im building the modded easyvibe (http://www.geocities.com/stompboxworktop) by pedro freitas, (gotta love that guy and his lunchboxes)
and i built the LFO part first, and it is not working. :evil:
the battery voltage is 8.64 volts and the lamp works.
how do you debug one of these?
im guessing you cant use an audio probe.
anyone?
i got the lamp working but only the 470k trimpot changes the brightness (turning it all the way up turns the bulb almoost off)
cant anyone help? :cry:
Bit of an odd circuit. It's a variation of a simple relaxation LFO, a non-linear triangle being tapped from the RC junction that sets the rate.
If the lamp's brightness isn't changing rhythmically then the LFO isn't oscillating.
What op-amp are you using? These circuits can be pretty tetchy in this respect, though the + input isn't being pulled to the rails due to the 150k comming off the divider, so plenty of amps should work.
If you're sure your connections are ok, try subbing another amp (different type to the one you're using). CA3130E should work.
I take it you don't have a scope? Do you have a log multimeter? If so, try sticking a large electrolytic cap in parallel with the 10uF connected to the 'Depth' pot. This will slow the LFO right down and enable you to track the voltage with your meter (I used to do this in the days before I had a scope) and you'll be able to see (literally) if your oscillator is working.
ah.....10uf, you say?
i seem to have put a 4.7 there by mistake :oops: :oops: :oops:
will that affect the oscillation?
im using a LM741CN
Quote from: lightningfingersah.....10uf, you say?
i seem to have put a 4.7 there by mistake :oops: :oops: :oops:
will that affect the oscillation?
im using a LM741CN
Because he's used a 150k & 470k divider to set the thresholds it's a little difficult to calculate the freqency of this circuit. He's obviously done this so that the + input isn't pulled too close to the rails meaning that the circuit shouldn't be too sensitive to different amps.
Whatever the frequency (shouldn't think it will be much higher than 10-12Hz max speed), using a cap less than half of what is recommended will speed up the LFO to more than double what it's supposed to be. It's quite possible then that this is the reason your lamp
appears to be constantly on - the sluggish response of the lamp making it impervious to changes that quick.
Try it with the proper cap. If still no joy stick a large cap in parallel with the 10u and see if you can measure the output of the amp with a multimeter. If you can detect no change in voltage then try subbing in a different amp - CA3130E, possibly a CA3140E
Incidentally, I wonder if you could replicate the sluggish response of a lamp with a LED & resistor in series (similar type of circuit) and a small value cap to ground from the junction of the two? Thoughts anyone?
nope, this thing aint oscillating.
i measured the pin votages, do these sound right to you?
pin1-0V
pin2-0.92V
pin3-0.35V
pin4-0V
pin5-0V
pin6-1.99V
pin7-2.36
pin8-0V
do they look OK?
Quote from: lightningfingersnope, this thing aint oscillating.
i measured the pin votages, do these sound right to you?
pin1-0V
pin2-0.92V
pin3-0.35V
pin4-0V
pin5-0V
pin6-1.99V
pin7-2.36
pin8-0V
do they look OK?
No!
Pin 7 is the V+ connection and should be 9V NOT 2.36V. Check your connections to this pin.
P.S. Measure your supply's V+ connection and make sure there's nothing funny going on there.
okay, i replaced the battery and resoldered the +ve supply wire and now all the +ve battery connections are as they should be, i bought a brand new chip just to be sure and triple checked the socket pins.
alas, still no oscillation. im sure this opamp should work and it is brand new i only took it out of its anti static package 5 mins ago. i tried the big cap thing to slow the oscillation down but now i am sure there is no oscillation.
im almost ready to give up now, but is there *anything* crucial i might have forgotten?
Post some readings again. Try the chips I recommended.
One thing you could try is the following. Set the speed pot to max resistance and set the depth pot for max (wiper opposite direction to ground). Now croc clip a resistor in parallel with the 150k comming off the 10k divider. Try another 150k and if this doesn't kick start the LFO into action (lamp should blink) try slightly smaller values.
If the LFO starts working then the problem is with the amp you're using and we can either re-jig some values to suit it or you could sub in one of the amps I metioned with the values as shown.
Can you take a measurement from the centre of the 10k divider and post it?
i have tried the chips you recommended, the chips the maplin guy recommended, the chips i always use for 741 circuits, and still there is no oscillation. this must mean the problem is not with the chip, right? :?
erm..chip readings,
pin1- 0v
pin2-2.97v
pin3-3.86v
pin4-0v
pin5-0v
pin6-6.36v
pin7-~9v unstable
pin8-0v
the voltage at the centre of the 10k divider is about 1.4 its a bit unstable err, i think i said before, but the lamp does work and the trimmers affect its brightness but the two pots(depth and speed) dont do anything. this is really stumping me now.
