please help debugging lamp/LDR tremolo!

[sunder]

I've built a really nice tremolo that uses a lamp/LDR in place of a FET. It works, too.



The circuit is much like the EA tremolo, except that I added a lamp driver (like in the Univibe) and used an LDR in place of the FET.

There are some slight issues, though:

1) You can hear the trem pulse in the background, when the guitar is turned low or when you aren't playing (when the effect is ON).

Like "pop pop pop pop pop"...

Do I have to use separate power supplies for the LFO and the preamp (signal) section? Would that help?

2) The lamp doesn't seem to like higher speeds, it gets blurry when the rate is high. I guess that's normal... anything I can do to make it flash faster? Higher gain tranny in the lamp driver section? I run it at 9/12 volts (variable power supply) and the lamp is a 7V / 0,1 A type.

3) What can I do to make it sound more intense, more choppy? Higher gain for the LFO tranny?

[gez]

1) You can hear the trem pulse in the background, when the guitar is turned low or when you aren't playing (when the effect is ON).

Like "pop pop pop pop pop"...

Probably your layout.  Is it on a breadboard at the moment?  Use seperate ground paths for the modulating element, the LFO's circuitry and the audio circuitry and join them at the -ve battery/power terminal.  Keep wires short, keep LFO circuitry as far removed from audio circuitry as possible, use shielded wire for audio input.  All these things can help.

The lamp doesn't seem to like higher speeds, it gets blurry when the rate is high. I guess that's normal... anything I can do to make it flash faster?

Try an LED instead? (will give you a little faster action).

What can I do to make it sound more intense, more choppy? Higher gain for the LFO tranny?

Depends on how you've done things.  Would be easier to advise if you posted a schematic.

Higher gain trannie will distort your sine a bit (bit of a waste of time), but to get it to square off you could buffer and clip the LFO's output.  Again, a schematic would help.

[sunder]

I've just played it a bit more... this thing sounds great! It has some mojo... rocks on slow blues stuff / jazz comping.

Anyway, yes, it is on a breadboard. I'll try separating the ground traces... if that doesn't work, I'll use a 9V battery for the preamp section and the PS for the LFO/lamp driver stuff.

It sounds much better at 12 V than at 9V, the lamp flashes a lot brighter and so it sounds deeper. The lamp really goes almost from off to full brightness. Sorry for ranting, but I've never seen that before

There seems to be not much difference between putting something over the lamp/LDR and leaving it open... even at room light, there's not much difference in sound. Of course in the dark, it is more spacey

I just used a random LDR, we measured some in my local techie store and this goes from 1K to about 100K.

I guess I will leave it with the lamp, because it sounds so good... I don't need ultra-fast tremolo anyway. This is old-style after all.

Right now it uses BC184 trannies for the LFO/driver and a BC108 for the preamp. I tried BC108 in the LFO, but apparently it didn't have enough gain. The driver tranny tends to get hot, when I put a BC108 in there I could barely touch its metal can!! I will try BC109 tomorrow.

I don't have a schematic right now, but it's really blood-simple. The LFO looks a lot like the EA trem, with some different values. Its output goes via two electrolytic caps (wired back-to-back) directly into the lamp driver's base. The driver tranny has a resistor between base and collector and the lamp between collector and V+.

The LDR is on the preamp's emitter, in series with a cap to bypass the emitter resistor. So it varies the preamp gain.

The devil is in the details, though; yesterday during LFO building, there was a lot of swearing.  It's difficult to match the LFO and the lamp driver.

[sunder]

OK, I settled on separate power supplies for the LFO and audio parts. Now the LFO popping is gone

The bad thing is, the audio part sounded better with 12 V as compared to a dwindling 9V battery...

Which leads me to the question, how can I use a single 12 V wallwart for this effect and, inside the pedal, "separate" it into two 12 V supplies (so that it acts as two separate wallwarts or batteries, if you will)?

I guess one way would be to use a transformer with two 12 V taps. Is there a more simple way?

[ExpAnonColin]

Also keep in mind that the LFO popping very much has to do with it being on a breadboard, the difference is quite shocking between the 2.

-Colin

[smoguzbenjamin]

Just run the two sections in parallel.

[sunder]

Also keep in mind that the LFO popping very much has to do with it being on a breadboard, the difference is quite shocking between the 2.

-Colin

uh-huh, this is the first project I'm developing on a breadboard, and it has already proven invaluable! Comfy. I guess I will put my finished circuits on breadboard again, too. It's just so easy switching resistor values, and going "I wonder what this will do".. it's a great tool.

[sunder]

Just run the two sections in parallel.

I'll try that as soon as the coffee is finished

[sunder]

Just run the two sections in parallel.

that doesn't seem to work. I think I'll have to look for a suitable transformer... it's just that I don't know much about powersupplies...

[smoguzbenjamin]

running the two sections in parallel power wise should work fine. Unless you are drawing too much current...

[sunder]

running the two sections in parallel power wise should work fine. Unless you are drawing too much current...

The lamp /LFO section draws 65-75 mA. The preamp should draw significantly less, it's only a one-transistor stage...

nope, it doesn't work... *pop * *pop* *pop*

of course I could just run the preamp from 9V battery as it is now...