Audio Amp questions/changes

[moody07747]

So I got a Behringer KX1200 amp for my drums in home use but I'm getting a his/buzz when only the power cords plugged in and I turn up the master along with input 1. It will start buzzing/hissing after 3 seconds when the amp warms up.

I have tried some adapters to redirect the ground without any luck.

Behringer products are not the best, they are like harbor freight tools

This is driving me crazy even though its really quiet because its going though to the recordings.

I posted at about three other boards for drums/guitars and one suggested switching out the resistors to metal film type.

if it 'warms up' and hisses, I'd like to suspect it's a resistor with a higher than usual (for that resistor) current running through it. The more power a resistor must disperse, the more thermal noise it will develop. I say go through and put in metal film resistors. They have superior noise characteristics (thermal and otherwise).

I opened the amp, some pics:
**broken link removed**

and to me, this thing just says death all over it...that coil looks like its from some death machine or something lmao

anyways I just don't feel comfortable enough working on this myself, i don't know that much about electronics and I do know there is enough current in this type circuit to be deadly.

I was wondering if it would be better to get a new amp with a 15" bass speaker, 5" mid range, and tweeter or just send this to an audio shop to have them swap out the resistors.

Would anyone here want to do it to save me some money and help me keep my fingers in place? lol
I would pay for parts and shipping.

btw, i would only send the amp head and unplug the speakers from the board

 

[Nigel Goodwin]

So I got a Behringer KX1200 amp for my drums in home use but I'm getting a his/buzz when only the power cords plugged in and I turn up the master along with input 1. It will start buzzing/hissing after 3 seconds when the amp warms up.

What if you turn up input 2 instead of input 1?.

I have tried some adapters to redirect the ground without any luck.

Behringer products are not the best, they are like harbor freight tools

This is driving me crazy even though its really quiet because its going though to the recordings.

I posted at about three other boards for drums/guitars and one suggested switching out the resistors to metal film type.



I opened the amp, some pics:
**broken link removed**

and to me, this thing just says death all over it...that coil looks like its from some death machine or something lmao

Looks quite well made inside?, and the transformer is a bog standard toroidal one.

anyways I just don't feel comfortable enough working on this myself, i don't know that much about electronics and I do know there is enough current in this type circuit to be deadly.

I was wondering if it would be better to get a new amp with a 15" bass speaker, 5" mid range, and tweeter or just send this to an audio shop to have them swap out the resistors.

It's unlikely to require resistors replacing with metal film ones, if it's not working correctly then there's something wrong with it - it needs repairing, not modifying!.

As you've just bought it, then it's under warranty, and either the store you bought it from, or Behringer direct, should sort it out for you. Behringer USA are VERY serious about providing good customer service, but their equipment is usually excellent, I've got almost all Behringer equipment and find it great!.

 

[moody07747]

this is a customer returned unit, I have known otheres who have the amp as well and they also have the same problem

ok heres another thing I just found

I unplugged the cord from the back of the amp that went to the "Out L" on the mixer and the buzz stopped but the hiss is still there no matter what level I turn up.

so that coil of death is a transformer,,,,,i knew that

further testing...I took the cord out of the mixer out port and the buzz went away so it seems my yamaha MG 10/2 mixer is causing the buzz.

this mixer is plugged in but the switch in the back is set to off.

the power cord has the transformer in it to cut back on audio noise in the mixer.

could it be I just need a better mixer?

 

[Russlk]

Those white things in the pictures are wire wound resistors; they are not noisy. Picture #12 shows an IC, what are the numbers on it?

 

[zevon8]

To me, the "buzz" , if it is power line frequency ( 60Hz in North America) , would make it appear like you have a ground loop. Two pieces of equipment that have grounded power cords, and are pluged into different outlets, or through various "power bars", etc, may end up creating a long enough connection betweem the chassis of each piece of gear that there is a slight differnce in what each "sees" as ground. This can cause enough current flowing along the ground of the interconnect cable to become part of the audio. Then you get hum.

In you case, removing the one piece of gear from the chain ( the mixer ) stops the hum, so either the amp or the mixer could be the problem. If everything else can be connected to the amp, and no hum, then blame the mixer, if the othe way around, blame the amp. Note that even when turned "off" the chassis will still be grounded anyways, so being turned off will not stop a ground loop.

