100Deals.com
11-01-2001, 08:28 AM
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100Deals.com
Just curious what everyone thinks about this website: www.100deals.com It takes a second to load but when it does, it's pretty quick to go through different pages. Every once in awhile, we have one of those shows, sponsored by this website, that come to town and they sell all the stuff real cheap. I heard all the electronic stuff is remanufactured, and not brand new. Anyway..what do you peeps think? 
11-01-2001, 08:48 AM
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Vehicle: 2000 Tib
i dont know much about amps, is this one any good? its only $100
Pyramid PB-780 1000 Watt Car Amp
Description:
4 channel amplification, tri-way configuration: 250w x 4 channel output or 500w x 2 channel bridged or 250w x 2 channel plus 500w x 1 channel, 1000 watt total output, remote turn on/off, 2 ohm stereo stable, MOSFET PWM power supply, built-in variable low-pass crossover (40 - 450 Hz) rear channel, bi-level input configuration, high level MOLEX input, power on LED indicator, visual light strip display, signal to noise ratio greater than 85db, less than 0.04% THD at 1 kHz.
[ November 01, 2001: Message edited by: YellowTiburon ]
Pyramid PB-780 1000 Watt Car Amp
Description:
4 channel amplification, tri-way configuration: 250w x 4 channel output or 500w x 2 channel bridged or 250w x 2 channel plus 500w x 1 channel, 1000 watt total output, remote turn on/off, 2 ohm stereo stable, MOSFET PWM power supply, built-in variable low-pass crossover (40 - 450 Hz) rear channel, bi-level input configuration, high level MOLEX input, power on LED indicator, visual light strip display, signal to noise ratio greater than 85db, less than 0.04% THD at 1 kHz.
[ November 01, 2001: Message edited by: YellowTiburon ]
11-01-2001, 10:23 AM
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Okay... A few warning bells... Prepare for yet another Essay by Dan...
It was apparently tested with a 1 kHz sine wave, not "typical music programme, and certainly not a pink noise track.
I don't see if that's rated at RMS or MAX wattage. For 1 kW, I'd pretty much assume that's MAX.
And the THD level sounds very good, at 0.04%, but remember, that's at a 1 kHz sine wave. NOT typical music program material, and again, certainly not a "pink noise" track.
Also unreasonable signal levels can be used, but you generally don't get reasonable THD levels doing that -- not even close.
Signal bursting can also increase power output. Basically, if you pulse the signal into the amplifier for less than a second, you get more power at the output. (In fact, almost double, with little or no penalty in THD or S/N ratios.
It also doesn't specify the input voltage that the amp was tested at. It probably is NOT 12V, meaning probably 14.4V. (Some of the bargain basement brands have been known to test at up to 28V -- They get their power rating just before the smoke gets out of the heat sink.)
Note that these omissions are also consistent with the product info at Pyramid's web page.
Now let's start with the number crunching.
250W/channel MAX is about 70% that in RMS. So now we're down to 175W/channel -- Assuming that there's no exaggeration going on!
Power output increases by a factor of 1.7 when tested with a sine wave tone, vs testing with pink noise. So that takes our 175W RMS down to about 103W/channel RMS, tested with pink noise. (Note, THD and S/N ratio also suffer under these conditions, and 95dB S/N ratio isn't THAT great to begin with.)
Now let's address voltage. If we assume that they test at 14.4V (Which many amp manufacturers do) you get typicaly a 25% increase in power. That gets us down to 80 odd watts per channel, as it would be tested by a manufacturer like Apline. So your "1000 Watt" amplifier might have a good 320W in it somewhere when you actually put it in your car. And they also may have done some monkeying around (like signal bursting) that I didn't mention, and you may have less, like 40WX4 RMS! eek.gif
To understand S/N ratio, my Alpine V12 amplifiers were tested at 102dB S/N ratio (Rated at 100 dB) At 95 dB there is nearly 4 times the "noise" output on the signal output vs, the rates 100dB that most quality manufacturers can and do rate their amplifiers at. Also, expect closer to 92 dB S/N ratio if you test those amps with pink noise. (Typically there is a 3dB difference)
THD will typically double when tested with a pink noise track, vs a sine wave input, so the 0.04% THD will be AT LEAST 0.1% -- And probably more, depending on the quality of the amplifier's internal active components and transistors. Note that the specifications with the amplifier running at 2 ohm is not listed, nor are the specs listed for running the amplifier bridged. In either event, expect the THD to be at least five times the rated level, and S/N ratios to drop by another 4-6 dB. Again, this is based on typical behavior of good quality amplifiers. Pyramid doesn't have that reputation.
