Recommend Class a Amp

This past weekend I purchased some Infinity QLS-1 Speakers and the gentlemen I bought them from was powering them with a Krell KSA-250. I was impressed, how the Krell drove those speakers. Most of my amps are tube and I would like to get me a keeper used well thought of class A solid state amp. I would like to stay in the Under thew 3K price range. Look forward to your recommendations.
I would see is I could find a used Bryson or Pass Lab amp that meets the output you are looking for.
You didn't state the efficiency of the speakers, but a Pass XA-30.5 sounded pretty darn good with our Watt Puppy 5.1's (at the time).

While these Wilsons were efficient, they were very difficult to drive.

The little Pass is an overachiever by any measure, and they can be purchased reasonably.

We liked it much better than the Pass X-250.5 (we still have 3 in our theater) - music was more lifelike - in many aspects. Immediately noticeable.

It's only weakness is bass dynamics - it runs out of steam. Even with sustained bass notes, this amplifier was very very good.

We're running a pair of XA-200.5's now and I still can't believe how good the XA-30.5 performed.

Highly recommended.
Those are not the easiest speakers to drive. Class A isn't out of the question, but it may not be realistic given your budget. If you could find a pair of Pass Aleph 0's or 1.2's, you should have no problems driving those speakers as long as you aren't in a really big room and demand loud volumes. Another option, if you like Krell is to find a good used KAV-250A. I used to have one and its very under rated because its part of the KAV line and not the KSA. I've seen several of them go in the last couple of years for well under 2k. Other than that, a Bryston 4 comes to mind, along with a McCormack DNA-250.
KSA aren't class A amps on the first place. 250wpc class A amp would be required to run in separate room preferably Freon cooled. it has pretty good range for class A power and that's why it can also work as local heater for room up to 220sqf.
So maybe you'd reconsider your objective..
I was hooked up on class T amps more than decade ago and never looked back. The way they sound to me is most natural and clean with no limitation to reproduce truly uncompressed recording material at any volume levels seriously. It's also cost effective as well. Try for very cheap BelCanto S300 and you would be surprised it won't be worse than with KSA 250.
"03-26-15: Czarivey
KSA aren't class A amps on the first place."

Actually, it may be. As long as the load doesn't drop below 3ohms (its either 3 or 4 ohms. I'm pretty sure its 3), the amp will be running in class a. So with the right speaker, it can be a class a amp.

Stereophile boys say you need around 200 watts and good current drive for the babies. That means a big solid state amp if you want the Class A sound as well.
The only one I can think of that would be a reasonable price S/H is a pair of Parasound JC1 monoblocks.
These have the wattage you need and more, but they also have a switch on the back that you can switch to a much higher Class A bias to give you that oh so sweet Class A sound to the upper-mids/highs and a hot heatsinks to boot, but you'll still have the big Class A/B wattage for the bass and lower bass.
And then you can switch it off to lower the bias and power consumption (cooler running) when you just need it for background music.

PS: Zd542, the old fan cooled KSA50 and KSA100 were Class A all the way to clipping. But are under wattage power for these speakers, unless you listen to low to medium levels only and sedate music as well.

Cheers George
Class A can be expensive, especially if you are looking for 200 wpc. In the ~$3K range, you are probably limited to older amps like the Krell KSA-250, Plinius SA-250 mk IV, CODA System 200, Threshold SA/12e or T800. Though these would probably need to be re-capped, if not already done.

Newer options such as Pass Labs, Clayton Audio, etc., would be well above your $3K price point. I would think that if you need that much power, 200 wpc, you would be better served by buying a Class A-A/B designed amp that may run rich in Class A, maybe up to about 25-50 wpc in Class A before sliding into Class A/B.
Another possibility might be the second generation Krell KSA 200, which I believe ran mostly in Class A. But be prepared to have the amp re-capped, if not done already, as Jmcgrogan2 mentions.
looks like Czarivey is correct in saying that the Krell KSA-250 is not full class-A. you can read a little more about that in the following link:

a cut & paste from that side-bar article in Stereophile:
"Looking inside the KSA-250, the emitters of the 12 pairs per channel of output-stage transistors appear to standing on series resistors of nominal 1 ohm value. The average voltage drop across these resistors was 110.5mV, implying a standing bias for each of 110.5mA; ie, a total of 1.33A. This will give a maximum power for true class-A operation into 8 ohms of 28.5W (14.5dBW) rather than 250W."
I agree that 200 watts of class A for 3k would be tough, except for considerably older equipment -- which might not be a bad way to go.

