Sunday, February 20, 2011

2010 - Behringer DC9 Compressor

The humble compressor.
An oft misunderstood, yet incredibly useful device.
I have two of these MXR clones. One modded, one stock.
Like the original, the stock version filters out a bit of bottom end, which gives the perception of a treble boost.
Modding it to get some bass back is as simple as adding a .1uf cap in parallel with the input cap. You don't even need to pull the PCB out to do the mod either.

I have a few different uses for these pedals.
One of them is to add a master volume control to my Peavey Delta Blues, via the FX loop.
The amp is far too loud for my flat. Actually even a 5w Valve Jr is too loud for my flat, but I can't do much about it. The Delta Blues on the other hand can be tamed.

Adding the modded CP9 to the FX loop and reducing the sensitity to minimum gives quite a bit of control over the volume of the amp. It's easy to get the clean preamp distorting at maximum volume, while still having good standing with the neighbours! If you need to add a little compression, it's just a turn of the knob.
This is especially handy in the FX loop after the Line 6 M13, which has compressors built in, but they don't reduce the overall volume nearly as well as this bargain basement clone.

The CP9 is also incredibly useful for driving a DI before a mixing desk when recording Bass.
It adds Volume obviously, but also allows the Bass to sound more controlled and clean into themixing board, perfect for manipulating with your favourite bass amp modeler.

My main use for the CP9 is actually something not really music related, ans certainly not for performance.
I use them in stereo to control the volume of my television!

That's right I'm using them on the TV and now I no longer have to put up with being blasted out of my chair by overly loud commercials or having difficulty hearing dialogue when the volume of the hifi is set to a sensible level for watching action movies.

Since there may be problems with impedance on some consumer devices, I recommend the addition of a simple circuit on the input. The unmodified pedals were fine with a DVD player output, but when it came to the TV output I was getting some strange noises due to mismatched input/outputs.

All that needs to be done is a 22k resistor in line with the positive lead and a 1k resistor from the positive lead to ground. This drops the output impedance of the TV to something that the pedal can handle and improves frequency response as well as noise rejection. I actually got the idea from one of Ken Stone's circuits, the Stomp Box Adapter V2.

I'm certain this mod would work on just about any pedal if one were inclined to mess about with processing the TV. that's why I just built it into a black jiffy box with sockets to plug into whatever I want. It's also useful for dropping Keyboard outputs to be used by the pedal (it's original intent I believe).


  1. which is the input capon the DC9?? and running another cap in paralell means just installing another cap in the same place, is that right? Many thanks for your blog and Greetings from the Roadside!

  2. hi!

    I just bought this pedal for use on my jazz bass. Actually obtained his lack of bass.

    I used your method Parallel capacitor (1uf 50v one dimention same as yours).
    The sound has changed dramatically for the better. Very very close to the original sound without pedals.

    This mod is really simple, useful and efficient.

    PS: I have used this pedal originally only 1h.
    PS 2: any non-polarized capacitor works.

    1. Good to hear that I'm not spouting rubbish!

    2. Greetings, I was about to do this little mod myself but your comment confused me slightly. Did you use a 0.1uf cap as mentioned in the original post or did you use a 1uf cap as mentioned in your comment. I would really like to get the low end back. Thanks in advance.

    3. I'm guessing 1uf is a typo.
      A 1uf ceramic or Mylar wouldn't fit in the available space.

  3. I don't see how a .1uF cap in parallel with the existing .47uF cap will possibly make a big enough audible difference. You are only going from .47 to .57uF. Laurent says he added a 1uF cap, that maybe will make a difference, but how the hell do you fit one in that case (unless it's electrolytic).

    1. I don't have either pedal any more, but I thought the input cap was really small for fx input, more like 0.047uf?

      Most of the pedals I build have .1uf input caps and are fine for both bass & guitar.


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