Mosfet vs. diodes for OD/Boost?

[Winklin]

Can anyone describe the general difference in tone, feel, gain structure or whatever between OD/Boost pedals that use diodes and ones that use mosfet tech to generate clipping?
Looking for a little enlightenment......
Thanks.

 

[wopr]

Bump. I'd like to know as well. I also saw something called "Cascaded, non-inverted gain stages" (pro-analog). How is that different?

 

[Marcus Dahl]

Germanium diodes are more compressed and squishy sounding
Silicon diodes are sharp focused and tight
Fets/Mosfet transistors are tubish and crunchy
LEDs are crunchy buzzy and less compressed

Cascading is like it sounds. It's something that is in series with or one right aftrer the other. You can do this with diodes, transistors, op-amps. Just about anything.

Non-inverting gain stages. You have an in-verting and a non-inverting side on on an op-amp. You can just use one or the other as inputs or to control your gain.

 

[StompBoxBlues]

Germanium diodes are more compressed and squishy sounding
Silicon diodes are sharp focused and tight
Fets/Mosfet transistors are tubish and crunchy
LEDs are crunchy buzzy and less compressed

Cascading is like it sounds. It's something that is in series with or one right aftrer the other. You can do this with diodes, transistors, op-amps. Just about anything.

Non-inverting gain stages. You have an in-verting and a non-inverting side on on an op-amp. You can just use one or the other as inputs or to control your gain.

Good answer. Just to elaborate, cascading is more specifically that amplifiers (op-amps, or transistors, or tubes) amplify and pass the amplified signal on to another amplification stage...it means more control because each stage then can stay more in its' boundaries of operation. I mean, instead of one amplification stage, where it is pushing it's limits, it can work less hard...amplify a little less and pass it on to another that can also have more headroom, etc.

 

[StompBoxBlues]

Germanium diodes are more compressed and squishy sounding
Silicon diodes are sharp focused and tight
Fets/Mosfet transistors are tubish and crunchy
LEDs are crunchy buzzy and less compressed

Cascading is like it sounds. It's something that is in series with or one right aftrer the other. You can do this with diodes, transistors, op-amps. Just about anything.

Non-inverting gain stages. You have an in-verting and a non-inverting side on on an op-amp. You can just use one or the other as inputs or to control your gain.

By the way...did you mean that about LEDs being less compressed?
I was surprised, because to me...they act as diodes that drop 0.7 (am I misremembering?) which would mean any voltage rising above 0.7v in the correct orientation, will clip immidiately after that point (unless there is a resistance in series that will move up the clip point) which would make me think it would be more compressed?

How come they are less compressed?

 

[Marcus Dahl]

By the way...did you mean that about LEDs being less compressed?
I was surprised, because to me...they act as diodes that drop 0.7 (am I misremembering?) which would mean any voltage rising above 0.7v in the correct orientation, will clip immidiately after that point (unless there is a resistance in series that will move up the clip point) which would make me think it would be more compressed?

How come they are less compressed?

Good question. I go mainly by my ears on this stuff. So I'm less technical than some of the other builders, but if memory servce me right. Silicon is .6v & germainium is like half, or round about. I would say that LEDs being less compressed would be from what materials they use to make them. I'm not sure what they measure, but from my experience with them they are less compressed sounding. Of course this changes some from color to color as well as the tone and even the clipping threshold.

 

[Don Rusk]

Right I thought LEDs as clipping diodes generally had more 'headroom'/higher clipping ceiling than 'regular' diodes ---

usually on pedals with diode or 'compression' switches - the regular diodes are the most clipped/compressed - LEDs for less compression and no diodes for least compression...

 

[Marcus Dahl]

Right I thought LEDs as clipping diodes generally had more 'headroom'/higher clipping ceiling than 'regular' diodes ---

usually on pedals with diode or 'compression' switches - the regular diodes are the most clipped/compressed - LEDs for less compression and no diodes for least compression...

Transistor - depends
Germanium - Most Compression
Silicon- less
LED's - even less
Nothing - depends on the circuit.

Remember overdrive and distortion is a type of compression.

 

[Marcus Dahl]

The tuning of each of these devices far outweighs the simple math of voltage drop vs. voltage drop, execution of design is more meaningful than the design itself. The components/devices listed can each be tuned with resistors, caps, biasing etc. to perform to varying degrees of compression, hardness, texture, transition ect. When a product lists the device used that is the MARKETING of the device, the disclosure of the device is used to conjure an image of tone in the potential buyers mind (terms like class A, FET, mosfet, tube, carbon comp, oxygen free etc.) none of these terms add up to a certain repeatable consistent tone that can be expected when the given device is used, to illustrate this think of all the non-tube sounding devices that have a glass window with a tube glowing inside. The best you can hope for is generalities that are most likely going to be misleading unless each device is used in a purely tradition sense without any creative tuning (most likely not boutique built).

Builders from large to small use marketing terms even if by accidental programming to do so, it is accepted and useful at leading potential customers to what might be a fitting product. Some device names just are not “sexy enough” to use as marketing tools, op-amps are probably the most successful device for stomp boxes with the most widely liked results, yet nobody seems to get excited about knowing a pedal has an op-amp inside (imagine sticker touting “op-amp inside”) the closest I have seen is the JRC4558D, there are many players that believe the 4558D has a specific sound, that it is responsible for the midrange of the TS pedals and that it somehow imparts midrange to any device to which it is installed.

The final results are likely more about the talent level, creativity and commitment of the designer to the product rather than of any specific device used within.

Finally somebody with a more eloquent writing skill than I, and he is right.

 

[Don Rusk]

Transistor - depends
Germanium - Most Compression
Silicon- less
LED's - even less
Nothing - depends on the circuit.

Remember overdrive and distortion is a type of compression.

Compression is also a form of distortion - distortion meaning 'change or alteration' ~~ compression is amplitude distortion.

 

[Marcus Dahl]

Compression is also a form of distortion - distortion meaning 'change or alteration' ~~ compression is amplitude distortion.

:AOK