If you cannot use SET amp, what is the best alternative amp for full-range single driver?

  • Solid-state amp with resistor to decrease damping factor

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Kreshna

...but I have to know.
Since the first time I read about full-range single driver loudspeakers --Fostex, Lowther, Audio Nirvana, and the likes-- I always wonder why single driver loudspeaker owners are mostly use SET amp or T-amp. Why do they never use traditional solid-state amp, for instance? Why does nobody drive Fostexes or Lowthers using traditional Sansui or Marantz solid-states?


1. Do full-range single driver loudspeakers only sound good with the purest, zero-feedback signal?

This is my first guess. SET amplifier is said to have the best signal purity, since it involves zero feedback. So it seems to me full-range single-driver loudspeaker sounds best with such pure signal, and will sound bad otherwise. And probably that's the reason people drive Fostexes and Lowthers using SET amp instead of traditional Marantz solid state amp.

But single driver owners also love to drive their speakers using T-amp; Tripath amp, which is class-D amp. And a friend of mine said all class-D amp, including Tripath amp, cannot function without feedback. So it seems T-amp does not sound as pure as SET amp.

So perhaps it's not about signal purity?


2. Do full-range single driver loudspeakers only sound good with warm, tube sound?

Since I never read about someone driving their Lowthers or Fostexes using Krell, McIntosh, or Bryston solid states, then probably full-range single driver loudspeakers only sound good with warm, tube sound.

However, people also drive their full-range single driver using T-amp, which is not tube amp. On the other hand, I've never read about someone driving their full-range single driver loudspeakers using push-pull tube amps either --only SET tube amps.

So perhaps it's not about warm, tube sound?


3. Do full-range single driver loudspeakers only sound good with low damping factor?

This is my last guess. As Nelson pass has wrote on his article (PDF here), due to their high sensitivity, full-range single driver loudspeakers only sound good with low damping factor. An amplifier with high damping factor will cause the highly sensitive full-range single driver to suffer from overdamping, which in turn causes significant loss in low frequency, making the said speakers sound shrill and strident.

Apparently, both SET amps and Tripath amps have such low damping factor, that they do not cause overdamping on full-range single driver speakers.

Am I correct so far? Please correct me if I'm wrong.


4. What is current source amplifier? What is voltage source amplifier?

On his article I mentioned above, Nelson Pass use the terms 'current source amplifier' and 'voltage source amplifier' repeatedly. I have the impression that current source amplifier is an amplifier with low enough current and/or low enough damping factor; examples are SET amp and T-amp. On the other hand, voltage source amplifier is an amplifier with high enough current and/or high enough damping factor; examples are traditional amplifier like QSC or Bryston. A voltage source amplifier is good to control thick cone woofers with heavy materials, because it has strong current and high damping factor to 'grip' the woofer cone properly. However, it will kill the bass on Fostexes or Lowthers due to overdamping.

Am I correct so far?


5. Using resistor in serial with full-range single driver to drive them using traditional amps?

On his article, Nelson Pass suggested to put a resistor in serial with full-range single driver loudspeakers, in order to get good sound when driving them with 'traditional' amplifier (voltage source amplifier). As Pass has said:

"Most of the examples we will examine do not require true current source amplifiers, only amplifiers of quite high output impedances. Most of these cases will be happy with an output impedance of approximately 47 ohms or so and prefer 47 ohms loaded in parallel with the output of a current source. That being the case, you can build a Thevenin Equivalent of such a current source by placing a large resistor (here later referred to as R0) in series with the output of a high wattage voltage source amplifier and get similar results.

I’m not saying it will equal a spiffy First Watt F1 (being Class A and no feedback and all), and your resistor will run hot. On the other hand, you probably already have such a voltage- source amplifier and some of these speakers are quite cheap, allowing you a taste of these forbidden pleasures without high expense."


In fact, Nelson Pass has run simulations and created the appropriate table to suggest the resistor to be used. For example, the resistor to be used with Fostex FE206E is 47 ohm.

So, has anybody tried the solution? Has anybody ever tried traditional solid-state amps, like Sansui and Marants, to drive their single driver loudspeakers, using resistor like Nelson Pass has suggested?


