Pure Class-A Amp under $2000 (USED)

Belles SA30 

Rogue ST100, with first 25w class A.

Are you a DIY type? Nelson Pass has provided many amplifier designs to the DIY community. Anything from 5 W/ch up to 100 W/ch, all biased into Class A. I have built the Aleph-J (25 W/ch) which is based on the original Aleph series of amplifiers with J-FET inputs instead of MOSFETs. A very popular design is the F5 (25 W/ch) and the F5 turbo (50 W/ch). Both the Aleph-J and F5 were sold under the First Watt brand as well, but can be hard to find on the used market.

$2000 is a tough budget for a good Class A amp. Your choices will be limited to older amps like the Krell KSA or the Plinius. The KSA are great amps but old which means you will be sitting on a time bomb. Rebuilding those amps will be expensive.  If you can wait and up your budget, the Pass XA25 is the current model and should drive your speakers just fine
 

I'm a big fan of the SONY TA-A1Es integrated amp,   Built like a tank and sounds amazing, can't believe how good it sounds for the price.  I thought Sony did a terrible job of marketing this amp, it should be far more well known than what it is.  

An amplifier that runs in pure class A operation does exist regardless of what some may say. There are some amps that switch to A/B when pushed in volume but there were amps designed to run class A always.  A killer and very inexpensive class A amplifier is the Forte Model Four.  50 watts per channel and a killer of an amplifier. Sold by Nelson Pass under the Threshold company but the amp was designed by a Swedish Engineer who worked for Nelson during that time. The Forte Four was the 1st amplifier I purchased 35 yrs ago with a Conrad Johnson tubed preamp when I first entered this hobby. I picked it up in a Stereo store in Manhattan NYC. I sold it 1 year later and moved in the direction of tube amplifiers. I’ve owned since about 50 amplifiers, all extremely good and now listen mostly to single ended tube amps. Never forgot how good the Forte sounded. After 30 yrs, I’m so happy to be he owner of the Forte again. I own 2 now with all the Jon Soderberg upgrades. If 50 watts per channel will be enough, the Forte Four is not just a good amplifier, it’s a killer amp. If you need more power, Vintage Threshold has a good line of amps. Krell KSA series was great as well, KSA 100 Mk 2. Good Luck.

Unfortunately, used $2k Plinius SA100 amps aren’t around any more. I believe people are hanging onto them. 100 watts 8 ohm, I believe 200 watts into 4. And flip the front panel switch to listen in A/B mode. 
 

They would drive anything.
 

These amps were some of the best available in 1999. Commonly available used everywhere for $2k. Their Mark III version was the finest Class A amp I’ve ever owned. But sadly today, those amps are gone. If you didn’t sample one in 1999, you truly missed out. 

soix Some valid points, most I would agree with, some you’re off the mark by taking points out of context.

You’ll note for DK8586’s benefit (+ others), I used the term "relatively" inefficient/power hungry speakers,

(S/F Venere: Nominal Impedance 6Ω, Sensitivity 88dB). Now for the sake of correlating lets use an apples to apples example, (ProAc D2: Nominal Impedance 8Ω, Sensitivity 88.5db). (Focal Sopra N°1, Nominal impedance 8Ω, Sensitivity 89dB). Now the (Coincident Triumph Extreme II, Impedance Flat 8Ω, Sensitivity 94dB)!

So as you can see yourself soix the S/F Venere’s are "relatively" hard to drive. Now that’s cleared up lets move on.

Your quote "a Class A amp, which out of the box affects how many Watts are required as they mostly double power into 4 Ohms". Where are you at on this comment soix? Mind you lets not be over critical.

1st of all, regardless if it’s an A/B amp or a pure Class A amp, any good quality amplifier doubles in power when it’s impedance is halved. Eg: 100W into 8Ω, 200W into 4Ω, it is not what defines a Class A amp.

2ndly 50watts is 50watts, regardless if it’s an A/B amp or a pure Class A amp. There are no magic watts for Class A amps. They sound different because they run flat out, making them faster and ...... warmer?

