm certainly no audio or electronics expert by a long shot, I just know what I hear. I used to have to push the volume control in order to hear more detail or play with an EQ or twist the bass knob. Now all the detail, and even bass transients are just there at any volume.

[GM]

Shouldn't a speaker determine how fast an amp sounds? The higher the Fs the quicker they sound?

No, it's a function of its slew rate. No, it's determined by its high frequency response pass-band.

GM

[Alien_Shore]

Man I love this board. Geek paradise!

[mah]

Someone can perceive the difference so it must be true. Or is it?

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[LowOhms]

I was very surprised at the jump in sound when I got my Heathkits. Prior I was using a 95dB sensitivity full-range speaker with a 3W steady state amp and could achieve 97db with the volume control halfway. Plenty for me. But the Heathkits at around 102dB? made a huge difference. I then jumped to a 15W OTL and have even more headroom.

I like what he mentions about amp speed. How fast an amp and speaker can go from 0-95dB makes a big difference in dynamics and listening pleasure for me, especially with good old-fashioned non-compressed music. I don't need volume to hear detail. It's just there, which makes it feel more fulfilling.

Alan,

You hit the nail on the head. " But the Heathkits at around 102dB? made a huge difference. I then jumped to a 15W OTL and have even more headroom."

The very best sounding amps for Altecs will be about 1 to 3 Watts. They require a LARGE efficient speaker, ( which IS your ALTEC at 102 dB. )

YES, you are correct, there is a HUGE advantage going from only 97 or 99 dB up to 102 dB when using such low powered amps.

Alan, IMHO, you did NOT need a 15 Watt OTL amp for "more overhead." Doing this, you traded off the possibility of having high quality for numbers, .... numbers of Watts (assuming the low powered amp actually was of high quality.)

What IS a high quality low powered amp? A good question. I have some definite ideas on that. I will define it, from my experience in amp building DIY.

The best SOUNDING amp will always be 1 to 3 Watts. You will rarely use more than 3/4s of a Watt on a well-set-up Altec speaker.

******** Amps, not speakers, are the weakest link and the "biggest turkeys" in the whole audio chain. *********

Below are some attributes "I" have found necessary to have a great sounding low powered tube amp, for use with 100 dB plus speakers:

1) It will be a tube amp, triode.

2) It will be only two stages, not three ( better transparency )

3) It will be direct coupled ( no series capacitors or interstage transformers)

4) It will have no global feedback

5) It will be single ended, not push-pull

In relationship to your comments on amplifier "speed and dynamics" the following must be present in the amplifier's design :

1) None of the filter chokes in the power supply will have over 20 Ohms of DC resistances. Nor will filter chokes have over three HY of inductance. ( Minimal energy "storage" effect ).

2) None of the power supply capacitors will be larger than 50-60 uF, so as not to "hog" instantaneous current from the Finals tube.

3) The amp will have SUPERB attention to internal wiring, maximizing transfer efficiency internally, and, a thoughtful layout.

Since the efficient speaker requires low power, we are primarily concerned with how the low-powered amp sounds at 1/10th to 1/2 a Watt, where it is being used 99 percent of the time.

Most high powered amps are dreadful sounding when throttled down on efficient speakers, radically deficient IMHO and experience.

I have worked about three decades now... in this precise area, and the above represents "my" personal conclusions. YMMV, that is fine and I do truly understand others who would think differently !!

Cheers,

Jeff