This Week on the Breadboard: The FireDrake

do the MOSFETs produce noticeably more harmonics than the other clipping options?

also, with the gain pot also being in the feedback loop, C13 interacts with it and really only comes into play in the highest gain settings, correct?
 
thunderaxe said:
do the MOSFETs produce noticeably more harmonics than the other clipping options?
Click to expand...
That was my observation with this circuit.

thunderaxe said:
also, with the gain pot also being in the feedback loop, C13 interacts with it and really only comes into play in the highest gain settings, correct?
Click to expand...
It's not that simple since there are non-linear elements (MOSFETs Q1 & Q2) in parallel with C13 & GAIN pot. In general, the effect of C13 will be more pronounced when GAIN is turned up, but it also depends on the strength of the input signal.
 
Apols in advance for the noob question but just wanting to have a crack at this and was trying to work out the orientation of the pots. Does the CW marker on the schematic relate to pin 3 or pin 1?
 
looking at this again, i'm curious why the output buffer/buffered output volume is necessary, in either the original or your redesign. wouldn't the impedance coming off the output of the treble filter op amp be almost zero already? so would there be any disadvantage to just sticking an output cap and passive volume control on the end there?
 
i'm just curious because it seemed like one of the goals of your redesign was to do it with the minimum required number of op amps.

do you prefer the op amp clipping sound of the CA3130 over that of a TL072?

i'd also be curious just in general which op amps you consider to have the most musical clipping sound to them. other than the LM308 which is pretty much unobtainium these days.
 
I wanted a rail-to-rail opamp for the clipping stage. CA3130 was the best choice I had at the time. I've since found another potential candidate and it comes in a dual.

As for clipping tone, the TL072 is pretty good if biased correctly. But it has a lot less headroom compared to the CA3130.
 
is that the TLC2272 by chance?

also is there anything more to biasing a TL072 properly for clipping than giving it a half-voltage VREF? or does it have an internal offset?
 
TLC2272 is one of them. TLV2372 is another.

When driven to saturation, the TL072's output can get closer to the +rail then to the -rail (GND). Setting Vref slightly above 1/2 Vcc will compensate for this and provide nearly symmetric clipping. We may not always want symmetric clipping, so it's up to the designer to decide what's best.
 
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