# Electrovibe LFO circuit voltages



## The Gator (Oct 7, 2022)

So i have built the circuit. Not in a box yet just testing it now. The LFO circuit is not oscillating it seems, as the lamp is just on.
The lamp driver circuit seems ok. The gain and bias make the lamp dimmer or brighter. If I plug in the pedal and use the gain to make the light dim and bright, you can hear the phasing so the signal path seems good.
I am looking for information on what voltage range I should see when measuring at the junction of Q2 emitter, R19 and + side of C14. Basically this is the connection point between the LFO circuit and the lamp driver circuit.
I'm only seeing 6 volts at that junction and nothing seems to change that.
Any thoughts or measurements would be greatly appreciated.
Thank you
Gator


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## Big Monk (Oct 8, 2022)

The Gator said:


> So i have built the circuit. Not in a box yet just testing it now. The LFO circuit is not oscillating it seems, as the lamp is just on.
> The lamp driver circuit seems ok. The gain and bias make the lamp dimmer or brighter. If I plug in the pedal and use the gain to make the light dim and bright, you can hear the phasing so the signal path seems good.
> I am looking for information on what voltage range I should see when measuring at the junction of Q2 emitter, R19 and + side of C14. Basically this is the connection point between the LFO circuit and the lamp driver circuit.
> I'm only seeing 6 volts at that junction and nothing seems to change that.
> ...



Are you testing with a light shield?


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## fig (Oct 8, 2022)

I checked my Mini at that node and I am seeing 4.6v  -  6.9v.
You said the LFO is not functioning. What are your symptoms?


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## The Gator (Oct 8, 2022)

I am using a simple 2 Amp 9 volt power supply that reads 9.1 very stable with a multimeter. When I plug into the Power Jack I see the lamp come on and it can be controlled by the bias and the gain trimmers.
That seems to be the only thing that changes the lamp. The lamp comes on and is constantly on no matter what knob you turn on on the face side. It does not matter what switch you move. To me I started looking at the circuit and thinking there's either something wrong with the capacitors in my LFO circuit or the transistors in my LFO circuit. And it could quite possibly be simply workmanship and I missed something. I usually tell other people that is the most likely reason. I have gone through the circuit with voltage on it and checked connections and everything seems to be connected. It doesn't make sense to me that I cannot fluctuate the voltage coming out of the LFO. My problem is I'm ignorant of how an LFO circuit actually works. I started doing some research on the internet last night to find some simple explanations of a similar circuit which of course immediately put me to sleep LOL. In my defense it was about midnight and I'm old.
The rest of the circuit seems to work if you use the game knob to pulse the lamp light voltage you can hear the circuit phasing


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## Big Monk (Oct 8, 2022)

The Gator said:


> I am using a simple 2 Amp 9 volt power supply that reads 9.1 very stable with a multimeter. When I plug into the Power Jack I see the lamp come on and it can be controlled by the bias and the gain trimmers.
> That seems to be the only thing that changes the lamp. The lamp comes on and is constantly on no matter what knob you turn on on the face side. It does not matter what switch you move. To me I started looking at the circuit and thinking there's either something wrong with the capacitors in my LFO circuit or the transistors in my LFO circuit. And it could quite possibly be simply workmanship and I missed something. I usually tell other people that is the most likely reason. I have gone through the circuit with voltage on it and checked connections and everything seems to be connected. It doesn't make sense to me that I cannot fluctuate the voltage coming out of the LFO. My problem is I'm ignorant of how an LFO circuit actually works. I started doing some research on the internet last night to find some simple explanations of a similar circuit which of course immediately put me to sleep LOL. In my defense it was about midnight and I'm old.
> The rest of the circuit seems to work if you use the game knob to pulse the lamp light voltage you can hear the circuit phasing



Do you have a light shield over the LDR and bulbs? That’s going to make a difference.


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## The Gator (Oct 8, 2022)

I forgot to answer big Monk. My apologies and thank you for your assistance. I really didn't think it would matter to have a light Shield since I did not see any fluctuations of light on the lamp or any fluctuations of voltage no matter what the speed knobs were set to. I did however create a light Shield from the plastic lid to a small spray bottle of eyeglass cleaner. I painted the outside of it flat black and trimmed it to size. It fits quite nicely and was just going in the trash anyway.
 From looking at the circuit it looks to me like the double pots are simply to not mix the circuits but have two speeds available for chorus, and two for vibrato.
They are C taper pots so turned all the way down would be the most resistance  right?
Im skeptical of them both having been installed wrong or defective but that would cause the circuit to just be wide open I believe.


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## Big Monk (Oct 8, 2022)

The Gator said:


> I forgot to answer big Monk. My apologies and thank you for your assistance. I really didn't think it would matter to have a light Shield since I did not see any fluctuations of light on the lamp or any fluctuations of voltage no matter what the speed knobs were set to. I did however create a light Shield from the plastic lid to a small spray bottle of eyeglass cleaner. I painted the outside of it flat black and trimmed it to size. It fits quite nicely and was just going in the trash anyway.
> From looking at the circuit it looks to me like the double pots are simply to not mix the circuits but have two speeds available for chorus, and two for vibrato.
> They are C taper pots so turned all the way down would be the most resistance  right?
> Im skeptical of them both having been installed wrong or defective but that would cause the circuit to just be wide open I believe.



