Bottlehead Forum
Bottlehead Kits => BeePre => Topic started by: cktc on September 01, 2016, 06:00:34 AM
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I came across buzz noise when my air condition started on. The noise will be gone after a second. I thought it either triggered by ac voltage dropped when air condition motor just started, or the air condition motor starting making a lot of ac noise. I tend to believe ac voltage dropped, because I had already have Furman IT-reference 20 for isolating noise.
If buzz is caused by ac voltage drop, I'm thinking to add more capacitors in the place of 220uf/250v to make them 440uf/250v. is it a good idea? any other suggestion?
Paul, doc B, anybody, please input.
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I think the problem is in the filament voltage circuit, not the high voltage power. So changing the high-voltage caps won't affect it. I see that the Furman IT-reference 20 has a voltage meter; if you check that you can tell how low the voltage goes when the A/C kicks in and the hum starts.
I'm a little out of the loop on the BeePre - I know this has come up, but I don't know what the standard recommendation is. Hopefully Doc B or Josh will post, but Doc is out of town at the moment.
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My Furman IT-Reference 20 is old model, it doesn't have meter in the front. I didn't measure voltage drop yet, it is just my educated guess. If the buzz was caused by filament voltage drop, there is already 10000uf capacitor in place. It seems like adding capacitors would not be helped. Am I right?
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My recommendation is to fix the underlying issue rather than monkeying around with the preamp. Since your issue is related to your air conditioner and it is now September, it is about to disappear anyways. Voltage sag from the compressor kicking on is just a fact of life when using an air conditioner (lights dim, TVs fuzz, et cetera).
A few thoughts do come to mind:
Your noise filtering device might be making it worse (i.e. slowing the recovery time from the voltage sag); try the BeePre plugged straight into the wall to see if it helps.
Try to work around this with your thermostat. Lower the set temperature before a listening session to cool off the house, raise it a bit higher than normal during the session, return it to normal after.
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More information:
I found out that the preamp actually has constant hum like ground loop if I just directly plug in the wall outlet. That ground loop like hum disappeared when I plugged it in Furman, but still hum shoot out when ac-power on.
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Try this. Get a extension cord and plug the ac unit into a different circuit use a heavy enough cord and see what happens
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I have the same kind of hum issue. I don't own a aircond. But the voltage in my house drops sometimes without reason. I tried to unplug all other devices except the ones needed for music. Even then the hum stays.
I live in a small aparmentblock and probably the source is outside my house.
There are two things that struck me:
1. The linevoltage never drops below 230v (lowest is 231,8). Humming may be present when voltsge drops under 234v. At 232v it is really loud. This is still above the standard to wich the transformers are designed. Read about some other areas here in the Netherlands where the linevoltage never goes over 230v. Can't imagine how loud that will be.
2. why is there that specific hum only in the left channel when the voltage drops? As the right channel is dead quiet. (There is an always present hum with ear close to the speaker, but this is a very different sound and not noticable a few inches away).