Now I’ve got to give you credit on two points. One, the recognition of Nominal Impedance. Two, the observation of higher than rated impedances at certain frequencies. The term Nominal Impedance recognizes that values fluctuate with dynamics, so a speaker that’s rated at 6Ω may drop down to 3.45Ω when reproducing low octive notes and/or sustained crescendos. (How Israel Blume over at Coincident gets a dynamic speaker to operate at 8ohms FLAT is by me). The second point, that impedances at certain frequencies rise, is new to me! So I’ve learned something. Thx.

Reading further into your text, unwittingly you seemed to have reinforced my point. "Further, I had the 2.5 in my system and will attest they were not hard to drive at all, and my 100Wpc Class A/B amp drove them to very loud levels without even nearly breaking a sweat". Well of course you didn’t have any trouble driving you Venere’s soix, when the impedance drops your A/B amp was pulling close to 200watts.

Now you say "And I’d have actually NO reservation saying a 50Wpc Class A amp would be more than sufficient to drive the Venere 2.5, which is why I recommended the Clayton S50 would be a great choice here". Well where’s the correlation between your 100Wpc A/B amp & an S50 Clayton soix?

If I may, let me share my experience with 6Ω speakers & Class A amps. Class A amps run hard, that’s why they’re hot, that’s part of their charm/ethos. Back in the 80’s-90’s a company called Sumo made a fantastic Class A amp that in my area got paired up a lot with low impedance Infinities. (Not implying the Venere’s are in the same boat). They often went up in smoke. Conversely, Mark Levinson made ML-2’s mono blocks that could drive a bus all day and not break a sweat. How an S50 Clayton holds up I would not presume, but Class A amps can be dodgy.

I used a Classe’ Audio DR3, 25Wpc, to run a pair of SB-E 100’s (37Hz to 22kHz. Impedance 6Ω. Sensitivity 95dB). They were used in a 15x25x7.5 room. The DR3 was the sweetest sounding amp you could imagine, and even though the SB-E 100’s were vastly more efficient than Venere’s, it did not have the power to fill a room of that size with the necessary SPL’s I was after, so it had to go. My point is this.

The lesson I learned is that all things being equal, it’s better to have power in reserve than not enough.

I’m not saying I’m 100% correct on this, but in the name of safety a good rule of thumb is to add 50+200=250, divided by 2 = 125watts.

@thehorn You’re likely not correct on this. Understand that you’re conveying general guidelines, but general guidelines are just that and don’t apply in all situations, and this is one of them. For one, the OP is looking for a Class A amp, which out of the box affects how many Watts are required as they mostly double power into 4 Ohms and given their more robust power supplies can provide plenty of headroom even above that. Then, there’s the speaker specs. Using stated specs can be indicative but not always determinative. Case in point, here are JA’s actual measurements of the Venere 2.5 whose stated specs are near identical to the 2.0…
“The Sonus Faber’s voltage sensitivity is specified as 89dB/2.83V/m; my estimate was a little lower than that, at 87.7dB(B)/2.83V/m. The impedance is specified as 6 ohms; the Venere 2.5’s impedance magnitude and electrical phase, plotted against frequency, are shown in fig.1. There is quite a large variation of impedance with frequency, the magnitude remaining below 6 ohms for most of the midrange and bass but staying above 9 ohms for the entire treble region. Though there is a minimum value of 3.45 ohms at 111Hz, the phase angle is extreme only when the magnitude is high. The Venere 2.5 will not be hard to drive.”

Further, I had the 2.5 in my system and will attest they were not hard to drive at all, and my 100Wpc Class A/B amp drove them to very loud levels without even nearly breaking a sweat. And I’d have actually NO reservation saying a 50Wpc Class A amp would be more than sufficient to drive the Venere 2.5, which is why I recommended the Clayton S50 would be a great choice here. I’d even say something like the Pass XA30 @ 30Wpc would be perfectly fine because, as Pass amps are conservatively rated, it’d have more than enough juice to drive the 2.0. Point being, using top-level, basic specs without looking further under the hood can lead to misleading conclusions despite whatever good intentions were involved.

Hello 8586,

How are you.

You wrote, " I think the wattage range between 30-60WPC for Class-A is powerful and popular".                                                                                                                                   I have no idea what "popular",  has to do with the price of tea in China when it comes to anything, let alone amps. Best to look at the spec data on your Venere's.                   

