volume control hum/noise

[cbutterworth]

My angst for total quietness has led me to do some signal wiring work on my Aikido. Yes, the DC heaters got rid of all 60Hz hum, so I'd strongly recommend going that route.

Anyway, I have a Goldpoint 100K stepped attenuator (mini-L type, I think). When I first installed it, the volume was really loud such that I could only use the first couple of settings. I fitted a voltage divider and that allowed me to listen at about the 12 o'clock setting on the attenuator.

But, then after I got rid of the 60Hz hum, I began to notice a higher pitched hum (maybe 120Hz) at my listening settings on the stepped attenuator. When the signal path is left opened (setting 0) no hum, and when on full volume (sans music) again no hum. So, it appears that a direct signal that avoids resistors in the attenuator is humless. In other words the hum appears to be attenuator induced.

So, I removed my voltage divider, in case the Vishay resistors were the source of hum. Anyway, I still get the hum, and at the same settings on the attenuator.

How about I go back to my old passive preamp with input selector, 50K ALPS pot between Aikido and power amp?

Any ideas?

Charlie

[Original Burnedfingers]

Charlie,

What do you have for a Power Amplifier? Does this amplifier have a input control? If it doesn't you could possibly put a control on the input of the amplifier and get more workable setting on your stepped control. I am assuming that your stepped control is on the input of the Aikido.

Joe

[cbutterworth]

I have an AKSA55N for my power amp. I don't have any volume control on it. I could install a voltage divider on the signal input inside the back of the chassis on the AKSA.

Without the voltage divider on the Aikido, the hum comes in with the Goldpoint set at around 2PM, but I can only use the first three positions on the stepped attenuator - mute, loud, bl**dy loud

If I installed the voltage divider inside my AKSA, I can build on a bit of perf board and use sockets for the resistors, which will allow me to swap out resistors for the best settings.


GREAT IDEA Burned Fingers!

Charlie

[Tweeker]

This is an inherently lower noise approach as your working with a lower Z signal (depending on source.)

[cbutterworth]

Tweaker,

OK I'll try it. The impedence on the AKSA is 47K, if I remember, so I can use an L-pad with 50K impedence, although I suppose it'll be off as I'll have to get resistors with nearest-part-values.

Could I also have installed my Goldpoint incorrectly? It has three pads - IN, OUT, GND. I have signal+ going to IN; signal GND going to GND. For the output, I have PCB IN+ comming from attenuator OUT; PCB IN- comming from attenuator GND. I suppose I am second guessing myself.

Anyway, I'll proceed with the AKSA input tweak.

Charlie

[Original Burnedfingers]

Charlie

If you wanted to try this you could cut a RCA patch cord and wire in the control to it without having to build something inside your amplifier. Radio Shack sells a 100K stereo pot that should work fine.

Sometimes things arriving from across the ocean are mismarked. When in doubt send a signal into the Aikido and hook the output to your scope or a set of headphone or something to monitor the output long enough to tell if its wired correctly.

If you use a pot

When looking at the back of the pot the left terminal will be ground, the middle is out, and the right is in.

[cbutterworth]

The Goldpoint is US made, so I assume that everything is marked correctly.

I have just ordered resistors from Mouser. I have plenty of room inside my AKSA to mount a small piece of perf board with standoffs.

Charlie