Quote from: gezSet the speed pot to max resistance and set the depth pot for max (wiper opposite direction to ground). Now croc clip a resistor in parallel with the 150k comming off the 10k divider. Try another 150k and if this doesn't kick start the LFO into action (lamp should blink) try slightly smaller values.
il try this tonite and post my results tomorrow
oh and thanks for all the help so far :D
okay i tried what you sed, with a 200k, 150k, 147k. 133k, 110k and 100k.
nothing.
im starting to think the schematic might have a mistake in it.
does it look ok to you?
Quote from: lightningfingerschip readings,
pin1- 0v
pin2-2.97v
pin3-3.86v
pin4-0v
pin5-0v
pin6-6.36v
pin7-~9v unstable
pin8-0v
the voltage at the centre of the 10k divider is about 1.4 its a bit unstable err, i think i said before,
Things are better but still a little iffy. Pin 6 is the output and by the look of things the amp you're using doesn't swing rail-to-rail at the output, so the reading is probably right.
The divider isn't quite right though. The value should be close to half the supply. It could just be loading by the input bias current drawn from the + input, but check the connections and values of the 10k to make sure you've not got the wrong values in there. If you sub in the CA3130/40 is the reading at the centre of the divider the same as you've been getting? These are MOSFET input so if it is loading by input bias current the voltage reading should be different.
What exactly do you mean by unstable? If your meter is flickering all over the place then your LFO is probably working! When taking readings near large value caps the caps ramp up and it takes time for the meter to settle, is this what you meant?
The circuit (though I wouldn't have done it like this or used an electrolytic as they bugger up things when they start leaking) looks ok.
I think the problem here might be the 150k connected from the -ve input to the lower end of the speed pot. Could you post a reading from the junction of this resistor to the 10u cap, speed & depth pots?
The large value resistor used may to be dropping a fair chunk of voltage and this may be what is preventing the trigger thresholds from being reached. Try reducing (shorting out even) the 150k connected to pin2 and see what happens.
when i say unstable, i mean the meter doesnt settle at all, it goes to a about 3.95, then down to about 1.4 then back up again. does this mean the oscillator is working ad if so why is the lamp always on full brightnesss.
ill get those readings up this afternoon, but the readings at that divider, are all the same with every amp and always unstable.
Quote from: lightningfingerswhen i say unstable, i mean the meter doesnt settle at all, it goes to a about 3.95, then down to about 1.4 then back up again. does this mean the oscillator is working ad if so why is the lamp always on full brightnesss.
Yes, it sounds as though your LFO is oscillating!
Try setting the depth control to min, adjust the trims so your bulb is barely on (or just off) and turn the depth back up again.
nope, i get nothing. im putting
everything on a new board tomorrow, and ill make sure none of the componants are buggered, and i have some of those amps that you mentioned, so ill use one of those
Quote from: gezI wouldn't have done it like this or used an electrolytic as they bugger up things
would it help if i used tanalums instead?
i have loads of them lying around
Quote from: lightningfingersnope, i get nothing. im putting everything on a new board tomorrow, and ill make sure none of the componants are buggered, and i have some of those amps that you mentioned, so ill use one of those
Quote from: gezI wouldn't have done it like this or used an electrolytic as they bugger up things
would it help if i used tanalums instead?
i have loads of them lying around
If you still have problems after transferring everything then I could always draw you up something, but I'd need to know the current draw for the lamp (if you measure it for the circuit you've got it would help).
Yes, tantalum would be my choice, but be careful with the polarity as they're easily damaged if you get it wrong.
CA3130E gives a symmetrical output and would be my choice in this type of circuit, but it's static sensitive so be careful how you handle it.
ok i spent most of yesterday and all of this morning making a new lfo with a completely new set of parts. every component is checked and working and still there is no oscillation.
i tried most of the things we discussed in the previous posts and nothing worked.
which leads me to this; about the only thing we havent discussed is the transistor(s)
could there be any problems related to them?
Quote from: lightningfingerswhich leads me to this; about the only thing we havent discussed is the transistor(s)
could there be any problems related to them?
If the Darlington is connected up ok then there's not a lot that could be wrong, they're not static sensitive or anything.
I don't really understand why two trimpots have been used, it seems a little odd. Does he give some advice on how to set these and if so could you link to it? What sort of resistance do you have on these trimpots? If the lower one is set to bugger all then there's the danger of loading/grounding the LFO's signal.
Are you still getting 'unstable' readings from the LFOs output? If so then it's probably working ok.
its here (http://www.geocities.com/stompboxworktop)
on the easyvibe page.
im still getting the unstable readings, yeah, but the light still wont work.
Quote from: lightningfingersbut the light still wont work.
