V
Victor
- Jan 1, 1970
- 0
I'm trying to decide which approach of two different shunt voltage
regulation schemes will result in the lowest noise for supplying a
LM3875 based home audio amplifier to drive high efficiency(100-107 db)
horn speakers. Granted, the LM3875 already has a PSRR and CMRR of 120
dB, but I'd like to take out the noise before it hits the chip.
The amp can draw considerable current(4-6.5 A) for short periods to
2-5 mS which is the reason I'm choosing shunt over normal in-line
reuglation. I don't want the max current rating of the regulator to be
the limiting factor in performance or have to add banks of capacitors
after regulation to make up for that shortcoming. Experimentation has
shown that 1000uf at the pins of the LM3875 prevent oscillation and
provide the best performance without making the sound sluggish.
To make up for that, I'll be using a a battery supply to avoid AC line
noise and provide the needed capacitance, but this has it's own set of
noise problems which can be viewed at the bottom of this page:
http://www.tnt-audio.com/clinica/regulators_noise4_e.html
Anyway, on to shunt regulation and noise filtering:
1. The Two-transistor Shunt Regulator can be found at the top of the
same page above and boasts an average noise level of -100dB across the
normal audio frequency range. It seems fairly simple and doesn't need
any tweaking.
Or
2. A precison hi current shunt regulator using TI's TL1431 "Precision
Programmable Reference" followed by LM833/2N4401 noise shunt which
boasts a 40dB noise reduction with careful construction.
The particular circuit "Precision High-Current Series Regulator"
can be seen in Figure 18. on page 13 of the datasheet at:
http://www-s.ti.com/sc/ds/tl1431.pdf
Ahich of thee two approaches seem best?
And, I'm hoping someone can tell me what rating resistors are best for
low-noise supply? I'm assuming 1 watt 5% wirewound will do, although
something tells me that 1% might be best in the critical Vref spots.
Also, are electrolytic caps best in these circuits and what mx voltage
rating?
Any advice greatly appreciated,
regulation schemes will result in the lowest noise for supplying a
LM3875 based home audio amplifier to drive high efficiency(100-107 db)
horn speakers. Granted, the LM3875 already has a PSRR and CMRR of 120
dB, but I'd like to take out the noise before it hits the chip.
The amp can draw considerable current(4-6.5 A) for short periods to
2-5 mS which is the reason I'm choosing shunt over normal in-line
reuglation. I don't want the max current rating of the regulator to be
the limiting factor in performance or have to add banks of capacitors
after regulation to make up for that shortcoming. Experimentation has
shown that 1000uf at the pins of the LM3875 prevent oscillation and
provide the best performance without making the sound sluggish.
To make up for that, I'll be using a a battery supply to avoid AC line
noise and provide the needed capacitance, but this has it's own set of
noise problems which can be viewed at the bottom of this page:
http://www.tnt-audio.com/clinica/regulators_noise4_e.html
Anyway, on to shunt regulation and noise filtering:
1. The Two-transistor Shunt Regulator can be found at the top of the
same page above and boasts an average noise level of -100dB across the
normal audio frequency range. It seems fairly simple and doesn't need
any tweaking.
Or
2. A precison hi current shunt regulator using TI's TL1431 "Precision
Programmable Reference" followed by LM833/2N4401 noise shunt which
boasts a 40dB noise reduction with careful construction.
The particular circuit "Precision High-Current Series Regulator"
can be seen in Figure 18. on page 13 of the datasheet at:
http://www-s.ti.com/sc/ds/tl1431.pdf
Ahich of thee two approaches seem best?
And, I'm hoping someone can tell me what rating resistors are best for
low-noise supply? I'm assuming 1 watt 5% wirewound will do, although
something tells me that 1% might be best in the critical Vref spots.
Also, are electrolytic caps best in these circuits and what mx voltage
rating?
Any advice greatly appreciated,