[bhobba]

I think its very important to get speakers that don't have wild impedance swings.  My speakers are an easy to drive load and even though they are about 90db sensitive my 8W Trafomatic Set drives them just fine - surprisingly so:
http://www.audiocircle.com/index.php?action=gallery;area=browse;album=5463

This was back in the days when I used a 15W Leben - now I use an 8W Trafomatic SET.

Thanks
Bill

[FullRangeMan]

nice set amps can be made w/6c33c tubes.  and 6c33c tubes are not expensive.  but some of these really are not low power amps.  i have a pair of audio mirror 6c33c amps that are relative bargains, imo, but at ~40-45wpc, they don't technically qualify for this circle.  that's what having a pair of 6c33c's per channel will do.     audio mirror makes another amp, similar topology, w/6as7 tubes; for 20wpc:
doug s.

I wonder If you could run your AudioMirror 6C33 in summer version, with only one 6C33?? (by umpluging one tube supply) to listen a SET amp.

[doug s.]

I wonder If you could run your AudioMirror 6C33 in summer version, with only one 6C33?? (by unplugging one tube supply) to listen a SET amp.

not sure if the amps could be run w/only one power tube, but, even then, the amp would still idle at over 300w, and a pair of single-tube 6c33c amps would still throw off a lot of heat...

i have several low power single-ended amps to choose from, but these are only making ~5wpc, so speaker choices are certainly different.   

doug s.

[seldenr]

Fantastic thread Josh:
I spent about 4 years looking for the right speakers and went through some typical subjects (NHT, Coincident, Audio Physic, Dynaudio, Reference 3a) until I heard the Avantgarde Duo Omega (NOT the original Duo, which did not integrate well at all) in Singapore.  I bought a pair and was never happier.  Then sold them due to change in room.  BAD idea.  Wish I had them back.

As I recall they were/are 107db sensitive with 14 ohm nominal.  The interesting thing (to me and maybe to some others) was the year-long search for an amp.  I still play music as often as I can (amateur status), so I value dynamics, accurate timbres and that elusive sense of presence. 

So I spent some money buying several amps and begged and borrowed others so I could have as many amps as I could get in my room at one time.  Here is a general summary of the amps and winner.  And no, I do not have anything to do with the winner, no affiliation, etc.  Just one guy's (ok, three, since I had other musician friends come repeat my test) opinion.

I really, really wanted to like the Cary 300B monoblocks the best, but although they were gorgeous in the midband, they had little bass and little high end.  So I tried the Bel Canto 211 based amp.  Similar midband, better bass, but not transparent.  A little like some mist between the musicians and me.

Tried (and also wanted to like) the Consonance 845 based monoblocks, but again could not make them sound as realistic as I would like.  What was great fun was the little Berning ZOTL headphone amp (I think about 1.5 watts) that worked fine.  Not in the running, but it was interesting that such low wattage was sufficient.

Then up next was the Art Audio PX25.  In less than 2 seconds both myself and my sax-playing non-audiophile buddy stood up and said "that's it!!"  It had realism that we could not believe.  At 6 watts total we could only get the preamp to about 11:00, and it was throwing us out of the room.  Bass?  I thought the amp must have a solid state driver (even though the Avantgardes have a powered sub the bass always reflected the essence of each amp, which was interesting).

Horns sounded so real, and kick drums felt like you were in the same room.  There was one particular sax solo on a Gordon Goodwin DVD-A disc that, with eyes closed, you would almost swear was in the room.

Next up was the version 2 of Audiopax KT88 based monoblocks.  They were also terrific, and probably came in 2nd (as much as I wanted to 300B to win, and KT88 tubes have never done much for me).  But it still did not have the clarity, live factor, dynamics or natural timbre to the instruments as the PX25.  By itself it was fantastic, but side by side was not in the same league.

Was it the Art Audio or just the PX25 tube itself?  I don't know and hope someone else might have experience with other PX25 amps.  I do know Art Audio's claim to fame is their proprietary transformers which they say are made in-house. And that is a big factor as you have pointed out.

My $0.0002 opinion of the combination.  And would love to hear if anyone has tried any other PX25 based amps.

[Shogun]

If money is not a issue and want something better than a Lowther without their weakness.

Rethm Trishna, a 6,5 inch wideband and dual woofers. 2w is enough because the woofers are handle by its own amplifier.
http://www.rethm.com/trishna_details.html

Feastrex 5 inch fullrange alnico driven by the Feastrex 10w amplifier. Impressive!
http://www.miketangaudio.ca/Feastrex_Product_Information.pdf

I haven`t heart it, but a owner of Festrex said the fielcoil version, it is something.

[DaveC113]

If money is not a issue and want something better than a Lowther without it`s weakness.

