Vibe noise

[alderbody]

My vibe clone creates a buzz while the bulb is lit, in bypass.
(It goes like: bzzzz_____bzzzz_____bzzzz...... at the Osc. rate)

When turned on, a light pop that follows the oscillation rate is heard.


I have to add that the LFO transistors are BD139 and the driver is a BD137.
The LFO Darlingtons are of course connected off board and obviously the wires are close enough to the input or something,
but the strange thing is that this was not happening before.

Could it be something with the nature of the (power) BD transistors drawing too much current?

Could someone help?

The supply is at 24V and i use one 500uF instead of two 1000uF (2000uF total) of the original design,
because my supply is quite well stabilised.

Should i go for bigger caps?

Any tips?

[no one ever]

24v AC or DC?


Wires running from my AC jack caused this kind of noise in my vibe.

[alderbody]

24v AC or DC?


Wires running from my AC jack caused this kind of noise in my vibe.

No, it's 24V DC. I use the regulator and the filtering.

One time i tried to "feed" the Darlington pair straight from the 24V but it didn't work (no output).
And i think that after putting it back, this buzzing started...

not quite sure though.   

[Eb7+9]

Alder,

I'm assuming you're using some kind of wall-wart and regulator arrangement ... if so then first make sure your wall-wart is not at fault, a poorly regulated supply will cause the problem you describe even with lines decoupled as I describe below ... I've found you need a wall-wart that is rated for at least 200mA even though the circuit might only pull 30~50 mA at most ...

next, you'll need to decouple the grounds and supplies on the whole circuit, especially if you're sinking serious mA's to drive the bulb - yet another bonus in using an extra-low power bulb ... on your board you need to cut audio ground from bulb/osc ground and same with supply lines to the audio ckt from the bulb/osc ... the trick is to tie the bulb/osc circuit supply before the 24v regulator and the audio supply after it - 500uF on the regulated side is ok, 1000uF better ... then star ground to the ground point of your regulator ...

... a side bennefit to running the bulb/osc at higher voltage is it will help the osc put out a larger signal at min speed and also extend the low-end speed range a little ... mine runs at 29~30vdc from a 24vdc/350mA wall-wart ... main thing is it gets rid of that problem

~JC

[alderbody]

Hey jc!

long time, no see... 

your tips are -as always- 100% on.

I'll try them and see what happens.

i guess when i powered the LFO Darlingtons directly from the 24V supply,
it didn't work because i didn't follow all the necessary steps.

this time i'll be more appropriately prepared for the job!...


thanks man!