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
Post all the correct schematics. The volume control and audio cables are very close to the transformer.
You could try temporarily removing the transformer from the chassis, to see if the hum is reduced.
You could try temporarily removing the transformer from the chassis, to see if the hum is reduced.
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The secondaries appear to be wrapped almost completely around the transformer. I think I remember reading that this may cause problems.
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.
Pleased to hear it has worked OK 🙂
(the hum was most probably ripple related rather than physical proximity of the toroid to the circuitry. SMPS aren't all bad 😉)
(the hum was most probably ripple related rather than physical proximity of the toroid to the circuitry. SMPS aren't all bad 😉)
Does that suggest that the cap multiplier wasn't working well or I didn't have it adjusted properly?
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 🙂
Im still learning about measurements but I do have a decent scope. Any tips about measuring ripple would be appreciated.
I would think that if moving the toroid had an effect, that ripple wouldn't be the issue, or at least not the leading issue.
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.