Rethm Trishna, a 6,5 inch wideband and dual woofers. 2w is enough because the woofers are handle by its own amplifier.
http://www.rethm.com/trishna_details.html

Feastrex 5 inch fullrange driven by the Feastrex 10w amplifier. Impressive!
http://www.miketangaudio.ca/Feastrex_Product_Information.pdf

I haven`t heart it, but a owner of Festrex said the fielcoil version, it is something.

Those are both very good choices, the Feastrex drivers are very, very impressive... it's been a while since I heard them, last time was at RMAF a few years ago where they were used open baffle with a subwoofer and active EQ. It was one of the best systems I've ever heard, but not exactly cheap.

For those on a budget, I haven't heard a better value in single driver speakers than Omega. I have the 4.5" XRS model driven by an EL34 SET in triode mode with no feedback. It makes ~5 wpc. For $4-5k a pair of Omega speakers with Omega sub and something like a Decware EL34 SET amp approaches some seriously high dollar systems costing 10x the price.

[Docere]

Hi all,

Disclaimer: I do not own a low power system, but have been reading, loosely researching and contributing to discussions about them for a while. I am finally having a system built: GPA 604-8H-III in a Scott Lindgren designed MLTL; I will build the amps (firstly, an all film-cap version of the 6c6 – 2A3 Radiotron amp; secondly, an optimised direct-coupled version, using low DCR power supplies etc.). So, please take my opinion with this in mind.

Firstly with regard to SET amplifiers, it is not simply the low power and variation in the ‘reflected’ load that provides a challenge, but also the high output impedance/ low damping ability (this is more important, I think). High sensitivity addresses the power challenge; relatively even impedance and minimal phase angles address the reflect load challenge. Plenty has been discussed and written about this.

Driver Qts is another factor that has been discussed in detail by the likes of Nelson Pass and others, yet still seems to be ignored by most folks. Qts is a measure of the driver’s ability to damp itself – to control / stop itself. The lower the Qts the greater the driver self-control. Speaker system Qtc refers to how well the speaker system – cabinet and driver combination – is damped, which relates mostly to bass performance (lean, dry, just-right, soft). The lower the value the more damped the system. A zero feedback SET amp has high output impedance and offers little control over a driver / speaker system; an ideal speaker system should not need much control from the amplifier. If you have an efficient speaker that sounds slow, soft… boring, it may use a mid-high Qts driver and/or be not well enough damped.

I have only touched briefly on the few factors especially relevant to speakers for low power high output impedance amplifiers. Of course, then there are other factors relating to the design of speakers in general. Speakers designed for ideal operation with low output impedance solid state arc welders amplifiers are not likely to be ideal for high output impedance amplifiers; they might work OK, but…

I opted for a custom design so that I would have a greater chance of success. I can’t tell you how well the system works because I have neither the speakers of the amp yet. Give me time.

Cheers,
Raymond

[planet10]

... GPA 604-8H-III in a Scott Lindgren designed MLTL

I'm familiar with that design , you must be from down under.

Driver Qts is another factor that has been discussed in detail by the likes of Nelson Pass and others, yet still seems to be ignored by most folks. Qts is a measure of the driver’s ability to damp itself – to control / stop itself. The lower the Qts the greater the driver self-control. Speaker system Qtc refers to how well the speaker system – cabinet and driver combination – is damped, which relates mostly to bass performance (lean, dry, just-right, soft). The lower the value the more damped the system. A zero feedback SET amp has high output impedance and offers little control over a driver / speaker system; an ideal speaker system should not need much control from the amplifier. If you have an efficient speaker that sounds slow, soft… boring, it may use a mid-high Qts driver and/or be not well enough damped.

This is almost right. What you are interested in is a low Qms, the abilty of the driver to damp itself. For the more graphic minded, the shape of the LF resonance peak is small (wide helps too)

dave

[Docere]

Hi Dave,

Great guess - yes, from Australia. I am not surprised you're familiar with the design: you did a wonderful job of drawing it up (and I would not be surprised if you contributed a little to the design as well). I am very eager to hear it. The build is coming along nicely; Ben does some very nice work, as you may know from his Frugal builds. He would not compromise my build to get it done quickly and I am thankful. I will post a progress pic in one of the relevent threads here.

Thank you for the clarification and being specific about the mechanical damping component (suspension-related) of the Qts (ie. Qms). Your comment about the impact on the resonance peak is very helpful and makes practical sense to me.  Do you think the electromechanical damping needs to be considered with regards to being driven by high output impedance amps?

One of these days I'd like to learn more about this stuff; in the meantime we have folks like yourself and Scott making it easier to build high quality systems that I could otherwise only dream about.

Cheers,
Raymond

[Lefatshe]

What's amazing about this discussion is the original question asked about speakers and about 80% of the posts are about amps.

Yes, low watt amps are great, but what are those speakers that have the right sensitivity, right impedance curves, etc. that are able to make wonderful music with low watt amps (let's say below 12 watts)?


