Class A V vs SET Vs Push/Pull....newby interested in Tube Amps

[mattjtaylor2809]

From my very limited listening to tubes I prefer the Class A SET sound & the LM @ 48 watts could just be enough to control my big Dyn's but when we hooked it up to my Ayre Pre as a power amp, something went missing in the sound?

 

It could be the output gain in the standard Ayre KX-5 pre & 6 months ago I was going to install a different resister which should give me a 3-6 dB bump in gain.

 

From Ayre...

 

"We use non-ferrous PRP brand resistors and either 1/8 watt or ¼ watt. But you could use ½ watt too. It’s been my experience that the higher wattage resistors sound ever so slightly warmer than the smaller wattage… But they all sound fine."

 

I bought x4 of the 1/2 watt from this crowd in the UK but I've not installed them as yet, but as I have a bit of time on my hands, I'll do this tomorrow.

 

https://www.hificollective.co.uk/components/tantalums.html

 

Replace the resister where the red arrow in pointing which is the output resister.

 

From the Ayre Manual...

 

6 hours ago, Ooogh said:

Did you get a chance to hook the Ayre preamp up to the LM Matt.?  That would be a very interesting exercise. To give some context, Matt’s Ayre preamp makes my AudioNote M5 sound broken....it is an absolute beauty in my opinion.

 

Anyone in Adelaide with a big Audio Research or VTL power amp? Given your listening preferences and power requirements I figure they might just hit the spot.  Then again we all know that in the end @Tubularbells just needed a shed full of SS power! 

Hugh - Thanks for the complements on the KX-5 Pre....I do agree it's a special piece of equipment. In terms of a suitable power amp, I think it's more to do with having the ability to grip & control my speakers which from listening to the LM-805iA suggests Class A & SET....or if not SET, one of the better designed SET in parallel designs, or maybe it's a 805 sound?

 

Keen to listen to Audio Research & VTL, also Icon Audio MB150's or MB90 Mk2...but not sure how much of this I'll get done over the coming months as I think we've all got more important things on our hands (so wash them!!).

 

Stay Safe everyone

Matt

 

BTW - The PrimaLuna EVO 400 is pretty nice, just not special but I have it for the rest of the week so I'll give it a bit more of a run.

 

 

 

 

Edited March 23, 2020 by mattjtaylor2809
attactments

[Gryffles]

Seems you have been bitten by the SET bug. 
Might not be a factor for you but did you play a wide variety of music?

If you listen to the likes of Metallica and or large scale classical it is here that a SET amp will fall apart. And more so with multi driver speakers with crossovers.

Cab be deceiving as it will still sound nice but the sound stage will collapse, bass will be muddy and the sound overall will be compressed.

Im not trying to put you off at all, my main amp for the best part of 10 years is a 3.8w SET 2A3, just a suggestion 
 

[Steffen]

9 hours ago, andyr said:

 

Shirley ... always (or rather - only) used to lower distortion measurements!

 

That sounds a bit cynical. It's not used to lower distortion measurements but to lower distortions. Global negative feedback also improves linearity and stability, and lowers gain (which is why you don't often find it in low-gain amps).

[sir sanders zingmore]

On 11/03/2020 at 5:56 PM, mattjtaylor2809 said:

Is this what you mean??

 

Dynaudio claims 88dB sensitivity for the Focus 380, a specification which accords well with our measured pink noise figure of 87.8dB.   Although this is on the low side for a speaker of these dimensions it still requires a nominal 4ohm impedance to achieve it, a figure entirely in accordance with our measured minimum modulus of 3.5ohm. Impedance phase angles are sufficiently high to result in a minimum EPDR (equivalent peak dissipation resistance) of 1.6ohm at 75Hz, so the Focus 380 is a moderately difficult load to drive without being a pig.

 

So if my speakers drop down to 1.6 Ohms at 75Hz, what effect will this have on my selection of valve power amps, if any?

My understanding is that some valve amps have a varying frequency response into different loads - particularly if the load is low (and 1.6 ohms is very low). So careful matching of valve amps is required. In other words, listen to the amp with your speakers first if at all possible

[mattjtaylor2809]

3 hours ago, Gryffles said:

Seems you have been bitten by the SET bug. 
Might not be a factor for you but did you play a wide variety of music?

