Greetings,
I have a couple ACA amps so I decided to use one as a headphone amp. The boards are by Rudy Ratlos as are the Jason Kuterman cap multiplier boards. The headphone is connected through 120 ohm Dale RN60 resistor, each channel. The positive side of each channel is connected to the Negative output (instead of ground when used as power amp). I seem to have read this recommendation on one of the ACA threads.
I am still getting a slight hum despite my efforts to eliminate. I have tried rotating the toroid transformer through about 90 degrees and it did lessen the hum slightly.
I attach a photo of the completed unit and would appreciate suggestions for eliminating the hum.
Thank you.
I have a couple ACA amps so I decided to use one as a headphone amp. The boards are by Rudy Ratlos as are the Jason Kuterman cap multiplier boards. The headphone is connected through 120 ohm Dale RN60 resistor, each channel. The positive side of each channel is connected to the Negative output (instead of ground when used as power amp). I seem to have read this recommendation on one of the ACA threads.
I am still getting a slight hum despite my efforts to eliminate. I have tried rotating the toroid transformer through about 90 degrees and it did lessen the hum slightly.
I attach a photo of the completed unit and would appreciate suggestions for eliminating the hum.
Thank you.
Attachments
The power supply rejection ratio (PSRR) of the ACA isn't great but it doesn't need to be when used with the SMPS for which it was designed because an SMPS output will have no 100/120Hz ripple component to it.
A linear supply will have substantial ripple, particularly given the high quiescent current draw and that will unfortunately superimpose onto the output.
Headphones will make it especially noticeable I would imagine.
Wiring and ground loops become extremely important as well because of the high charging currents that are flowing.
A linear supply will have substantial ripple, particularly given the high quiescent current draw and that will unfortunately superimpose onto the output.
Headphones will make it especially noticeable I would imagine.
Wiring and ground loops become extremely important as well because of the high charging currents that are flowing.
It is possible although you would have to do some real measurements using a scope to see if any ripple were present on the DC supply to the ACA.
The ACA has such a very low voltage gain that it is hard to see it being induced hum into the inputs (it is not like a high gain phono preamp stage or even most other power amps that have pretty high voltage gain for example)... so measurement is the key
The ACA has such a very low voltage gain that it is hard to see it being induced hum into the inputs (it is not like a high gain phono preamp stage or even most other power amps that have pretty high voltage gain for example)... so measurement is the key
Well you need to make sure first of all that you don't introduce an unwanted groundloop via the scope and its test lead (assuming a mains operated scope with three core lead).
For the ACA you would look at the ripple on the amp board itself by measuring across the 24 volt input.
The frequency of the ripple is a good clue to its cause. If it is a 'buzz' and at 100 or 120Hz then it's most likely ripple on the supply and/or grounding issues.
If it is a pure deep 50/60 Hz tone then it is most likely induced hum.
Yes it could be... measurement is needed to determine what is going on
This shows the ACA with NO input signal applied and with 1 volt of ripple on the supply. Grounding in an example like this is 100% perfect. With a higher impedance load the ripple is around 30% higher.
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