There are no current loops inside a decently designed CD player. One board, one ground plane, one DC ground potential.
The problem Jocko was referring to is related to a noisy ground plane. Only certain part(s) of this plane have REALLY low noise level. The trick is how to design the ground plane and preserve this very low noise figure across the whole PCB.
Power supply decoupling capacitors couple the noise to this ground plane. The noise should find the quickest way to the ground plane. These capacitors are everywhere and are crucial in digital circuits as to keep the power supply rail noise as low as possible. Noise comes from everywhere, in particular from switching circuitries like uPC's, clock oscillators, filters, DAC's (they are switches after all...). If the ground plane noise is high, this noise will be injected back in to the power supply rails via these caps - from the ground plane!!! This is very often the case, unfortunately, in cheap CD players / DAC's. Sometimes I can't believe my eyes at the level of noise surrounding digital filters / DAC's in some very respectable semi high end equipment. Shocking! But, there are consumer level CD players and DAC's that measure pretty well in this regards.
I think the first step to serious modifications approach should be to consider how to cut the ground plane noise. Sometimes this may be very expensive - in which case isolating the noisy parts / sections will give some benefits as well.
Once you have a low noise ground plane environment, go ahead and spend some money on good quality capacitors. They are actual going to decouple those power supply rails okay, for a change....
Extreme_Boky
The problem Jocko was referring to is related to a noisy ground plane. Only certain part(s) of this plane have REALLY low noise level. The trick is how to design the ground plane and preserve this very low noise figure across the whole PCB.
Power supply decoupling capacitors couple the noise to this ground plane. The noise should find the quickest way to the ground plane. These capacitors are everywhere and are crucial in digital circuits as to keep the power supply rail noise as low as possible. Noise comes from everywhere, in particular from switching circuitries like uPC's, clock oscillators, filters, DAC's (they are switches after all...). If the ground plane noise is high, this noise will be injected back in to the power supply rails via these caps - from the ground plane!!! This is very often the case, unfortunately, in cheap CD players / DAC's. Sometimes I can't believe my eyes at the level of noise surrounding digital filters / DAC's in some very respectable semi high end equipment. Shocking! But, there are consumer level CD players and DAC's that measure pretty well in this regards.
I think the first step to serious modifications approach should be to consider how to cut the ground plane noise. Sometimes this may be very expensive - in which case isolating the noisy parts / sections will give some benefits as well.
Once you have a low noise ground plane environment, go ahead and spend some money on good quality capacitors. They are actual going to decouple those power supply rails okay, for a change....
Extreme_Boky
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