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10/28/20 at 00:35:19†


       


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Bias switch setting (Read 308 times)
thethanimal
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Posts: 17
Bias switch setting
08/10/20 at 01:54:34
 
On my new SE84UFO running 99 dB full range speakers I get a decent amount of hum if I flip the bias switch back towards the input tube. I also hear a big jump in treble energy. Is this expected on high efficiency full range drivers?

-Than
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Geno
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Without music, life
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Re: Bias switch setting
Reply #1 - 08/10/20 at 03:44:56
 
Than, I experimented with the bias setting a good bit when I first got my amp. I finally decided I liked it in the position closest to the input tube. That is where mine has stayed. My full rangers are 99dB also. I never have gotten a hum, but this setting is definitely a little louder than pointed to the front. You may run that by Steve, as you should not have any hum.
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SE84UFO (25th Mods) / CSP3
PS Audio DS DAC JR / Cambr. Audio CXC / L.Raven Audio PC / ZBIT
Technics 1210 MK5 (KAB Mods)- KAB/Ortof ProS 40 cart / ZP3 (25th Mods)
Otari MX5050 R2R
Lii Crystal 10 Open Baffles / Lii W-15 Bass Baffles
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Geno
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Without music, life
would be a mistake.
Nietzsche

Posts: 1021
Re: Bias switch setting
Reply #2 - 08/10/20 at 03:50:35
 
Also, you might try a different input tube just to make sure you donít have a faulty one.
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SE84UFO (25th Mods) / CSP3
PS Audio DS DAC JR / Cambr. Audio CXC / L.Raven Audio PC / ZBIT
Technics 1210 MK5 (KAB Mods)- KAB/Ortof ProS 40 cart / ZP3 (25th Mods)
Otari MX5050 R2R
Lii Crystal 10 Open Baffles / Lii W-15 Bass Baffles
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CAJames
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Re: Bias switch setting
Reply #3 - 08/10/20 at 15:06:39
 
Sounds like the input tube to me, esp. if it is 60 cycle hum. It is possible the hum will go away after several hours and the tube breaks in.
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thethanimal
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Re: Bias switch setting
Reply #4 - 08/11/20 at 01:18:08
 
Well the hum and treble brightness are gone. (Actually a little hum if I get my ear within a foot of the speaker but even then itís marginally above ambient room noise.) I did go from bare wire connections to banana plugs and removed the nearby receiver and the speaker wire running from it to my KEFs. So maybe some environmental EMI was removed or the tube/amp broke in a little more, or some of both. Either way it seems like Iíll need more time on the amp before settling on the bias switch position, and maybe I should revisit the Hi/Lo switch as well.
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