Prowler conversion

[lalala]

I bought a used Peavey Prowler and I read that it was almost identical to the Valveking 112. I analyzed both schematics and there are very few differences. I'll note some of them:

       Prowler - Valveking
R122 =  470k   -   220k
C105 =  2.2nF  -   absent
C149 =  820pF  -   1nF
R173 =   47k   -   3.9M
R148 =  100k   -   56 (marked as R4)
C134 =    1nF  -   270pF (marked as C2)
R150 =  220k   -   150k
R151 =  100k   -   330k

These seem easily replaceable. However, there is a part of the preamp that I did not fully understand and I would really appreciate if somebody could lend me a hand deciphering what are the differences between both schematics on that part. That tricky part is the tone stack on the distortion channel.

Prowler schematic:


Valveking schematic:


Apparently, the Prowler has active EQ while the Valveking 112 has passive EQ. Is there a way to convert the Prowler's tone stack into the Valveking's?

Moreover, there is another difference near the end of the preamp. The difference is that the Prowler includes 4 extra diodes (all 1N4148). What are these diodes for?





Schematics:
Peavey Prowler
Peavey Valveking 112

[Jazz P Bass]

[QUOTE=Apparently, the Prowler has active EQ while the Valveking 112 has passive EQ. Is there a way to convert the Prowler's tone stack into the Valveking's?

Moreover, there is another difference near the end of the preamp. The difference is that the Prowler includes 4 extra diodes (all 1N4148). What are these diodes for?QUOTE]

I would not say the Prowler is "active".
That usually includes a transistor or an opamp in the circuit.

The whole preamp send circuit is different on the Prowler.
Not just the diodes.
The circuit is a buffer.
It is active.
The diodes are for clamping the input & output of the transistor.
It helps with noise imunity.

[Fael]

I would not say the Prowler is "active".
That usually includes a transistor or an opamp in the circuit.

You're right. It's more like a semi-active tone stack (that's what I was told by Peavy support too).

The whole preamp send circuit is different on the Prowler.
Not just the diodes.
The circuit is a buffer.
It is active.
The diodes are for clamping the input & output of the transistor.
It helps with noise imunity.

Please excuse my ignorance but is that better or worse, tone-wise? What's the tonal difference?

I went through the schematics and didn't find any differences apart frome those I already listed. Thanks for pointing that out.


Someone at the Peavey customer support recommended modifying the tone stack to match the Valveking's. How would this affect my tone?

[Fael]

Nevermind. I'm starting to research the FVM vs Baxandall tone stack stuff. I think I'm going to leave my Prowler with the Baxandall tone stack.

I will try some other mods, though...

[Jazz P Bass]

[QUOTE Originally Posted by Jazz P Bass
The whole preamp send circuit is different on the Prowler.
Not just the diodes.
The circuit is a buffer.
It is active.
The diodes are for clamping the input & output of the transistor.
It helps with noise imunity.
Please excuse my ignorance but is that better or worse, tone-wise? What's the tonal difference?QUOTE]

Just for the record, the Preamp Send circuit, the one in question with the diodes, has ZERO effect on your tone.
It is a dead end send signal.
It has nothing to do with the tone.

[Enzo]

Someone at the factory actually suggested you change the circuit? Or someone on the Peavey forum?

As to that tone stack, I see no active-ness in it at all, it is a completely passive circuit. Signal comes from the preceding stage plate, and feeds through this tone network and on out the FX loop stage.

I agree with JPB, that transistor circuit has nothing to do with your tone, it is only a buffer for the FX send. Those four diodes are there to clamp any voltages to the power rail and ground. So nothing at the FX send jack can drive the voltages at that transistor beyond the rails, which would cause a reverse voltage condition at the transistor. That is the only condition that causes those diodes to conduct at all. They are otherwise invisible.

[Fael]

Someone at the factory actually suggested you change the circuit? Or someone on the Peavey forum?

As to that tone stack, I see no active-ness in it at all, it is a completely passive circuit. Signal comes from the preceding stage plate, and feeds through this tone network and on out the FX loop stage.

I agree with JPB, that transistor circuit has nothing to do with your tone, it is only a buffer for the FX send. Those four diodes are there to clamp any voltages to the power rail and ground. So nothing at the FX send jack can drive the voltages at that transistor beyond the rails, which would cause a reverse voltage condition at the transistor. That is the only condition that causes those diodes to conduct at all. They are otherwise invisible.

Cool, then that means that the Prowler is slightly better there, right? Buffer > no buffer.

By the way, the guy from Peavey said: "The main difference (schematically) between the Prowler and VK112 is the EQ section....this is what I would mod. The Prowler has a quasi-active EQ and the VK112 has a standard passive tonestack."

I'm no seller or anything but I do have to mention that Peavey's customer support has always been of astonishingly supreme quality. I don't care if other amps sound better (some do sound better), I'll always be a Peavey consumer exclusively because of their customer support. Also, note that I was asking for an opinion. That's definitely not Peavey's official stand, that's just the opinion of the tech in question. And I respectfully disagree. I think I'll leave the tone stack as it is and I'll do some other mods (like a bias mod).