# amp hum NOT alt whine....stumped



## leonpiper69 (Feb 19, 2017)

Got a weird question. Just got a hum from the amp and it's NOT alt whine. I know what ALT whine is and have had it in other vehicles.

This an 07 Tahoe non-bose.

Running Factory HU into an LC2i

JL C5-650s in the front Console stealth box.

I started out with an Alpine MRV-F300. Sounded decent, a little harsh on the hi's but lacking on the bottom end.

so then I went to an Alpine MRV-F345. The hi's were kinda dull compared to the F300 but the bottom end sounded great. I had a clipping problem in the front stage and I was convinced the X-over had an issue and too much base was getting through to the mids.

So then I just put in a used Alpine PDR-F50.........FREAKIN LOVE IT!!!

Was going great for a couple days tweaking things and eventually was really happy.

Then......yesterday a weird humm happened and I think it might be Tahoe specific. When I opened the door and the lights come on the amp humms (maybe around 250HZ or so) and after shutting the door and then eventually the light goes off....the amp powers off and the hum goes away.

I fire the truck up and the hum comes on regardless of if the radio is on or off.

I unplugged the RCAs and it made no change so that tells me to look at the amp. 

I pulled the amp out and put the F300 back in just to have music for now and see if the noise was gone and sure enough (so far) it is clean.

So I put the amp on the bench and could not reproduce the sound.

Any thoughts?


----------



## Sine Swept (Sep 3, 2010)

I will throw this out there. Ditch the audiocontrol piece, that amp has speaker level inputs. Try using them and see if that yields better results. Consider running a dedicated ground wire and wire all amps to distro blocks at + and -.

Sometimes issues in noise will arise using an OEM radio that actually puts out a balanced signal to an OEM amp that accepts this balanced signal. I can't say this is your issue, but I have on occasion heard it and it is a hum, not alt whine.


----------



## The Tube Doctor (Nov 24, 2009)

If the amp hums, 
it probably doesn't know the words.............

Sorry, old guy joke. I couldn't resist.:laugh:


----------



## leonpiper69 (Feb 19, 2017)

Sine Swept said:


> I will throw this out there. Ditch the audiocontrol piece, that amp has speaker level inputs. Try using them and see if that yields better results. Consider running a dedicated ground wire and wire all amps to distro blocks at + and -.
> 
> Sometimes issues in noise will arise using an OEM radio that actually puts out a balanced signal to an OEM amp that accepts this balanced signal. I can't say this is your issue, but I have on occasion heard it and it is a hum, not alt whine.


Ground loop popped into my head as well but I am using a dist. block for both power & GND. 

The amp does have speaker level in but the LC2i I am using to facilitate remote turn on and bass restoration. The factory HU removes bass as volume increases so this was supposed to fix all those issues in one deal.

I just hate any aftermarket HU. Looks like trash. Aesthetics is the only reason I insist on keeping stock one.


----------



## Weightless (May 5, 2005)

A distroblock will not prevent a ground loop.

Can you take a recording of the noise? 

Sent from my SM-N920P using Tapatalk


----------



## leonpiper69 (Feb 19, 2017)

Weightless said:


> A distroblock will not prevent a ground loop.
> 
> Can you take a recording of the noise?
> 
> Sent from my SM-N920P using Tapatalk



I might be able to later today or tomorrow but I will have to pop the other amp back in real quick and that means I have to wait till the baby is sleeping (wife is out of the country so no help).


----------



## Sine Swept (Sep 3, 2010)

Also when it comes to noise, try 1) Acc on 2)Key to start - engine off 3) Key on engine on

See if it makes a difference to your noise.


----------



## leonpiper69 (Feb 19, 2017)

Sine Swept said:


> Also when it comes to noise, try 1) Acc on 2)Key to start - engine off 3) Key on engine on
> 
> See if it makes a difference to your noise.


When I did it the other day that didn't make a diff. Even key off, no key, key on, engine running etc made no diff. It just stopped after a few mins then later when I left my office it of course came right on when I opened the door and it wouldn't go away after 5 or so mins so I unplugged the RCAs and it was still there.....then I ripped out the remote to kill the amp and it stopped.....but then of course I couldn't hear my blinkers which was annoying.


----------



## leonpiper69 (Feb 19, 2017)

So I played around on the bench ad could not for the life of me get it to reproduce the hum.

the 300 I swapped into the truck ran without a hitch for several days.

Last night I put the F50 back in and it has been running fine since then.

The only thing I can think it may have been if there is nothing wring with the amp itself is....while hooking it back up and checking each connection I tug on each speaker wire to make sure it has a good connection and one came right out eve though it was tight.

I put it in and pulled and it came out again. I didn't have a lot bare wire exposed and the insulation was keeping it from going all the way in very easily (it's a lot deeper holes that I have seen on a lot of amps).

I am wondering if a loose speaker connection could cause some kind of hum??? maybe that is all it was.


----------

