boost vs overdrive

[m7b52000]

I have built a handful of drive pedals and now think I have some understanding of soft and hard diode clipping. Using LEDs as hard clipping diodes gives more headroom as their forward voltage is higher than other diodes so if the gain is turned down and the volume up, is the circuit really functioning as a boost rather than an overdrive?

[Mark Hammer]

In a great many instances, ANY boost, no matter how much headroom it has, serves as an overdrive, simply because the amplifier's input stage is expecting a more modest input signal.  The coloration produced may not be painfully obvious or particularly saturated, but it may be there, unless the amp is designed to have especially high headroom, like some keyboard and pedal steel amps are.  The question is whether the boost adds any coloration itself, over and above what it does to the amplifier.

[m7b52000]

In a great many instances, ANY boost, no matter how much headroom it has, serves as an overdrive, simply because the amplifier's input stage is expecting a more modest input signal.  The coloration produced may not be painfully obvious or particularly saturated, but it may be there, unless the amp is designed to have especially high headroom, like some keyboard and pedal steel amps are.  The question is whether the boost adds any coloration itself, over and above what it does to the amplifier.

Thanks but you have answered the opposite question - Is a boost acting as an overdrive? My question is: if there is not yet diode clipping is the overdrive simply acting as a boost?

[POTL]

In a great many instances, ANY boost, no matter how much headroom it has, serves as an overdrive, simply because the amplifier's input stage is expecting a more modest input signal.  The coloration produced may not be painfully obvious or particularly saturated, but it may be there, unless the amp is designed to have especially high headroom, like some keyboard and pedal steel amps are.  The question is whether the boost adds any coloration itself, over and above what it does to the amplifier.

Yes
Thanks but you have answered the opposite question - Is a boost acting as an overdrive? My question is: if there is not yet diode clipping is the overdrive simply acting as a boost?

[iainpunk]

In a great many instances, ANY boost, no matter how much headroom it has, serves as an overdrive, simply because the amplifier's input stage is expecting a more modest input signal.  The coloration produced may not be painfully obvious or particularly saturated, but it may be there, unless the amp is designed to have especially high headroom, like some keyboard and pedal steel amps are.  The question is whether the boost adds any coloration itself, over and above what it does to the amplifier.

Thanks but you have answered the opposite question - Is a boost acting as an overdrive? My question is: if there is not yet diode clipping is the overdrive simply acting as a boost?

depends on the threshold and what comes after it. if it hard clips with Ge diodes which is followed by a big muff tone stack without recovery gain, its an attenuator, if the headroom is high, like Si diodes or LED's, it could act as a boost.

cheers, Iain

[antonis]

My question is: if there is not yet diode clipping is the overdrive simply acting as a boost?

Not enough data about:
Input signal amplitude
Stage gain
Headroom
Diodes forward voltage drop
Amplifier input sensitivity

[m7b52000]

This question arose while I was looking at the LEDs and seeing how hard I had to hit my Strat in order to make them light up. So, if the LED are not lighting up then the LED forward voltage is high enough and the input amplitude is low enough to prevent clipping. The amp is not important as I am not asking about the effect of a boost on the amp. I just wanted to confirm that I was right in thinking that a hard clipping LED drive was acting as a boost if it hadn’t started to clip and if the output vol was greater than unity.

[iainpunk]

This question arose while I was looking at the LEDs and seeing how hard I had to hit my Strat in order to make them light up. So, if the LED are not lighting up then the LED forward voltage is high enough and the input amplitude is low enough to prevent clipping. The amp is not important as I am not asking about the effect of a boost on the amp. I just wanted to confirm that I was right in thinking that a hard clipping LED drive was acting as a boost if it hadn’t started to clip and if the output vol was greater than unity.

yes, it acts like a boost

[Mark Hammer]

In a great many instances, ANY boost, no matter how much headroom it has, serves as an overdrive, simply because the amplifier's input stage is expecting a more modest input signal.  The coloration produced may not be painfully obvious or particularly saturated, but it may be there, unless the amp is designed to have especially high headroom, like some keyboard and pedal steel amps are.  The question is whether the boost adds any coloration itself, over and above what it does to the amplifier.

Thanks but you have answered the opposite question - Is a boost acting as an overdrive? My question is: if there is not yet diode clipping is the overdrive simply acting as a boost?

I guess I was busy thinking about dinner preparation and didn't complete my reply.  So...

If one has set an overdrive for the cleanest possible sound, BUT the volume is set higher than bypass, it may be set to function as a boost, but the end result may well be overdrive, simply because the output is hotter than the amp might be expecting.  So the answer to your question is "yes", if the pedal's volume is not set too high, but "No" if the volume is cranked.

Indeed, nearly all the "clean boosts" of the late '60s and '70s  - LPB-1, MXR Micro-Amp, DOD Bi-Fet Preamp, Stratoblaster, et al. - were intended to be used AS overdrives, even though they provided no clipping internally.  My first "overdrive pedal" was actually a Univox Compressor, whose Volume control I would manipulate with an EHX Hot Foot.  Clearly, compressors are designed NOT to clip, but when I cranked the volume, the amp gave me sweet overdrive.

[m7b52000]

Thanks all