6. Full-range single-driver loudspeakers for home theaters?

One may ask; why do I bother asking all these questions? Well, because Fostex FE206EN in double bass-reflex enclosure really stirs my interest. The double bass-reflex enclosure seems to be easier to make than the back-loaded horn solution, and it might be great for home theater. Single-driver loudspeakers seem to have very excellent stereo imaging and sound stage depth, so with a subwoofer or two, they could make really impressive speakers for home theater. In fact, Bose Accoustimass speaker set has such great imaging because each satellite speaker is point-source loudspeaker (single driver).

However, acquiring 5-channel SET amp for such home theater purpose could be difficult.

So which one is better? Building a sufficiently powerful 5-channel Tripath amp to drive five full-range single driver loudspeakers for home theater? Or drive them using traditional 5-channel amplifier like ATI or Emotiva with Nelson Pass' resistor solution?

How about using this amplifier with full-range single driver? It seems it needs Nelson Pass' resistor, because it isn't SET amp. However, the tube input stage is interesting.
 
I use SET because that's all I have, 3 to be exact. I'm gathering parts for a PP and we will see what that's like. You can use a resistor, a capacitor, or an inductor. Or all three together aka: notch filter on the + side of your FR driver.AN10 Filter.jpg
 
Ah yes, the BSC circuit. But Nelson Pass suggested a resistor in addition to BSC circuit when driving full-range single driver using traditional SS amp. Has anyone tried it?
 
single driv. w/ resistor? been done many times. Usually IMO is to add a small ohm to raise the speaker ohms to best match impedance or to stop a speaker going too low in ohms.. i.e. 4 ohms dropping to 2 ohms and clipping amp. Or flip is increase from 8 ohms to more european 10 ohms in some models with stated rated ohms.. just to get the specs in.

Single driver?
https://www.pinterest.com/pin/463307880387122436/?lp=true
Just for pics.. I did join but if I get nagged I'll dump it.
bink.
 
single driv. w/ resistor? been done many times. Usually IMO is to add a small ohm to raise the speaker ohms to best match impedance or to stop a speaker going too low in ohms.. i.e. 4 ohms dropping to 2 ohms and clipping amp. Or flip is increase from 8 ohms to more european 10 ohms in some models with stated rated ohms.. just to get the specs in.
How does it sound?
What SS amp models have you used to drive your single-driver?
And how much does a Nelson Pass' resistor reduce sensitivity?
 
One thing might be because SET is a class-A type, which doesn't have any weird kinks when the waveform gets very low near zero amplitude (as class-AB amps tend to before feedback). Class D also doesn't do anything radical near zero crossings than elsewhere in the waveform.
T-Amps actually have very good damping factor at lower frequencies, their damping (and response) only goes to heck up near the top of the audio band.
 
On his article I mentioned above, Nelson Pass use the terms 'current source amplifier' and 'voltage source amplifier' repeatedly. I have the impression that current source amplifier is an amplifier with low enough current and/or low enough damping factor; examples are SET amp and T-amp. On the other hand, voltage source amplifier is an amplifier with high enough current and/or high enough damping factor; examples are traditional amplifier like QSC or Bryston. A voltage source amplifier is good to control thick cone woofers with heavy materials, because it has strong current and high damping factor to 'grip' the woofer cone properly. However, it will kill the bass on Fostexes or Lowthers due to overdamping.

Am I correct so far?

I'd look at it this way.

A single driver will typically have an impedance peak at the low end, at it's resonant frequency, and will rise again at the high end.

A voltage amp with a high damping factor will deliver current relatively independent of the impedance of the speaker, but a current amp with a high output impedance will deliver lots more current into a higher impedance, so it will extend the bandwidth to some degree, delivering more current at the low and high end where it can help in that respect.

A compression driver is another good application for a current drive amplifier. impedance rises as it rolls off on top.

The problem with current amplifiers is that you have to know the speaker and how it works with a given amp, especially if somewhat flat response is a goal. Crossovers totally complicate the situation and are best avoided with very high output impedance current amps.

Low damping factor is useful for commercial amps that will be used with various unknown speakers.

Non feedback SE amps will have a moderately highish damping factor as voltage amps having some current amp characteristics. with a couple ohms output impedance.

I once enjoyed a demo of the same $50000 300B SE amp that our engineers set up with a switch for voltage amp (maybe 2 ohms out), currrent amp (maybe 30-50 ohms output Z), and a setting somewhere in between. Speaker was a field coil Western Electric TA-4165 12" full range from the early 1930s in a big horn baffle. Current amp operation was more organic, more extended, more open and had a lot more richness, bloom, and texture. Voltage amp was a little tighter and more controlled, not as psychedelic. The current amp setup was very intriguing, for sure.

