Thoughts about First Watt F1: am I right?

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Thoughts about First Watt F1: am I right?

Recently I read a lot about the F1 from First Watt and was impressed by the idea to supply current instead of voltage to the speaker. The advantage is clear. Current is proportional to the movement of the speaker so delivering current from the amp would give quite a better result than delivering voltage. Also parasitic effects like resistance and inductance of wires and the voice coil will be of no importance any more. So far the theoretical basics.

As we all know it is impossible to realize ideal voltage or current sources. Both of them have internal resistance. Each real world voltage source delivers - as we all know – only a limited amount of current. Also real world current sources have a limitation in output voltage.

From theory we also know that a real world voltage source can be composed of an ideal voltage source with a resistor in series (Rs) and a real world current source can be composed of an ideal current source with a resistor (Rp) in parallel. We also know from theory that a real world voltage source with its resistance Rs could be substituted 1:1 by a real world current source with Rp = Rs.

Now back to the F1. It is real world current source with Rp = 80Ohm. Using a speaker with 16Ohm this leads to a damping factor of 0.2. As I read the F1 with a fullrange speaker leads to a very good result for the mid and high region and a very undamped bass.
My system is an active F.A.S.T. (Usher 6-channel poweramp, AER MD 1B as open baffle 16Ohm) http://freerider.dyndns.org/anlage/images-ripol/RIPOL-Prototyp.jpg x-overed at 100Hz so bass should be no problem. But I have no F1!

No problem! Accordingly to the theory above a voltage source (e.g. conventional amplifier) with a series resistance Rs of 80Ohm should give the same result. Interesting isn’t it? All you need to do is increase the amplification of the fullrange accordingly to the loss of power over Rs. For 16 Ohm speakers the output voltage has to be increased by factor ????.

Those 80Ohm seemed to be a lot so I started with two 15Ohm power resistors I bought today. Before installing them I made a frequency measurement. Then I increased the amplification by 6db inserted the resistors and measured again. With the resistors installed I got nearly the same frequency response but above 3kHz the response increases linear up to +4db at 20kHz. Interesting isn’t it? Inserting Rs leads to better mid and hight performance!!! With the Rs of 15Ohm installed the damping factor is decreased down to 1.0 lower than most tube amps.

Then I sat down and listened while switching to and forth between the two configurations. The improvement was really tremendous. I heard things I never heard before. Listening the Friedmann SACD the strokes to the strings of its guitar were astonishing real, much more live than before. Also the room got more width and depth. Female voices got much smoother. I gut the impression a curtain was removed playing over the serial resistance. I had the impression the full range really played freed and much more open.

Now the electronic store is closed so I could not test the 80Ohm alternative :-(

The first test was really encouraging. So may this be the final solution to improve mid and high quality. Just take a big conventional amp (you need power to compensate for the voltage loss over the 80Ohm resistor) and a series resistor to reduce damping factor and therefore provide current instead of voltage to the chassis.

What did you think about my thoughts? Am I right?

Charly
 
Think about it!

As you change the output res. your speaker will gain more level
in the mids or highs because your impedancy is rising (inductivity from the voice coil).
When you read nelsons papers, you will see that you could adjust
is with a R-C parallel after the "output Resistor" in your case 15 or
80 Ohms.
Hope this helps.
Andreas
 
Charly,

F1 is the absolutely best amplifier for fullrange speakers.
I listended my F1 clone by AES in Kassel ( http://www.aes-kassel.de/breitband.htm ) with Oris horns and AER speakers.
I listened Fostex FE206E too . It was a short decision, I´m owner of a pair Fostex ! (The AER are expensive...) I built the Fostex in my old enclosures and I listened the whole night! I heard things the I have never heard bevore. Crazy! Have a look here: http://www.diyaudio.com/forums/showthread.php?postid=758536#post758536

Man, you should build F1 and you have with the AER´s the best system which you had.

Best Regards
Adam
 
SY said:
You can make it as efficient as you like. Using a resistor is a nice let's-see experiment, but not the way an amp should be designed.
Current amps have big advantages right! The way I tried it is ineffcient true. But I have a power amp with more than 100 Watts so what?
The question for me is: Is a current amp with 80Ohm the same as a voltage amp with 80Ohm? Theory says yes. If you say no where is the difference?
 
