Saturday, May 11, 2013

Behringer AM-400 and DR-400 input signal mod

Behringer Acoustic modeler AM-400 and Digital Delay/Reverb DR-400 input signal mod

The input signal circuit of the AM-400 and DR-400 are the same, try out the mod:

  • Change the input capacitor 22nF to 47nF (for more bottom) and remove the pF capacitor after a 10K resistor (for more open sound), see the picture:

* This will help the AM-400 annoying hiss (white noise) problem, caused by increasing the attack button to compensate the lack of treble. By removing the cutting capacitor, you won't need to increase the attack to obtaining more highs.


  1. Please tell me which capacitor i should remove,C31 or other one? Tell me its name.

  2. I dont remember de codes, but the 22nF is always a big green capacitors. Identify the input jack, plug the guitar cable, folow the inner of the cable plug with a multimeter (select the bip mode) to the big green capacitor terminal. The other terminal of the green capacitor is linked to a 10K smd resistor (103), the other side of the 10K (103) resistor is conected to the a very little smd capacitor (near to the 10k resistor). The other side of the little capacitor is conected to the ground, this is the guy.... who steal the hights. Thank you....

  3. Ok, I have received the pictures. Sorry, the green capacitor is only in the acustic simulator, in DR400 it is a smd. At DR400 circuit board remove C38, increase C39 (put a 22nF capacitor in parallel for example).... tks

  4. Thanks for this post. I got yelled at by a tech for the hiss from my DR400. I'm going to have to give this mod a try. I'll report back, but if you've got any other tips for reducing the hiss, please pass them along.

  5. The another try is a noise reducer stomp...It works good, because the his has a long decay time after U stop playing. The Larger guitar simulation option is the noiser.
    This hiss is generated by a digital circuit/processor I guess, and the schematic was impossible to me to find in internet (AM400 and DR400 circuit are not like the boss brothers). I wish Behringer made a new version with a "hiss" control or a independent treble control, the attack control down put the treble down too.