If you listen to the likes of Metallica and or large scale classical it is here that a SET amp will fall apart. And more so with multi driver speakers with crossovers.

Cab be deceiving as it will still sound nice but the sound stage will collapse, bass will be muddy and the sound overall will be compressed.

Im not trying to put you off at all, my main amp for the best part of 10 years is a 3.8w SET 2A3, just a suggestion 
 

With the PrimaLuna I did think on occasion it struggled to keep up in either UL or Triode mode but I'm pretty sure it's new, out of the box & after a few days it seems to have settle down.

 

With @Grizzly Line Magnetic LM805iA we didn't notice any collapse of sound stage or the bass loosing definition, even at 95 db+ playing all types of music, from Tool, Metallica & some classical so at the very least, the 48 watts of class A SET supplied by the LM seems enough juice......BUT, this was using the LM as an intergrated, it didn't seem to sound agood when installed as a power amp but I'll hook it up again & try once I've installed the new resisters to increase the output gain from my Ayre pre.

 

Thanks for the heads up none the less.....I do plan to listen to as many amps as possible.

 

[aussievintage]

3 hours ago, Gryffles said:

If you listen to the likes of Metallica and or large scale classical it is here that a SET amp will fall apart. And more so with multi driver speakers with crossovers.

I think a whole lot of things contribute.    Getting a micro-line cartridge helped, so the stylus tip struggles on this stuff (if you are playing vinyl).  Valve preamps also helped a lot.   Interesting point about crossovers, but I also feel full-range drivers struggle with this stuff as well.

 

The other thing is that we tend to want to play these types of music subjectively louder.  Even if we play them at the same real volume as an acoustic jazz trio, it sounds like they are too quiet, so we turn it up.  Hence the low power of the SET amp means we are pushing it into higher distortion and it then struggles.

[RoHo]

2 hours ago, sir sanders zingmore said:

My understanding is that some valve amps have a varying frequency response into different loads - particularly if the load is low (and 1.6 ohms is very low). So careful matching of valve amps is required. In other words, listen to the amp with your speakers first if at all possible

Any amp with low power will struggle to supply the current demanded by such a low impedance.

Also if the speaker impedance has large swings any amp with a high output impedance/low damping ratio will have its frequency response modulated by these impedance swings.  GNFB lowers the output impedance and so feedback-free amps will likely have high output impedances.

Typical ported loudspeakers have large impedance swings in the bass area unless the designer has put particular effort into reducing these swings, which is unlikely.  So I'm wary of using low power valve amps with such speakers.

[mattjtaylor2809]

This has always been my understanding, i.e. big SS amp do better with Dyn's so I never really bothered to investigate tube amplification.....but then I demo'd the LM-805iA I was just surprised how good everything sounded (bass weight, definition, holographic sound, huge soundscape, warm cuddles) with the 48 watt Class A SET it got me excited about tube amplification.

 

What I don't want to do is spend $$$$ on a high powered tube amp that ends up sounding like a SS amp, so if I'm going to go down this road, I do need both the power to control my Dyn speakers with the tube sound (whatever that is...!).

 

I think the Icon Audio monblocks maybe the ticket as they say they're Class A front end so this should give me the juice on tap for big dynamic swings??

 

Specifications and Features

- Comprehensive manual supplied
- All hand wired point to point
- Class A, all Triode front end
- Output Ultralinear (110W) or Triode (60W) switchable*
- 4x KT120 matched valves (per pair)
- 2x 6SL7 2x 6SN7 driving valves (per pair)
- Signal to noise level -90db
- Frequency response 20hz-20kHz +0 – 0.5db
- THD typically less than 0.1% 1khz
- 4 & 8 ohm loudspeaker taps
- Beautiful valve cover included in the price
- SCR hi fi audio capacitors
- Silver plated pure copper PTFE audio cable
- Tertiary winding output transformers
- Big custom wound PSU with Choke
- Gold plated Input & speaker terminals
- 450mv (high) & 950mv (low) input sensitivity.
- 230/240volts 200watts approx
- Consumption: 38w standby, 88w quiescent, 200w Max
- C E, ROHS

[aussievintage]

10 minutes ago, RoHo said:

Typical ported loudspeakers have large impedance swings in the bass area unless the designer has put particular effort into reducing these swings, which is unlikely.  So I'm wary of using low power valve amps with such speakers.

