I must be too stupid for DIY...
I made a small passive preamp (just an alps in a box), but when I connect it to a small digital amp for testing, an audible hum is introduced to the otherwise fine signal. The hum does not appear when the volume is either at zero or at max volume, so only when the wiper is on the track.
Wiring is as follows:
The alps takes input from two RCA's, and sends the signals out to two RCA's as well.
The returns of the RCA's are wired to the ground pin of the Alps, the IN signal wires to the IN pin and the wipers are wired to the signal of the OUT RCA's.
IMG_9617 by ctjr, on Flickr
I made a small passive preamp (just an alps in a box), but when I connect it to a small digital amp for testing, an audible hum is introduced to the otherwise fine signal. The hum does not appear when the volume is either at zero or at max volume, so only when the wiper is on the track.
Wiring is as follows:
The alps takes input from two RCA's, and sends the signals out to two RCA's as well.
The returns of the RCA's are wired to the ground pin of the Alps, the IN signal wires to the IN pin and the wipers are wired to the signal of the OUT RCA's.
IMG_9617 by ctjr, on FlickrEach input is a two wire pair.
You must take two wires from the input socket to the vol pot for each input
Each output is a two wire pair.
You must take two wires from the vol pot to the output socket.
Those two wire pairs need to be close coupled along their whole route from source to receiver. Use either coaxial cable, or utp (Unshielded twisted pair), or stp (shielded twisted pair). The screen of the coaxial is the Signal It must not be connected to the metal case/chassis. The screen of the STP must be connected to the case/chassis at both ends. The metal parts (that are not the signal) of the vol pot should also be connected to the case/chassis
At the RCA sockets I can see a BIG gap between the Signal Flow (white, or red) and the Signal Return (black). Those BIG gaps are susceptable to picking up interference.
You need to keep the Return VERY close to the Flow to minimise the gap and thus minimise the interference.
The Alps does not have a "ground" pin.
It has a pin that is common to both the input and to the output. That common sees two wires, one coming from the input socket and one going to the output socket. It is not ground. It does not get connected to ground, nor to the case/chassis.
You must take two wires from the input socket to the vol pot for each input
Each output is a two wire pair.
You must take two wires from the vol pot to the output socket.
Those two wire pairs need to be close coupled along their whole route from source to receiver. Use either coaxial cable, or utp (Unshielded twisted pair), or stp (shielded twisted pair). The screen of the coaxial is the Signal It must not be connected to the metal case/chassis. The screen of the STP must be connected to the case/chassis at both ends. The metal parts (that are not the signal) of the vol pot should also be connected to the case/chassis
At the RCA sockets I can see a BIG gap between the Signal Flow (white, or red) and the Signal Return (black). Those BIG gaps are susceptable to picking up interference.
You need to keep the Return VERY close to the Flow to minimise the gap and thus minimise the interference.
The Alps does not have a "ground" pin.
It has a pin that is common to both the input and to the output. That common sees two wires, one coming from the input socket and one going to the output socket. It is not ground. It does not get connected to ground, nor to the case/chassis.
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Thanks, Andrew. So, bending the tips of the tabs further in and twisting the wires should solve the problem?
Also, I used this pic from hifi collective (and others basically saying the same thing), would you say that this diagram is wrong?
Also, I used this pic from hifi collective (and others basically saying the same thing), would you say that this diagram is wrong?
An externally hosted image should be here but it was not working when we last tested it.
Because in the original manual of the Audiosector chipamp, the wires connecting pot to input/board aren't shielded nor twisted (matter of fact, they are just bare copper wires!). I put too much trust in that, apparently. Back to the drawing board.
When you use shielded wires inside the box - do these need to be twisted?
And when using a separate shielded wire for signal and return (again, inside the box, presumably having no "case earth" from signal source box connected) then where do you connect the shields?
If you buy off-the-shelf, then yes. But this is DIYaudio - a TVC can be created relatively inexpensively in parts even though its undoubtedly fairly heavy on the time investment.
true, true. And they look just awesome. However, I'd like to get this dinky little box working in the meantime
true, true. And they look just awesome. However, I'd like to get this dinky little box working in the meantime
Connect the ground to the metal of the pot, link the two grounds on the pot left and right, that is it.
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The case is plastic, so the case can't function as a ground.
I tried twisting the wires and soldering them directly to the RCA instead of connecting them to the tab. This made no difference at all.
What still puzzles me, is that there is only hum when the pot is between either ends; at maximum "volume" (i.e. turned fully open) the hum disappears.
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