Fun with Lightbulbs and the SOZ...

[opc]

Hi Guys,

Just thought I'd post a picture of my half baked Son of Zen (SOZ) amplifier I built tonight instead of doing a PDE's assignment.

I've seen people use light bulbs as power resistors on the classic Zen series of amplifiers, but I'd never seen it done with the SOZ. I figured with the requirements put on the power resistors by this amplifier, it's a perfect candidate for lightbulb treatment!

I wasn't expecting much, but low and behold it turned out to be the lowest hum, best sounding low power amplifier I've ever heard. If you keep the volume within reason, it actually sounds better than my Aleph 2's. My wife also told me it looked very "Tesla", which I thought was kinda cool.

Anyhow, for anyone out there that has $60 to blow on 16 - 300W light bulbs and fixtures, this makes a pretty amazing one night project. I already had the mosfets on hand, along with a 500VA transformer, so I set it up with 25V rails to make a glorious 10 watts. It was one of those things that just fell into place.

Anyone have any ideas for a chassis this can go in?

Back to my assignment...

Owen

[Vix]

Nice!

This must have been "the big fun amp"

If you intend to make a real amp out of it, I suggest you put a bigger heatsink for the mosfets, as the one on pic looks smallish. Capacitors don't seem particularly large as well, but if there's no hum, ok!

About the chasis, I just imagined two wooden vertical boxes, (two monoblocks) , with a somewhat larger base (to secure it from falllling down). Actually, they would look like two tall narrow floorstanders, except that instead of line array of speakers you'd have eight lightbulbs per channel

Just an idea..

regards,

Vix

[Dennis Hui]

Hi Owen,

That looks like fun. Did you get those bulbs in the Toronto
area? If so, can you tell me where? (I didn't find
anything useful the one time I looked at my local
Home Depot.)

Good luck with your PDE assignment!

Cheers,
Dennis

[Vix]

By the way...

What is your DC offset?

[lineup]

Originally posted by opc
Hi Guys,

Just thought I'd post a picture of my half baked Son of Zen (SOZ) amplifier I built tonight instead of doing a PDE's assignment.

I've seen people use light bulbs as power resistors on the classic Zen series of amplifiers, but I'd never seen it done with the SOZ. I figured with the requirements put on the power resistors by this amplifier, it's a perfect candidate for lightbulb treatment!

Owen

My lineup answer
is some weeks old
but we share the some idea
Sure is worth try.
As you say FUN!

Originally posted by lineup

I have praised the genius ZenLite by Pass several times before in this forum.
Besides, it is a spectacular amplifier to show to your friends
with that glowing bulb on top!




I already had this idea, after thinking about this very thread yesterday:

Why not try the same concept for a Single Supply single ended Class A
PREAMPLIFER

Could be called
----------------------
PreLite
----------------------

I am already thinking about what lower wattage bulb
with a suitable resistance could be fit for such an amplifier.
Maybe something used in cars ... ??
Preferably should be a a light bulb with some nice and attractive colour.


lineup

Posted: 1st December 2006
Link: http://www.diyaudio.com/forums/showt...76#post1069576

[opc]

Hi Guys,

Thanks for the feedback! Vix, you're absolutely right about the size of that heatsink, it needs to be a little bigger, and needs to be mounted in a more appropriate position for air flow. It hits about 70 degrees (C) after two hours of use.

As for the capacitors and the power supply, I have no idea how it's working this well, but somehow it is. Infact the whole thing is terribly built, with the bias being off by a sizeable margin. Those caps are only 10,000 uF, giving a total of 40,000uF for the whole supply. If I built these properly, I'd use at least double that amount. As it is, the amp is magnitudes quieter than my Aleph 2's which have inductor coupled banks of 120,000uF. I'm listening to the amp on a pair of Lynn Olsen's Ariels, and at 92db/1w/1m I can't hear a thing with my ear 1" away from the tweeter. As for DC offset, it's also incredibly low at 0.04V without a speaker attached. I think I just got lucky with this though, as the bulbs and mosfets are not at all matched.

