Guitar Amp buzzes off of power inverter, will this filter work?

[silentblackhat]

I just put a 700 watt power inverter in my car(its a modified sine wave inverter so i know its not 100% clean power). When i went to hook my guitar amp to it(the car isnt running so theres no engine noise in play). I am guessing that this buzzing is because of the inverter not putting out 100% clean power. I know that the amp is DC power instead of 120V AC. So i am wondering if I put DC power noise filters(consists of 2 caps and the inductor) on those power wires, if it will stop the bussing sound. The picture is below of the blue wire pointing to the set of wires that carry the DC current.

This is an Ibanez TB25R Guitar Amp.

An externally hosted image should be here but it was not working when we last tested it.

Any help would be appreciated.

 

[silentblackhat]

I am just wondering if I need to get a true sine wave inverter or if i could get thosefilters to work for me. I have the picture of a true sine wave compared to a modified sine wave from an inverter. I see that the filters might be able to help quiet the amp since the inductor would smooth out the 'edges' of the modified sine wave.

An externally hosted image should be here but it was not working when we last tested it.

 

[clem_o]

Take a look at your figure - the notice how the modified sine wave doesn't have the same PEAK voltage as the real sine wave. Filtering the modified sine so that it becomes a "clean" sine wave, if even close to successful, will result in an undervoltage for your amp - it will probably work, but don't expect full power from the amp...

Cheers

 

[silentblackhat]

would I be able to just connect the 2 red wires together so i would only have to get 2 filters instead of 3?

 

[clem_o]

Howdy,

That certainly made me have a closer look...

The wires you are referring to are the output of the transformer inside your amplifier. The output of the transformer is AC, not DC. You can't use a DC filter there.

Cheers

 

[silentblackhat]

doesnt the amp run off of DC tho? would an A/C filter work there?
I am going to get a true sine wave inverter (later on tho, i have to save up for one, ill maybe get one off of ebay)because i think thats the problem where the voltage drops to zero for a period of time and then goes the other direction. would a true sine wave inverter solve my problem with the buzzing?

 

[clem_o]

Hi -

After the transformer, there are two bridge rectifiers (the two black squares in your first picture, right near the wires of the transformer where it enters the PCB). The output of those two bridge rectifiers would be DC.

If you do get a TRUE sine-wave inverter, yes, it would solve the problem.

Be wary though, I've seen claims to being 'true' sine wave, but the output waveform from the unit I tested looked pretty much like a modified sine you posted...

Cheers!

 

[silentblackhat]

so getting a cheap one off of ebay probably wont be a true sine wave? This is the one I was thinking of getting off of ebay.(link below)

http://www.powerbright.com/aps300.html

 

[clem_o]

It *looks* promising - there's a distortion spec of 4% on the manual. If that spec is true, it should be ok!

Cheers

 

[silentblackhat]

alright ill probably order it soon then. I will take it up to my local highschool(i graduated 3 years ago tho) because I know the physics teacher there so he would be able to use the osciliscope to test the wave form out. thanks for the help

 

[clem_o]

It might be easier to just put it into the car and give it a go - ultimately that's what it will be used for anyway...

Good luck!

Cheers

 

[d3imlay]

The pure sine wave inverters are likely a PWM design. If you look close at the output you'll probably see some high frequency trash. This may or may not effect the guitar amp. The standard spec for inverter THD is less than 5% and each harmonic is less than 2%.

 

[silentblackhat]

so that since wave inverter isnt good at all?

 

[john_ellis]

Hi

I can't tell exactly where your power lines are from your photo, but the best way I have found to stop inverter noise is to place a coil inductor in series with each of the power lines to the amp. and a capacitor to ground also on each rail, on the amp. side. (for amps with + and - rails)

I think there is only a single + and ground (-) supply on your amp, so one inductor might be all you need on the + supply with a capacitor to ground, on the amp. power side. Try using a hefty cap. like 1 mF or so (suitable voltage rating) with low series inductance and resistance (like a normal power cap.).

If that fails, or instead of the above, you can add a normal line-type filter at the input of your amp (X1 - Y1 caps and a common mode choke). This may help to suppress switching noise, but the parallel cap will take large current spikes due to the fast switching signal. This may affect your inverter and would need to be high current to survive.

cheers
John

 

[clem_o]

so that since wave inverter isnt good at all?

It's much easier to filter HF hash from a true sinewave inverter, and it won't stress the inverter, unlike if you had a step-sine type. It's entirely possible that the hash won't even affect your amplifier in the first place.

Cheers