555 Charge Pump Noise

[fritter]

Hi there folks. Long time lurker, first time posting.

I'm working on a Valvecaster/Valvemaster build. I wanted more headroom so I decided to use a charge pump to get a >9V on the plates. Unfortunately, none of the local shops carry the common charge pump chips (MAX1044, LT1054, LC7760S), so when I found a design here for a 555-timer based chip, I jumped on it. The design I'm using was originally posted here: http://www.diystompboxes.com/smfforum/index.php?topic=80007.20

And the schematic:


I'm using identical component values, except the NE555 is actually a TLC555CP - a CMOS based 555 chip, and the input voltage is +9V instead of +12v.

The first 2 stages of the charge pump 'ladder' (first 4 diodes) get me up to ~22V, 3rd gets me up to ~27V, and the 4th gets the voltage up to ~33, using an old 9V battery. If I run the ValveMaster circuit using only the first 2 stages (Plate voltage ~22V), everything is fine. Circuit is quiet (no buzz/hum), but I'm still looking for a little more headroom. However, trying to use the 3rd or 4th stage for more voltage results in an extremely obnoxious buzz or hum. Changing the 100pF cap (which IIRC changes the frequency of the 555) changes the frequency of the buzz/hum, but I seem to be unable to eliminate it entirely. Does anyone have any suggestions on filtering out the noise? I'd like to try to stick with the 555 timer based charge pump, but if I can't push it much higher than 20V without getting switching interference or whatever it is, I'll probably just have to bite the bullet and find some proper chips.

[Seljer]

You need more filtering, up the 10uF caps to some bigger

[duck_arse]

it won't hurt to use low esr type electros, if you can get them.

[PRR]

The original '555 would source AND sink 200mA.

TLC555CP will sink only 100mA and can sink a puny 10mA.

When you multiply-up voltage to the tube, you conversely multiply-up current demanded from the "555".

Also from the battery. "An old 9V battery" may not hack it.

I think you could try again with a genuine transistor (not CMOS) '555 and a fresh battery.