Electronics > Repair
strange low frequency switching noice from diy sg3525 smps
Herschel:
--- Quote from: T3sl4co1l on September 19, 2024, 10:10:14 am ---Ok, output filter choke, that's a start.
Looks to be single-side layout, which means no ground plane, and all the stray inductances wreak havoc on the EMI response in the 10s of MHz where those traces cease being good conductors but stray inductance takes over.
Tim
--- End quote ---
Even though, there are some design flaws in the amp, these amps are getting crazy good local reviews in youtube, and those reviews are true. The product seller tested the amp before my eyes, and it sounds great with a really faint humming why? they where using transformers instead of smps. So, really low noise
anyway I'm using this class D amp just to drive the subwoofer. maybe I should try adding CMC+ filter caps before the class D amp, so the noise may not affect other class AB amps connected to that smps
Phil1977:
I´d propose to check your DIY-SMPS for control loop oscillations anyhow. They easily occur, they often are easy to prevent by adding some dampening into the control loop. But if they occur, they do not only produce noise, they stress all the power components of the SMPS in an extreme way.
It´s just a good advice: If you can check your SMPS with a scope then do it. Check that the control loop does not oscillate between its extremes. Small oscillations in the control loop show that it´s doing its job, but if e.g. the current through the optocoupler LED oscillates between 0 and some saturated value, then something is definitely wrong.
T3sl4co1l:
--- Quote from: Herschel on September 19, 2024, 11:21:51 am ---
--- Quote from: T3sl4co1l on September 19, 2024, 10:10:14 am ---Ok, output filter choke, that's a start.
Looks to be single-side layout, which means no ground plane, and all the stray inductances wreak havoc on the EMI response in the 10s of MHz where those traces cease being good conductors but stray inductance takes over.
Tim
--- End quote ---
Even though, there are some design flaws in the amp, these amps are getting crazy good local reviews in youtube, and those reviews are true. The product seller tested the amp before my eyes, and it sounds great with a really faint humming why? they where using transformers instead of smps. So, really low noise
anyway I'm using this class D amp just to drive the subwoofer. maybe I should try adding CMC+ filter caps before the class D amp, so the noise may not affect other class AB amps connected to that smps
--- End quote ---
This doesn't mean very much...
Understand that correct operation in one very limited set of functions (in this case, audio amplification) says nothing about operation in a completely different scope (RF emissions).
It's pretty easy to make a class D amp sound alright. That's everything below 20kHz.
It's not even that hard to make one measure well. Notice these are already two different things, because "sounds good" is already a wide margin above what a typical amplifier might measure as: the gain/flatness might be off by many dB, the distortion might be several percent, the noise and hum background might be noticeable in one setting but not another; and most of all, listeners are notoriously fickle in their perception, it takes an expert listener to properly assess an amplifier (in whatever way a listener can assess one accurately at all, which again, still isn't fantastic compared to electrical measurements).
We're talking about anything from 100kHz to 100MHz, very different ball game -- and absolutely nothing you can hear, unless it gets stuffed sideways into an amplifier, rectified and detected, in which case hum, squealing, beeping, clicking and so on are all possibilities.
Tim
Herschel:
I think, I've found the problem... It was the optocoupler!
the original circuit was using a 4n25 opto ic, the feedback voltage going into the opto ic was stable when I tested it with an LED,
But when I tested the output from the optocoupler, the led was blinking, also the blnking speed+ frequency of that weird sound changes/increases when I connect the led to the opto ic
So i decided to replace the 4n25 with a pc817 opto ic I had, and that low speed ticking sound just vanished! still has a faint, normal smps high frequency with 50Hz hum
what did that opto ic just had to do to make that sound?
anyway, i hope there wasn't any 100khz/100mhz noise as my contraption with a 1volt incandescent light and the 474j capacitor didn't glow while testing
so what about the classD amp? it just simply amplified the noise in the smps output powerlines as it had a builtin opamp for gain, as opamps aren't happy with noisy powerlines...
T3sl4co1l:
Compensation problem, then?
Again, completely in the dark without an oscilloscope -- you're seriously handicapped without one, we can only guess.
Tim
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version