Hi everybody,
I've spent the last few days building two channels of
the mini-a. I built a single power supply with 70000uF
on each rail. Each channel sounded fine when hooked
up to the power supply but when I tried hooking both
up to the same supply, I got buzzing sounds (high frequency)
on certain music material. I tried powering this with
two different transformers. With a cheap radio shack
12.6-0-12.6 centre tap transformer, the buzzing occured
at higher volume levels. I then tried a 300VA 2x12V toroid
and it was much worse. The buzzing was noticeable even
at very low volume.
(I don't think this is ground loop
since it's not a hum, but rather a crakling type buzz on
the tweeter.)
Any idea what the problem might be?
Another thing: The AC hum at the output seems to be worse
with the toroid than with the cheapie transformer.
Thanks in advanced for any suggestions.
Merry Christmas!
Dennis
I've spent the last few days building two channels of
the mini-a. I built a single power supply with 70000uF
on each rail. Each channel sounded fine when hooked
up to the power supply but when I tried hooking both
up to the same supply, I got buzzing sounds (high frequency)
on certain music material. I tried powering this with
two different transformers. With a cheap radio shack
12.6-0-12.6 centre tap transformer, the buzzing occured
at higher volume levels. I then tried a 300VA 2x12V toroid
and it was much worse. The buzzing was noticeable even
at very low volume.
(I don't think this is ground loopsince it's not a hum, but rather a crakling type buzz on
the tweeter.)
Any idea what the problem might be?
Another thing: The AC hum at the output seems to be worse
with the toroid than with the cheapie transformer.
Thanks in advanced for any suggestions.
Merry Christmas!
Dennis
When you run into this sort of stuff, you need to isolate
the problem down to the following categories:
oscillation: high requency buzzing, none of the other
approaches helps: play with frequency compensation,
look at output with a scope.
ground loop: If the problem doesn't go away when you
disconnect the source and short the inputs, it's not a ground
loop, probably.
transformer pickup: Move the transformer / bridge / cap
assembly away physically, and the problem foes away.
poor ripple rejection: CLC or CRC filter in the supply
fixes this.
the problem down to the following categories:
oscillation: high requency buzzing, none of the other
approaches helps: play with frequency compensation,
look at output with a scope.
ground loop: If the problem doesn't go away when you
disconnect the source and short the inputs, it's not a ground
loop, probably.
transformer pickup: Move the transformer / bridge / cap
assembly away physically, and the problem foes away.
poor ripple rejection: CLC or CRC filter in the supply
fixes this.
Hi Dennis
I had this problem too. I solved it by installing a 4.7mH choke in a CLC config. The choke is a ferite core / 1.4mm wire diameter from a cross over. My mini-A is biased at 1.6A and has 66000uF pr. rail pr. channel.
The complete supply for both channels looks like this:
66000uF -> 4.7mH -> 66000uF (pr. rail.)
The amp is now 'dead silent'. The only penalty is a voltage drop of about 0.6 V across the choke.
I had this problem too. I solved it by installing a 4.7mH choke in a CLC config. The choke is a ferite core / 1.4mm wire diameter from a cross over. My mini-A is biased at 1.6A and has 66000uF pr. rail pr. channel.
The complete supply for both channels looks like this:
66000uF -> 4.7mH -> 66000uF (pr. rail.)
The amp is now 'dead silent'. The only penalty is a voltage drop of about 0.6 V across the choke.
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