Need help: Safety Valve... tremolo?

Hey hey,
i was trying to build the safety valve and somehow it is more a tremolo than a distortion. Has anyone an idea why that could be the case? I triple checked everything and already resoldered it once (first time it just did single clicks, after resoldering it’s at least a wee bit more chatty)
My only idea now would be to start from scratch on a bread board before starting to solder again…


Welcome in the forum :slight_smile:

maybe that can help you ?


How fast is the tremolo?

I can imagine that if you have a power supply that can not deliver enough current, that depending on the load a periodic fluctuation of the supply voltage may occur, which may be audible. Have you checked the power supply? Is the voltage stable?

The heating filament of the tube takes quite some current relative to other modules. Is the power supply up to the task?


I think @Jos has mentioned the most likely area to check.
Being old enough to have used many a valve in anger, most valves pull a fair whack to get up to temperature but by default many will restart that pull if the required heat is not met. Then it’ll waver like a tremolo.
Not as clear an explanation as I’d hoped.
So if no physical error is found and you’ve mastered grounding and not putting gear near microwaves or striplights, blenders etc, then look at the temperature and power usage.
Even less clear, apologies folks. As you were.


thanks a lot for the feedback

@Dud did all of that already and I wasn’t able to find anything about this tremolo in the other threads about the safety valve.

@Jos and @Farabide I was using the in-built powersupply of the niftycase. Because it’s a fairly cheap bundle I double checked with the power supply from the Doepfer A-100 system which has plenty of power I guess but I got the same result.

the tremolo tempo can be varied from 16th at 130 BPM up to about 17-19 Hz depending on the position of the gain and tone pot.
I guess I will just wait for some missing parts to arrive and try a second time.
It still was my first try in soldering together a module and maybe I was a little too overconfident, that it would work immediately

Thanks for all your kind replies!


Sounds like you’re on the right path. Do let us know how it goes.


yes I knew that there was not this precise problem, but on the other hand advice and method to check a circuit which does not or almost does not work :slight_smile:

good luck


I’m actually quite interested in what makes it behave like that to maybe make an actual tremolo out of it.

My first thought was also the filaments drawing too much current.

Since it reacts to the pots:
The tone control pot and coupling capacitor may have quite a low time constant which would change as you turn the tone pot.
Is there any chance the tone circuit is feeding back somewhere? I’m guessing the gain control would then also have an influence on this effect.

I think you should maybe carefully inspect all the solder connections. It can be easy to short tube socket pins (stranded wire for example) , but of course also stripboard traces.
I’ve had shorts between traces that i couldn’t even see but were definitely there.

I carefully run a small hacksaw between the traces, and this speeds up my troubleshooting by about 90% :grin:

If you find the problem, please give us an update :slight_smile:

Edit: maybe also check if none of the grids (pins 2 and 7) are accidently referenced to the positive rail. This circuit might oscillate much like a cathode coupled (schmitt) multivibrator, when some little mistakes have been made


Starving a circuit of power is great fun. One of my all time favourite synth noises is the sound you got if you unplugged a Bit 1 synth while it was playing. It was a woosh and a distinct pop which got sampled many times.
What’s fascinating is the odd and random effect that controlled starvation produces on many different circuits and chips.
So if you build a module that does something odd just switch to Microsoft Mode, call it an ‘undocumented feature’ and see what you can short, starve or power the unique feature at will.
Blue smoke is your friend.