Could anyone explain hi-cut vs prescence (with specific regards to Recto Red)

themaidenmaniac

themaidenmaniac

Experienced
Hi guys,

Having dialed in a stormer of a recto tone, I thought i'd just enquire about something which has been bugging me a bit. On the recto red new and im guessing a couple of other amps maybe the vox- the presence control turns into a hi-cut control.
I understand it is something to do with negative damping, but thats where you gurus come in as I havent got a clue when it gets a wee bit deeper like that!

I am trying to work out basically how it converts to a real world rectifier, as a hi-cut control obviously works kind of backwards in comparison to a prescence control. Should it just be treated that way?

I have also noticed that the depth knob on the new recto red appears to do nothing at all. Is that because a recto has no resonance knob? (apologies- I only own a 5150!)

Cheers for any hints and tips chaps!

Kev
 
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Looks like Im getting there with the search function :D


I guess what Im really after is a translation of what an axe fx hi-cut setting would be in terms of a real life rectifier's prescence dial. I have heard this dial changes dramatically on the red channel in real life anyway- so maybe it turns into a real life hi cut control :S Very confused haha.

EDIT!

Ok found this little gem of info online... from the schematic it looks like the prescence knob is just like the treble roll-off "switch" on the Orange channel but with a 25k variable resistor instead.

Therefore, I figure I would be correct to say this knob was simply working backwards in the Axe FX when in comparison to the real deal. E.g. 12 oclock = 12 oclock, but 9 oclock on the axe would be 3 oclock on the Mesa.

Anything wrong with that?






Also useful info of course in the manual helped me.


PRESENCE/HI-CUT – Boosts (or cuts) the upper frequencies from the power amp simulator by varying the
negative feedback frequency response.

Increased presence can help a sound cut through a heavy mix.

Amps with no negative feedback circuits in their design cannot utilize a presence circuit.

If DAMPING (which determines the amount of negative feedback) is set to “0.00,” PRESENCE becomes a simple high-shelf
equalizer at the output of the power amp, and its label changes to “HI-CUT.” This allows you to control the high-frequency
response of the power amp for models that don’t have any negative feedback. When changing to a model with no negative
feedback (i.e. Class-A, Mr.Z, Recto Red), be sure to check your presence settings as settings higher than zero might darken
the sound undesirably.

Note: Unlike previous Axe-Fx models, the virtual presence circuit on the Axe-Fx II now operates from 0-10
instead of +/-5. Set it as you would on a regular amp.
 
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According to the Dual Recto's documentation:

"In the Red Channel the Presence circuitry is quite advanced because it switches from one type of Presence located in one part of the power section, to a different Presence circuit located earlier in the pre-amp section."

"When the Modern High Gain Mode is called up, the Presence makes the move to a new place in the circuit and gets revoiced to work on a lower frequency. Just right for adding attack and urgency, this Presence is the aggression control. It is normal for high settings of this control to make Modern Red seem extremely loud in comparison to the other Modes. This is a result of unclamping what worked as the Presence in the other two Modes and letting the DUAL or TRIPLE RECTIFIERS ponies run free."


How do you mimic the Recto Red's presence control? Why doesn't the Recto Red model just copy the Mesa's Presence new circuit location in the preamp instead of changing it to hi-cut?

If we could insert the graphic eq located in the amp block to in between the preamp and power amp we could probably replicate this if we knew the center frequency. (But then again I would like to do this anyways on the Mark IV model since its graphic EQ is before the power amp, not afterwards like the Axe-FX.)
 
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A Dual Rectifier's "Presence" control in the Modern modes is a high-cut. It's just called Presence. The model is correct but the operation of the control is reversed (for continuity with other models).
 
FractalAudio said:
A Dual Rectifier's "Presence" control in the Modern modes is a high-cut. It's just called Presence. The model is correct but the operation of the control is reversed (for continuity with other models).
Click to expand...

So by leaving the hi cut at zero, is that the same as turning the presence on the actual amp to 10?
 
Not specific to the Recto, but it might help to understand what Presence does in a real amp.

