ashbass Randall RVC and RD5C RD5 Diavlo More Bass Mod
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RVC and RD5C Diavlo Front Controls
Click image to see RVC and RD5C Diavlo side by side.

I recently purchased a Randall RVC single-channel Class A 5W 1x10 combo amplifier. The RVC was a Guitar Center exclusive version of the Randall RD5 Diavlo minus a ground lift and an emulated XRL instument out. The following More Bass mod is for both amps considering that the circuit boards are the same; the Diavlo just has more stuff on it.

The controls are Gain, Tone, and master Volume. It is a tube amp and uses (2)12AX7 & (1)6V6 tubes. There is a small On-On-On toggle switch on the control panel that accesses three unique EQ voicings: full-bodied lead tones, rock, and scooped metal. It has an 8 Ohm 10 inch speaker and a jack in the back for an external speaker. Also in the back is an instrument level FX loop send and return.

RVC and RD5C Diavlo Rear Panel
Click image to see RVC and RD5C Diavlo side by side.

RVC and RD5C Diavlo Circuit Board Gut Shot
Randall RVC Ciruit Board.

RVC and RD5C Diavlo Controls
Click image to see a larger version of the controls.


On to the Mod:

There are two capacitors on the amp's circuit board that you can change in order to get more bass response from the amp. The stock capacitors are a very small value and they stop practically all of your bottom end from getting through the amp. The goal of this restriction is that the bass notes don't get muddy when playing at high gain. But when playing lower gain, or clean, you are left with a weak low end output. The goal of this mod is to let more of your bass signal through the amp.

To remove the chasis to change tubes or as the first step of the More Bass mod, remove the circled screws. Be carefull as this back panel can easily slide off and drop out of your hands.

RVC and RD5C Diavlo Back Panel Screws to Remove




To gain access to the amp's circuit board you need to remove the four circled screws.

RVC and RD5C Diavlo Chassis Screws to Remove




To remove the board from the chasis. First remove the knobs and jack nut.

RVC and RD5C Diavlo Knobs and Jack



Remove the three screws that hold the board in place inside the chassis. Then pull the LED out of its socket and pull the two green connectors off. This all that I needed to do to be able to pull the circuit board up and out of the chasis.

RVC and RD5C Diavlo Circuit Board Remove



Here are the two capacitors that you need to change in order to get more bass in your signal. The circled capacitors are cathode bypass capacitors for V1a and V1b (if you don't know what that means don't worry about it). The cap on the left is labeled C23 and the cap on the right is labeled C20. The stock capacitors are .68 uf and as already mentioned are a very small value that stops practically all of your bottom end from getting through the amp. The More Bass mod involves replacing those .68uf capactitors with 22uf capacitors.

RVC and RD5C Diavlo Circuit Board top



Here is the underside of the circuit board showing where the .68uf capacitors are, and where the 22uf capacitors will be, soldered onto the board.

RVC and RD5C Diavlo Circuit Board Gut Shot


And that's it. Close the amp up and listen to the new bass frequencies coming out of it. As a bonus, the Gain control becomes more usefull as crunchy gain is reached farther along the control than before. Also, the Tone control will have more effect on the sound as there is more bass to filter out now at your command.


A NOTE ON CAPACITORS
The .68uf caps in this amp are Polarized Electrolytic Capacitors. Polarized caps have a definite Negative and Positive side. The negative side is labled with a white strip containing "-" signs. It is important that the negative and positive leads (wires) of your new 22uf capacitor go in their respective holes on the circuit board. This circuit board has the + and - sides specified on the board itself as a handy guide. The .68uf caps are rated 100 volts. I replaced mine with 35 volt rated caps to no ill effect.







BONUS:
I love switches and I love having options. For my RVC(RD5C) I've used a DPDT toggle switch to select between Up = .68uf, and Down = 22uf.
        |     .68uf
(  )  
  |     22uf

RVC and RD5C Diavlo Bass Mod Toggle Switch


RVC and RD5C Diavlo Bass Mod Toggle Switch


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