On the Pass 30s, I have the corresponding integrated the INT-30A, and while I love it, I diverge a bit from the commonly stated opinion that these amps are up to driving thirsty speakers: I've not found mine to be a great match for them, compared to more robust A/AB designs.

For a very nice A/AB option in your price range, you might also consider Odyssey.

Be also noted that old KSA series will most-likely need complete overhaul before you can actually use'm. They run extreamly hot and may develop dried out DC caps.
Good call by Czarivey and Bombaywalla. I dug out the original Stereophile issue to see if there was a manufacturer's comment in response to what JA had to say, and there was not.

To the OP: If I were you I would forget about pure class A operation and jump on this refurbished Threshold S/500 Series II, being offered by a dealer at $2495. I note, though, that in addition to being listed at the dealer's site he is offering it with a "buy it now" option at a well known auction site, so it could be spoken for at any time.

I have no affiliation with or knowledge of the seller.

-- Al
This could be interesting...

Looks like it can be run Class A/B or A, and it comes in at half your price target. 120 Wpc but doubles to 240 Wpc into 4 Ohms I'm guessing in A/B and 100 Wpc in Class A that may well double into 4 Ohms. Here's the kicker, you can buy two and still be within your budget and probably be at 200 Wpc pure Class A. I've heard Peter's amps and they are quite special. Very well made and designed and consistently get stellar reviews. I'd be sorely tempted if I were you given your budget and requirements. No ties to seller BTW.
Soix, the short answer is no. Even both of'em won't be in pure class A 200wpc. My best guess they will work 2...5Wpc each in class A.
Yeah, in a quick search I wasn't able to find specs other than a reference to the Whitney in this Ultra Audio review, which is where I got my 100Wpc Class A spec from.

I know that's kinda weak. BTW, what does "2...5Wpc each in Class A" mean? Not sure I follow. I know Peter does seem to favor using relatively large transformers in his amps, which made me think 100Wpc Class A could be possible. He is also very high on the power and performance of his amps in mono, so I was kind of (maybe incorrectly) extrapolating that those past design elements may have also made it to the Whitney. But again, not having seen the specs I could be completely off base here.
Thanks Almarg! :-)

Nobody has mentioned the Plinius SA-250Mk4 class-A/class-AB power amp? I've heard this power amp driving B&W N803 speakers & it sounded very nice to me. There's a switch in the front that toggles between class-A & class-AB & it believe there is a DIP-switch inside that sets the time that the amp is in class-A before it transfers to class-AB if it's not being used (of course it stays in class-A if it's being used). These used to go for $5000 used.
I think it's still a very good amp.
The top-plate got scalding hot & i'm sure that the heat sinks were at 55C or higher (never measured them but taking a guess based on my experience with some class-A amps).

Excuse my ignorance, as I'm from down under (Australia), but why every time I suggest to you American lot, the Parasound JC1 monoblocks I always get a stoney silence?

These John Curl designed beauties are a steel new and s/h, when you live in US. We get charged over $12000K new for them here in Oz, and over $8K second hand. But I've seen them s/h over there for under $4k

Is there a anti highend vendetta against Parasound because they make cheap stuff as well, as these JC1's are firmly placed in the Krell league.

Cheers George
03-27-15: Bombaywalla
Nobody has mentioned the Plinius SA-250Mk4 class-A/class-AB power amp?

I did, earlier in the thread. ;^)
i re-read your post. Indeed you did. sorry about that. I must have read your post in a hurry the 1st time around....
maybe this is why:-

not directly applicable but maybe many others have had similar experiences???
If you value bass quality, ignore what Tjassoc wrote above regarding the low wattage Pass full class A amps. While I haven't owned the xa30.5 I do own the older Aleph 5 which is a 60wpc full class A model. AND I also own the newer x250.5 which is the 250wpc class A/B behemoth. So I do direct comparisons frequently. While the full class A Aleph delivers absolutely delicious mids and high frequencies, the bass quality isn't great.

