For those who might be curious about what goes into these things, here are some answers. A single inductor is by the power supply input, along with the one discrete (bipolar) transistor that appears on the circuit board. It seems like a circuit intended to deal...
For those who might be curious about what goes into these things, here are some answers.
A single inductor is by the power supply input, along with the one discrete (bipolar) transistor that appears on the circuit board. It seems like a circuit intended to deal with voltage fluctuations, and maybe confer a degree of idiot-proofing, and I approve.
Most of the other parts in evidence are the minimum needed to do about a third of what this amp''s spec sheet claims. Aside from some small value mylars and a couple of ceramics, all of the capacitors are Taiwanese, aluminum electrolytics. At least 3/4 of the resistors appear to be carbon-based. Buffering is provided by a UTC4558 dual op amp chip. Amplification is provided by a 4-channel amp-on-a-chip, the $2.50 STA540SAN. At 12 volts, this chip is good for 4 channels x 9 watts @2 ohms, but can be bridged to provide 2 x 18 watts @4 ohms instead. That''s exactly what we have here.
If I were making this amp, I''d spend an extra couple of dollars to use higher quality resistors and capacitors, because they''d last longer and sound better. On the other hand, it''s not much over $20, and I couldn''t build one of them for that. Parts are a lot more expensive when you buy a few, than when you buy thousands at a time, and I''d probably get gouged for >$10 for the box alone.
Yes, it''s cheaply made, and inflates its wattage from 36 to 100. My "90 watt" Pyle amp produces 6-8 watts per stereo channel. Inflation of car audio specs is SO nearly universal, that doing 36% of what''s claimed is, relatively speaking, not bad at all. If you use it in a car and are maintaining something close to the 13.8v maximum that most alternators can produce, you might hit 25 watts a channel. If you''re driving a couple of subs with it, that will give you sound levels about 17 dB over the efficiency of your speakers, so if you bought efficient speakers, let''s say 96 db/watt, you''d get about 113 dB. That''s loud enough to damage your hearing pretty quickly, and is more than most buyers would ever want. Continuous exposure to over 90 dB is deemed harmful for hearing, and a pair of 98 dB/w speakers could do that on about a twentieth of a watt per channel. (Hey, if you bought 82 dB/watt speakers and need 7 watts to get to 90 dB, don''t blame me... )
One thing I found in the data sheet for the STA540SAN, was mention of the idea that manufacturers could save themselves the cost of a part, plus circuit board real estate and insertion costs, by using a single DC-blocking capacitor for both of the stereo channels. They also mention, in vague terms, that it will harm stereo separation to do that. While I did see some pairs of caps on the board, none of them were very near the output stage, so I suspect that Boss may have done that with these amps. If you''re using them for subs, you''ll never know or care, but if you''re using one for higher frequencies and get crosstalk, that might be why. It''s common in budget amps. In the rare event that an output capacitor fails by becoming a short circuit, it can allow the DC power supply to flow directly through both channels of your speakers, which is likely to fry many drivers almost instantly. I''d have felt better if just that one cap was a solid type, rather than an aluminum oxide paste cheapie.
But hey, did I tell you it was only about $20?