[NEW] vacuum nonsolidstate distortion...

[puretube]

first new distortion idea of the millennium (?):

why not use incandescant bulbs in feedbackpaths
or "to-ground",
as "limiting-elements"?

they behave similar to diodes*, and do so in both directions...

just lay the circuit out for low impedances...

* low resistance when cold - starts to rise, lighting up, when appropriately driven...**

(and this is not talking about compressors or limiters with derived control-voltages - and might be done with thermistors, too).

** [edited] rather: similar, but oppositional, and do so for both halfwaves

{FFT: food for thought}

[ibanezts808]

please, I've made at least 12 of those today, and don't ask me to prove it either. lol, j/k one day I'll fully understand what you just proposed.

[Somicide]

puretube, are you suggesting something like a typical light bulb?  I guess you'd have to use a flashlight bulb...  but is that the gist of it?

PnL,

Jeff

[vanhansen]

Now that would rock.  Distortion pedal and stage uplighting in one package.  

[Tim Escobedo]

I've recalled a compresser circuit that used a light bulb in the circuit path in such a manner.

And those "Zen" amplifiers that use light bulbs as current sources are kinda neat. I've been playing with a scaled down power amp like this. Not quite satisfied yet...

[doug deeper]

some of those metasonix pedals use light bulds in the loop...

[Somicide]

interesting interesting; maybe a ds-1 mod is in order  :wink:

PnL,

Jeff

[amz-fx]

those "Zen" amplifiers that use light bulbs as current sources are kinda neat. I've been playing with a scaled down power amp like this.

I have a mosfet/lightbulb Zen practice amp in my studio  

they behave similar to diodes*

They behave more like big power resistors...  there is no clipping at small signal voltages.

regards, Jack

[R.G.]

They behave more like big power resistors... there is no clipping at small signal voltages.

More to the point, there is no clipping at audio frequencies. The thermal time constant for heating/cooling the filament is such that there is no noticeable change in resistance at 50/60 Hz.

This should not be a surprise - they're designed that way so they *don't* flicker on AC line frequencies. At audio, they're essentially a constant resistance for individual cycles.

No clipping. Big or small signals.

[brad]

I've wondered whether a Vacuum Fluorescent Display could be used in such a fashion.

[Samuel]

LFO Maybe? Back-to-basics Wein bridge?

[puretube]

constant at individual cycles: yes;
but envelope-depending over a longer time...?

at least you could get: "sag", nonlinearity, compression, and (so-called) "sustain"...
(yes I gotta admit, it plays into the optical compressor game, at 2nd thought...)

[R.G.]

constant at individual cycles: yes;
but envelope-depending over a longer time...?
at least you could get: "sag", nonlinearity, compression, and (so-called) "sustain"...
(yes I gotta admit, it plays into the optical compressor game, at 2nd thought...)

Congratulations. You have (re) invented the principle behind the Hewlett Packard 200 signal generator.  

Hewlett's (or was it Packard's??) masters degree thesis was on the use of the slow time varying resistance of an incancescent light bulb with current to stabilize the amplitude of a Wien bridge oscillator at a low distortion point. The two began to build them in a garage (literally) and from that sprang Hewlett Packard.

Similar setups were used for compressors in the Golden Age, I believe. You have to work hard; the variation in resistance is only about 7:1 to 10:1 if I remember correctly.

[brett]

Hi Tim! (and others)

And those "Zen" amplifiers that use light bulbs as current sources are kinda neat. I've been playing with a scaled down power amp like this. Not quite satisfied yet...

I'm also working on a simple MOSFET amp, but it's a follower with a simple current source (2 x MJE3055 in power darlington arrangement, controlled by a Zener reference voltage).  A lightbulb would certainly look cool, but how good are they as current sources?  (apologies for going off-topic).

cheers

[toneman]

hey PT,
the subject seems 2 have drifted......................................
how is an incandesent bulb,
whether in series or parallel with the output, or even in the feedback path,
a "distortion device"??
And, how do they "behave similar to diodes in both directions"??
I thought it was "just" a (temperature dependent) resistance??
Very low 2 start with, B4 the filament heats up HOT, then higher/steady R.
Now, in my HOT Tubes, i think there are some LEDs at the base of the tubes(?)
Gives it a snazzy, a la (what i call the) "ZVex Effect"....(?)
B nice if the LEDs pulsed.. :twisted:    (working on it)    
And, BTW, The sound is great!! also!!  
stayHOT, ouch ouch ouch ouch
tone

[lovekraft0]

We used to wire a small incandescent bulb in parallel with PA horns to protect them from being fried - no audible distortion, but as puretube mentions, as the signal gets louder, the lightbulb glows brighter and keeps the tweeter at a safe level, kinda like a poor man's compressor. Would something like a 3 volt pilot light bulb in an opamp feedback loop do the same thing?

[puretube]

We used to wire a small incandescent bulb in parallel with PA horns to protect them from being fried - no audible distortion, but as puretube mentions

Hughes & Kettner got this tweeter-protection in some of their 15/3 `s, too.

(proved to not work fast enough, when a fan hits the stage, grabs a mike to sing along, while standing in front of the boxes...).

[puretube]

Now that would rock.  Distortion pedal and stage uplighting in one package.  

That`s what it comes down to!  

FACT is, that when I wired a 12V/0.1A pilot lamp in series with a 1k/5W
variable resistor (pot "Rv"),
and hooked this in parallell to the speaker of a 12W (2xEL84) tube-amp,
I got:
a) a light organ
b) unwanted audible distortion artifacts, when Rv was set to a rather low resistance.

IIRC, this happened with NFB amps, as well as with "open loop" ones.
IIRC, it was rather a "cut speaker cone" kind of distortion, which however was not the predominant sound, but rather a raunchy "background" noise.

[puretube]

hey PT,...
how is an incandesent bulb,
whether in series or parallel with the output, or even in the feedback path,
a "distortion device"??
And, how do they "behave similar to diodes in both directions"??
I thought it was "just" a (temperature dependent) resistance??
Very low 2 start with, B4 the filament heats up HOT, then higher/steady R....

I think it`s the non-linearity of resistance/applied voltage/current-draw
(I edited the 1st post, btw. ... :wink: )

...Now, in my HOT Tubes, i think there are some LEDs at the base of the tubes(?)..

if it`s the "pure tube" E-H Hot Tubes, it`s an incandescent pilot bulb,
positioned physically between the tube sockets
which acts as a dummy load for the filament supply,
in case a dummy user doesn`t read the manual, and pulls the tubes
while powered on...
and to mislead veteran FX-designers...
[no veterans from this forum, though!!!],

oh yes: and to add some optical warmth... :lol:

[zachary vex]

i think i remember that incandescent bulbs start out very low resistance (couple of ohms) and rise exponentially in resistance until they reach the burnout point.  if you put a small light bulb in series with a resistor on the output something that can source enough current, the signal will be small across the lightbulb at small signal levels, but will dramatically increase across the lightbulb as the signal increases and the ratio increases between the resistor and the bulb.  if you monitor the signal across the resistor, say by putting the lightbulb first and the resistor to ground, you will probably see a very compressed signal because so much of it will be dropped across the bulb as the bulb heats up.