Hi all please advise :)

[stk2008]

Hi all I am building an arcade machine its nearly done.

I am trying to run a small amp made for arcade machines and made to be ran off a 12v like the computer PSU.

I have wired it to the psu and all works apart from there is noise from the speakers.

I have read that computer PSU`s produce a lot of noise along with the HD,Fans etc etc.

I am wondering if I could make a very simple filter and if so how and what should I use?.

Please advise as I am so close to getting this fininshed.

 

[alec_t]

The noise could be due to spikes on the 12V rail or picked up on the amp input through inadequate screening or a ground loop. What sort of noise? Hum? Hiss? Is the amp running with an open circuit input? Does the noise disappear if the amp audio input is shorted to ground?

 

[stk2008]

Hi there thanks for the reply.

I am a total noob when it comes to electronics so please keep that in mind LOL.

its all sorts of sounds

Pop
Hiss
Crackles

Thing is as soon as I turn the PC on I get no noise only when it gets into windows so maybe its some thing to do with the on board sound casuing noise? could I check/fix this?.

When the pc plays a sound its good and clear just when it plays no sounds its noisy

 

[alec_t]

If your sound-card has multiple inputs and you are only using one, make sure all other inputs are set to zero volume, muted, or are actually grounded. If the noise then persists the culprit would seem to be a noisy sound-card.

 

[stk2008]

great advice thanks so much I will try that.

If its not the onboard sound and turns out to be some thing else can I just make some kind of filter that goes from the 12v rail (PSU) into the amp just to clean up the 12v in?.

If I can do this please please advise how and what I should use.

Your help is much appriciated.

 

[duffy]

When the pc plays a sound its good and clear just when it plays no sounds its noisy

This could be a pair of DC blocking caps back-to-back causing a problem with float voltages. Try putting a 1k resistor across input and ground on the audio amp.

 

[alec_t]

The filter could be a series choke followed by a shunt capacitor. The choke would need to be rated to carry the load current. What current does the amp draw (or what are its current/wattage/VA ratings)?
But if the noise disappears when the PC is booting up it seems the source is unlikely to be the PSU +ve rail, so filtering that may make little/no difference.

 

[stk2008]

DOH not sure if I have fixed it I am not at home at the moment but......

The cable that comes from the sound card to the amp there is three wires + and - and there is another bear wire whice I assume is earth/sheilding this one I did not attach to an earth so its floating.

If I attach this to the earth of the amp could this possibly help it?.

Thanks

 

[alec_t]

The bare wire is indeed the earth/screen/shield. Connect it to the amp earth point and see if it helps (but if the pc sound card is already earthed elsewhere this may create a 'hum loop' which would not help!).

 

[stk2008]

Damn ok I will try tomorrow when I get back home.

This is a circuit some one else used in an arcade machine

https://www.mameworld.info/ubbthreads/userfiles/246883-psfilter.gif

would need help?.

Thanks again

 

[stk2008]

Hi again.

Well I ran the sheilding from the 3.5mm jack to the earth of the amp and made no diff but here is where it gets very odd.

If I go into the recording setting of windows (I wanted to mute the mic input) the screen freezes this may be a driver fault I am not to worried about that but when I go into the record setting the noises stop and I can only hear a very little amount of unwanted noise.

Its very very weird I dont get it.

As soon as I close the record window settings the buzzing and other noises start back up again.

Please advise this is one odd problem.

thanks

 

[alec_t]

If the screen freezes it looks like you have a software fault. That may be setting play volume levels at max.
Which program are you using for setting record and play levels?

 

[stk2008]

Yeah I will reinstall Win XP at the moment I am using win 7 and the drivers are not available for the hardware I am using so I put it in compatiblity mode it normally works ok but not on this set up.

Its still wierd why the buzzing etc stops as soon as I click the record setup (the standard windows icon bottom right of screen).

Oh well I will stick a mic in the mic socket see if this helps or as suggested grounding the mic socket to earth.

If not I will reinstall using win XP and see how I get on.

 

[stk2008]

Ok reinstalled XP I still have issues with unwanted noise.

I wonder if I should connect the 12v plug that I use to drive my Amp to my oscilloscope and see if it really is a noisy signal?.

Should I do this with the computer and all the other parts connected eg hard drive,CD drive,fans etc etc this way I could discnect them and test again to see if I could eliminate what is casuing the problem though my bet is its just the output from the PSU as they are known to be a noisy output.

Is it safe to connect the 12v plug to my oscilloscope with the other power outputs still connected to me pc?.

And all so if it does turn out to be just a poor 12v signal please advise on the best way to clean it VIA capacitors and a resister I have no idea what I am doing really so I would be looking for some expert advice on this please .

Thanks in advance.

 

[stk2008]

Sorry to keep banging on if I make this could I attache it to the 12v I use to run the small AMP?

**broken link removed**

Just for ref this is the amp I am using

**broken link removed**

Thanks

 

[duffy]

Did you try what I suggested?

 

[stk2008]

Hi duffy Thanks for the reply.

No I have not because I dont know what to do I am a total noob at electronics please could you give me a fitting a instructions for an idiot

this is the amp should I fit a resister across the +12v and to the ground of the screw post you see in this

**broken link removed**

 

[alec_t]

That link says the item is no longer listed.

should I fit a resister across the +12v and to the ground

No, NOT to the 12V point. Connect it between the tip and barrel connections of the audio input jack.

 

[stk2008]

hi thanks for getting back to me.

I am using a STD 3.5mm plug it has three wires the tip is I assume + I then have a smaller centre part I assum - then I have a bear wire I assume this is ground/shielding.

Real sorry I am no good at electronics .

BTW the amp I have only has two inputs for the 3.5mm plug so I assume I should wire the shielding part of the 3.5mm plug to a ground say on the amp itself?.

Thanks

 

[alec_t]

From what you describe the plug you have is a stereo one, having tip, ring and barrel connections. The tip and ring are for the two stereo signal channels (not + and -) and the barrel is the common earth connection of both channels.
The sound card puts out stereo signals on the two channels (or may put out the same mono signal on both channels).
The amp as described has a mono input. Therefore you will need to combine the two stereo signals into one mono signal to feed into the amp. This can be done with a respective series resistor (say 1k) in each stereo path. I'll draw a 'how to' pic and post it later.