IC AMP AUDIO POWER 40W or 120W? Repair.

[Briantrey]

HI,

I'm new here. I don't know to much about this stuff. I did take some school for it so I can follow it a bit. But, I have a 120W Audio Amp(PA system) and it got fried. I know its the IC AMP. I can see its been melted. But, I looked up the numbers on it and it says its a 40W amp chip. But on the PA unit it self it says its a 120w PA AMP. So, I found a 120W IC and the 40W IC also. So, Should I get the 120W to prevent it from blowing out again, or would the 120W give it too much power and then end up blowing something else out?

P.S the 40W IC amp is what it came with.

Please help I'm alost.

I only know vary basic things about this stuff so, Plz explane it to me as simple as possible.

Thanks,
Briantrey

 

[Nigel Goodwin]

Your post doesn't make any sense?. Chips don't come labelled with their power ratings, they have model numbers on them - what are the numbers on the chips?.

You also can't just replace one chip with a completely different one!, the circuit is designed specifically for the chip it uses.

The main criteria for the output power is the supply voltage and the speaker impedance, from those you can easily work out the maximum power the amplifier is likely to deliver.

 

[spuffock]

Use the chip it came with. The amp will give 40 watts. It always did. The salespeople have dreamed up a whole new mathematics, incomprehensible to us poor engineers, specially to provide bigger numbers for the output. The best I've had to date is an amplifier marked 960 Watts on the box, with a chip that would make a quarter of a watt on a good day.

 

[Nigel Goodwin]

Use the chip it came with. The amp will give 40 watts. It always did. The salespeople have dreamed up a whole new mathematics, incomprehensible to us poor engineers, specially to provide bigger numbers for the output. The best I've had to date is an amplifier marked 960 Watts on the box, with a chip that would make a quarter of a watt on a good day.

That applies to many items (particularly in the USA), but PA amplifiers usually have honest RMS ratings.

 

[Briantrey]

Ops

Sry guys. Let me try again.

Here the link to the IC AMP 40W that was in the PA system https://www.electro-tech-online.com/custompdfs/2005/12/LM2876.pdf

The question is "Putting a 120w AMP IC in it. Would/should it work and will it give me more power and/or prevent it from burning out again?"

Seeing that I'm taking it apart maybe I can upgrade it, is what I was thinking. And if by putting this IC in would it give more power. Or at least prevent it from burning up the IC again.

Thanks, sry like I said not to good in this stuff Plz bare with me.

Thanks again,
Brian

 

[Briantrey]

Ohhhh Sry ignore my last post

I understand. I got the IC number then looked it up and got the 40W rating from it.

Thanks for the advice I'm just going to order the same IC AMP chip

Heres the IC number# LM2876TF

And this is the number of the 120w # LM4780TA

Thought they would be the same but with a higher power rating.

Mainly I don't want the IC Amp chip blowing out again. I'm happy with its current power. hate to have to do this every week.

Thanks again guys.
Briantrey

 

[Nigel Goodwin]

Re: Ops

Sry guys. Let me try again.

Here the link to the IC AMP 40W that was in the PA system https://www.electro-tech-online.com/custompdfs/2005/12/LM2876-1.pdf

The question is "Putting a 120w AMP IC in it. Would/should it work and will it give me more power and/or prevent it from burning out again?"

As I said before, the power output is directly proportional to the supply rails, 40W into 8 ohms requires an output swing of 52V, which (due to losses) means you're looking at something like a 60V HT rail (probably +/-30V). 40W is the maximum possible power that you can get from this supply voltage, UNLESS you use a bridged circuit.

Seeing that I'm taking it apart maybe I can upgrade it, is what I was thinking. And if by putting this IC in would it give more power. Or at least prevent it from burning up the IC again.

So simply fitting a different IC won't increase the power at all, but assuming you can get a 100% compatible 120W IC, that will work off these lower supply rails, it 'should' be more reliable.

But I'm puzzled as to why a PA amplifier would be rated at 120W with only a 40W chip in it?, this isn't how PA amps are rated!. What else is in the amplifier?, and is it more than one channel?. Do you have a make and model for the amp?.

Another thing, what were you doing when it died?, is it a combo amp?, and were you feeding the wrong impedance speakers off it?.

 

[Briantrey]

Its a PYRAMID PA205 120W.

I got it from eBay **broken link removed**

I was using my head phones when it went out on me. As soon as I pluged in my Zoom 505 II effects processor I heard pop pop then smoke then the power went out. I check the fuse and it did blow. So, I hope it did not blow out my transformers. But I'm hoping for the best.

But I'm puzzled as to why a PA amplifier would be rated at 120W with only a 40W chip in it?, this isn't how PA amps are rated!.

I thought the same thing, When I looked up that chip and it said 40W I was like WOW what the ****! It says 120W on the AMP its self. as you can see in the pic at the eBay page.

But hope I did not blow anything else out. Just going to order that IC amp and hope for the best. $8 for it. So its better to try to fix it then spend another $60 $70.