Sensitivity: 88dB. Nominal Impedance: 6 ohms. Suggested amplification: 50W-200W. These are relatively inefficient/power hungry speakers, that will inevitably "clip" an under powered amplifier. The maker recommends 50-200W. I'm not saying I'm 100% correct on this, but in the name of safety a good rule of thumb is to add 50+200=250, divided by 2 = 125watts. Although they "do" over lap, do not confuse power with volume/dB, think more along the lines of authority as well as head room.

Therefore if you're bent on a pure Class A amp, take heed from (pwerahera) suggestion concerning the Krell KSA 150 and 250, or (jeffseight's) suggestion on a Threshold. Someone wrote that these amps might be overbearing. You did say that a different Pre-amp was in the cards. For approx $2G's, a good tube Pre-amp (VTL Ultimate, ARC-SP8, Audible Illusions Modulus, or an Ampex 402) will get a tiger amp to purr. If tubes aren't your thing, a Classe' Audio DR5 is a good SS alternative that blends well with a pure Class A amplifier.

Enjoy the music.

Classe Audio real class A amplifiers are : 

DR-2, DR3, DR3-B (25 Watt - 65lbs.)

DR3-VHC (45Watt - 99lbs)

No one is mentioning Plinius SA 100 ? This amp can even powered my Andra Eggleston and it’ redefine Class A category per Stereophile review.

I recently sold my Classe Audio DR-8 power amplifier ("Pure Class A", hence the name) built in Canada and designed by David Reich. It served me very, very well with Vancdersteen 2c models and most recently with Magnapan LRS. I replaced it with a Schiit Vidar (not class-A). I am still considering the wisdom of the new v. old amplifier but class-A was very satisfying for me for a very long time.

Try looking for the Forte brand . Made a Model One that was 50 watts and later upgraded the line to a Model 4 (Fifty Watts ) and then 2 Monoblocks ! Don’t recall that model # . Had the Model 4 loved it but parted with it going up the audio chain ! The thing about a Class A amp is that most of them generate a lot of heat so take that in consideration! Good hunting in this crazy hobby !

Most “class A” amps are not “pure class A” because they are extremely inefficient and get very hot, even with massive heatsinks. They are basically space heaters. 
 

Even amps like the Pass XA25 (50 watt class A envelope) are not pure Class A for this reason. 
 

Also, it’s my experience that even high efficiency speakers can really benefit from the headroom afforded by higher power, >100WPC amplifiers. It isn’t so evident in a vacuum of course, but power a 90db sensitivity speaker with 50 WPC, then power it with 250 WPC and this truth becomes very evident, especially at lower volumes. Just food for thought. In many cases one is better off using an amp that is heavily biased into class A, for a dozen watts or so. 

If you can find a refurbished Sumo The Nine Plus, it's a great sounding Class A amp. I wouldn't buy one though unless it's been thoroughly updated with new caps, etc. by a professional service tech. It does use a cooling fan so be aware of that.

Keep checking audio gon and usmart for a nice class A amp, as I told another seeker, ne ready to jump on it if your ready.

those nice class A amps go fast. Keep classe, pass labs in your everyday search, and get when you find t one don’t worry, most used ones will be a good bit affordable, I almost hit “buy” button on a pair of pass labs amps years ago, I waited another day, and a pristine pair of McCormack dna-750’s went up for sale, messaged the seller, am I had made my decision, grabbed the pair with shipping for a steal, 600-650W at 8 Ohm and over 1000W rms at 4 Ohm. Stable below  four Ohms. I then started looking for the LD-2 preamp, and the UDP-1 spinner. 
new price for those 3. Pieces would be 17K plus new, I did a good job with all 3. 
could not be happier, patience is the key to happiness,  and looking few times a day.

good luck!

30years ago I owned a Threshold 400A. For 30 years now I kick myself for letting it go. They come up now and again here and elsewhere, recapped and tested within your budget. Loved that amp.

+5 Schiit Aegir,

-50 on the Schitt Aegir

I had a pair and they couldn't handle the LSA Statement 10 which is a 83db 10ohm bookshelf nor a pair of Fyne F501 which is 90db 8ohm. Both amps would shut off at any music past 88db volume. Both speakers worked perfectly on my Sony surround receiver at volumes well past 88db. 

