Hi all,
I just finished building my BA-3 Preamp, biased it up properly, and have thrown it into my system (active dynaudio's for the moment) ... and it sounds wonderful! Crazy soundstage and clarity - can't thank you all enough for your shared knowledge (especially 6L6 for his build guide).
However...
I am having some issues with buzzing and hissing in both speakers. It's not apparent at low to medium volumes, and I'm able to use it as is, but I plan on building an F4 paired with some high efficiency Klipsch's so it'll definitely be an issue down the road.
The hissing is always present and the buzzing (120hz) increases when i turn the volume pot up. When inputs have load, it's only noticeable when I get really close to the speakers - when there's nothing connected to the input, its VERY LOUD!
My first test was to check if its being pushed too hard and has too much gain: my results from a sine 1k test.
-In: 0.847vac
-Out: 6.22vac
I don't believe that is too far out of the range of what its supposed to be, correct?
Next, on the advice of another member, I removed the PSU from one channel to check for ground loop, hum and buzz remained
Lastly, I plugged the preamp into a ground remover plug and turned on very briefly, problem persists.
I'm still leaning to think it is a ground loop problem, but i'm quite novice so it may in fact be something else entirely. I've attached a build photo along with a graphical layout of my build.
I'm certain you all know more than I do here so any help would be greatly appreciated 🙂
I just finished building my BA-3 Preamp, biased it up properly, and have thrown it into my system (active dynaudio's for the moment) ... and it sounds wonderful! Crazy soundstage and clarity - can't thank you all enough for your shared knowledge (especially 6L6 for his build guide).
However...
I am having some issues with buzzing and hissing in both speakers. It's not apparent at low to medium volumes, and I'm able to use it as is, but I plan on building an F4 paired with some high efficiency Klipsch's so it'll definitely be an issue down the road.
The hissing is always present and the buzzing (120hz) increases when i turn the volume pot up. When inputs have load, it's only noticeable when I get really close to the speakers - when there's nothing connected to the input, its VERY LOUD!
My first test was to check if its being pushed too hard and has too much gain: my results from a sine 1k test.
-In: 0.847vac
-Out: 6.22vac
I don't believe that is too far out of the range of what its supposed to be, correct?
Next, on the advice of another member, I removed the PSU from one channel to check for ground loop, hum and buzz remained
Lastly, I plugged the preamp into a ground remover plug and turned on very briefly, problem persists.
I'm still leaning to think it is a ground loop problem, but i'm quite novice so it may in fact be something else entirely. I've attached a build photo along with a graphical layout of my build.
I'm certain you all know more than I do here so any help would be greatly appreciated 🙂
Attachments
Your inputs are connected with unshielded wires. Use a shielded audio cable or a computer network U / FTP-6.
A metal cover may be needed for the transformer.
Mains filter against interference.
What do you hear about the volume at 0?
In the photo it is not clear where the grounding point of the case is.
Caution! The power cable is too thin and it is not clear if the insulation is suitable for the mains voltage.
BA-3 Amplifier illustrated build guide
A metal cover may be needed for the transformer.
Mains filter against interference.
What do you hear about the volume at 0?
In the photo it is not clear where the grounding point of the case is.
Caution! The power cable is too thin and it is not clear if the insulation is suitable for the mains voltage.
BA-3 Amplifier illustrated build guide
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I agree, this is likely the dominant issue. The build guide clearly shows shielded cabling. Bare twisted pair used unbalanced doesn't provide a great deal of shielding, and in this case it doesn't appear to at least be routed close to the chassis that could. Wiring right up to the board should be redone.
As an aside, whenever a PCB provides space for a film capacitor of size "ludicrous" to begin with, people will obviously go for size "insane" and then go to great lengths to make that fit. 🙄 It's not super critical at this point, but still, not ideal.
Indeed (which I guess is why the build guide suggested a "shielded transformer"), but be careful not to provide a second connection between the chassis and the central bolt. This would act like a shorted turn.
Secondaries aren't twisted but should be. Additional electrostatic shielding may be advisable.
I'm less worried about mains wire gauge but at least an extra layer of heatshrink tubing would be required to get the wiring up to IEC Class II (double insulated) standard if it needed to be.
A transformer of what looks like 50-100 VA is way oversized. This thing needs like 20 tops. Then he might even stand a bit of a chance of going Class II without having to get a xfmr with a shield winding.
The CL-60 NTC with its ~10 ohms would be keeping the worst of ground loops at bay, but if the F4 is the same, things are getting a tad low in impedance for my tastes. Computer sources may prove a bit problematic. This is why large-scale hi-fi manufacturers will go to great lengths in making their gear Class II with as little mains coupling as possible. Alternatively, the pro audio world uses balanced interconnections and gets rid of the problem that way.