Here is a link to ground loops:

https://www.soundonsound.com/sos/1994_articles/aug94/groundloops.html

The hiss could be digital noise generated by some of the input control / switching logic. It could also be self generated by the amp oscillating or having a noisy pre-amp circuit.

If it is digital noise, some bypass caps at each of the IC's DC power terminals may cure that for you. If it's in the power/pre-amp it may be due to its design or choice of components, and harder to fix.

 

[moody07747]

Those white things in the pictures are wire wound resistors; they are not noisy. Picture #12 shows an IC, what are the numbers on it?

You mean the pic labeled "inputs_Chip"?

I'm not sure, I'll have to open the amp again and read it as I didnt mark it.

I dont have any rework station so removing that chip might be hard if thats what your thinking.

 

[moody07747]

To me, the "buzz" , if it is power line frequency ( 60Hz in North America) , would make it appear like you have a ground loop. Two pieces of equipment that have grounded power cords, and are pluged into different outlets, or through various "power bars", etc, may end up creating a long enough connection betweem the chassis of each piece of gear that there is a slight differnce in what each "sees" as ground. This can cause enough current flowing along the ground of the interconnect cable to become part of the audio. Then you get hum.

In you case, removing the one piece of gear from the chain ( the mixer ) stops the hum, so either the amp or the mixer could be the problem. If everything else can be connected to the amp, and no hum, then blame the mixer, if the othe way around, blame the amp. Note that even when turned "off" the chassis will still be grounded anyways, so being turned off will not stop a ground loop.

Here is a link to ground loops:

https://www.soundonsound.com/sos/1994_articles/aug94/groundloops.html

The hiss could be digital noise generated by some of the input control / switching logic. It could also be self generated by the amp oscillating or having a noisy pre-amp circuit.

If it is digital noise, some bypass caps at each of the IC's DC power terminals may cure that for you. If it's in the power/pre-amp it may be due to its design or choice of components, and harder to fix.

I was also thinking this was the case...ill look into it and do some testing

if this isn't easy to fix ill be getting another amp.

Others have had this problem as well so im really starting to think its just the design of the amp circuit.

 

[moody07747]

same thing even with a good cable away from any power lines.

i was thinking it was my cable as i made it from wire at allelectronics.com with their cable ends....sometimes they give me trouble on the drums (something with the cable ends for that)

im going to post a recording of the buzz/hiss putting the cable in and out.
(five minutes later)
audio link.
https://www.tindeck.com/audio/my/1d3yi

just so you all know exactly what im hearing.

 

[Nigel Goodwin]

Others have had this problem as well so im really starting to think its just the design of the amp circuit.

I've heard nothing but good about the KX1200, it's a very useful little amp, as it can be used for so many purposes.

As it only does it when the mixer is connected to it, it might well be an earth loop - where BOTH items are earthed - this is always a common problem with audio equipment. Try disconnecting the screen at one end of the lead connecting the mixer and amp together (I'm presuming you are using screened leads?).

 

[Dr.EM]

I have the Yamaha 10/2 mixer too, and know that it uses an unearthed double insulation type transformer (it is not internal to the unit) so I guess that rules out the ground loops with those bits of equiptment?

Another note, the mixer has both +4db outputs and -10db outputs, but the -10 are only available on the phono rec outs right. You should probably try to use these outputs as the +4db is probably not the level the amplifier expects. That said, I have used this mixer with an old home brewed PA system just a few days ago (using it live tomorrow) and it worked fine with the +4db outs, definately some hiss present when the mixer is on as opposed to when it is off, but certainly nothing thats a problem for live sound (it is also being used to amplify and electric drum kit).

 

[zevon8]

It's definitely 60Hz hum ( just listened to the clip .) Now you just need to eliminate it at the source. Ungrounding one end of the shield to the mixer as in Nigel's suggestion would likely do it. You can still get a ground loop even if one component has no ground pin on the power cord. Cable TV ground loop hum is pretty much legendary, and I don't recall ever seeing a TV with a 3 prong cord. All you need is 2 pieces of equipment that are connected together, and there is a potential difference between what each of them considers "ground".

 

[moody07747]

I've heard nothing but good about the KX1200, it's a very useful little amp, as it can be used for so many purposes.

As it only does it when the mixer is connected to it, it might well be an earth loop - where BOTH items are earthed - this is always a common problem with audio equipment. Try disconnecting the screen at one end of the lead connecting the mixer and amp together (I'm presuming you are using screened leads?).

