Hi, I'm planning a 2-way bi-amped system using a mini-dsp. The amp box will contain a mini-dsp, preamp/tone control board, power supply(ies) and amp(s). I was advised to avoid running two different amp boards from one power supply. I'm expecting a crossover frequency around 500 Hz, so I'll need a bigger amp for the bass drivers than the midtweeters. Can I use two different power supplies, one for each amp, and use only one a/c input? How does that go together? I don't want to have to plug it in twice...
Sorry if my question is too basic--this is my first project involving electronics.
Sorry if my question is too basic--this is my first project involving electronics.
You really don't need two complete separate power supplies. Using a single transformer of adequate power with one bridge rectifier and filter caps for each amplifier channel works just fine. Minimizing crosstalk is usually determined more by the wiring and layout than anything else.
Mike
Mike
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Have you measured this?
How much is the crosstalk improved by having separate PSU's?
I would really like to know.
Allowing for the very high power supply rejection ratio, the "improvement" will be at best minimal and then only at very low frequencies where crosstalk is irrelevant.
I don't have any "noticeable" crosstalk due to a common power supply in my amp.
Frank
allso, for the same money as 2, or 3 smaller powersupplys one can go for a far bigger one.
bigger does not automaticly makes it all that better, but still i'd prefer something that can push those OOOOMPS when needed.
a larger powersupply can safely support a larger bank of reservoir capacitors.
that makes a difference up to a point.
bigger does not automaticly makes it all that better, but still i'd prefer something that can push those OOOOMPS when needed.
a larger powersupply can safely support a larger bank of reservoir capacitors.
that makes a difference up to a point.
the more detail you provide the better info can be given. this is a bit much for your 1st foray into "electronics"
1) note most folks find out after the fact, that power timing is needed between powering up amps and the analog filtered pre-amps not sure about dig filters. PA turned on last and turned off 1st otherwise speaker damage may result.
2) plan for some rework before final packaging
1) note most folks find out after the fact, that power timing is needed between powering up amps and the analog filtered pre-amps not sure about dig filters. PA turned on last and turned off 1st otherwise speaker damage may result.
2) plan for some rework before final packaging
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It varies significantly. The benefit of multiple supplies is governed by the ratio of power consumption between channels and hence depends on which channel in a biamp (triamp, quadamp, etc.) one's considering and how well implemented they are. Intro to the maths here for linear supplies; various other threads over in the supplies forum discuss the motivation for PSRR requirements in the 120 to 140dB range. You'll likely also find tomchr's measurements and related input CMRR discussion in the Modulus-86 thread over in the vendor's bazaar of interest.
The answer ultimately depends on supply implementation, amplifier dissipation, CMRR, PSRR, crossover and EQ selection, program material, and performance requirements. Assuming adequate PSRR and internal layout within an amplifier channel there really isn't an onset of diminishing returns for offloading supply requirements to amplifier input CMRR. Increasing CMRR from 0dB to 40dB costs cents and 60dB to 80dB or even 100dB costs dollars in DIY quantities. In comparison a second supply starts at tens of dollars. So, in sensible implementations, additional supplies mitigate error terms already suppressed by CMRR, good grounding practice, and loop gain. The Modulus link above is to an example showing the resulting frequency dependence.
The difficulty is more that most amplifier implementations are not very sensible in these regards. 0dB CMRR and 50-70dB PSRR is common.
This does not work.
Each channel has it's own Main Audio Ground connected to it's own PSU Zero Volts.
But BOTH these Zero Volts are connected to the transformer Centre tap.
That creates a loop in the two amplifier channels.
You have a choice on how to do it properly.
ONE PSU zero Volts supplying BOTH channels, and the channel Power Grounds should be close together with a very low impedance connection between them.
or
Two dual rectifier PSU from isolated 4 secondaries, so that each channel has a separate Main Audio Ground.
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