Dennis: Those bulbs are Phillips Clear 300W and I got them at Home Depot for about $3.60 CAD each. Once they heat up, two bulbs in parallel give about 10.5 ohms, so I really need to place another 100W - 200W bulb in parallel with the existing two to get down to 8 ohms.

Lineup: I love the layout! Looks just like my little ST-70. It's funny, the glow from the bulbs is almost appropriate give how close this thing sounds to a tube amp when you run it with a SE input. It's got that smooth midrange and twinkly top end that you only get from tubes. Maybe it's the poor damping (made worse by the 10.5 ohm bulbs) that gives it this qulity.

Anyhow, thanks for the tips, it's always fun to toss some junk together and have it work so well the first time you plug it in.

Cheers,
Owen

[GRollins]

Common Mode Rejection Ratio, aka CMRR.
It's the ability of a circuit to ignore a common mode signal (i.e. something presented to both sides of the circuit...and yes, the rail voltage counts). Now, granted, the SOZ doesn't have a great CMRR, but it's better than nothing.
If you want to increase the CMRR, use a CCS under the differential. I started a thread on that once upon a time. You'll not only save heat, but you'll have more control over the bias.

Grey

[flg]

I don't know where everyone finds these low R bulbs??? I tested several again recently and the best bulb was a 300W GE clear (Home Depot) at around 27 ohms. Depending on the V and I of coarse...
I also ran into a 4500W 220VAC heating element for a water heater. So, I tested it too. The data is picture below It dosen't seem to have quite the heat sinking ability without the water but, it is more like a resistor

[GRollins]

Light bulbs aren't particurarly linear as resistors. No surprise, given how they work. I asked Nelson how much distortion resulted; his reply as I recall was something along the lines of "not much."
Water heater elements, by their very nature, should be more linear given that they're not run into incandescence. However, they don't look nearly as cool. Might I suggest a bucket of water? An aquarium, better still. An inverted forest of these things in an aquarium could look interesting and would stabilize the temperature.
There are other things of potential interest, one being the resistive element out of a clothes dryer. Various items have been suggested over the years, but light bulbs still look the coolest.

Grey

[opc]

Hi Grey

Nelson puts the PSRR of the SOZ at 26dB, but drawing a few hundred watts from that supply, I would have thought the ripple would be through the roof with only 20,000uF per rail.

As for the CCS, the whole point with the bulbs and stuff was to keep the thing simple and keep the heatsink size to a minimum. To be honest, I'm not sure the noise level of the amplifier could be any better than it is now. I've seriously never heard anything as quiet as this thing is, you'd swear it wasn't even on. An increase in efficiency would be welcome though, so maybe someday if I decide to go all out on it.

flg:

At the current and voltage I'm using, each 300W bulb looks like a 21 ohm resistor. I measured the current through each bulb and the voltage across it to get that value, so I'm sure about it. As you already know, the bulbs aren't at all linear, so as you up the voltage and current, the filaments heat up, and the resistance increases. My filaments are just barely glowing a dark red, so I'd imagine if you pushed them harder, the resistance would increase quite a bit. I did some calculations, and I think two 300W and a 200W in parallel would give you about 8.3 ohms for the drain resistors, and two 300W and a 100W in parallel would give you 9.0 ohms for the source resistors. This would give you exactly what Nelson spec'd in the original design, and a 25V supply means you get 10 watts of output. I'm going to buy the extra bulbs today and give it a try.

The part of this design that I find the most interesting is that the power output is now only limited by the power supply and the heatsink size / power handling of the fets. Those bulbs are good for 300W each, so if you wanted to make a 100watt SOZ, the bulbs would be more than up for it!

Maybe if I run across a 3KVA supply at the right voltage, I'll give it a try... or not.

Cheers,
Owen