Screened leads?...you mean shielded?

im not following ya.

ok so on the other side of the room the new circuit starts for our finished basement.....I plugged the mixer into the power strip over there, plugged the amp into the mixer and no noise what so ever...thats strange

I got out my tester and the ground for both outlets are fine as well.

I must say this Yamaha mixer really is a fine piece if equipment, im not saying that it's the problem here.

I have always been a fan of their equipent since my Casio keyboard broke down after just 6 months and I switched to a Yamaha.

btw the circuit my drums and all are plugged into is also running a big TV, tivo/dell computer, surround sound system, my desktop here, and the speakers/monitor on it.

so what im going to try and do is get the power strip out of the current #20 circuit and plugged into the other 21 circuit here the in the basement.

if all else fails ill just run a new line in 15 or 20 amps just for my audio equipment to cut out any equipment from the room....ill also unplug the old unused TV from the other 21 circuit so its sure not to do anything....this is a great time to neaten up all my wires...

 

[moody07747]

OK I just rewired everything making it nice and neat, keeping all the power lines away from any of the audio lines.

I plugged the drum module, keyboard, amp, Roland micro cube amp, and LED power plug into one surge protector strip one one circuit and the mixer is now plugged into the wall without any power strip on a separate circuit from everything else.

I also tried plugging the mixer in with everything and the amp into the wall by itself.

Now I'm getting that pop on the amp when I turn the mixer on...Never got that before but its normal from what I have read and to counter it the amp should be turned down to stop that when powering the mixer up.

I'm still getting the buzz when hooking the mixer and amp together.

The line cable is stereo and the jack at the back of the amp (#1) is stereo, (manual says its for a mic with that type end.)

The mixer port is mono though...I'm feeding the "L mono" from the feeder down a stereo cable with stereo ends to a stereo port on the back of this one amp which makes it mono so that really does not matter....

Now what I could do is head to the shack and get a few mono cords...from there I can run 2 mono cables from L and R main out on the mixer to inputs 2 and 3 on the amp.

Inputs 2-4 on this amp are mono so it would match the mixer nicely.

I don't see any need for stereo as this is just one speaker...a mono setup...I could get another and link the 2 but I have not found a great deal on another amp yet nor do I have the room for another.

This ones loud enough as is anyways.

 

[audioguru]

Wire that is used for lamps and speakers is a lousy audio cable because it isn't shielded. An unbalanced shielded audio cable usually has RCA plugs on it in North America. It is something like TV co-axial cable with a center conductor, insulation then an overall shield, except it is much more flexible.

 

[moody07747]

this isnt lamp wire although I used cheaper audio wire to wire the triggers in each drum.

this is the wire im using from allelectronics.com

items 3CS22 and 2CS22

https://www.allelectronics.com/cgi-bin/item/3CS22/search/3-COND._22GA_SHLD_CABLE_W_DRAIN_.html

in that 3 wire theres the black, white, and red insolated conductors, a thin metal wrapper around all that, and the grey ground wire outside the metal wrapper.

when I hook my leads up to them all I remove the wrapper and grey wire and use the black, red, and white wires for each solder point on the stereo connectors.

should I be hooking the grey wire to the big ring/ground on the audio ends?

it could just be I have been wiring these wrong. Yet the radio shack cables I tested with this also do the same thing.

 

[Dr.EM]

The thin metal wrapper is the shield, yes it must be connected to the ground on your connectors, or it will have no effect! The grey wire outside the rest appears to be the shield.

 

[moody07747]

thanks for the info, ill rewire all the wires later today.

 

[Nigel Goodwin]

To be honest, that's looks really poor cable for audio - use proper audio screened cable instead!.

 

[moody07747]

To be honest, that's looks really poor cable for audio - use proper audio screened cable instead!.

yea its not the best for the audio connections but its great for the triggers-module.

wheres a good online store to buy good mono and stereo wire and cable ends for them?

I have been meaning to change out some of those wires anyways.

For the next wiring I'll be hooking into jacks 2 and 3 in the amp and that will be from the out L and R on the mixer so ill mainly need cable and ends for a mono cable setup.

 

[audioguru]

You MUST connect the drain wire to the circuit's ground for audio cables to avoid hum. Without the drain wire connected then the cable isn't shielded.
The "tinfoil" is actually metallized plastic film and is a very good shield. It is not very flexible and will break if bent too many times.