Bright-Cap Modification

This modification is suggested for and works with all AC30/15 models of the CC series. It may or may not be of use/application for other series

Needed:
– Soldering experience and a soldering iron
– Desoldering wick (optional)

You might have noticed that the AC30 is kind of a bright amp with lots of high frequenceys. When using overdrive pedals, especially in the top boost channel, the distinctive bright character of the amp can become an issue leading to a harsh and screechy distortion in the worst case (especially in the CC series). Fortunately, there is a simple and effective way to tame the brightness of the top boost channel: the bright cap modification (also known as treble-cap mod). This mod replaces or even completely removes a tone capacitor of the circuit leading to a more warm, rounded and overally balanced sound. As a result, it also significantly increases the pedal capability of the channel as well, especially when the player looks for a more warm and fat kind of overdriven sound.

Attention/Disclaimer: At this point, we need to state clearly that the autors of this site are not reliable for any damages due to any amp modifications. There still may be high voltages remaining in the capacitors which may cause mortal injuries. Therefore, all modifications are to be done at own risk and may cause a loss of warranty! If you do not exactly know what you are doing, please contact a qualified amp tech.

This mod is quite simple: You just need to remove the tone capacitor labled C13 (at least for the AC30 CC). It is located right beneath the volume knob of the top boost channel. To access the capacitor, you need to remove the backplate of the amp. The chassis does not necessarily have to be removed. However, this step is highly recommended for a more comfortable soldering work. For a clean removal of the capacitor, you may use some desoldering wick. After desoldering, the capacitor can be softly pushed out of the circuit. Then, some careful shaking of the chassis should make it fall out at the side. It is a good idea to carefully keep the capacitor at a safe place, so, if necessary, you can easily undo the mod by simply putting it back in its’ place. If you have no experiences in soldering, you should have a qualified amp tech doing this job for you.

There are also solutions in-between. If you find the amp too bright with the stock capacitor (120pf), but too dull without, you may just be fine with using a capacitor of smaller value like 68pf.

Lage des C13-Kondensators beim AC30CC

Position of C13-capacitor in AC30CC series

Further information, discussion, experiences and opinions related to this modification can be found all over the web. Just do some googling with terms like ‘bright cap’ or ‘treble cap’. Below are some links to related discussions:

http://forums.vintageamps.com/viewtopic.php?f=2&t=85573
http://www.thegearpage.net/board/showthread.php?t=407871
http://forums.vintageamps.com/viewtopic.php?f=2&t=62689
http://forums.vintageamps.com/viewtopic.php?f=2&t=85570

Author: moco

2 thoughts on “Bright-Cap Modification

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