Per Stereophiles measurements and ASRs' (49w @1% THD and 23w @.5% THD) Schiit severely lied on their published specs for mono rating. When confronted with the above publications and when I requested my money back, I got no response.

Here's the tests 

If you’re fortunate to find a used Clayton Audio S50 while your radar is up I’d say consider yourself hugely lucky and that you jump on it ASAP.  50 and 100Wpc of sweet-sounding and pure Class-A power into 8 and 4Ohms, respectively.  Read the reviews of Clayton amps and I think you’ll find them quite special too.  Best of luck in your search!

https://www.usaudiomart.com/details/649787192-clayton-audio-s50-class-a-amplifier/

The Sonus Faber would like power, especially if you play loud.  Most Class A amps are small 30 W or less.  I had a Schitt.  Sounded good but not enough grunt.  You need an amp with some weight, a big transformer, etc.

There are several AB amps that would sound quite nice. Parasound, Anthem, etc.  Look on here or other places you will be set.  

PS.  I personally will always own a class A amp but high efficiency speakers make it easier.

There’s a minty looking Krell KSA 200 on Audiomart @ $2100

+4 on the Aegir. I have one in my main system for my 88 dB 6 ohm Ohm 1000 speakers and it easily goes to my loudest needed volume (about 85 dB average) without strain. (Full disclosure, I also use a sub.)  And, I love the sound -- previously had a Bel Canto amp and then a VTV Hypex that were both higher wattage but didn't sound as good. 

Schiit offers a 15 days trial with a 5% restocking fee if you try and don't like. $40 to try it out (plus returning shipping) which is a pretty good deal. And, there is also a solid used market for Schiit gear -- you can use it for a year or two and not be out all that much if you choose later to move on.

+3 Schiit Aegir, I have one it drives my speakers with finesse in stereo mode. 😎

Mike

+1 Schiit Aegir(s) x2 monoblocks.

I currently run a pair of Schiit Aegirs into my Wilson Benesch speakers which are, I believe a 6 ohm speaker with no difficulty at all, 80 watts per monoblock and I never have it over 25%. Lovely sounding class A, first 10 watts are pure class A, balance of the wattage is something called class A "continuity". You will have to check with the website to get the details, listed as Class A in Sterephile. I beleive they cost me $ 2,500.00 new delivered in Canada so you should find a pair used well within your budget. 

FWIW...there is a First Watt M2 available right now for $1850. It will work well with 6-ohm speakers. Your sensitivity at 88dB is lower than I would like but you will get decent sound as long as you don't expect to rock the house. I have an F6 controlled by an NAD C658 connected to Focal Kanta No.2 speakers rated at 91dB efficiency and frankly they sound great and can put out enough volume to drive the wife out but I like MORE so I just ordered a set of Tekton DI's rated at 98dB efficiency. 

My 2 cents

Used First Watt M2 for Sale | HifiShark.com

Have any one try the Krell KSA50S, it's about $1500 in my country including the shipping.

KRELL KSA 50 or KSA 100, both fantastically musical amps, and when funds permit an Audio Research pre an SP9 or LS2B.

I know they are old uns but are good uns, maybe not as detailed as later models but more engaging and less Hifi sounding.

whatever you do, steer clear of that Emoteva tripe.

gain is ultra high, you will have tweeter hiss

plus the service on them is a disgrace to audio.

they are ok for what they are entry level stereo separates .

nothing more.  i did hear the new flagship speaker was fairly descent, despite the very low Watts/current allowed. for such a good size speaker, i think its only 250W

i do like the folded horn tweeter if the source material is well recorded.

heavy metal through the Emo amps was painful, they are bright, even with a 92 1w/1m pair of old speakers i had 15+ years ago.

they were ok for country, or reg rock, but metal,...aaaarrrgggghhhhh shrill, i even switched speakers, and still shrill and molar grinding.

had the xpa-1 monos.  big bulky, and those knight rider like blue meters on the front were making the amp look cheap and low end. as it is. i had them shut off from first warmup.

if you know about class A, im sure you know about that Emo mess

I have a LUXMAN 550ax2 in my tannoy system but just picked up jungson ja88 used for £400 ($470) and amazed ... Need to drop into the main system as think it could be as good as the luxman ... It's a bit more powerful 

https://www.enjoythemusic.com/magazine/equipment/0809/jungson_ja88d.htm#:~:text=The%20JA%2D88D(09)%20was%20a%20joy%20to%20use,quickly%20got%20used%20to%20it.

