My Amp is Dimming

**JamesB** · 05-05-2002, 10:59 PM

Your Jensen is likely a perfectly fine amp.
My first amp was a Jensen and I was thourougly impressed with it - so don't listen to anybody who knocks your gear.

Most importantly though: the reason your amp is dimming is because it is entering a protection mode to prevent failure. The problem is twofold:

1) you should ALWAYS use a large gague wire for the amp - check what the fuze rating is to determine the gague of the wire required. For your 400w amp, the following is true: always use the "maximum" rating by the way (for power consumption)

amperage = watts % voltage

assuming you are running at 12.5v, your amp will draw 33.3 amps, so you will need both a 35-40 amp fuze and a wire gague that will accomodate this current. Be sure to select the proper DC amperage / wire gague as the AC values will differ (in wire size).

2) you are feeding the amp with either TOO MUCH input voltage, or TOO LITTLE input voltage. Ie. your sound card is not properly "line balanced" for the amp. My guess is that you are feeding it with too much. Most amps (non-high end) are only meant to be driven with up to 4v (ie. a 4 volt input source from the RCAs). Higher quality amps such as the high-end (expensive) Pioneer, Alpine amps and ALL phoenix gold amps accept up to 8v input.

If your soundcard is not outputting enough voltage, you can (and should) buy a "line driver" to PROPERLY boost the input level to an acceptable voltage for your amp.

If you are "under-driving" the amp with a low input signal, you are likely introducing a large degree of noise causing a "clipping" effect. (clipping is when the output from the amp goes too high for the electronics and is "flattened out" causing DC output (amps are designed to aomplify an AC (music) signal). Think of clipping as when you look at a sine graph and draw a line at 45' (0.707) on the Y axis both positive and negative - then erase all the "peaks" of the wave crests and leave the flat line .. then erase the line between latent waves.

Does this explain enough for ya? If not, let me know ;-)

**C4M** · 05-06-2002, 05:13 AM

Originally posted by Gutter
First of all, Alives, STFU. Your opinion is no longer requested. You have my sincerest apologies that Jensen amps trouble you so. As I said in the other thread, I just needed a cheap way to amplify the sound coming from the soundcard. I'm not about to spend $200+ on an amp to power my stock speakers. Maybe if I had better speakers or actually gave a flying ****, I'd spend more.

Methinks he has serious issues on Playing Nicely With Others.

Originally posted by Gutter As for the amp, I fixed the problem. I ran 10 gauge wire from the battery and it doesn't dim anymore. It sounds great, and had my stock speakers rockin'.

Make sure that you have an appropriate sized fuse inline between the amp and the battery. IASCA competition requires that the fuse is within 18 inches of the battery. I know that you don't care about competing, but fuses are way cheaper than amplifiers (even Jensen ones

).

**C4M** · 05-06-2002, 05:14 AM

Originally posted by Alives
sounds like my suggestions helped

Not really. 10 gauge is actually smaller than your suggested 8 gauge.

**JamesB** · 05-06-2002, 12:52 PM

Actually .. the use of a fuze to protect the amp is a bit of a misnomer.

The fuze is to prevent an open circut in the event of an electrical short along the power-line. Ie. if you are invloved in an accident and the vehicle body pinches the power-wire, causing a short .. you want the fuze to blow to protect your car's electrical .. and to prevent fire.

C4M is correct in saying _within_ 18 inches. Some people actually say 12" max.

PS: Don't run any "signal wires" on the same side as you run the power wire. Just another "no no" =)~

**wizardPC** · 05-06-2002, 03:44 PM

okay, I have been lurking on this post but I just realized that you bought the amp that I want, for half the price I can get it

I am 350 miles away from the nearest BestBuy, but I am going there wednesday. Was that a Weekend special or are they still on sale (everywhere)?

**Gutter** · 05-06-2002, 03:58 PM

No, it was a discontinued, open item. It was $92, but they dropped 10% more just because it's an open item.

$79.60

They said they're not getting any more in, so you better call before driving all that way. All the amps were on sale, so you might still be able to find a good deal on something else. But make sure that whatever you buy, check with Alives and make sure it pleases him.

**jboy** · 05-06-2002, 04:20 PM

Originally posted by JamesB
Actually .. the use of a fuze to protect the amp is a bit of a misnomer.

The fuze is to prevent an open circut in the event of an electrical short along the power-line. Ie. if you are invloved in an accident and the vehicle body pinches the power-wire, causing a short .. you want the fuze to blow to protect your car's electrical .. and to prevent fire.

C4M is correct in saying _within_ 18 inches. Some people actually say 12" max.

PS: Don't run any "signal wires" on the same side as you run the power wire. Just another "no no" =)~

The fuSe is to CREATE an open circut in the event of an electrical short along the power-line.

fuses do help protect the amps and other components if they are sized right and fast acting, magnetic circuit breakers are the best for this

**JamesB** · 05-06-2002, 06:02 PM

Well noted, jboy. I should have said closed circut ;-)

One thing to note is that amps which _require_ a fuze have a fuze well (receptacle) built-in. In most cases, cheaper amps have fuzes on the power side of the amp .. that fuze is meant to protect the amp .. otherwise the in-line fuze is to protect the vehicle (and you).

**wizardPC** · 05-06-2002, 11:03 PM

well, $92 is still better than $160

Why the hell isnt there a mobile electronics section on the bestbuy webpage? GRRR

oh, and I'm not going to drive 350 miles just to save $60 on an amp (my girlfriend lives about 2 miles from the nearest best buy)

**spud42** · 05-06-2002, 11:34 PM

JAMES B said:-
"If you are "under-driving" the amp with a low input signal, you are likely introducing a large degree of noise causing a "clipping" effect. (clipping is when the output from the amp goes too high for the electronics and is "flattened out" causing DC output (amps are designed to aomplify an AC (music) signal)."

this is incorrect.you cannot get clipping from underdriving an amp.
you just get low output volume. clipping is when the input signal is too high , the amp has a fixed ammount of gain and a maximum pos and neg rail voltage. if the input signal is so large as to exceed these rail voltagesthe signal cannot be amplified any more and the output is clipped to the maximum rail voltage. this is bad because the output sine wave then approaches that of a square vave.which has lots and lots of harmonics. this is what is known as distortion.the larger the input signal the more distortion. this is good if you are a korn guitarist ;-)) but not if you want clear clean sound!!!

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