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I didn't know 30 stood for your watts, Mr. L30 II!


Addicted to Fun and Learning
Aug 5, 2021
Yeah, you read that right: FIFTEEN | (15) | {one-five} | [30/2] | \5*3/ watts...... per channel!!!

And they sound great, too - right up 'til clipping (probably that nice nested feedback!)
Pictured below is a 150mm woofer playing 44Hz in a sealed box. Its efficiency is 85dB/w, -6dB @ 55Hz, -12dB @ ~35

Small caveat: it only puts out 10 volts at frequencies down to 52Hz (at least with these speakers...) down at, say, 32Hz, the voltage can only reach like 8.3. Still decent! Still decent!

.. I did not expect this amount of power!!! I know - weird thing to do: solder some 14 gauge wire to a stereo 1/4" jack and then use the output to power some speakers! It's the first step I've taken to starting the project of my low powered active system. The speakers I'll be using are my ATC SCM20 Pro PSL Mk2s. The idea is, for lower powered monitoring, I'll use the active amp / filter combination to drive them, and when I want to listen louder, I'll use the passive crossover. I plan to use some high quality high current multi-pole switches so that I can just flip a switch and press a button on each speaker (or under - I'm not sure if I'm going to make some really nice enclosures yet - the stock boxes are pretty good with bracing and the material is 1.5" (front) and 0.75" (sides/back) constrained layer damped (CLD) material. Anyway... they've got a good passive 3rd order butterworth crossover which takes up the entire back of enclosure with massive high gauge air-core coils & capacitors. Which is great.. but no passive crossover, no matter the quality and design, can beat active! (obviously it has to be properly implemented and such, which I plan to do entirely)

So my plan was to use the L30 II to power the tweeters, then either my Arcam A18 (50WPC class ab), Kinergetics KBA-280 (140WPC, class a), or my Arcam A32 (100WPC ab) for the woofer. The Kinergetics has bass that feels authoritative (probably has something to do with its almost thirty 200 watt Sanken output transistors working in parallel...), but it's out of commission right now...

I've also got a Topping L70... If it can put out 25 watts per channel, maybe I'll use it for the woofers! (obviously I wouldn't use it near 25W... I could also use another L30 II... 15 watts is enough for the low powered mode! It's not like I can't swap in the future...

Hint to see how far the woofer is moving: look at where the wire for the voice coil pokes through (it's the light spot)

Edit: The thought just occurred to me.. the 15VAC adaptor which powers the L30 II, I'm not home now so I can't check... but I think it's only rated for 1A or 1.5A (the physical size is consistent with it). Drawing over 2.4A on the output would definitely pull the voltage down to probably around 11V. This might be the cause for clipping, at frequencies at abd above ~50 Hz. When I get home I will try testing just one channel at a time. This could be even better news for my using it to drive tweeters! I'm thinking one configuration at 1.6kHz 24dB, another 3rd order at 1.8 (instead of the 2.1 of the passive crossover)
Say 20 or 25 watts for 1.6kHz and above at 24dB/oct- the low pass portion would be 75-100W! If, driving one channel, the L30 II can do 30W, I could buy another and go full power with either my 100 or even 140W (140 class A batter) amp!
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Instead of the one channel test, I decided to increase 120VAC to 143VAC so that 15VAC turned into 18VAC. If there are 25V caps internally, this is the limit

Anyway, with 18V, the power output into 8 ohm nominal (~6.5 ohm minimum - in the bass region anyway -) increased by the expected amount with no additional distortion.

If I can find a higher current 15VAC supply there will be less droop under load, and I'll be able to get more power out of Mr. L30 II without causing harm to his caps!

It sounds beautiful guys!

A bit odd about the way Topping's NFCA amplifier (s?) clip - once clipping starts, you need to back down a bit for it to cease!


[I was right: 1000mA]
Sorry for the aim... single handed sideways shot (if that's an excuse lol).

This is what the L30II is capable of when supplied with a transformer rated for 1000mA (its stock wall-wart), outputting 18VAC (instead of 15 because 143VAC was supplied to it instead of 120) and connected to two 8 ohm nominal, 6.8 ohm average in the bass (30-250Hz sans the half octave centred on the res peak).

I'm going to put the scope on the AC supply to see what it's drooping to under a load like the one below (which, specifically, is Billy Idol - Crank Call)


Edit: funny how the average power in the 50ms snapshot on the scope is just under 1 watt (2.47VRMS and 6.8 ohms), but the peak is 21! (12V, 6.8 ohms)

In relatively consistent SPL genre of rock too. Pre 1991 rock, though (known as the compression catastrophe - that's the name I gave it, it's not technical, but very descriptive) So there was still some dynamic range in it. That 50ms is nothing special though - literally a kick with single bass note going + electric guitar - maybe some synthetic in the back, too)
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Something else to add if anyone in the future wants to use their L30 II as a 6-8 ohm amplifier - the optimal supply voltage for maximum output for full-range music playback is 17VAC. Except if your genre is bass tests or music that sounds like bass tests. Then the normal 15VAC will probably do you best. Heck, 13V might even do you better!

For higher frequencies, power output might be helped with even more than 17V, but likely not much more. Anything over 20.5V literally causes undesired operation (ie. immediate and very apparent distortion), so don't do that.

I'm doing a couple temperature tests right now. Starting with 15V supply voltage and 0.5W RMS
It's not funny! 0.5W RMS per channel is louder than you usually listen to music, unless you've got insanely inefficient speakers or a massive listening room (then you might be at 0.5W). For reference, a 100W RMS amplifier rarely puts out more than 10W RMS unless it's clipping
Then I'll test the same power with 18V supply and 12V supply.

The 15V test has been going for about 2/3 the required time to stabilization and the unit is 48.4C. Idle temperature is 37.6C (like a person lol), and I expect 15V 0.5W to reach no higher than 51C, or ~+14C > baseline.
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