The x250.5 provides a more balanced sound in my opinion and will drive any speaker you are likely to come across. It's the better choice for most people -- unless you are one who only listens to small scale classical or acoustic music.

Class A sound can be addictive however and many fans are okay with the tradeoffs. But the beauty of the Pass AB models like the x250.5 and x350.5 are that they deliver 90% of the sound you will be listening to at most sound levels in class A but can supply the extra grunt when you really need it.
I drove Martin Logan CLS IIz for years with McCormack monoblocks and they never failed me. Best sweet sound I ever experienced, and those speakers were not exactly ballerinas.
03-28-15: Abrew19
If you value bass quality, ignore what Tjassoc wrote above regarding the low wattage Pass full class A amps. While I haven't owned the xa30.5 I do own the older Aleph 5 which is a 60wpc full class A model. AND I also own the newer x250.5 which is the 250wpc class A/B behemoth. So I do direct comparisons frequently. While the full class A Aleph delivers absolutely delicious mids and high frequencies, the bass quality isn't great.
I would not extrapolate any conclusions about the bass quality or any other aspect of the sonics of the XA30.5 from experience with the Aleph 5. They are completely different designs, starting with the fact that the XA30.5 is a fully balanced design while the Aleph 5 is not only not balanced but is not even push-pull, being single-ended.

That said, I am not asserting that the XA30.5 would be a suitable match for the QLS-1. I couldn't find efficiency or sensitivity specs for the QLS-1 (although I note that it is recommended for use with amplifiers rated from 100 to 500 watts), but I suspect that its efficiency and sensitivity are much lower than those of the Wilsons Tjassoc referred to, as well as its impedance characteristics being difficult. FWIW my guess is that the XA30.5 would often be struggling to some degree when driving the QLS-1, especially with recordings having loud orchestral peaks or other instances of wide dynamic range. I say that despite Stereophile's measurements indicating that the XA30.5 can provide 195 watts into 4 ohms (more than twice as much as the Aleph 5, btw), although not in class A above about 60 watts.

-- Al
As stated, a Pass INT-30A owner:

While I've not heard other low watt Pass designs, I completely agree with Abrew regards the trade off: even with high efficiency speakers (Al, I'm now running the Ulysses :), you are trading low end authority for super yummy mids and highs. The very fine Odyssey dual mono that my Pass replaced was conspicuously superior down under (up the range, not so much :)

I mostly listen to "small" music, particularly of the "girl with guitar" variety, so as Mark at Reno HiFi promised, a good trade off for me.

But I think, not for everybody, depending on speaker preference and listening habits.

Wow! Congratulations, John. I seem to recall that you were thinking of the Ulysses a while back. Hope you are enjoying them as much as I do mine!

And re the INT-30A, I **would** expect your experience with it to be likely to have relevance to the XA30.5, in contrast to what I said about the Aleph 5.

Best regards,
-- Al
Almarg, yes I know you are right when you said we should not lump the Aleph and XA.5 designs together. For that reason, I almost didn't comment at all on the post about the xa30.5. But I have heard too many commentaries from xa30.5 owners that sounded similar to my own experience with the A5 to ignore a conclusion. Even Pass factory folks themselves are aware of the pros and cons of both A and AB designs (hence the reason they offer 2 separate designs of course) and they are always interested in 2 things when you probe for recommendations, especially regarding their class A amps: what kind of music you will be listening to, and what speakers you will be driving.

I own B&W speakers that are not inefficient but which respond well to the grunt that the AB designs deliver. They specifically recommend the AB designs in my specific application over the class A models.
I own B&W speakers that are not inefficient but which respond well to the grunt that the AB designs deliver.
isn't this a contradictory statement (it sure looks like one to me)?
Since the passing of John Bowers himself in the mid-1980s I haven't seen a B&W that is efficient. Yeah, they have a 90dB or sometimes even a 92dB SPL number but they almost always (with rare exception) respond best to high current current amps.

it's interesting to see that Pass Labs recommends their class-A/class-AB design over their pure class-A design for B&W. I'll have to dig around a little to figure out why.....
Thanks Al!

