Does these numbers mean anything at all? For comparison with other design, may be.
Some designs may give too high THD increase at higher power. I don't know the "standard" with car amps, but they are lower than home amps, so 0.01% at 1W 4R 1KH is probably too good (depends on the price). The reason is because in most mosfet (vertical) designs, the more the drive (or the power) the better the mosfet performs. This means that the distortion near full power may not be as suffering as bipolar amps of the same performance at 1W.
The amp came in with the Bias setting completely off (different settings for each channel), treshold for protection circuitry was off and there is too much noise caused by the pre-amp.
My goal is really very simple. On a short term, I want this amplifier to perform as good as possible without modifying the PCB. It's easier (and more economic) to change component values in a production than to change the PCB itself.
For the long term we have to decide if we want to make changes to the amplifier itself, but for this to work I need a better understanding of Mosfet amplifier design.
I've already fixed the protection circuitry to react at the right tresholds, both with resistive as reactive loads. Second up is the bias setting, we want to determine the bias setting procedure so we can inform the manufacturer on how to set the bias from now on.
After that I would like to reduce the noise caused by the pre-amp/filter stage.
My goal is really very simple. On a short term, I want this amplifier to perform as good as possible without modifying the PCB. It's easier (and more economic) to change component values in a production than to change the PCB itself.
For the long term we have to decide if we want to make changes to the amplifier itself, but for this to work I need a better understanding of Mosfet amplifier design.
I've already fixed the protection circuitry to react at the right tresholds, both with resistive as reactive loads. Second up is the bias setting, we want to determine the bias setting procedure so we can inform the manufacturer on how to set the bias from now on.
After that I would like to reduce the noise caused by the pre-amp/filter stage.
Since these amps mount directly onto flammable materials, its a good idea to set the bias low enought that the case barely get warm on idle.
Vertical fets like these, FQP's are planer stripe type vertical fets BTW, are very rugged compared to BJT's but suffer from a nasty exponential transfer and significant drop in Gm at lower currents. This is why they show 'less distortion' at higher levels or if used in class A, and also why they require more bias current than BJT's at class AB bias range.
- Status
- Not open for further replies.