When you turn the trimpot(s) does the light change, i.e. can you make it go from off to on, or is it permantly off/on? (nothing to do with the LFO here, just want to find out if the Darlington is working ok).
yeah adjusting the trimmers will make the light go off, on and everywhere inbetween.
i put a new darlington pair in there when i replaced the board so it should be ok.
definately having some fun with this one :wink:
Quote from: lightningfingersyeah adjusting the trimmers will make the light go off, on and everywhere inbetween.
i put a new darlington pair in there when i replaced the board so it should be ok.
definately having some fun with this one :wink:
Don't know what else to suggest other than do you know someone with a scope?
Quote from: gezDon't know what else to suggest other than do you know someone with a scope?
no i tried my school but they wont let me use thiers
do you know of another LFO that might work in this circuit?[/quote]
Quote from: lightningfingersdo you know of another LFO that might work in this circuit?
PM me with your email address and I can sort you out with something if you like.
just click that link down there that says "email" :wink:
Can't send attachments via the forum which is why I asked for your address...
I drew this up a few weeks ago and posted it here. Not exactly what I had in mind but It'll probably do
(http://hometown.aol.co.uk/Gezpaton/FETvariresist.gif)
Use a BS170 for the MOSFET supplying the 4049UB. Adjust the wiper of its trim down from 5V til you measure 3V at the source. In theory it's possible to get ones with large thresholds (in which case you'd get voltages under 3V and wouldn't be able to get higher), but I've never come across any - all have worked in this type of circuit so far.
Stick your lamp from V+ to the drain of the other MOSFET (the one connected up to the depth pot). I don’t know what the current draw of the bulb you intend to use is, but you’ll probably have to use a power MOSFET there. Adjust the wiper up from ground til you get an even range across the Depth pot.
ESR have all the parts
www.esr.co.uk
It's a triangle wave. If you wanted a sine, I suppose you could use something along the lines of the EA trem's LFO and hook it up to the MOSFET driver shown above (plumb the LFO output in via the 4u7 cap). The trim for adjusting the MOSFET could be slung across the rails, or you could keep the regulator.
okay, ill get some parts tomorrow and let you know how it goes.
and thanks for this it is greatly appreciated :)
Forgot to add, ground the inputs of the unused inverters of the 4049UB.
okay its done and the bulb oscillates, but how fast is it supposed to go? it seems to get too fast at the high end, and the bulb loses its oscillation
Quote from: lightningfingersokay its done and the bulb oscillates, but how fast is it supposed to go? it seems to get too fast at the high end, and the bulb loses its oscillation
Well what do you expect if you use bulbs instead of LEDs! :)
Top speed is around 12Hz. All you have to do to slow it down is increase the 130k resistor (don't worry it won't affect amplitude or anything). Try a 160k (just under 10Hz) and if that’s still too fast then 180k (just under 9Hz). If you want the lower range to go slower then decrease the value of the 1k stop-resistor attached to the 10k pot (this may upset the linear ‘feel’ to the pot though - depends how slow you take it).
PS if anyone's wondering why the ciruit runs at 3V it's to reduce current consumption and to reduce current spikes. The spikes are so miniscule at this voltage you get tick-free operation (though this isn't guaranteed, it's still advisable to obey the rules of good layout!). Current draw is usually under .5mA for the LFO alone (if you use the regulator stated - it's micropower). Adjustable regulator could be used to get the 3V but it would add a few milliamps onto the bill.
Quote from: lightningfingersim building the modded easyvibe (http://www.geocities.com/stompboxworktop) by pedro freitas, (gotta love that guy and his lunchboxes)
and i built the LFO part first, and it is not working. :evil:
the battery voltage is 8.64 volts and the lamp works.
how do you debug one of these?
im guessing you cant use an audio probe.
Hi LightningFingers,
I assume you use the layout that is available on the net.
Make sure, there is no short on the PCB. I spent a couple of hours to figure out why my EasyVibe would not LFO only to find that there was a small connection from the LFO LEDS to ground. I scraped away the wrong connection (possibly due to a not so good toner transfer) and voila.
Kind Regards,
Electron
Quote from: ElectronMake sure, there is no short on the PCB. I spent a couple of hours to figure out why my EasyVibe would not LFO only to find that there was a small connection from the LFO LEDS to ground. I scraped away the wrong connection (possibly due to a not so good toner transfer) and voila
Now you tell us!!! :D
Quote from: electronMake sure, there is no short on the PCB
well i perfed it so that wouldnt be an issue :)
and also the one gez drew up works well :mrgreen:
:shock: :D :shock: :oops:
Seems like my response from 9.03 am was somehow lost in interspace.
Anyhow, I did not mean to rain on anyone's parade, especially not GEZ´s.
With my Easyvibe it was my fault, since, as said, the toner transfer did not come out very nice.
Glad you were able to fix it LightningFingers!
Do you plan to do the Feedback mod?
I wish my EasyVibe had a bit more warmth.
Cheers!
Electron
:wink:
actually the feedback mod adds a lot of *interesting* tones. try it you havnt already :D