I got lucky with a local enthusiast who is moving and needed to downsize. They are non-poly v. 1s, but so far feeling little pressure to consider updating them :) I may be picking your brain regards set-up, though i'm pretty happy with where I have them now.

Regards the present topic, 30w of Pass makes a nice match for these speakers, with a claimed sensitivity of 97 db or so, but I could also imagine greater ease at higher volumes with more grunt.

I own B&W speakers that are not inefficient but which respond well to the grunt that the AB designs deliver.

isn't this a contradictory statement (it sure looks like one to me)?

Hi Bombaywalla: not really the same thing. When I mentioned "not inefficient" I meant simply the Sensitivity rating of 90 spl is not considered low (or inefficient). It is fairly average (if there is such a thing). But this doesn't mean that the speakers don't work better with amps that can grip them and drive them the way the loudspeaker designers intended. It's not all about the Sensitivity and nominal impedance ratings. There is also something referred to Qts that plays a big part. I don't pretend to understand it myself; I am just pointing out that even the amplifier manufacturers recognize that the amp-loudspeaker relationship is complex and even they have some challenge explaining.
03-28-15: Abrew19
......Class A sound can be addictive however and many fans are okay with the tradeoffs....
I somewhat agree but, yeah, there are many who would sacrifice a class-A sound since getting a bigger class-A amp to satisfy their needs would be very expensive.

But the beauty of the Pass AB models like the x250.5 and x350.5 are that they deliver 90% of the sound you will be listening to at most sound levels in class A but can supply the extra grunt when you really need it.
the "grunt" you are talking about is, I assume, the current delivery capability of the power amp? If yes, this ability is set by (or limited by) the power transformer. For example: take the XA30.5 power amp. I'm guessing it uses a secondary 20VAC transformer. You can get a 400VA/20VAC transformer, dual secondaries. Such a transformer would be capable of 10A/ch. As a 2nd example, take the X250.5 power amp. I'm assuming this power uses a secondary 45VAC transformer. You can get a 1000VA/45VAC dual secondary transformer. Such a transformer is capable of supplying 11.1A/ch.
So, the current capability of both the XA30.5 & X250.5 amps is very similar. Yet the X250.5 is recommended by Pass Labs for speakers such as B&W. Why is that?

The answer lies in the DC rail voltage of the power amp section. For the XA30.5, the DC rail will be 29VDC. For the X250.5 the DC rail voltage will be 63V - more than 2X the rail voltage of the XA30.5!
So, when you have a speaker like B&W which has some really crazy impedance & phase responses over the 20Hz-20KHz region esp. impedances where the resistance is gets high, the XA30.5 power amp will simply run out of voltage headroom. As an example, say, the speaker resistance at a particular freq is 4 Ohms. If the max rail voltage is 29VDC, if the power amp supplies 7.25A, the voltage on the output will be 29V & the output stage of the power amp will be saturated i.e. it will start clipping. So, the XA30.5 is capable of delivery 10A max but you cannot even make use of that capability 'cos the power amp output stage saturates. OTOH, if you are using a X250.5 & the same 7.25A is supplied, the 29VDC generated in the output stage is much lower than the max 63VDC rail voltage & the X250.5 doesn't even break a sweat.
THAT is why Pass Labs recommends the X250.5 over the XA30.5 for many/most speakers. It's quite clearly stated on the Pass Labs website in the answer to the question "What is the difference between the XA.5 and the X.5 amplifiers?"

The XA30.5 would be great for a speaker with a benign impedance curve i.e. an impedance curve which remained relatively flat over the 20Hz-20KHz region. There are a few speakers that do this & for better for worse they all happen to be 1st-order x-over time-coherent speakers.
Crazy impedance curves are due to high order x-over circuits that need to compensate for sub-standard speaker drivers which change their impedance widely over their (frequency) band of operation.