Thanks,
Briantrey

 

[Dean Huster]

That applies to many items (particularly in the USA),

In the 1960s, the advertising got totally out of hand in the U.S., with consumer amplifier systems being rated in "peak music power", ending up with skyrocketing numbers that meant nothing. They'd calculate power based on peak voltage rather than RMS voltage and some would use the very short-term power the supply could put out for transient peaks and calculate power based on that for some really startling numbers. The Federal Trade Commission in the late 1960s or early 1970s had some laws passed that stated that ALL amplifiers had to be rated in RMS watts into 8 ohms. Now I notice that in this age of surround sound, we're back to the old tricks. I don't know what happened to the old laws that'd been passed.

In the case of this 40W chip, if we assume an 8 ohm load, that would calculate out to a speaker voltage of 17.9 vrms. If we change that to peak voltage, we get abaout 25.3 volts peak and recalculating power with that same 8 ohms gives us 80 watts peak and doubling the voltage to get peak-to-peak volts can give us 320 watts peak-to-peak. Or we can take the peak voltage and recalculate the power into 4 ohms and get 160 watts peak (and that might be where they got their 150 watts). We can have all sorts of fun with stuff like this to make our amps look like monsters. Remember the days before switching supplies when a 500-watt (rms) amp weighed in at 50+ pounds because of the power transformer?

Dean

 

[Nigel Goodwin]

Its a PYRAMID PA205 120W.

I got it from eBay **broken link removed**

I was using my head phones when it went out on me. As soon as I pluged in my Zoom 505 II effects processor I heard pop pop then smoke then the power went out. I check the fuse and it did blow. So, I hope it did not blow out my transformers. But I'm hoping for the best.

But I'm puzzled as to why a PA amplifier would be rated at 120W with only a 40W chip in it?, this isn't how PA amps are rated!.

I thought the same thing, When I looked up that chip and it said 40W I was like WOW what the ****! It says 120W on the AMP its self. as you can see in the pic at the eBay page.

But hope I did not blow anything else out. Just going to order that IC amp and hope for the best. $8 for it. So its better to try to fix it then spend another $60 $70.

Thanks,
Briantrey

With the model number a lot becomes clearer :idea:

You can download the manual at https://www.electro-tech-online.com/custompdfs/2005/12/PA205.pdf, which shows the 'manufacturers' URL as http://www.pyramidcaraudio.com/. "Car Audio" makes the wildly exaggerated spec clear, car audio specs are completely imaginary!. But having said that, the website does clearly state "40W RMS at 10% distortion", as did the original Ebay advert.

As you mention a Zoom effects pedal (my daughter actually has a Zoom bass pedal!), I'm presuming you're using it for a guitar?. This amplifier isn't a musical instrument amplifier, it's basically for voice use only, along with background music - such as used in a shop for doing announcements. A dead giveway is the transformer coupled output, which allows you to connect different speakers, including 70V line ones.

If you had a guitar plugged directly into it (or through a pedal), you were probably greatly over driving it, as it only has mike inputs, and NOT ones suitable for a guitar.

 

[audioguru]

Pyramid isn't a name brand PA equipment manufacturer so they can put any numbers on their stuff.
It says 40W Mono 10% RMS at 8 ohms on E-Bay's description for the thing, so it is probably only 30W at clipping (10% distortion produces a severely clipped square-wave). Since its power is rated only at 8 ohms then its output transformer for multi-speaker connections probably can't pass much power.

PA amplifiers have an output transformer for their multi-speaker connections at 70V. The IC was probably destroyed by the inductive flyback voltage from the transformer since it wasn't connected to a proper load. Frequently, PA amplifiers have a jumper at their output to be removed if the transformer isn't needed which would have eliminated the inductive spike.

 

[Briantrey]

Hi,

Thanks everyone, Vary informative. I was using the Zoom Pedal for my voice, but it does have a pre amp in it. I plugged it into the back, so it will by-pass the PA AMPs pre amps. Its like the LINE IN for a PC sound card VS the MIC IN. At first it was over driving. Then I seen the line in by-passing the mic pre amp. Then it sounded realy clear. I was happy till a day later "Pop pop smoke" lol.

I guess I learned something about the RMS. I will be sure to look for this If/When I look for a new PA amp.

hopefully The new IC will fix it and I can work with it for now. Just wish there was something I can do to keep it from blowing out again something simple. Any ideas?

Thanks Again everyone,
Briantrey

 

[Nigel Goodwin]

hopefully The new IC will fix it and I can work with it for now. Just wish there was something I can do to keep it from blowing out again something simple. Any ideas?

Don't overdrive it!, the instruction book warns that doing so can blow the amp.

 

[Briantrey]

I'm happy to report that after ordering the Original Chip and soldered it in. It now WORKS! At first there was a loud bussing. So I figered that the baord was not grounded so I cheack the ground connections and then the bussing stop, and now its seems to be clearer then ever. Not 1 bit of bussing. Before it had some. Baybe I got a better chip brand or something.

Thanks for all your help and advice.

Thanks again guys,
Briantrey