Some differences between real JP2C and AxeFx models?

https://forum.grailtone.com/viewtopic.php?t=73823

There was an interesting discussion on the "Boogie Board."

Title: "Does anyone feel the JP2C is overly compressed?"

Opening sentence:
"There's no doubt that the JP is much more compressed than the original, it's the first thing you notice when you A/B them. I know with my other Boogies as you increase the gain it gets more compressed, and the JP has a TON of gain on tap."

The discussion was about swapping out a 12ax7 (μ=100) in the JP-2C
for a less powerful tube with a lower amplification factor
-- such as a 12AT7 (μ=60) or a 5751 (μ=70, the SRV tube.)

Just saying, it never hurts to see what preamp tubes you have, especially in a used amp.
 
Postretro said:
@zazanroger, more specific USA JP-IIC "Presence Shift" switch information:

"Presence Shift" switch OFF (default) == Mesa "Treble Pull" OFF (IIC+) / Mesa "Fat" switch ON (Mark IV)

"Presence Shift is Presence pull. Tone stack effectively has fat switch on."

On the JP-2C:
By default, Mid is at 250 Hz. When the "Presence Shift" is OFF. (1000p tone cap)
The Mid shifts up to ~500 Hz. When the "Presence Shift" is ON. (250p tone cap)
-- "Tonestack Freq" display will not change. It will still show 250 Hz.

The 250 Hz tonestack-center is the Mesa Lead tonestack.
The 500 Hz tonestack-center is like a Fender tonestack.


https://mesa-boogie.imgix.net/media/User Manuals/070494-JP2C-160317-download.pdf
From the Mesa JP-2C Manual:
"The Two PRESENCE Modes Set Up Very Differently! Pushing and Pulling Will Probably NOT Give You Two Great Sounds! You Need To Set The PRESENCE Control Differently For Each Voicing Mode! See Below “Setting”!"

There is a lot more specific and helpful information about the PRESENCE mode in the Mesa JP-2C Manual.


From the Amp Guide:

"Similar to the FAT switch on a Mesa Boogie. A popular control for lead tones because it adds body to the tone."

"The key to a good Boogie sound, IMO, is the Fat Switch. This is the treble Pull Shift on the IIC+ and the Pull Fat on the Mark IV. Mesa knew this and the Lead 2 modes on the Triaxis all had the treble shift engaged by default."

“Emphasizes midrange and adds “body” by shifting the tonestack center frequency.”

"The Fat switch simply alters the tone stack treble capacitor. So the effect depends on the location of the tone stack."

"The Fat Switch multiplies the tone stack treble cap by four.
Depending upon the type of tone stack, tone control settings, position, etc.
The effect can be more or less noticeable."

"The Fat switch changes a value in the tone stack which changes the response of the stack, shifting the mid dip down and making it less pronounced. The "Tonestack Freq" parameter frequency scales all the reactive components in the tone stack which is something quite different."
Click to expand...
Hi, Thanks for your help, from I understanding the FAT switch is already build into the JP2C modeling, behave different from IIC+ and Mark IV modeling, The presence pull pot on JP2C is not FAT Switch and behave different from Mark IV too.
 
@zazanroger, yes, after carefully rereading the JP-2C manual again, I think I understand you, now.

The IIC+ "Treble Pull" and the Mark !V "Fat" switch are basically the same.
The IIC+ is pushed in to be "Fat" and the Mark IV is pulled out to be "Fat."

And, the JP-2C is like the IIC+.
EDIT: I am wrong here. I misunderstood. FAT switch ON is built into the channel's tonestack.

BUT, the JP-2C also makes an adjustment to the Presence control itself, depending on whether the "Presence Pull" is in(Fat) or out(Fender.)

The PULL PRES switch also "allows two very different Presence frequencies to be selected."

1) "When PULLED, the time-honored frequency we have used for 45 years appears,
which allows control over a much higher range of top end than that of the TREBLE control."

-- With the Presence pulled / Presence switch ON -- The presence frequency stays the same as it has always been.

2) "When left PUSHED-IN, the PRESENCE control operates on a lower frequency that is still above the TREBLE, but adds “increased cut and focus” lower than the traditional PRESENCE that in some applications can sound more cohesive for high gain Crunch rhythm sounds."

-- With the Presence pushed in / Presence switch OFF -- The presence frequency is shifted lower.

-- This is the same as using a larger NFB capacitor.

If I am reading the manual correctly, it states that because
1) of this frequency shift in the Presence NFB circuit,
2) and because of the taper of the Presence pot,
The presence control has to be re-adjusted when the "Present pull"(Fat switch) is reset (pulled-out/pushed-in, switched-on/switched-off.)

"The deactivated PUSHED-IN Mode will require you to set the PRESENCE control HIGHER to achieve a balanced (open) sound,"

"The PULLED-OUT Mode will require you to DECREASE the PRESENCE control to blend in these higher frequencies and achieve a warmer sound."