Amps that use negative feedback (pretty much all Class AB amps and some others) take some of the output and mix it back into the input, but out of phase. That's why it's called negative feedback - negative because it's out of phase and feedback because it's fed from the output back into the input.

It helps to make the power amp more linear (in particular smoothing out crossover distortion between the 2 halves of a Class AB design), as well as reducing overall gain because the negative feedback subtracts signal. On the Axe FX, Damp sets the amount of negative feedback.

A presence control cuts the amount of highs in the feedback circuit, so less highs in the negative feedback is the same as more highs overall (less highs being subtracted = more highs getting through).

FWIW the Depth control works the same way to boost lows by reducing lows in negative feedback. Sometimes it's a low-shelf type of cut while other amps use a mid to low frequency notch in the feedback to produce a peak type of low-end boost. Amps often label this as a Resonance control.

So when you turn Damp off on the AxeFX, there's no negative feedback for the Presence (or Depth) to cut, so Cliff can do other creative and useful things with these controls.
 
GM Arts said:
Not specific to the Recto, but it might help to understand what Presence does in a real amp.

Amps that use negative feedback (pretty much all Class AB amps and some others) take some of the output and mix it back into the input, but out of phase. That's why it's called negative feedback - negative because it's out of phase and feedback because it's fed from the output back into the input.

It helps to make the power amp more linear (in particular smoothing out crossover distortion between the 2 halves of a Class AB design), as well as reducing overall gain because the negative feedback subtracts signal. On the Axe FX, Damp sets the amount of negative feedback.

A presence control cuts the amount of highs in the feedback circuit, so less highs in the negative feedback is the same as more highs overall (less highs being subtracted = more highs getting through).

FWIW the Depth control works the same way to boost lows by reducing lows in negative feedback. Sometimes it's a low-shelf type of cut while other amps use a mid to low frequency notch in the feedback to produce a peak type of low-end boost. Amps often label this as a Resonance control.

So when you turn Damp off on the AxeFX, there's no negative feedback for the Presence (or Depth) to cut, so Cliff can do other creative and useful things with these controls.
Click to expand...

This is one of the simplest and clearest explanation of Negative feedback and presence and depth control I've ever seen. Despite researching this for my own edification, this has never been so simply laid out.
Thanks. I've relatively uneducated when it comes to how amplifiers work, so this was very helpful.
 
Patzag said:
This is one of the simplest and clearest explanation of Negative feedback and presence and depth control I've ever seen. Despite researching this for my own edification, this has never been so simply laid out.
Thanks. I've relatively uneducated when it comes to how amplifiers work, so this was very helpful.
Click to expand...
you're welcome, Patzag ;)
 
GM Arts said:
Not specific to the Recto, but it might help to understand what Presence does in a real amp.

Amps that use negative feedback (pretty much all Class AB amps and some others) take some of the output and mix it back into the input, but out of phase. That's why it's called negative feedback - negative because it's out of phase and feedback because it's fed from the output back into the input.

It helps to make the power amp more linear (in particular smoothing out crossover distortion between the 2 halves of a Class AB design), as well as reducing overall gain because the negative feedback subtracts signal. On the Axe FX, Damp sets the amount of negative feedback.

A presence control cuts the amount of highs in the feedback circuit, so less highs in the negative feedback is the same as more highs overall (less highs being subtracted = more highs getting through).

FWIW the Depth control works the same way to boost lows by reducing lows in negative feedback. Sometimes it's a low-shelf type of cut while other amps use a mid to low frequency notch in the feedback to produce a peak type of low-end boost. Amps often label this as a Resonance control.

So when you turn Damp off on the AxeFX, there's no negative feedback for the Presence (or Depth) to cut, so Cliff can do other creative and useful things with these controls.
Click to expand...

This is an excellent explanation of negative feedback and how it relates to presence and depth...thank you!
 
babuka said:
According to the Dual Recto's documentation:

"...the Presence circuitry is quite advanced because it switches from one type of Presence located in one part of the power section, to a different Presence circuit located earlier in the pre-amp section."
Click to expand...

HaHa! I love Mesa's BS marketing crap. It's actually a pretty simple circuit.
 
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