Hiss generator

[wavley]

So, I've down all sorts of things to my RE-101 Space Echo to make it less of a hiss and hum factory which I believe lets more of the tapey goodness shine through.  Ditched the terrible low impedance bandpass filter on the input in favor of a Mini-Booster, re-capped it, replaced any noisy transistors, added a better output buffer, shielded stuff, built up the power supply and filtering, and just general making stuff better here and there.

Problem is that sometimes I miss the hiss when sending it into self oscillation, when the hiss was around it went into oscillation a lot easier because of the self noise signal already present and had this whooshing wind sound that was just awesome.  I was thinking about building a circuit to add the hiss back in when I want it and the From PA jack is useless so I can put a pot there for level and if I need a switch, I can use the hole where it kills the echo because that is also useless being that I just use the footswitch.

Anybody got a good simple hiss circuit?

[mth5044]

That is the strangest problem 

Frequency Central did a white noise.. hiss.. type thing on here somewhere. A wind noise maker. I'm blanking on the actual name.

[PRR]

http://www.diystompboxes.com/smfforum/index.php?topic=105885.msg955626;topicseen#msg955626

[wavley]

Perfect.

Thanks guys.

I know it's a strange problem, but sometimes the imperfections of things are what make them great and you miss them when they're gone.  I just want to be able to turn off the noise when I don't want it.

[Mark Hammer]

A radio, tuned between stations?

Al though I suppose it depends on where you live.  Some regions don't have that many blank spaces between adjacent stations.

[merlinb]

In case you want to get all fancy schmancy with true white and pink noise, here's a white noise generator:
http://edn.com/design/analog/4420926/White-noise-source-flat-from-1Hz-to-100kHz
And a pinkening filter:
http://www.diystompboxes.com/smfforum/index.php?topic=81602.msg944432#msg944432   

[R.G.]

Or, you could use a single 8 pin IC to do it. The article Merlin references mentions a 12C508 PIC to do it. I did my own version of that, but customized for long-term uncorrelated noise.

From last May: http://www.diystompboxes.com/smfforum/index.php?topic=102782.20  See the next to the last post.

A 10F200 is cheap, and if I did the math right you get white noise that doesn't repeat for nearly two million years.   

Zeners and broken base-emitters are OK, but 9V is marginal, and you have to amplify the noise to get it up to a usable amount.

... presumably with vintage carbon comp resistors!   

[electrosonic]

http://sound.westhost.com/project11.htm

Another simple white noise generator - filtered to make pink noise.

[PRR]

The broke-down emitter is marginal at 9V. Hageman/EDN uses a 12V Zener with 18V supply to reduce 1/f noise. The old-old for-purpose chip is hard to find. Using a CPU (even a $1 job) seems overkill, isn't in my drawer, long repeat is probably not essential here, and needs programming.

My TL072 approach should work (TL072 is reliably hissy<g>). It may need a lot of side parts but they are all in a well-stocked drawer. The 1/f noise "flaw" is a partial virtue because we can use smaller capacitors.

There is the question of how well the 1/f noise corner is known. The plot in the specsheet is not guaranteed and not tested except grossly (if other tests are wobbly because of 1/f noise they may look into it). If 1/f gets better with newer Silicon process they won't bother to change the specsheet. So if the 1/f corner moves to 50Hz on new parts, and my cap values assumed the old 200Hz(?) corner, there will be a few-dB dip around 100Hz. This would be poor for Hageman's use. I doubt Wavley would notice, since he just wants "some" hiss to shorten the start-up time of his echo oscillations.

I've wondered what Wavley needs for "pinkening". The hiss he removed to get into this problem was probably mostly flat with some 1/f, or else a 6dB/oct integration tape preamp. Frankly I think he should K.I.S.S. and just do a hard high-cut at 1KHz. The sub-KHz wobbles should start his oscillation quick enough, and there's little treble-hiss to annoy the ear.

[Mac Walker]

Did someone say simple?

http://darrenyates.com.au/electronics/archives/40

I think any npn will work, maybe upsize the output cap for more pink..

[anchovie]

Power a booster with a cheap & nasty SMPS wall wart.