Now, if you can live with that, and think that the $100 for an amp (Probably last year's model, as it's not listed on Pyramid's site as a current product) that's closer to 300W than 1000W is a good deal, and can live with it not having a waranty, either, then go for it.
Oh. You won't want to compete in SQ with that amp, they'll class it as the 1000W that it's rated at (Bogus though that may be) and it's not going to sound NEARLY as good as the people that you compete against. (Of course in dB competition, they only count woofers, now, not wattage.)
FWIW, I bought a $40 200W (50X4) Pyramid amplifier once, just to bench test it. I found that it would put out the rated wattage (50WX4) into a 2 ohm load, if the DC rails were run at 16VDC, I used a 1kHz sine wave as input, burst for 0.5s and would accept a THD rating of about 7% or so. Oh yeah, the input 1kHz sine wave was an 8V signal, too. None of these conditions could be met in my car. I determined that it was about 6W/channel under real conditions. Quite a rip-off at $40.
For the record, I apologise for the length of this post...
[ November 01, 2001: Message edited by: Dan ]
It was apparently tested with a 1 kHz sine wave, not "typical music programme, and certainly not a pink noise track.
I don't see if that's rated at RMS or MAX wattage. For 1 kW, I'd pretty much assume that's MAX.
And the THD level sounds very good, at 0.04%, but remember, that's at a 1 kHz sine wave. NOT typical music program material, and again, certainly not a "pink noise" track.
Also unreasonable signal levels can be used, but you generally don't get reasonable THD levels doing that -- not even close.
Signal bursting can also increase power output. Basically, if you pulse the signal into the amplifier for less than a second, you get more power at the output. (In fact, almost double, with little or no penalty in THD or S/N ratios.
It also doesn't specify the input voltage that the amp was tested at. It probably is NOT 12V, meaning probably 14.4V. (Some of the bargain basement brands have been known to test at up to 28V -- They get their power rating just before the smoke gets out of the heat sink.)
Note that these omissions are also consistent with the product info at Pyramid's web page.
Now let's start with the number crunching.
250W/channel MAX is about 70% that in RMS. So now we're down to 175W/channel -- Assuming that there's no exaggeration going on!
Power output increases by a factor of 1.7 when tested with a sine wave tone, vs testing with pink noise. So that takes our 175W RMS down to about 103W/channel RMS, tested with pink noise. (Note, THD and S/N ratio also suffer under these conditions, and 95dB S/N ratio isn't THAT great to begin with.)
Now let's address voltage. If we assume that they test at 14.4V (Which many amp manufacturers do) you get typicaly a 25% increase in power. That gets us down to 80 odd watts per channel, as it would be tested by a manufacturer like Apline. So your "1000 Watt" amplifier might have a good 320W in it somewhere when you actually put it in your car. And they also may have done some monkeying around (like signal bursting) that I didn't mention, and you may have less, like 40WX4 RMS! eek.gif
To understand S/N ratio, my Alpine V12 amplifiers were tested at 102dB S/N ratio (Rated at 100 dB) At 95 dB there is nearly 4 times the "noise" output on the signal output vs, the rates 100dB that most quality manufacturers can and do rate their amplifiers at. Also, expect closer to 92 dB S/N ratio if you test those amps with pink noise. (Typically there is a 3dB difference)
THD will typically double when tested with a pink noise track, vs a sine wave input, so the 0.04% THD will be AT LEAST 0.1% -- And probably more, depending on the quality of the amplifier's internal active components and transistors. Note that the specifications with the amplifier running at 2 ohm is not listed, nor are the specs listed for running the amplifier bridged. In either event, expect the THD to be at least five times the rated level, and S/N ratios to drop by another 4-6 dB. Again, this is based on typical behavior of good quality amplifiers. Pyramid doesn't have that reputation.
Now, if you can live with that, and think that the $100 for an amp (Probably last year's model, as it's not listed on Pyramid's site as a current product) that's closer to 300W than 1000W is a good deal, and can live with it not having a waranty, either, then go for it.
Oh. You won't want to compete in SQ with that amp, they'll class it as the 1000W that it's rated at (Bogus though that may be) and it's not going to sound NEARLY as good as the people that you compete against. (Of course in dB competition, they only count woofers, now, not wattage.)
FWIW, I bought a $40 200W (50X4) Pyramid amplifier once, just to bench test it. I found that it would put out the rated wattage (50WX4) into a 2 ohm load, if the DC rails were run at 16VDC, I used a 1kHz sine wave as input, burst for 0.5s and would accept a THD rating of about 7% or so. Oh yeah, the input 1kHz sine wave was an 8V signal, too. None of these conditions could be met in my car. I determined that it was about 6W/channel under real conditions. Quite a rip-off at $40.
For the record, I apologise for the length of this post...
[ November 01, 2001: Message edited by: Dan ]
