Hey guys,
I've breadboarded an input buffer into a single supply Lm1875 running on a 24v smps (laptop psu). I'm getting this high pitch noise and I'm not sure if it's to do with the psu, some oscillation or breadboard layout. Is anyone able to give me a push in the right direction where to start? I can get my schematic together and post if that's helpful too.
Hum/Whine
I've breadboarded an input buffer into a single supply Lm1875 running on a 24v smps (laptop psu). I'm getting this high pitch noise and I'm not sure if it's to do with the psu, some oscillation or breadboard layout. Is anyone able to give me a push in the right direction where to start? I can get my schematic together and post if that's helpful too.
Hum/Whine
PSU, put a small 100 nF and a 2200/35V in parallel from positive to ground, see what happens.
Or near those values, whatever is handy.
Small cap is for higher frequency noises.
Or near those values, whatever is handy.
Small cap is for higher frequency noises.
Thanks mate, I tired that earlier but went wayyyy too small on the 2200 value. The 2200 lowers the noise volume significantly but doesn't completely remove it. The larger cap made a difference but the 100nf didnt seem to effect it. If I Increase the 2200 by replacing it with a larger one or putting 2x in parralell would I expect it mostly silence it?
It should, and also try a bigger value than 100 nF for the smaller cap.
Too big a cap might load the supply too much. Don't go above 4700/63V
Too big a cap might load the supply too much. Don't go above 4700/63V
Could also be over gain from source, just check the source level, if it is low, the amp could pick up noise.
Earthing and shielding also have to be proper.
Earthing and shielding also have to be proper.
Could still be the SMPS. Find a linear one, even if it is a small one to rule it out. SMPSes can be very noisy in audio (but YMMV).
Yeah, my problem is that local laws make it illegal for anyone but a electrician to wire a socket to a transformer... Makes it hard to get anything linear in a voltage usable ☹️
If the source volume is low, the background noise also gets amplified.
So check if that is correct or high / low.
So check if that is correct or high / low.
Wha? You don't need to do that, just wire up a power cord to a transformer and off you go!
I tired the larger cap (4700) and while it quietened it a bit more ita still definitely still there. I re did my breadboard and when I tested the buffer circuit (stage before the amp) the same noise was there with the bypass caps across the power supply and disappeared when it was removed which I found odd.
This is how I've got my psu set up currently, with the 9v and 4.5 coming from the lm317 and vd, while the 24 is "raw" and the 12v bias is from the other vd. Would regulating the 24/12 with an ldo work in cutting out the whine?
Also should the psu electrolytic caps be low esr, and should the power filtering be on a separate breadboard while testing? Sorry for all the questions!
This is how I've got my psu set up currently, with the 9v and 4.5 coming from the lm317 and vd, while the 24 is "raw" and the 12v bias is from the other vd. Would regulating the 24/12 with an ldo work in cutting out the whine?
Also should the psu electrolytic caps be low esr, and should the power filtering be on a separate breadboard while testing? Sorry for all the questions!
Attachments
😬 Oh dear.... I was going to regulate the 24v further but I don't want to lose the voltage. The 4.5 and 12 are just biasing references so I didn't think they would be an issue.
You use a breadboard and then expect your amp to be silent? Ambitious. Please post a pic of what you did to clarify. Breadboards are notorious picking up all sorts of interference.
Also, what territory do you live in? Not even allowed to connect a power cord to a transformer? You sure?
Also, what territory do you live in? Not even allowed to connect a power cord to a transformer? You sure?
I'm in Western Australia. This is from the regulations that I have enquired about. I have asked since a transformer wired by an electrician can be used my myself as the secondary takes it below 50VAC / 120DC.
As for the breadboard side of thing, I'm not expecting it to be dead silent, but I'm not sure if it's due to the circuit design itself or the breadboard. I'm even starting to think the PSU might be running under minimum load increasing the noise.
Once I'm home I'll take some happy snaps and get the schematics drawn up 🙂
As for the breadboard side of thing, I'm not expecting it to be dead silent, but I'm not sure if it's due to the circuit design itself or the breadboard. I'm even starting to think the PSU might be running under minimum load increasing the noise.
Once I'm home I'll take some happy snaps and get the schematics drawn up 🙂
Not work, it is a hobby
high pitch noise is from switch mode.
a amplifier with no case is prone to all kinds of noise.
high pitch noise is from switch mode.
a amplifier with no case is prone to all kinds of noise.
Yeah, I read further into it and it voids all personal and property insurance and makes you liable if someone gets injured .
it sucks but I have asked the question regarding it anyway.
What's the best way to filter out that noise all together? I've been looking at PI and LC filters.