I've completed my first amplifier build. It is a dual-mono Mofset design utilizing two LMK60MK2 amplifier modules that I purchased from Michael Chua @ AMPSLAB. I started with a broken ADCOM GFA-2535 which I gutted except for the two hefty transformers and heat sinks. Two power supply modules with 40,000uf per channel were built and installed. Star grounding utilized. LMK60 amplifier modules are rated @ 60Watts although I suspect the actual output somewhat exceeds rated output.
Anyway, the finished amplifier sounds terrific, IMHO! The only thing that bothers me is a slight hum at idle. A little more pronounced in the right channel. Once I turn the volume up, the hum is unnoticeable. Is a little hum acceptable?
The only additional feature of this amplifier is a 12Vdc trigger circuit for an In-Rush current limiter. I built a 12Vdc power supply which controls the two relays on the in-rush circuit board. The 12Vdc power supply and current limiter boards are mounted on the rear panel. This was the only area of the "box" where I could squeeze them in. When I physically move the audio input wires around, the hum changes (slightly) in intensity.
Looking for some collective wisdom on whether to just enjoy the amplifier (as is) or to try and eliminate the hum. The hum could be coming from the 12Vdc power supply that I built. This power supply is based on a CUI module from Mouser (https://www.mouser.com/ProductDetail/490-PBO-15C-12). This DC power module also requires emissions/filtering circuitry which I added via breadboard construction. I thought of changing the amplifier inputs from un-shielded to shielded wire. The other option would be to remove the in-rush circuitry. Any and all suggestions appreciated.😊
Anyway, the finished amplifier sounds terrific, IMHO! The only thing that bothers me is a slight hum at idle. A little more pronounced in the right channel. Once I turn the volume up, the hum is unnoticeable. Is a little hum acceptable?
The only additional feature of this amplifier is a 12Vdc trigger circuit for an In-Rush current limiter. I built a 12Vdc power supply which controls the two relays on the in-rush circuit board. The 12Vdc power supply and current limiter boards are mounted on the rear panel. This was the only area of the "box" where I could squeeze them in. When I physically move the audio input wires around, the hum changes (slightly) in intensity.
Looking for some collective wisdom on whether to just enjoy the amplifier (as is) or to try and eliminate the hum. The hum could be coming from the 12Vdc power supply that I built. This power supply is based on a CUI module from Mouser (https://www.mouser.com/ProductDetail/490-PBO-15C-12). This DC power module also requires emissions/filtering circuitry which I added via breadboard construction. I thought of changing the amplifier inputs from un-shielded to shielded wire. The other option would be to remove the in-rush circuitry. Any and all suggestions appreciated.😊
Congratulations on your first build 🙂
Also is it hum as in hum (deep and pure at 60Hz) or is it really more of a buzz with harmonic overtones? Both have different causes, neither may be easy to resolve.
Only you can answer that one. If it bothers you then no, its not acceptable. If its audible a foot or so from the speakers then its bordering on to much.
Also is it hum as in hum (deep and pure at 60Hz) or is it really more of a buzz with harmonic overtones? Both have different causes, neither may be easy to resolve.
Can you temporarily disconnect the 12V circuit and see if the hum is gone or reduced?
Bear in mind that such noise may be from more than one source, simultaneously.
Bear in mind that such noise may be from more than one source, simultaneously.
Thanks, Mooly.
I figured the answer would be "It's subjective". The noise is more like a buzz w/harmonic overtones. Clearly audible from right speaker at 6'.
I figured the answer would be "It's subjective". The noise is more like a buzz w/harmonic overtones. Clearly audible from right speaker at 6'.
That is too much hum/buzz, and should not have to be tolerated.
Post some close, clear photos of your amp construction, and the schematics.
Does the noise occur with the inputs shorted to ground?
This is total dual mono construction, with L/R grounds only connected
together at one point?
Post some close, clear photos of your amp construction, and the schematics.
Does the noise occur with the inputs shorted to ground?
This is total dual mono construction, with L/R grounds only connected
together at one point?
Ohhh. No easy answers I suspect.
It sounds look you are hearing 120 Hz buzz (twice mains... ripple frequency) and that frequently is down to a problem in the ground wiring connection points.
Have a look at this, you need to get past the first few posts. Expand the diagrams I posted:
https://www.diyaudio.com/community/threads/3-stage-lin-topology-nfb-tappings.101321/