 

I just found this resource  http://education.lenardaudio.com/en/12_amps_8.html     which has quite a good analysis of the situation of valve vs SS driving speakers

 

Quote

Current drive as with most valve amps is best suited to sealed critically damped speaker cabinet designs, with constant impedance passive crossovers, and active systems where each amplifier is matched to its speaker.  

 

[mattjtaylor2809]

Another option maybe the Icon Audio MB150?

 

Specifications and Features

•  Comprehensive manual supplied
•  Full instructions for valve change included
•  All hand wired point to point
•  No printed circuit board to ‘colour’ sound
•  Class A, all Triode front end
•  Output circuit Ultralinear or Triode switchable*
•  8x KT90/KT120′s precisely matched for best performance
•  4x 6SN7 phase inverter valves
•  Standby switch to prevent cathode stripping on startup
•  Standby switch to save valve life and power.
•  Optional automatic HT delay to prevent cathode stripping
•  150w RMS continuous per channel
•  100 Watts RMS in Triode mode
•  Signal to noise level -100db
•  Freq response better than 20hz-20kHz +0 – 0.5db
•  Total harmonic distortion typically less than 0.1% 1khz
•  4 & 8 ohm loudspeaker taps
•  Japanese steel EI transformers with low oxygen copper
•  Attractive valve cover included in the price
•  High quality 2W metal film, & wire-wound resistors
•  Blue LED mains indicator
•  Polypropylene audio capacitors
•  Silver PTFE audio cable
•  Custom hand wound output transformers
•  Big custom wound PSU Choke
•  Ceramic valve holders for minimum leakage
•  Centre tapped heater circuit for minimum hum
•  ‘Soft start’ device incorporated
•  Gold plated Input & speaker terminals
•  400mv (high) & 1200mv (low) input sensitivity.
•  230/240volts approx (115v available)
•  Consumption: 60w standby, 130w quiescent, 300w Max
•  CE, ROHS, WEEE compliant where applicable
•  Size in mm W200, D523 (560 overall), H195 (218 inc cover), 22kg ea. (For shipping cm: 36x32x66 (2) 25x31x42 52kg)

 

Anyone had any experience with either of these mono blocks from Icon?

 

Cheers

Matt

 

PS - I'll have a read of that article comparing SS with Valves.

[doogie44]

I love valve amps of all kinds. For years I drove my Artemis EOS speakers (88.5 dB sensitivity; 6 ohm minimal impedance) with VTL 300W monoblocs (ultralinear), then VAL 211 monos (20W output SET). All good. Then when using Magneplanar 1.7s I found that the current requirements meant that only the Wyred4Sound 1000W class D into 4 ohms was satisfying. Still always using the Leben valve preamplifier. Must have valves in the chain. It took a lot of effort to convince myself that not having a valve power amp would be second-best. But the bigger ones are so expensive...and the re-tubing costs!!

 

My point is that even with the best SET amps, as people have discussed here, you are going to encounter their output limits with speakers that make too great a demand on their current delivery. Yes, they can play at satisfactory levels but they can't provide much headroom. Surprisingly you do need this with some vocals and forte piano for a full sound. A valve pre + SS power 'might' be the better option.

 

Personally I would stick with the Line Magnetic 805 integrated (a magnificent amp and sound) and find the best speaker for it--but that's just me.

 

My 2c worth

[mattjtaylor2809]

My initial research was into changing over speaker to a higher sensitivity to give me more options...then for giggles I listened to the LM805-iA & this changed my mind but happy to look at both aspects.

 

The main issue with speakers is my limited selection in SA & the it's difficult to home demo whereas home demo'ing power amps is easier but I'll do whatever is best to achieve the best sound, even if that means a tube pre (PS Audio BHK??) with powered speakers like ATC?

 

Cheers

Matt

 

[cafe67]

Quote

Had a Giggle at this

 

[Guest deanB]

On 24/03/2020 at 10:06 AM, mattjtaylor2809 said:

My initial research was into changing over speaker to a higher sensitivity to give me more options...then for giggles I listened to the LM805-iA & this changed my mind but happy to look at both aspects.

 

The main issue with speakers is my limited selection in SA & the it's difficult to home demo whereas home demo'ing power amps is easier but I'll do whatever is best to achieve the best sound, even if that means a tube pre (PS Audio BHK??) with powered speakers like ATC?