Manipulation was via changes in a current feedback circuit. Not something that could be applied to typical amp circuits.

Unfortunately, it was not something that we could sell because who knows what speakers users will hook it up with?

If i wasn't so darn lazy I would have built the current amp 2A3 SE I've been planning already. Should be just the thing for my single driver collection.

Older speakers tend to have more restorative/self damping force built in and light paper cones with less inertia, so they work well with higher output Z/less damping factor. Heavy, more compliant speakers need that damping factor or else they flub out.

A current source amp requires more of a systems approach overall. it is a toy for nerds not the shelves at Best Buy.

I used a cheap SMSL T amp on a few different 8" full range drivers and a pr of Snell Ks and it was remarkably good. Still have it set up on my Snell Ks in my computer room. The speaker terminals on most of my cabinets cost more than the amp! I think this is not a bad way to go in general. Depends how exotic and $$$ you want to get, but I listen to this modest setup a lot and it does the trick.
 
Very interesting. By the way, how about tube push-pull with full range single driver? Anyone tried it?
 
Very interesting. By the way, how about tube push-pull with full range single driver? Anyone tried it?

I have many many times. I'm listening to 755As with a Dyna SCA35 right this minute. Quite good matchup. The Dyna was not so impressive on the 10 and 12 inch versions of the same speaker line. Why? Who freakin knows? I had a Dyna ST-35 on 12" 728Bs before and I thought it worked great at the time. Every case is different, even when it is not THAT different.

The SE vs. PP question is independent of the damping factor question. However, feedback vs. no feedback impacts this consideration greatly.

for example, the Western Electric 124, which could be called a stock amp for the WE 755A single drive features PP 6L6 with no feedback in the output stage. Output impedance is listed as 1/4 of the nominal tap impedance, in other words moderately high. The same tubes could have a quite low output Z with global feedback introduced.

As always, one must be careful of generic abstract categories like SE, PP, single driver, etc.

My Altec 755As respond well to power and come alive even more in some respects with a beefy amp. I have a pr of Pioneer PIM rated at 6 watts max. Those suckers might catch on fire if I pump 20W into them.

A PP amp can be 2W or 60W. A full range driver can be a delicate flower or a manhole cover. These are non-specific terms but somehow they accumulate huge masses of rule of thumb overlay that obscure the individual character of every real implementation.

Like I said above, a systems approach is often mandated. One must consider the details of specific setups. And even then, you often can't know anything until you try it because in audio, history. i.e. specifiic unique experiences, trumps mathematics and abstract rumination..
 
.... awww, I'd pay you to write! ;)

SCA-35, eh? There's one of those upstairs (no 755s, though). Stock circuitry?
Sorry for the thread diversion!

EDIT:
PS: Remember All generalizations are false, including this one.

:)
 
Send me the ST-35 and I'll write about it. Promise! :rolleyes:

As a Philly boy, i have a soft spot for Dyna gear. The ST-35 was my favorite model. I don't own any Dyna now except the SCA35 I just picked up. Gave a PAS to a dude in Latvia a few months ago. Most Dyna tube gear is decent if not outstanding in any way.

You never know until you try something out, especially with single driver setups which can be somewhat idiosyncratic.

Trying different things is part of the fun and definitely educational. That's how I learned that it is impossible to generalize.
 
You never know until you try something out, especially with single driver setups which can be somewhat idiosyncratic.

Trying different things is part of the fun and definitely educational. That's how I learned that it is impossible to generalize.
My single driver speakers aren't supposed to work well with mere milliwatts of power behind 'em. I'm glad I tried it.

On the flipside, my wimptastic amps sounded like pure, unadulterated crap on my buddy's speakers, which are also efficient, fullrange drivers. I'm glad we tried that, too.
 
My single driver speakers aren't supposed to work well with mere milliwatts of power behind 'em. I'm glad I tried it.

On the flipside, my wimptastic amps sounded like pure, unadulterated crap on my buddy's speakers, which are also efficient, fullrange drivers. I'm glad we tried that, too.
Think of how boring this hobby'd be if that weren't the case!
The fourms would be full of nothing but "Is it OK to connect two amps to one pair of speakers?" posts.
Oh -- wait...

;)
 
About TPA series (TPA 3116, 3110, dsb), do they have low enough damping factor to work well with Fostex single-driver?
 
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