How to measure output voltage of a pedal?
- diagrammatiks
- Solder Soldier
well if you take out the diodes you'll change how the pedal sounds but it will increase the output voltage swing significantly.
as too what the maximun input voltage of a transistor amp is...
that's hard to say.
it should theoretically be a little bit less then half the maximun supply voltage.
however it will clip way before that so most of that signal will be squashed at the input anyway.
as too what the maximun input voltage of a transistor amp is...
that's hard to say.
it should theoretically be a little bit less then half the maximun supply voltage.
however it will clip way before that so most of that signal will be squashed at the input anyway.
- FiveseveN
- Cap Cooler
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Nope. LEDs are not current-limited. They will destroy themselves if you just apply voltage to their terminals, they don't "know" how much current to pull, you have to set it by using a resistor.With leds the extra energy goes into light, and not shortcircuit therefore right?
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- DrNomis
- Old Solderhand
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Leds will typically draw up to about 20mA of current before they burn out and, or explode, the current limiting resistor prevents that from happening....
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- FiveseveN
- Cap Cooler
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Yeah, that's what I meant. I guess one could use them as (bad) low-power fuses
Anyway, it's one more reason to use such a resistor.
1N4148s and the like have 200 mA continuous / 450 mA peak forward current rating, which means an opamp would fry before it can damage the diodes.
Anyway, it's one more reason to use such a resistor.
1N4148s and the like have 200 mA continuous / 450 mA peak forward current rating, which means an opamp would fry before it can damage the diodes.
Ignorance more frequently begets confidence than does knowledge. (Charles Darwin)
- mictester
- Old Solderhand
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No - you still need a current-limiting resistor (just like connecting an LED across a battery). If you're going to use LEDs you can use a 1k resistor from the output of the op-amp.Lonkero wrote:
When using leds are diodes, shouldn'vt I be able to leave the 10k resistor out, since it's doesnt sound like a short circuit when the leds start conducting since they lighten up? (vs. other diodes)
With leds the extra energy goes into light, and not short circuit therefore right?
If you do use LEDs, there will be much more level available (about 1.8 V p-p), so you'll have plenty of signal to put into a passive tone control. This could be a useful addition to a simple pedal like this - making a DOD 251 perhaps?
"Why is it humming?" "Because it doesn't know the words!"
- Lonkero
- Solder Soldier
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Thanks for the info guys. I have one MXR plus modded and boxed clone, and reason I was asking about this resistor so much is because I'm using only one led there as clipper, and there's no resistor on output of op-amp ( i left it out when i noticed on bredboard the sound is better without it)
I haven't noticed any problems what so ever yet after a couple months of playing (even the led is still working), but it's better that I install a 1k resistor there.
I haven't noticed any problems what so ever yet after a couple months of playing (even the led is still working), but it's better that I install a 1k resistor there.