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05/01/25 at 08:48:56

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Bias switch setting (Read 3337 times)

thethanimal Senior Member Posts: 52	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

Seasoned Member

Without music, life
would be a mistake.

Posts: 2219

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.

(2)SE84UFO(Balanced Monoblocs) OR Sansui AU222
Cambrge Audio CXN(ModWright)
Crown XLS-1002
SL1210MK5(KAB Mods) Soundsm Aida MKll cart • Darlingt.Labs MP8b
Otari MX5050-Bii2 R2R
ZLC Power Cond
Lii Audio PT-10 OR F-12 OR Betsy Alnico 8"/ W-15 in Open Baffle

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Geno Seasoned Member Without music, life would be a mistake. Posts: 2219	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 don’t have a faulty one.
Back to top	(2)SE84UFO(Balanced Monoblocs) OR Sansui AU222 Cambrge Audio CXN(ModWright) Crown XLS-1002 SL1210MK5(KAB Mods) Soundsm Aida MKll cart • Darlingt.Labs MP8b Otari MX5050-Bii2 R2R ZLC Power Cond Lii Audio PT-10 OR F-12 OR Betsy Alnico 8"/ W-15 in Open Baffle IP Logged

CAJames Seasoned Member "I've run every red light on memory lane." Posts: 2447	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

Senior Member

Posts: 52

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 it’s 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 I’ll 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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