Low power amplifer recommedation for Altec 511B horn

**VolvoHeretic** · January 25th, 2013, 12:26 AM

Maybe I should plug my 511s into my Stax (class A) electrostatic headphone amp/preamp?

GM · January 25th, 2013, 01:52 AM

Originally Posted by alancohen

I read an article by the designer of my OTL. I quote: "A good rule to follow is that amplifier output impedance must be at least ten times lower than speaker impedance for good control of cone motion. This is called damping factor. Amplifier output impedance must be less than one ohm for best performance."

And why it's not normally a good plan to drive a woofer with a low DF amp, but like most things, it depends. Anyway, this subject is no trivial pursuit, requiring a fairly good understanding of both the electrical and mechanical physics of audio system design that goes well beyond a simple marketing white paper.

Compression horns OTOH are normally very highly damped electrically and acoustically in their usable pass-band, hence its response fairly closely responds to how the driver performs in a plane wave tube [PWT], so if driven with a high output impedance, it adds a 'smiley face' EQ to it, flattening it both electrically and acoustically over a much wider BW while remaining damped enough that it's still over-damped from a transient attack [impulse response] POV, so in some cases it may need to be higher than a matching impedance to achieve a 0.5 Qt 'critically damped' [transient 'perfect'] response.

To accomplish the same thing with a cone/dome driver requires a < ~ 0.25 effective Qt, combined with a 0.5 Qt OB, sealed, or aperiodic alignment, so can be done with some of Altec's and others drivers and why they are sometimes marketed as horn drivers.

GM

**LowOhms** · January 25th, 2013, 02:19 AM

Hi everyone,

I have some extensive experience in this topic of low powered amps on Altecs, and would like to contribute up here.

The best sounding amp for an Altec speaker system in high fidelity home use will be a good one Watt amplifier.

It will be tube, two stages, and direct coupled. It will have about a two (or three) hundred Watt power supply, and it will be a "gated" one ( or two or three ) Watt audio amp.

It exists, and has since 1989. They are about $15,000 for a pair of mono amps. I know two people who run them at home on GPA 604s. Most all of you have never really had a good opportunity to hear them, but I have in numerous systems and rooms, hence my posting. I am posting this, just to set the record straight.

I suppose I better disclose, the fellow who builds these is a very close friend of mine, and has been for maybe twenty five years. I have NO financial interest in this, and am just introducing you to what I believe to be the best there is for Altec speakers, "IMHO". When you get a good chance to hear it, with good source material, only then can you easily understand.

Here we are :

Welcome to Serious Stereo. The ultimate SET amplifier, passive attenuator, High Effienciency Speakers, Vacuum tube amplifier, tube amplifier, single-ended amplifier, triode amplifier

Read the reviews, have fun.

Jeff

EDIT, On August 29, 2012, there was a forest fire in Montana, that has caused huge disruptions in this company's operation. ( GOOGLE : Pine Creek Fire, MT ). If anyone wants to contact this small artisan manufacturer, let me know and I will provide new phone numbers, etc.

**MerlinVSM** · January 25th, 2013, 07:21 PM

Some amplifiers that I at the moment investigate is the Parasound Halo A23 , class A up to 2,5 Watt, and balanced input, but solid state, 1000USD. Other class A amps come to my mind.

The Decware brand as the Mini Torii about 3W 4ohm seams interesting.

Any recommendtaions and comments appreciated.

**fpitas** · January 25th, 2013, 09:08 PM

I noticed that Reno Hi-Fi has a used First Watt F3 for sale this month:

First Watt Products

FIRST WATT F3

**VolvoHeretic** · January 25th, 2013, 09:24 PM

Sorry guys, but my son took it apon himself to take my 15 years dead Crown 150 wpc DC300A with him over Christmas and just reported that it is breathing again. Just have to send in my Stax SRA-12S pre-amp, send in my 416-8A woofers for recone, and get a matched pair of pascalite diaphrams to get the A7-500s back in shape, and I will be back to rocking 120db music. Nothing beats POWER. You can keep your 1 watt, I also listen to my stereo outside, in -30 below temperatures when no one is around to call the police.

**bowtie427ss** · January 26th, 2013, 09:43 AM

Originally Posted by VolvoHeretic

Sorry guys, but my son took it apon himself to take my 15 years dead Crown 150 wpc DC300A with him over Christmas and just reported that it is breathing again. Just have to send in my Stax SRA-12S pre-amp, send in my 416-8A woofers for recone, and get a matched pair of pascalite diaphrams to get the A7-500s back in shape, and I will be back to rocking 120db music. Nothing beats POWER. You can keep your 1 watt, I also listen to my stereo outside, in -30 below temperatures when no one is around to call the police.

Never apologize for knowing and stating what YOU like.

That said, leaving a DC300 to lay in state for 15 years might be a tad sacrilegious.

**fpitas** · January 26th, 2013, 12:50 PM

I wouldn't be happy with only one watt either; like you, sometimes I listen loud. In my friend's situation he's on a budget, and a $109 amplifier that sounds pretty good at moderate levels is a keeper.

Originally Posted by VolvoHeretic

Sorry guys, but my son took it apon himself to take my 15 years dead Crown 150 wpc DC300A with him over Christmas and just reported that it is breathing again. Just have to send in my Stax SRA-12S pre-amp, send in my 416-8A woofers for recone, and get a matched pair of pascalite diaphrams to get the A7-500s back in shape, and I will be back to rocking 120db music. Nothing beats POWER. You can keep your 1 watt, I also listen to my stereo outside, in -30 below temperatures when no one is around to call the police.

**MerlinVSM** · January 26th, 2013, 01:10 PM

Originally Posted by fpitas

I wouldn't be happy with only one watt either; like you, sometimes I listen loud. In my friend's situation he's on a budget, and a $109 amplifier that sounds pretty good at moderate levels is a keeper.

Note, recommedation for the power amplifier I am looking for will only be used with the Altec 511B horn(s) not for the woofer(s).

How much power is needed and how much, may be too much ?

**Altec Best** · January 26th, 2013, 01:48 PM

One thing would always concern me with a low power amp (especially 1W) is. Driving the amp into clipping,which would be very easy to do with a low power amplifier.