You mention in your article that you bought and tested various types of lamp for use in this project and determined that a standard incandescent was the most suitable. For the benefit of those of us on the wrong side of the pond (and elsewhere) who have a 230V mains voltage could I please ask what other types of lamp you tested and with what results.

To give a similar resistance to a 120V 150W or 300W lamp, a 230V lamp would need to be 600W or 1200W, which is clearly impractical since they are not made in these sizes (150W is normally the largest).

A check of some main suppliers in the UK reveals that 110V lamps are only available in low wattages (eg 15W pigmy bulbs and 60W standard bulbs for safety handlamps etc), with one exception. 110V 300W and 500W tubular double-ended lamps are available but these are a tungsten halogen type for use in industrial floodlights and the like.

I am sure that there will be a number of people who would be glad of any further advice you can give regarding alternative lamp types.

LBA (Light Bulb Amplifier)


Now you have gone and done it!, and invented the Light Bulb
Amplifier(LBA). Looks like the great Sierra mountain air has done nothing to deteriorate your brain.

You realise you have opened up "Pandora's Box)" to a
multitude of questions such as, what brands,Westinghouse,
GE,Sylvania,Phillips,etc,etc,and then later someone will be saying that the GE seems to muddy the highs but gives a great low end response, the Westinghouse has great imaging,
Of course I am just funning you and would like to congratulate you on the new web site.

You have breathed some fresh air into this forum.
Geoff said:
To give a similar resistance to a 120V 150W or 300W lamp, a 230V lamp would need to be 600W or 1200W, which is clearly impractical since they are not made in these sizes (150W is normally the largest).

The largest 220v bulb commonly available is 300w, and uses a bigger base (i think is called "Goliath"). I have an OSRAM 300w 220v right here, and measures exactly 13 ohms (cold, of course), for whatever's worth.
A Light Bulb Amp!?!?!

I just came from the new Pass site, great site! But that new "Zen-lightenment" amp is way to cool!!! I will have to build one of these just for the kicks! My only question is what is the rms wattage of this design?

Also I need to know what substitutes we can use for the bulbs, since I live "Down Under".

Surf, Sun & Sound
A single 120V 300W lamp will have a 'nominal' resistance of 48ohm. To achieve the same 'nominal' resistance at double the voltage rating will require four times the power ie 1200W. This could be achieved in the UK by using eight 150W lamps in parallel but is a little unrealistic if an acceptible 110/120V alternative could be found. Hense my question to Nelson about which other types of lamp he had tested.

I have tried the circuit with a number of different bulbs and have found the Western Electric 300W to be the best performer. Of course these are only available as new old stock. The very best are from pre-1965 lots with the black base. You may be able to find the military (JAN-300W) version if you're lucky. I know a guy who's selling these in matched pairs for $500.00 a set. The Western Electrics have the most incredible midrange bloom I've ever heard. The image is fantastic, and the mid-bass hump apparent in the GE's is much less pronounced. Of course, all of this presumes you're using a ceramic socket of the finest quality and silver-plated wiring throughout.



Nelson Pass

The one and only
Paid Member
2001-03-29 12:38 am
General responses...

Try the Sylvania website, where you can see
incandescents up to 1500 watts. I was tempted
by these, but they require a mogul base.


You can of course parallel the 240 bulbs till you
get the right impedance, which will be somewhat
less than the full voltage rating at the 25-65
volts in the project. The 300 watt 120V bulbs I used
were about 35 ohms or so at these voltages, where they
would be more like 48 at 120 volts.

The best glow is to be had with about 30 volts across
the bulb, and to extrapolate this to 240 volt bulbs,
we would probably want 60 volts, or 75 volt supplies.

I did not use Halogens as I understand their life to
be short if not used at full voltage.

If a bulb dies, the amp stops playing. There is no
damage and no thump.

Vacuum tube filaments are rated at lower voltages
than we probably want, but you can operate them
in series....

I am very gratified by the response, thank you all.
We have a lot of amplifier designs in the queue, but
I just had to get this one out of the way first :)
Heeeee Mr Pass.... so the grado's can be driven by a BoSoZ , without modification ... I've been wanting to try that for some time now... I guess the output impedance really doesn't matter much in headphones ... So I will finaly modify my grado cord for balanced operation.... just to compare bthe sound with the SE-MOSFET-headphone amp from HEADWIZE

I once suggested using the heater elements from clothes dryers. I seem to recall that they're about 3 or 4 ohms, and they're cheap--free, if you pull them from junked dryers. It would be about the same as the resistors (which look like heater elements to me) that John has pictured.
As long as the resistance is there, the circuit will work. Whether there is any sonic benefit or loss to using such a resistor, I couldn't say. No one ever admitted to trying my idea...perhaps they didn't need to dry any clothes at the time.