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Hissing sounds!

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Chewit View Drop Down
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    Posted: 19 March 2021 at 9:47pm
Iv got some 100w 2” BM-D750 loaded into my horns on my Mt121s. I power the two comps of a t.amp 800w, 2x 350W @ 8ohm. So got penalty of headroom! 

I get a constant hissing sound from the comps, when music is played louder you can’t hear it! I read up and been told this is just distorted sound leaving. Just want to see what you guys can tell me. Also form time to time, the comp will start making a clicking sound every couple seconds. Maybe a fuse in the amp I’m not sure! Brand new amp and comps. Any help is appreciated! Maybe be nothing maybe be somthing. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cravings Quote  Post ReplyReply Direct Link To This Post Posted: 19 March 2021 at 10:04pm
all the noises most likely the amp... they work fine, but it is a real budget amp. maybe if you have an opportunity to borrow or try another one you could compare it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 19 March 2021 at 10:50pm
With nothing attached to the amp except the comps and amp gains turned down, do you still get the clicking noises and hiss? If so the amp is the problem, cheap class D are known for this, try substituting something that isn't class D and don't turn up the gains any more than necessary.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doller Quote  Post ReplyReply Direct Link To This Post Posted: 20 March 2021 at 9:41am
Are you using a lms dsp? Crossover analogue or digital? I get horrible hissing from my dbx driverack analogue not so much .
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 20 March 2021 at 12:51pm
I think you are discovering what a noise floor is mate :)
Compression drivers are very sensitive - look at those dB per Watt figures and compare them to cone drivers. There's usually at least 10-12dB difference. And that is a BIG difference what with dB's being a log scale and all.
So you are just hearing what your equipment classifies as "silence". Most people just live with it; it's normally only a problem in very critical listening environments, where you'd use better equipment anyway. It can be noticeable if you're using the rig to play back a film soundtrack with high dynamic range. But for general purpose raving, nobody will notice ;)
I have also noticed the dbx Driverack PA to be comparatively noisy, more so than the Behringer DCX. More expensive gear = lower noise floor. It takes quite a lot of electronic engineering to shave a few dB's off the "no signal" level. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 20 March 2021 at 1:42pm
Originally posted by Conanski Conanski wrote:

With nothing attached to the amp except the comps and amp gains turned down, do you still get the clicking noises and hiss? If so the amp is the problem, cheap class D are known for this, try substituting something that isn't class D and don't turn up the gains any more than necessary.


Most probably this - but it is a process of elimination.

Disconnect everything other than the amp. Noise there, or gone? Check with pots at 0 and full up.

If gone, reconnect each bit of equipment you will normally have in the chain and see if the noise appears. Sometimes "clicks" come come from dodgy signal cables as well.

Good luck!  Smile


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chewit Quote  Post ReplyReply Direct Link To This Post Posted: 20 March 2021 at 11:56pm
Thanks for all the help and suggestions! Will have a play around tomorrow! I also have a T.amp 1200w and when plugged into that the hissing sound is less and no clicking. Yes it dose make the hissing sound with all the gains down! Yeah a lot of people tell me they have the same sound on there comps! I just wanted to check it was a obvious major issue that needed looking into! I’m going to play around with plugging, unplugging, useing different cables etc and see if it changes, if not I may live with it as the sound can’t be heard when playing loud music. Am looking to upgrade these amps eventually for the tops...... one day haha
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chewit Quote  Post ReplyReply Direct Link To This Post Posted: 20 March 2021 at 11:58pm
I have a high end amp, so going to try it with that and if no hiss then it’s clear it’s the budget amps! 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Chewit Quote  Post ReplyReply Direct Link To This Post Posted: 23 March 2021 at 7:36am
Right it is 100% the t.amp 800

I ran the comps on the T.800, t.1200 and my cvr all with nothing else connected or music playing (also tried different cables) 

Both the 1200 and cvr have a slight hissing sound but nothing to noticeable. but the t.amp 800 has a buzzing sound! When turned up it disappears over the Sound. So I reckon it may be just because it’s a cheap amp like you guys said. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 23 March 2021 at 11:14am
what's the music source?
Kevin

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 23 March 2021 at 1:26pm
Ok - just had a look - and the t800 is not Class D, nor have a SMPS, so the hissing is not from residuals that often appear with those with insufficient filtering.

What about the clicking you were talking about? Is that still there?

In any case - if the hissing drops when you dial up the pots, then it could be an earthing problem, but most probably a bad cap somewhere - maybe in the power supply. Try "wiggling" those and see what happens. And check for any cap that has a bulge on the top. A sure sign of problems.

Also, take a pen, pencil or back of a screwdriver (anything non-conductive) and go around tapping the board. That should reveal any bad/dry solder joints - which can be like 60%-70% of the faults on cheapo electronic boards.  Cry



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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 23 March 2021 at 3:17pm
I would suspect a crappy op-amp chip somewhere in the signal path that's become a noise generator. Else one that's lost its negative feedback resistor and is trying to multiply silence by 10000000. The buzzing does suggest an additional earthing issue, but could also be the same fault.
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