Author Topic: Fender Roc Pro 1000 Distortion isolation? Anyone?  (Read 247 times)

brokenstarguitar

Fender Roc Pro 1000 Distortion isolation? Anyone?
« on: August 11, 2018, 02:51:20 PM »
Ok what im trying to do is take the distortion section from the amp and duplicate it into a stompbox. The only schmatic i found is a blurry copy from google that i cant really make out. Anyone done this before that can share or know where to start? Thanks guys your help is appreciated!


mth5044

Re: Fender Roc Pro 1000 Distortion isolation? Anyone?
« Reply #1 on: August 11, 2018, 04:09:38 PM »
Here’s a link to schematic and layout:

http://schems.com/bmampscom/fender/Roc_Pro_1000_schematic.pdf

I wonder if schems.com got written consent from Fender to post it  ::)

dschwartz

Re: Fender Roc Pro 1000 Distortion isolation? Anyone?
« Reply #2 on: August 12, 2018, 09:05:50 PM »
Notice how the tubes are used as clipping diodes...
----------------------------------------------------------
Tubes are overrated!!

http://dsmnoisemaker.blogspot.com

teemuk

Re: Fender Roc Pro 1000 Distortion isolation? Anyone?
« Reply #3 on: August 14, 2018, 12:07:07 PM »
As noted, the stage that principally produces the clipping distortion is made out of a dual triode tube (12AX7) wired as two generic shunt diode clippers. (Basically vacuum tube dual triode wired as two diodes instead). The OpAmp gain stage(s) preceding it provide sufficient voltage gain for clipping to occur. There's also an implemented "dual mode feature" in the overdrive channel (Red and Yellow modes), which introduces different signal paths for gain control of Yellow and Red modes, and also alters the DC reference voltage of the shunt (vacuum tube) diode clippers in order to produce different thresholds for clipping. The same arrangement also features gain compensation for different threshold levels. Aforementioned features are toggled with multitude of FET switches and associated control logic circuitry.

But it's not all. The Roc Pro amplifier follows the typical "Pre & De-emphasis Distortion" circuit architecture Fender has employed ever since the late 1980's Red Knob SS amps. As name implies, the circuitry introduces pre and post distortion emphasizing for signal and ultimately it is in its completeness what pretty much defines the tone of the OD channel. How clipping is achieved is more or less inconsequental.

The pre-emphasizing circuitry mimics frequency response of a typical (Fender) preamplifier while the post emphasizing circuitry acts sort of like a "cabinet emulation" and in modern Fender amps also implements the tone controls of the overdrive channel.

Effectively where all this starts is the very first gain stage of the preamp. As you can see, after that the signal splits into "Clean" and "Overdrive" channels; clean channel introduces tone controls there while OD channel precedes to introduce even more enhancement with a passive T-notch filter circuit. The notch filter is then followed by OpAmp voltage gain stages and the vacuum tube diode clipping stage. Following the clipping stage are post distortion emphasis stages, which also implement tone controls and a channel-specific volume control. These are all essential parts of the distortion circuit.

The overdrive channel ends to OpAmp stage around U5B, which is effectively a mixer stage for clean and overdrive channels. Stage input is controlled by pair of FET switches and (again) associated control logic circuitry. So, the distortion circuit is pretty much all those stages in the upper part of the circuit diagram.

brokenstarguitar

Re: Fender Roc Pro 1000 Distortion isolation? Anyone?
« Reply #4 on: August 17, 2018, 05:47:06 PM »
Thanks for the replies guys. Tell me if im understanding. Ive "sectioned" the schematic to what i believe would be the proper way to duplicate the distortion part. Please keep in mind im not good at reading a schematic this complicated.

"Sel 3, Sel 4, Sel 1" would be on a toggle. That would be different clipping options correct? Or am i just not understanding properly? Thanks in advance!