Did you tube the trimmers with the light shield on?

Does the gain trimmer dim the bulb and the bias trimmer change the “width” of the pulse even with the shield off?


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## The Gator (Oct 8, 2022)

Lol. Dang still not a straight answer when I  read it  back. Sorry. I could not hear the effect working with the shield on.


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## The Gator (Oct 8, 2022)

There is no pulse Big Monk.
The LDRs and the lamp are inside the shield. The gain and bias change the lamp voltage and in turn brightness.


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## Big Monk (Oct 8, 2022)

The Gator said:


> There is no pulse Big Monk.
> The LDRs and the lamp are inside the shield. The gain and bias change the lamp voltage and in turn brightness.



If things are working properly, the gain should change the brightness and the offset/bias should change the “width” or duration of the pulse of light. 

Without pictures I’d say check all your joints and do a once over on everything. 

Is this boxed up?


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## fig (Oct 8, 2022)

Big Monk said:


> If things are working properly, the gain should change the brightness and the offset/bias should change the “width” or duration of the pulse of light.
> 
> Without pictures I’d say check all your joints and do a once over on everything.
> 
> Is this boxed up?


No box per OP.


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## The Gator (Oct 8, 2022)

Thank you to both of you for replying. I appreciate the support most definitely. I have a fall fly-in at a local strip to go to today.(different hobby that is much more expensive lol). I will start by removing the pots and tesing them. I  have charted all the components in the LFO circuit on the board layout itself. I will go through the one at a time.


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## fig (Oct 8, 2022)

I would advise against removing/replacing parts unless necessary. Can you post some clear pictures of both sides? I've seen these folks spot things you wouldn't believe.


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## Big Monk (Oct 8, 2022)

fig said:


> I would advise against removing/replacing parts unless necessary. Can you post some clear pictures of both sides? I've seen these folks spot things you wouldn't believe.



I second. Frantically replacing perfectly good parts always ends badly. Ask me how I know…

Post pics and let the Sherlocks take a crack


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## The Gator (Oct 9, 2022)

Ok.  We ended up flying 'till dinner time and then went to an after party for dinner. Didn't get home 'till almost midnight.
Pictures will be taken after breakfast!
The more I think about the circuit design the more I feel like it is a problem with the series resistors and pots in the LFO.
But I  will post pics first.

Thank you again
Gator


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## The Gator (Oct 9, 2022)

Anybody know the maximum attached file size?


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## The Gator (Oct 9, 2022)

Hete are two pics.
If these are not good enough please let me know.


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## The Gator (Oct 9, 2022)

Two more that are closer to the LFO portion of the circuit.


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## The Gator (Oct 9, 2022)

I believe I found my mistakes.
I  put a 5K1 ohm resistor in R12 instead the modded size of 5M1 ohm.
Big difference!


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## The Gator (Oct 9, 2022)

Swapped it out and the lamp started flashing as soon as I  powered it up!
I will say, the lamp goes solid "on" at high speed. Perhaps 2k7 on R14 and R15 is too low.
3K3, 4K3, or stock 4K7 is the question now.
After that it will be time to sheield the back of the double pots and put holes in the box. After I box it up I will fine tune it.

Thank you for reminding me to slow down and just look things over thoroughly.

Gator


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## The Gator (Oct 7, 2022)

So i have built the circuit. Not in a box yet just testing it now. The LFO circuit is not oscillating it seems, as the lamp is just on.
The lamp driver circuit seems ok. The gain and bias make the lamp dimmer or brighter. If I plug in the pedal and use the gain to make the light dim and bright, you can hear the phasing so the signal path seems good.
I am looking for information on what voltage range I should see when measuring at the junction of Q2 emitter, R19 and + side of C14. Basically this is the connection point between the LFO circuit and the lamp driver circuit.
I'm only seeing 6 volts at that junction and nothing seems to change that.
Any thoughts or measurements would be greatly appreciated.
Thank you
Gator


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## andare (Nov 2, 2022)

The Gator said:


> Swapped it out and the lamp started flashing as soon as I  powered it up!
> I will say, the lamp goes solid "on" at high speed. Perhaps 2k7 on R14 and R15 is too low.
> 3K3, 4K3, or stock 4K7 is the question now.
> After that it will be time to sheield the back of the double pots and put holes in the box. After I box it up I will fine tune it.
> ...


Any updates? What value did you use for R12?


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## The Gator (Nov 4, 2022)

A 5M1 at R12.
Sounds awesome. Super slow is possible when combined with a 2.2 uF at C8.
I think 3k3 or 2k7 could probably be used at r14 and r15 now for the high speed


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## andare (Nov 4, 2022)

The Gator said:


> A 5M1 at R12.
> Sounds awesome. Super slow is possible when combined with a 2.2 uF at C8.
> I think 3k3 or 2k7 could probably be used at r14 and r15 now for the high speed


I did all those mods and I socketed R12, we'll see. Thanks


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