Plinius SA-250

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Believe it or not, at this point in my life completing a large class A project is something I don't have enough time for. As time goes on, and I sit and listen to how badly my present tube amp drives my 88db speakers, and dream of owning a big fat class A.

I certainly look forward to having the time to sit down and construct my own 'baby', but it's not going to happen any time soon! :(

In the meantime, an opportunity to purchase a second hand Plinius SA-250 has come my way, obviously for a second hand price.

I was wondering if any of you had any experience or comments in regards to plinius or this amp. From the reviews I've read it sounds like it could be a good building block for my 'reference' system.

Any feedback welcome!

<a href="">Product Information from the Plinius site</a>

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Yeah. "Nice heatsinks". Sounds like a good line for a Tshirt ;)

The one I'm looking at is sadly finished in Matt black. I suppose it would be fopar to pull it apart and sandblast it back to silver? ;)

Then again, once I started modifications it wouldn't stop. Next would be replacing those long toggle switches, leds, and of course obligatory temperature, idle dissipation and output meters. :)
Wow, cool looking amp. Lots of parts in there. Reminds me of looking under the hood of a Jaguar XJ-12. I'd leave the cover off...
What are those wires sticking out? And where are the input, output, and power connections? I just see switches.
Sorry I don't have anything useful to say...just that you could buy it for looks alone.
I own the baby of the Plinius line, the 8100 integrated. It's a great amp -- very smooth, but still detailed. The circuit topology is similar to the big class A bruisers, but it's a class AB amp.

I've heard the SA-250s several times and they're great amps, too. If you can get one for cheap, you're a very lucky man.

It might be interesting from a DIY perspective to try to reverse engineer one of the Plinius amps. They have some rather interesting design quirks.

The 4 transformers in the pictures you posted are due to the fact that they use two transformers per side: on for the positive rail, one for the negative. They claim it's better than a single large transformer per channel.

The amplifier circuit, too, is quirky. Plinius only uses NPN transistors for the output. And contrary to popular belief, they do use MOSFETs -- there's a IRF9620 in my amp, I believe as the phase splitter.

Maybe I'll try to work out the circuit some weekend when I'm free...

Having heard one of these baby's they sound tremendious, Effortless and detailed. They are indeed fine amps. That said, they do have a character to their sound that is unique to their amps. I quickly grew to like the character, as it is very subtle. It is not like any tube or other solid state amp I have heard.

Being made in a city i spent many years living in, I may be a fraction biased though.

Cheers, Adrian
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More information can be found <a href="">on the Plinius website</a>.

It weighs 145 pounds, and seems to retail for around 8,500 (US, or Australian (and in one review I read, UK pounds)). Bizarre, considering the exchange rates and shipping costs. I am looking at picking it up for about half that.

This is for me still a rediculous amount of money, but its probably not a terrible investment as I feel it should hold the price for a few years to come should I need to get rid of it (and for example, swap it for a small car ;).

[Edited by Jason on 10-11-2001 at 07:53 PM]
Check my website out!

Well well... those heatsinks look very familiar. Now where have I seen those before?

Those interested can check my website out

After posting this i'm pretty sure I will never find more of these heatsinks again at the local scrap metal yard. The Plinius folks in Palmerston North will be on the phone talking to their aluminum foundry. The ones I bought were annodized wrong and in the same barrel there were also black ones. I should of bought the whole drum barrel but at the time I didn't know who Plinius was.

For the mean time, i'll salvage what ever heatsinks I find from now on.
Class A ?

I forgot to mention. I know a guy online that has mentioned one of the Plinius reps prefers the sound of the dual SA-100 (mono-bloc) over the SA-250.

I'm sceptical about how Plinius advertises their SA-250 as a "Class A" amplifier. Anyone that can shed some light on the definition of a TRUE class A amp please post a reply.

An amp that does 450 Watts per channel into 4 Ohms. How many KVA does the power supply draw? Let's mention about the maximum CONTINUOUS current draw a house's main lines are? (say around 4 KVA tops?). If it's 5KVA+ - do people spend the money for a carpenter to cut out the walls and run new heavy duty lines for a higher amp circuit breaker in the circuit breaker panel? How about running low freq. bass music (where the amp sees a 2 ohm load) - how many watts and what current draw will the amp draw? Do the math!
Class A math

True definition of class A operation is the following:

Either single-ended or push-pull amplifier stage operates in true class A if all the active devices comprising the circuit are always in the conductive state. The only exceptions may be the extreme positive or negative peaks of the amplified signal.

For the push-pull stage this means that both halves of it's circuit must fully amplify both half-cycles of the signal waveform.

If the active devices have linear I-V curves(this applies to bipolar transistros first!), the idle current must be at least half of the maximal allowable output current. The amplifier efficiency never exceed 50%. Indeed, it is always much lower due to the numerous losses in both the amplifier and power supply circuits. The typical figure for a solid-state amplifier with unregulated power supply is 30-40%.

Next, to ensure the linear operation and tight bass responce, the amplifier must have at least threefold reserve in the output current. This means that an amplifier which will be happy driving most of the real world speakers with good dynamics, must put quite something into 2 ohms, and, moreover, this current must be available even for pure reactive load.

Finally, if one wants to have an amplifier which always operates in true class A, it will be either a 15-watt-into-8-Ohms-baby, or an Elephant.

In fact, I know but one solid-state amplifier, which was true class A rated even at 2 Ohms. It was Mark Levinson ML-2 monoblock. This amplifier was rated just at 25 watts into 8 ohms, but it consumed 500 watts from the mains all-time.

For a stereo pair, multiply by two.
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Firstly, I must thank you all for your input. I really appreciated it.

Secondly, I am the proud new owner of a 145 pound, 2kw, Plinius space heater. :)

<b>CD Player:</b> <a href="">Marantz CD17 Mk2</a> (still with mute transistors)
<b>Pre:</b> <a href="">Penny and Giles RF 11 Pot</a> ;)
<b>Amp:</b> Plinius SA250
<b>Present speakers:</b> DIY SE-1P's, <a href="">Mike McCalls</a> (now unavailable :( design. Vifa P17WJ 6.5" woofer and D27-TG-45 tweeter.
<b>Speakers for the future:</b> DIY <a href="">Eire's</a> (been working on getting them finished for 2 years now ;)

What can I say, it sounds absolutely fantastic. It makes my little 2 ways sound like they are on steroids!

The sound is big, wide, clean, crisp and defined. Elements are completely seperate, there is no question of blurring between them. During the presence of even the most complex deep bass, the midrange and tops don't flinch.

The best part about it was something subjective that I realized after playing music very loudly for 8 hours straight. I am normally the kind of person that finds even moderate levels 'annoying' to my ears. I crave to turn the volume down. This I attribute to my having a degree of <a href="">hyperacusis</a> from many years living in night clubs. But after blaring the system for 8 hours straight I had the most amazing revelation - it sounded like I had only just started listening! My ears weren't ringing! There was an amazing lack of listening fatigue, the likes I have not experienced before.

I'll follow up with some more detail after some further critical listening...
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