 

Cheers

Matt

 

And slip one of these in between the Ayre preamp and the ATC actives (which can really rock).

Line Magnetic AS-123 buffer with transformer coupled balanced output.

[mattjtaylor2809]

Ok, what does this thing do, just it just give the signal to the active speakers a tube sound?

[andyr]

1 hour ago, mattjtaylor2809 said:

Ok, what does this thing do, just it just give the signal to the active speakers a tube sound?

 

It adds tube harmonics to the signal which goes into it.

 

Whether this delivers the same 'tubeyness' as having a tube preamp (and no AS-123 buffer) ... is the $64,000 question! 

 

Andy

 

[mattjtaylor2809]

Wow, that’s expensive .

 

I’ve now replaced the output resisters & thankfully all

is working well & I do

notice a bump in output without any discernible reduction in SQ, if anything it sounds clearer, more detailed but that could be the PL EVO breaking in?

 

Unfortuneatly I did get the chance to hook up the LM-805iA before @Grizzly, practicing the best social

distancing retrieved said amp for a demo in Melbourne, how rude .

 

anyways, enjoying the sounds with my Pre definitely a few notches lower in volume compared to the factor resisters.

 

Cheers all

Matt 

[mattjtaylor2809]

On 24/03/2020 at 10:25 AM, aussievintage said:

 

I just found this resource  http://education.lenardaudio.com/en/12_amps_8.html     which has quite a good analysis of the situation of valve vs SS driving speakers

 

 

Interesting summary.....

 

This fundamental difference of physics between Valve and Solid-state amps is rarely understood or referred to by the majority of self proclaimed audio experts, audiophile reviewers, text books, web sites or forums.   Almost all explanations about differences between Valve and Solid-state amps is based on romantic subjective twaddle.

 

 

 

[acg]

@mattjtaylor2809

 

I have SET amps.  I love SET amps.  I would not recommend SET amps unless:

1. The loudspeaker to which they are attached has been designed for a relatively flat impedance curve otherwise your bass response will be off.  Something like the locally produced Elsinores can be used with any amplifier of any output impedance (I've never heard that speaker).  Best results are probably to be had from horns.
2. or, you use multiple SET channels, as I do, to minimise the back EMF and other issues SET's can be burdened with.

 

If you are looking for a more forgiving SET amp, I would recommend something based on the Russian 6C33C tube.  It can be used to make about 17w of SET power before clipping, but the tube itself has a very, very low (for triodes) plate resistance which translates into a low output impedance, which is the secret sauce to compatibility with speakers.  My 6C33C channels have 0.19R output impedance and zero global negative feedback...that is as low a number as a lot of SS amps.  Still though, I think that 100dB/w/m sensitivity speakers are required to get the most out of SET's...my speakers are 110dB/w/m.

[Guest deanB]

On 25/03/2020 at 1:12 PM, mattjtaylor2809 said:

Ok, what does this thing do, just it just give the signal to the active speakers a tube sound?

It's designed to be an impedance and gain matcher between pre/amp and converts a single ended signal to balanced as well as to tame overly digital sounding sources. But yeah, I was suggesting it as a way to keep your Ayre preamp and add some valve/output transformer flavour to the chain.

Of course you can go with a valve pre but all ATC amps are specced at 10k ohms minimum input impedance so that limits valve preamp choices considerably because of the high output impedances of so many valve pre's on the market (see Stereophile measurements of Lamm, PrimaLuna and Cary preamps for examples). The nominal spec is not the full story! Audio Research are good enough to state a minimum amplifier input impedance when using their preamps (28k ohms?). CJ solve the problem of runaway output impedance by using a mosfet buffer in their preamps.

I'll eventually get ATC actives and that LM buffer will be front and centre, especially if I go with a preamp like this (15k ohm output impedance)-

Audio Space WE-300L 

 

Just joking! Or am I?

 

[mattjtaylor2809]

49 minutes ago, acg said:

@mattjtaylor2809

 

I have SET amps.  I love SET amps.  I would not recommend SET amps unless:

1. The loudspeaker to which they are attached has been designed for a relatively flat impedance curve otherwise your bass response will be off.  Something like the locally produced Elsinores can be used with any amplifier of any output impedance (I've never heard that speaker).  Best results are probably to be had from horns.
2. or, you use multiple SET channels, as I do, to minimise the back EMF and other issues SET's can be burdened with.

