Input cap selection

[lefizz]

Should the input caps of my power amp be chosen to cut bass at the low end, to prevent waffle and conserve amp power? My current input cap should be enough to go down to 3hz but it seem this might be overloading the 10" speaker at extreme volume levels and the digital amp is powering off becuase it has reached it power limits. What would be a sensible cut of frequency for a guitar amp, baring in mind backing track are also played through the unit.

ANy input greatfully recieved.

[teemuk]

Well, there are no absolute answers, just some rules of thumb: Lowest fundamental note of standard-tuned guitar is 82.4 Hz, bass-band starts at 50 Hz and anything below that is considered "sub-bass", most people won't hear frequencies below 20 - 16 Hz.

[lefizz]

That perfect i am gonna swap out the 3.3uf which is meant to go down to 3hz and stick in a .33 uf which has a cut off at 70 something. Do you recon this will allow the guitar amp to go louder without distorting, i recon it should have a possative effect.

[benzer]

consider also the freq response of the speaker
some speakers cuts off lower than 70hz
some others let you hear 40 hz sound

[joecool85]

That perfect i am gonna swap out the 3.3uf which is meant to go down to 3hz and stick in a .33 uf which has a cut off at 70 something. Do you recon this will allow the guitar amp to go louder without distorting, i recon it should have a possative effect.

It shouldn't really make any difference unless you had been running some low frequencies into it to begin with.  If you are just plugging in a guitar, it will be just as loud now as before.  Thats not to say the cap choice is a bad idea, it isn't.  The cap cutting off at 70hz will help reduce unwanted distortion and pickup of low frequency, no point in boosting signals you don't want anyway.

[teemuk]

That's right. It will reduce stuff like handling noises and low frequency feedback. Maybe even more important, it will prevent those from overdriving the amplifier. Reducing the amplitude of lower frequencies will make slightly distorted tones a bit clearer since you'll be reducing the amount of low frequency clipping, which is a thing that often removes a lot of signal content. For example, see the plot in the center of this picture:

http://pages.cpsc.ucalgary.ca/~hill/papers/conc/images/clip.jpg

Now, think if that low frequency component had a lower amplitude. Reducing the low end is one of the commonly used tricks to reduce distortion in low power amps. This of course removes adequate (low frequency) signal information as well (which is not very HiFi) but often this can be done without any "harm" since such amps are usually hooked to small speakers that couldn't reproduce very low frequencies anyway. Think portable radios and computer speakers. They won't have an ideal bendwidth from 20 Hz to 30 kHz.

I believe this effect also increases sensed loudness in a psychoacoustic way, similarly to soft clipping: You can have a bit more overdrive until clipping becomes annoyingly apparent or before too much high frequency signal information is lost. Saving that content is often crucial since that information defines the characteristic tone of instruments. If you reproduce only the fundamental note frequencies your guitar will sound like a synth; lifeless and boring. For that reason it is worthwhile to use gain controls that reduce the bandwidth on higher gain.

[lefizz]

HI well it tried it and it certainly helped however the amp is still hittign distortion before the we get the SPL we need. Looks like the 12 watt Class-T will get swapped out and th 100 watt will go in it place. Bit worried about the effect this will have on battery life but they are very efficient so hopefully that will help.