It does suck about 380w from wall and get warm which is fine here in Scotland ....

Built very nice but heavy at 27kg and big so you need space on a rack or sideboard.

It seems that Sugden is quite favourable by many users, and they look very nice

@pwerahera how do you feel about the sound of Krell? I heard they have a very forceful bass.

@darkknight8586 I believe Krell KSA 150 and 250 operate in Class A and deliver plenty of power. There are some other Krell models such as sustained plateau biased models also operate in pure Class A. There is one KSA 150 available for $2,500 if you are interested. KSA 150 burn 300W when at idle! Class A efficiency is very low around 10-15% tops. For this reason, I purchased little brother in this series KST 100, but Class AB biased. Imaging, depth, spacing around instruments are outstanding.

If you are looking for a pure Class A (not a class A rated) power amplifier then PM me and I can send you a LUX kit pure class A amplifier for you to hear.

SUGDEN

If you want pure class A and high power you need a push/pull amp. While very rich class A no push/pull amp stays class A into all impedances at high power. Only a single ended amp(which can only be class A due to circuit topology) is ALWAYS class A and they are almost all low power.

Then again an amp that is say class A up to 30 watts is almost never out of class A and if it is it's for mili seconds mainly> For instance the 30 watt calss A Pass amps are 30 watts class A to 30 watts but then become class B up to around 75 watts(why he calls them 30 watt class A amps. If I recall correctly(someone may know better) if a push pull amp is class A at 8 ohms at a given power it stays class A only at lower power into lower impedances.

NAD C300

There was a very good made-in U.S.A Coda 100 wpc pure class -A for sale for $2k just last week 

if I didnot have so much going on I would have bought it .

  Off topic , but would it be possible ? Could you request an A/B amp from one of the boutique builders like Van Alstine or Odyssey and have the bias set to  the extreme towards class A ? Just a random thought and I apologize in advance for my ignorance. 

1. SUGDEN
2.  

@darkknight8586 I'm using Tekton Lore Reference but I also use Dynaudio Special 40s---the S40s love the Sugden despite it being being only 23 wpc. They appreciate the high current from the A21. Hope this helps.

@ozzy62 I think with 6ohm, the power would be 1.5x. But we need to confirm this with Schiit Team. 

@timski Yeah, I’m eyeing on some of the Nelson Pass amp such as First Watt F7 or Aleph 5. Nice suggestion bro

@bluorion Let me check the Sugden; which speakers are you using with the amp?

@arcticdeth tbh, I like the great watt amp, but for the Pure Class A, over 100wpc will cost huge amount. Unless I jump in the Class AB territory 

if you  like some volume, low watt amps are not for you, if you just like mid volume, then you may be fine with the proper speakers.

me, i like loud, raven, venom, celtic frost, pat travers, motorhead, living death, assassin, bathory, humble pie, hirax, bitches sin, onslaught, jungle rot, malevolent creation, etc so i need my amps and my speakers which are warm (less treble, not searing) which makes for more relaxed, listening time for me.

if you like some JAM time, get min 200-300W rms. there will be no clipping, no loss of sound, no muffled anything.

if you just like barry manilla, james taylor, ravi shankar, etc, the low watt will sound great!

Perhaps look at for a Sugden A21 Signature or SE demo unit. I went through Goldprint Audio and got a demo A21 at a good price--great customer service as well. The A21 is pure class A---super sweet sound, 23 wpc.

You might consider one the First Watt amps.  I’ve had the First Watt F7 in my system for the last few years paired with a Schiit Freya (OG) and Tekton Double Impacts and have really enjoyed it.  Lot of bang for the buck.  I’ve recently upgraded my amp, but felt like I had to spend over twice as much (retail) to make it worth my while.  The F7 is rated at 20W into 8 ohms and 30W into 4 ohms.

The Aegir will double power into four ohms when used as a stereo amp. As monoblocks, 80 watts into 8 ohms. Not recommended for a four ohm load as monos. The OP might get by with his 6 ohm SF, but I’d reach out to Schiit and ask.