 

If you are looking for a more forgiving SET amp, I would recommend something based on the Russian 6C33C tube.  It can be used to make about 17w of SET power before clipping, but the tube itself has a very, very low (for triodes) plate resistance which translates into a low output impedance, which is the secret sauce to compatibility with speakers.  My 6C33C channels have 0.19R output impedance and zero global negative feedback...that is as low a number as a lot of SS amps.  Still though, I think that 100dB/w/m sensitivity speakers are required to get the most out of SET's...my speakers are 110dB/w/m.

My current speakers are Dynaudio Focus 380's which possibly dip down to 1.6 ohm at 75 Hz so I appreciate my speakers are more than likely not designed for valve amplification but they did sound the best I've heard them with the LM-805iA (48 watt Class A SET) & very close 2nd with a PrimaLuna EVO 400 (70 watt UL/38 Watt Triode) so this is what's confusing me.

 

I have written to Dyn audio & have asked them to better explain resistance Vs frequency response of my speakers & what tube implication they suggest, if any?

[Guest deanB]

You've demoed these amps in your environment @mattjtaylor2809 so trust your ears and endorphins.

The info overload may (partially) be the source of your confusion.

I have always theoretically thought that Dynaudio and se valve amps would be a no go but now that ain't necessarily so, is it?

If @Grizzly gets hold of the LM-150, give it a good go with your Ayre preamp. I've read the HiFi Advice LM amp shootout, the author rates the LM push-pull pair ahead of his own PrimaLuna.

You seem to have a bit of budget flexibility so if your initial impressions about the LM/Dyn interface change down the track, a solution shouldn't be out of reach.

Efficient speakers with their wide baffles and big bass drivers are making a comeback!

 

Heco Direkt and big brother Heco Dreiklang.

 

 

 

 

Edited March 30, 2020 by deanB

[acg]

3 hours ago, mattjtaylor2809 said:

My current speakers are Dynaudio Focus 380's which possibly dip down to 1.6 ohm at 75 Hz so I appreciate my speakers are more than likely not designed for valve amplification but they did sound the best I've heard them with the LM-805iA (48 watt Class A SET) & very close 2nd with a PrimaLuna EVO 400 (70 watt UL/38 Watt Triode) so this is what's confusing me.

 

I have written to Dyn audio & have asked them to better explain resistance Vs frequency response of my speakers & what tube implication they suggest, if any?

 

No probs Matt.  You hear what you hear.

 

See below for the impedance plot of one of my subs that I power with a 9w 6C33C SET...1.1R with resonance at 44Hz 3.2R.  It is the output transformer of the SET amplifier that does all the heavy lifting:  in this case it presents a 1000R load to the tube (which is the ideal load in this circumstance) and a 1R load to the speaker (also ideal).  This sub gives me 115dB in room flat down to 18Hz...from a 9w SET amp. 

 

 

 

 

 

Where you get into trouble with SET's, or low output impedance amplifiers in general, is if the speaker manufacturer has assumed a low output impedance amplifier and you are not using one.  With higher output impedance amps, the more those impedance (blue) and phase (red) lines vary from straight the more the loudness varies with frequency.   In the case of my plot above 40Hz would be noticeably louder than both 30Hz and 70Hz if I used an amplifier with say 10R output impedance.  SET amps can have output impedances in the hundreds or even thousands of ohms if you are not careful, and they would sound absolute shite on my subs.

 

Your Dyns might present an easy load,  but I doubt it.  Happy to be proved wrong though.  Trouble with SET's is that once you notice the thing about the sound that they are not getting right you then hear it in everything you play. It can't be unheard, and it will eat at you, and then it is either the amp or the speakers that have to go (I'd swap the speakers)...   

[sir sanders zingmore]

8 hours ago, mattjtaylor2809 said:

Interesting summary.....

 

This fundamental difference of physics between Valve and Solid-state amps is rarely understood or referred to by the majority of self proclaimed audio experts, audiophile reviewers, text books, web sites or forums.   Almost all explanations about differences between Valve and Solid-state amps is based on romantic subjective twaddle.

 

 

 

Surely it can’t be that simple?

if it were, you could make solid state sound like valves (and vice versa) simply by adding some eq

[muon*]

According to that my mids should be scooped out compared to the lows and highs, and that is definitely not the situation.

 

Not that simple, far from it.