That's a pretty inefficient way to do things.
I made some calculations. Take a voltage amp delivereing 100W in 8Ohm. Such an amp outputs aprx 29V. Using a resistor Rs of 47Ohm and speakers with 16 Ohm you will loose aprx. 10W over Rs and have aprx. 5W at the speaker. If 5W are enough this approach seems not to be that inefficient. In this case damping factor will be 0,34!
My point is: There is no true voltage and no true current amp on this planet. Each real amp is anywhere between. High damping factor meens the amp is more at the voltage side, low damping factor means the amp is more at the current side.
This also means tube amps (low damping) are more on the current side than on the voltage side. Despite destortions may this be a reason why they sound better especially at fullrange speakers?
 
Oehlrich, what I'm trying to say is that you can retain all of the amplifier's power by changing the way that feedback is taken so that it presents an 80 ohm (or whatever) output impedance without losing most of the power through a series resistor.

Certainly to the extent that highish source impedance will cause frequency response variations, that is an explanation of the different sound of some tube amps. Better tube amp designs have a low enough source impedance that this is much less of an issue and the explanation of sonic differences must lie elsewhere.

In my experiments, I found it quite easy to turn a pentode amp into a current source merely by removing the feedback loop, then knocking down the gain of the driver stage.
 
The one and only
Joined 2001
Paid Member
oehlrich said:
Current is proportional to the movement of the speaker so delivering current from the amp would give quite a better result than delivering voltage.

In general, the acceleration is directly proportional to the current,
and the "movement" is an integral of the acceleration. This tends
to work out nicely for cone drivers, as the excursion cancels flat
against the acoustic resistance.

Having said that, current source amps are not for most speakers.

:cool:
 
Mr Pass
workhorse claims that quasis are the best amps,infact he claims
they are better than the fully complementary and that professional audio is better than high-end or high-fi, As a professional designer I am stunned with this Guy, what are your views about this ,is great to see you back here, you are truly one of the best

As one of the great Legends of power amps, is distortion
taken seriously in your top of the range/premium commercial
products

Also this Guy advocates Class-D as the way to go for high-end
in the future what do you think about most efficiency vs least efficiency in
relation to sound quality, i can understand why as a PA amp
manufacturer having these views, but his claims about
quasi and class-d being better than class-a and high-end
to say the least in my views are ridiculous, what are your thoughts
on these claims



cheers
 
What? Nelson left? Silly me, I hadn't realized it.
For someone who claims to be a 'professional designer' I imagine that you're already familiar with the pros and cons of complementary vs. quasi-complementary output stages. As the expression goes,"You pays your money and you makes your choice." Why ask Nelson about it? The Alephs and XAs are quasi (from a certain point of view), and the X amps are complementary...and you expect Nelson to say one is always the best?
Does Nelson take distortion seriously? Have you bothered to read Nelson's posts?
Sigh.
Class D isn't ready for prime time. Whether it will be in the future is open to question. It's light weight, efficient, and small...all useful characteristics for road gear. Whether it's up to snuff as high end gear is another matter entirely. The time may yet come when class D amps sound as good as their hype...but in the meantime, you might conduct a survey of Nelson's product and count the number of class D amps that he is offering for sale.
For that matter, survey the product lines of all the high end manufacturers. How many class D amps do you see?
If you truly feel that another member's claims are absurd, then why ask for someone else to bolster your position? 'Professional designers' aren't swayed and dismayed by other peoples' opinions...especially designers whose signatures boast that they specialize in class A amps.

Grey
 
Re: Re: Thoughts about First Watt F1: am I right?

Nelson Pass said:
In general, the acceleration is directly proportional to the current,
and the "movement" is an integral of the acceleration. This tends
to work out nicely for cone drivers, as the excursion cancels flat
against the acoustic resistance.

Having said that, current source amps are not for most speakers.

Dear Mr. Pass thanks for craification. I run an AER MD1B in an open baffle so the F2 seems to be right for me ;-)
But please answer this question:
What is the difference of a current source amp terminated with 15 Ohm and a voltage source amp with 15 Ohm in the serial? With both I have with my speakers a dampinf factor of 1. Theory says there is no difference. Is this statement also true for amps?
Charly
 
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