I built a tri amp two years ago with three separate power supplies, one for the base amp, one for both mid and high frequency amps and one for the controls, filter and attenuator. This took up a large cabinet but works fine.
I intend building another tri amp with all the amps using discrete components due to obsolete chips. The power supplies for this tri amp would be separate for each of the amplifiers and a fourth ps for the controls, filter and attenuator.
The space requirements would mean a very big cabinet.
My question is - could switch mode power supplies be used without creating interference problems. I have never used a switch mode ps and have only read of the interference problems with them in the past.
I intend building another tri amp with all the amps using discrete components due to obsolete chips. The power supplies for this tri amp would be separate for each of the amplifiers and a fourth ps for the controls, filter and attenuator.
The space requirements would mean a very big cabinet.
My question is - could switch mode power supplies be used without creating interference problems. I have never used a switch mode ps and have only read of the interference problems with them in the past.
It depends on the particular supply. Some run at very high frequencies meaning all the EMI is far above the audio spectrum, but some of the SMPS chips drop frequency on low load, meaning the frequencies drop into the audio range at times which is bad news. Overall the trend is for higher switching frequencies as this reduces size and weight, so in general more modern supplies will tend to be more audio-friendly.
Good filtering can mitigate/eliminate the problem of a noisy supply however. Having supplies in a separate box can help with EMI flying around.
Some cheap supplies aren't great with highly variable loads too, having trouble regulating with rapid changes in output current.
Not a clear cut answer I'm afraid, I have seen some SMPS's advertized for audio amp use however, presumably meaning they are good with bursty loads and low EMI, indeed I have such a supply that's earmarked for a project, but not used in anger yet 🙂
One last issue - using more than one SMPS can lead to beat-notes between their switching frequencies, and that can easily be in the audio band - especially with identical supplies as they are not normally quartz-accurate in their oscillators. You'll need to be careful that the individual supplies cannot intermodulate each other, keep them entirely separate except for a single star-ground.
Good filtering can mitigate/eliminate the problem of a noisy supply however. Having supplies in a separate box can help with EMI flying around.
Some cheap supplies aren't great with highly variable loads too, having trouble regulating with rapid changes in output current.
Not a clear cut answer I'm afraid, I have seen some SMPS's advertized for audio amp use however, presumably meaning they are good with bursty loads and low EMI, indeed I have such a supply that's earmarked for a project, but not used in anger yet 🙂
One last issue - using more than one SMPS can lead to beat-notes between their switching frequencies, and that can easily be in the audio band - especially with identical supplies as they are not normally quartz-accurate in their oscillators. You'll need to be careful that the individual supplies cannot intermodulate each other, keep them entirely separate except for a single star-ground.
Thanks Mark, the only good thing is that all the power supplies are in a separate box but my existing ps is already approx 450w x 500d x 80h. I didn't really want to go any bigger.
Its takes quite a lot of design to do the power supplies (and money) so I need to be fairly confident it will work.
I have no experience at all of switch mode power supplies.
Its takes quite a lot of design to do the power supplies (and money) so I need to be fairly confident it will work.
I have no experience at all of switch mode power supplies.
The biggest problem is that higher-power SMPS tend to be strictly IEC Class I, and in smaller ones suitable for Class II the leakage current from mains filter capacitors can cause issues. If you only need balanced inputs and the amplifier can be Class I just fine, that's not a problem, but with unbalanced inputs it may very well be.
For a Class II amplifier you generally want a transformer with a shield winding as well (which for the common DIYer may mean looking at options for medical applications), so that capacitive coupling pri-sec is greatly reduced.
Do you need this many (big) transformers anyway? Why not just rearrange the grounding scheme and I/O layout to suit the minimum number of transformers absolutely required (depending on voltages needed)? Plenty of AV receivers run 7 power amplifiers on one big power supply. It's definitely feasible if you know what you're doing.
For a Class II amplifier you generally want a transformer with a shield winding as well (which for the common DIYer may mean looking at options for medical applications), so that capacitive coupling pri-sec is greatly reduced.
Do you need this many (big) transformers anyway? Why not just rearrange the grounding scheme and I/O layout to suit the minimum number of transformers absolutely required (depending on voltages needed)? Plenty of AV receivers run 7 power amplifiers on one big power supply. It's definitely feasible if you know what you're doing.