(Yes, I will see if there are more up-to-date discussions, or post a new question.)

[JLM]

What's amazing about this discussion is the original question asked about speakers and about 80% of the posts are about amps.

Yes, low watt amps are great, but what are those speakers that have the right sensitivity, right impedance curves, etc. that are able to make wonderful music with low watt amps (let's say below 12 watts)?


(Yes, I will see if there are more up-to-date discussions, or post a new question.)

Not amazing when you consider that this is a "low wattage" not a "high efficiency" circle, so the orientation is amps versus speakers.  And my experience bears that out.  Too bad because the real challenge of low wattage amps is finding good, affordable speakers.

[Guy 13]

Hi all,
I own a Decware SE84C+ (2wpc) driving a Omega 7F (Open baffle dipole) and I am very happy with it,
probably my last system before I kick the bucket.
The Decware and Omega are a very, very good match
and the smaller size Omega speakers are very affordable.
I would also recommend (Even if I never heard one) the new Wright Audio mini el84 at 795 USD.

Guy 13

[planet10]

For the last couple months i have been using a pair of Pass Amp Camp Amps. They are 5w/channel and i have been amazed that they are sufficient to drive almost any speaker in my stable (84-92 dB) to satisfying levels (except the lowest efficiency at louder than normal levels). Kits (stereo pr) are $300 at diyAudio.

dave

[fritzspeakers]

Besides efficiency ratings, you do want to look at the impedance and phase curves of the loudspeakers to get an idea of how well they will work with any given tube amp.  The smoother the better.  Unlike a solid state amp, I believe tube amps will put out more power at higher impedance loads.  If there is a big bump, it will result in an uneven frequency response.  Also, a complex crossover with many parts & large coils isn't good for lower powered amps.  Simple first order series crossovers usually work very well on speakers driven by tube amps.

Here is a link to an article written by Steve using an 8 watt 300B Audio Note amp that he built from a kit with a pair of my loudspeakers with series crossovers with paper based mid/bass drivers.

https://stevefolberg.wordpress.com/2015/08/25/equipment-review-the-fritz-speakers-carbon-7-se/

Happy listening...  Fritz

[planet10]

Unlike a solid state amp, I believe tube amps will put out more power at higher impedance loads.  If there is a big bump, it will result in an uneven frequency response.

That is a generalization based on the more typical output impedances of tubes & solid state amps. SE solid state amps typically have higher output impedances so you have take the same care looking for a speaker with a smooth output impedance.

dave

[Duke]

Yes, low watt amps are great, but what are those speakers that have the right sensitivity, right impedance curves, etc. that are able to make wonderful music with low watt amps (let's say below 12 watts)?

Daedalus and Omega are "locals" that come to mind.  Vapor also has a couple such models, as does yours truly.  Danny Ritchie of GR Research has done some excellent high efficiency SET-friendly speakers in the past, check with him as well.   

I agree very much with the posts above that suggest the shape of the impedance curve is particularly important.  Fritz gives the example of an 88 dB speaker that worked well with 8 watts, which on paper looks like a mis-match but the impedance curve was benign and so it worked fine.   Unfortunately this isn't something that is apparent from a spec sheet, so best to contact the speaker manufacturer if you have questions about compatibility with your particular amp. 

[FullRangeMan]

Duke,
What is the effect from the inductance on a low watt tube amp?
The driver is a 12'' 98dB 1mH wide range.
Thanks

[luckyguy]

I've been listening to my 500 htz salad bowls by Edgarhorn hooked up to TAD 2001s with a parallel 2A3 amp putting out 4.5 watts for the past 6 months.  Experiencing my old 802D Altec drivers with 511s and a history with a pair of 604Cs with a Yamamoto 45, a 6 watt 300B and a 3 watt 2A3 as guides, I would guess the TAD/Edgar combo puts out at 110 db @ 1 meter.  Mids and bass comes out of a pair of A5 boxes dinked by Altec 515s and powered by a heavily modded set of Heath W6ms with original outputs.  Sound is absolutely effortless and represents my best efforts so far in recreating realism.

[Duke]

Duke,
What is the effect from the inductance on a low watt tube amp?
The driver is a 12'' 98dB 1mH wide range.
Thanks

That seems to me like a fairly high inductance for a wideband driver, unless it's a 16-ohm driver. 

Relative to being driven by a solid state amp, I would expect to get more top end from that wideband driver when driven by a low watt tube amp, assuming the amp has a fairly high output impedance (low damping factor), which is generally characteristic of designs that have little or no global negative feedback.

[FullRangeMan]

Thanks Duke for your honest reply.
The driver is this pro audio:
http://lsv-achenbach.de/daten/beyma/bey_12G125.pdf
The inductance is at the botton left.