Electrovibe - no slow speed (LFO stalls)

[Kester]

Hi,

I just finshed wiring up an Electrovibe, and there seems to be an issue with the speed controls:
When the speed is turned up full, or almost full, the bulb is turning on and off as it should. However, when I turn the speed control down the lamp stops pulsing and just stays on, although not quite as bright as the maximum brightness when the speed control is up. It does exactly the same thing for both speed controls.
Does anyone know what a likely cause of this could be?
Where would be a good place to start troubleshooting?

Thanks,
Kester

 

[zgrav]

what is the amperage on your Mooer? at least 500 milliamps? or 250 ma?

 

[Big Monk]

what is the amperage on your Mooer? at least 500 milliamps? or 250 ma?

I can't imagine the EV draws more than 100 mA

 

[Kester]

what is the amperage on your Mooer? at least 500 milliamps? or 250 ma?

It's 2000mA apparently! Quite a bit more than I was expecting

 

[zgrav]

It's 2000mA apparently! Quite a bit more than I was expecting

that is hefty and would not be an issue.

 

[zgrav]

I can't imagine the EV draws more than 100 mA

I think the lamps are a factor here, although I have not measured it. Plus the voltage doubler.

 

[Big Monk]

I think the lamps are a factor here, although I have not measured it. Plus the voltage doubler.

The bulb is usually 40-50 mA full-on, which it never is so it would be that and whatever the draw from the charge pump is at the specified voltage.

 

[zgrav]

The bulb is usually 40-50 mA full-on, which it never is so it would be that and whatever the draw from the charge pump is at the specified voltage.

I thought the lamps were a bigger power suck than that. Good to know.

 

[Chuck D. Bones]

This type of LFO is notorious for stalling, particularly at low speed. C7 - C9 need to be low leakage. I recommend tantalum.
Your build quality looks very good.
Make sure there is no flux residue on the board, particularly around the LFO, SPEED pots and SPEED switch.
Did you sub any parts?

 

[Kester]

Your issue suggests some sort of installation or workmanship error.

Like I said, there shouldn't be a scenario in "normal" operation where the bulb goes full on. If anything, the only time it should get anywhere near full on is if you have the trimmers set to high brightness and you are on a FAST speed, not slow speed like you are seeing. On slow speeds, the bulb should be pulsing very slowly.

Go through the LFO section and Lamp section and inspect all your work. Also inspect the Intensity and speed pots.

Been really busy the last few days but will inspect and double-check everything this weekend!

 

[Kester]

This type of LFO is notorious for stalling, particularly at low speed. C7 - C9 need to be low leakage. I recommend tantalum.
Your build quality looks very good.
Make sure there is no flux residue on the board, particularly around the LFO, SPEED pots and SPEED switch.
Did you sub any parts?

Thanks for the comments!
The only parts I subbed were the resistors for unity gain (2M2) and higher speed (2k7), as I saw recommended on here.
I’m going to try cleaning the board thoroughly with isopropyl, and I’ve got hold of some tantalum caps for C7, C8 and C9, so we’ll see!