Abrew, I think I understand that amp-speaker selection is not only sensitivity & nominal impedance ratings & that Qts does play a role in this selection. The Qts information is very difficult to get a hold off. However, measured resistance & phase plots are much more accessible to the public (thanks to Stereophile) & reading these impedance plots one can get a pretty good idea of what sort of power amp one might need to get superior sonics.
Good info. Thanks for the detailed analysis Bombaywalla.
no problem, Abrew19.
for completion i should also add that one could have solved the issue of the amp output stage clipping/saturating by buying a bigger XA series pure class-A amp for a lot more $. I.E. if one was made of money, one could have stayed with the XA series to solve the issue of driving hard speaker loads. Since Pass Labs knows most of their clients are not made out of money they recommend the more economical route of using their class-AB designs.
Georgelofi, The JC1s have gotten good reviews and I've read posts praising them on this forum, but for whatever reason, they just don't generate a lot of buzz here.

Stereophile has them ranked in Class A with amps that cost many tens of thousands of dollars and even $100,000+ amps. They get a star for their longevity on the list and $$$ signs for their being a bargain. The description takes up 2/3 of the column and is an absolute rave. It ends stating that the amp is the "Joint Amplification Component" for 2003!!!

Maybe you should start a thread about why they aren't more popular. We might find out or maybe no one would reply.

I think maybe it's because of the Parasound name having too many entry level products.
They are very popular in Australia, they get snapped up s/h as soon as they are listed which is very rarely.
And they will drive anything, as they keep almost doubling they're wattage all the way to 2ohms. Giving an incredible 4,200watts into 1ohm.
And you also have that "magic" switch which gives you a real nice Class A touch to the sound.
And they have the cred of being designed by John Curl, up there with Nelson Pass.
And you guys can pick them up soooo cheap over there.


Cheers George
"03-28-15: Mig007
I drove Martin Logan CLS IIz for years "

Never seen this automobile before.
Did you mean Aston Martin?

Not only did Stereophile give the Parasound JC1 monoblocks a great rap Tomcy6, but also this site, with lab test also to back them up.

Cheers George
Not that I'm in the market for 1, but where do you pick them up for cheap? Those are $9000 USD amps.

I've seen them S/H in the US for $5k on ebay and here.

When they first came out this is the price in the US from Stereophile

"Price: $6000/pair. Approximate number of dealers: 20. Warranty: 10 years parts, 5 years labor (US, Canada)."

Cheers George
Oh ok. Thanks. Yeah, I don't think they're worth no $9k.

I heard a pair Dave, driving a pair of Wilson Alexia's there were many other big esoteric amps there also worth $20k+ tubes and S/S and they couldn't come close to what the JC1's could do.

Cheers George
Hmm...well, it is a mass market (or semi-mass market) product, though true? I remember reading here that they did not use the superior Nichicon filter caps for a while.

Anyway, I have pooh-poohed Parasound here on the other boards I'm on, however I wouldn't mind putting them up to the big boys.
The JC1 sounds great, super transparent, super powerful, great value. Doesn't have the sweetness of the Pass Labs.

Trade offs basically.
Dave, no I would not call the JC1 nor any $4000 amp mass market or even close to "semi-mass market." To do so would be to not understand the big picture of the market. Personally, I would call Sony mass market. And Marantz, Yamaha, Peachtree as semi-mass market (they try to cater to the masses who want something better than average, but yet they still distribute their products via mass market big-box retail channels). In the big picture Parasound (and especially their Halo line) are 'high end' or boutique or whatever you wanna call it.
Abrew19, and 99.7% of the people in the world would agree with new.
It really dawned on me recently how nutso this hobby has become when I saw an ad in one of the mags for a phono
cartridge whose bold headline was" And only $5999.00" .
Ahh, YOU not new
My sense is that people think the JC1's are good, but less good than Pass monoblocks - and so they get overshadowed a bit.
Ok, Abrew, I see your point. Personally, I'm not going by price but by performance. And to me and other audiophiles, most of Parasound, minus the Halos I suppose, is upper mid-fi. Again, I'd love to hear how they compare to Pass Labs and even higher end stuff.