Hi. I've built my own streaming amp step by step. Starting with a digital streamed source I controlled volume via my phone (app). All fine - no ground hum at any volume. Then I added an EIZZ 3 position input selector - outputs L, R, Common Ground. Again, all good, no ground hum. Finally I've added an ALPS RK 27112 pot. No matter how I configure the ground connections, I get hum at low volume levels. At the moment I've connected left and right channel ground pins on the ALPS to the EIZZ CommGnd, and the amp L/R Ground wires. I've read a lot on the Internet, but nothing seems to explain how to configure this. Any ideas, or links to further reading greatly appreciated.
Thanks
Thanks
Input grounds and Volume control grounds need to connect to the input ground and nowhere else.
This will avoid a hum loop.
This will avoid a hum loop.
Had the same problem with Khozmo attenuators. Big hum when volume reached 1/2 or so that increased with increasing volume. Grounding the case with a wire worked wonders. The mounting threaded shaft/nut did not provide the desired ground for some reason.
I tried all the suggestions, but didn't get rid of the hum. I haven't tried grounding the volume control case. Will give this a go, along with re-soldering the connections in case that's where the problem lies. Thanks to all for your advice.
The volume control case needs to be properly grounded to act as a shield. Relying on the fixing of the pot via the nut to the case may not be good enough because depending on your case, paint or anodising may insulate. The pot is very vulnerable to noise in that instance.
Problem solved. I've learnt a lot - including the importance of providing all relevant info. In my defense, this is my 1st DIY electronics project, and I (still) have a lot to learn. My case is wood and aluminium sheet - custom build to match my RP1 turntable. Alu base and back plate; wood on top, base frame and sides (see pic). When trying to ground the pot (blue Alps so 1 metal face) I touched my ground wire to the alu back plate (all my inputs/outputs are attached) and the alu base plate (internal electrics attached). Hey presto - the audio ground hum disappeared! Once I've tidied up the wiring, I'll post another pic which I hope will make it clear to anyone else who may have this issue. Many, many thanks for all the advice.
Great stuff! And nobody is immune to 'basic' mistakes. My preamp was buzzing at the test stage (on an open chassis). Tightening the screws up (and therefore improving the ground connection) silenced it. Who would have thought? Not me as it turns out!
I've still not tidied the wiring, but here's the photo showing the grounding between the back and base plates. I test with an old pair of Kef Q Series Compact speakers (8 ohm impedance) and can't hear any hum on any source. I hook upto my main Monitor Audio Radius 270 (6 ohm) and I can just hear something when there's no audio output for the selected source. I can live with it though 😊
Further improvement possible! Your connection to the front panel. Bared wire secured with a nut. You want a solder tag and to solder the wire to it so that the nut and bolt force it completely flat onto the panel. Good and tight. And oh dear ... That looks to be the wrong size nut and/or cross threaded! So you are not getting as good a connection there as you need. Same applies to other end of that ground connection - a solder tag would improve things.
Also, those wires coming from the pot - they really should be a shielded cable.
Even though they are short, they can pick up interference.
Will try shielded cables too. I've plenty, and was wondering about using it to replace the wiring provided as inputs to the amp anyway. Thanks
I've now re-configured the internal positions to keep all the power supply wiring (soft start amp/raspberry pi) well away from all audio signals wiring - which involved applying all the suggested upgrades and redesigning my back plate. Really enjoyed doing all this, and now have what I think is a very good (possibly audiophile quality) streaming amplifier. It sounds great to me. I'll add a parts list soon and in the hope this post can help others.
I've only got L/R speakers outputs, and I'd quite like to add headphone out, but don't know where to start. Summary - various inputs switched to single audio out routed to volume control then to amp and out to speakers. I've searched the forums, but no joy. Hopefully one of the previous responders knows roughly what needs doing and can point me in the right direction.
Many thanks to all who have helped.
I've only got L/R speakers outputs, and I'd quite like to add headphone out, but don't know where to start. Summary - various inputs switched to single audio out routed to volume control then to amp and out to speakers. I've searched the forums, but no joy. Hopefully one of the previous responders knows roughly what needs doing and can point me in the right direction.
Many thanks to all who have helped.