"The Two PRESENCE Modes Set Up Very Differently! Pushing and Pulling Will Probably NOT Give You Two Great Sounds! You Need To Set The PRESENCE Control Differently For Each Voicing Mode! See Below “Setting”!"

Finally, "Presence Shift" is still the Fat Switch, as FAS has stated.
EDIT: I am not sure about this. I may have misunderstood what FAS said. Still trying to understand.
EDIT: Yes, I misunderstood. There is no Fat switch. It is built into the Red channel, and the Yellow channel too I suppose.
Still not sure about the Green channel.

The "Presence Shift" switch is also located on the "Power Amp" page of the amp block next to the "Presence Frequency" control.
I don't see the "Presence Frequency" change. But, I didn't see the "Tonestack Freq" change with switching ON or OFF, either.
So, I am betting that FAS modeled it to include the NFB Presence frequency shift.

Which also makes sense. Since, it requires a readjustment of the presence control when used.

I hope this helps. I don't have a JP-2C to confirm this. But, I think this is correct.
 
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Postretro said:
@zazanroger, yes, after carefully rereading the JP-2C manual again, I think I understand you, now.

The IIC+ "Treble Pull" and the Mark !V "Fat" switch are basically the same.
The IIC+ is pushed in to be "Fat" and the Mark IV is pulled out to be "Fat."

And, the JP-2C is like the IIC+.
EDIT: I am wrong here. I misunderstood. FAT switch ON is built into the channel's tonestack.

BUT, the JP-2C also makes an adjustment to the Presence control itself, depending on whether the "Presence Pull" is in(Fat) or out(Fender.)

The PULL PRES switch also "allows two very different Presence frequencies to be selected."

1) "When PULLED, the time-honored frequency we have used for 45 years appears,
which allows control over a much higher range of top end than that of the TREBLE control."

-- With the Presence pulled / Presence switch ON -- The presence frequency stays the same as it has always been.

2) "When left PUSHED-IN, the PRESENCE control operates on a lower frequency that is still above the TREBLE, but adds “increased cut and focus” lower than the traditional PRESENCE that in some applications can sound more cohesive for high gain Crunch rhythm sounds."

-- With the Presence pushed in / Presence switch OFF -- The presence frequency is shifted lower.

-- This is the same as using a larger NFB capacitor.

If I am reading the manual correctly, it states that because
1) of this frequency shift in the Presence NFB circuit,
2) and because of the taper of the Presence pot,
The presence control has to be re-adjusted when the "Present pull"(Fat switch) is reset (pulled-out/pushed-in, switched-on/switched-off.)

"The deactivated PUSHED-IN Mode will require you to set the PRESENCE control HIGHER to achieve a balanced (open) sound,"

"The PULLED-OUT Mode will require you to DECREASE the PRESENCE control to blend in these higher frequencies and achieve a warmer sound."

"The Two PRESENCE Modes Set Up Very Differently! Pushing and Pulling Will Probably NOT Give You Two Great Sounds! You Need To Set The PRESENCE Control Differently For Each Voicing Mode! See Below “Setting”!"

Finally, "Presence Shift" is still the Fat Switch, as FAS has stated.
EDIT: I am not sure about this. I may have misunderstood what FAS said. Still trying to understand.
EDIT: Yes, I misunderstood. There is no Fat switch. It is built into the Red channel, and the Yellow channel too I suppose.
Still not sure about the Green channel.

The "Presence Shift" switch is also located on the "Power Amp" page of the amp block next to the "Presence Frequency" control.
I don't see the "Presence Frequency" change. But, I didn't see the "Tonestack Freq" change with switching ON or OFF, either.
So, I am betting that FAS modeled it to include the NFB Presence frequency shift.

Which also makes sense. Since, it requires a readjustment of the presence control when used.

I hope this helps. I don't have a JP-2C to confirm this. But, I think this is correct.
Click to expand...
Cliff's post from the Axe Wiki: "If you have pulled the presence knob on the amp you have to activate the Presence Shift on the model. Otherwise they will sound VERY different. Presence shift gives a much more focused sound. I always use the Presence Shift. You can't compare the amp with a switch engaged to the model without the equivalent switch engaged. Of course it will sound different. The tapers of the other controls should be very close including the Presence and Master Volume"
 
Thank you, @zazanroger. I took me a while to realize that the Presence Shift was not a Fat switch. I saw the quote. But, I missed the context of the quote and missed the idea that the "Fat Switch" was built-in to the channel's tonestack. I am fairly sure rest is accurate. But, I always appreciate correction. I need to get it right.
 
It is worth noting, that since the Master and Presence control tapers of the model matches the JP-2C amp, that the Presence control will need to be re-adjusted on the model in the same way that the Presence control would need to be re-adjusted on the JP-2C amp after the "Presence Pull"/"Presence Shift" is reset.
 
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