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July 27, 2021, 05:48:17 PM

Author Topic: beepre right channel hum [resolved]  (Read 217 times)

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Offline bgf

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beepre right channel hum [resolved]
« on: July 19, 2021, 04:41:31 PM »
so i bulit this about seven years ago. it goes with the two mono blocks and an eros phono preamp. i worked on getting rid of the ground loop hum but now i have developed and loud hum right channel only not dependent on volume control intermittent in nature.  comes on as tubes warm up then disappears and reappears randomly with time. three peaks measured by advanced spectrum smart phone app at 64 hz 129hz and 236 hz.  the loudest hum peaking at 129hz.  i might add that this noise changes in volume.  again only the right channel.  i have also played with switching tubes and it still is only coming from the right channel.  any help would be much appreciated.  thanks.
« Last Edit: July 23, 2021, 10:33:37 AM by Paul Birkeland »
brent fauss

Offline Paul Joppa

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Re: beepre right channel hum
« Reply #1 on: July 19, 2021, 05:25:49 PM »
What is your power line voltage? A low voltage will cause a loud hum in the original BeePre. The whole USA seems to be pretty warm right now, and air conditioners can draw the voltage down.
Paul Joppa

Offline bgf

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Re: beepre right channel hum
« Reply #2 on: July 20, 2021, 09:42:01 AM »
line voltage if i measured it correctly at plug is 120 volts with air condition unit going.
brent fauss

Offline Doc B.

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Re: beepre right channel hum
« Reply #3 on: July 20, 2021, 09:45:34 AM »
Next step is to check voltages and post any that are off.
Dan "Doc B." Schmalle
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Bottlehead Corp.

Offline bgf

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Re: beepre right channel hum
« Reply #4 on: July 21, 2021, 05:39:31 AM »
ok you are working with a basic guy here who a long time ago i finished my degree in chemical engineering unfortunately not electrical so i need simple "how to instructions" to provide you with the numbers. thanks.
brent fauss

Offline Paul Birkeland

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Re: beepre right channel hum
« Reply #5 on: July 21, 2021, 06:50:35 AM »
These are in the construction manual we provided with the kit.  You would have had to complete them after building your kit originally. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline bgf

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Re: beepre right channel hum
« Reply #6 on: July 21, 2021, 07:30:19 AM »
thanks found the construction manual and working on it. 
brent fauss

Offline Paul Birkeland

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Re: beepre right channel hum
« Reply #7 on: July 21, 2021, 07:31:03 AM »
The terminals of immediate interested would be POS IN and POS OUT on the noisy channel.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline bgf

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Re: beepre right channel hum
« Reply #8 on: July 21, 2021, 10:26:05 AM »
terminal      voltage
1                4.48
2                 97.5
3                 0
4                 9.72
5                 0
6                 147.1
7                 0
8                 0
9                 0
10                184.7
11                147.1
12                0
13                0
14                0
15                 184.6
16                 5.02
17                 98.6
18                 0
19                 9.84
20                 0
21                 0
22                 211.6
23                 0
24                 0
25                 211.7
26                 0
27                 0
28                  (0) .041   
29                  6.62
30                   

6.62
31                   13.30
32                   0
33                   0
34                    (13.6) 11.8 ?
35                    (6.8)  5.17 ?
36                    (6.8)  5.16 ?
37                    0
38                    0
39                    0
40                     211.3
41                    0
42                    0
43                      211.3
44                    0
45                    0
46                       211.3
 47
48                     0
49                     0
50
51                     0
A1
A2                     (0)  96.5    ?
A3                     (90-110)   0
A4

B1
B2                      (0) 98.3    ?
B3                      (90-110)   0
B4

c1,d1 
c2,d2                 
c3,d3                  4.48    3.48
c4,d4
c5,d5
c6,d6
c7,d7                   147     147
c8,d8
c9,d9                   146.8   146.7

ok voltage check.

right channel   POSIN  13.11   POS OUT  9.93 this is the channel of interest
left channel      POSIN  13.33   POSOUT   9.85  for a check

« Last Edit: July 21, 2021, 11:11:37 AM by bgf »
brent fauss

Offline Paul Birkeland

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Re: beepre right channel hum
« Reply #9 on: July 21, 2021, 03:24:37 PM »
Can you post some build photos?  There isn't anything immediately obvious from the voltages.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline bgf

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Re: beepre right channel hum
« Reply #10 on: July 22, 2021, 08:22:03 AM »
build photos let me know if you need some other views.
brent fauss

Offline Paul Birkeland

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Re: beepre right channel hum
« Reply #11 on: July 22, 2021, 08:49:04 AM »
I would pop the power supply boards off and reflow the joints under there. 

I would also post pictures of the bottom sides of the PC boards on the noisy channel.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline bgf

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Re: beepre right channel hum
« Reply #12 on: July 23, 2021, 07:18:02 AM »
reflowed joints right channel no change added pictures
brent fauss

Offline Paul Birkeland

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Re: beepre right channel hum
« Reply #13 on: July 23, 2021, 07:21:14 AM »
It's very likely that there's a loose cap or some other connection in here that you need to track down.  One way that I do this is to run the preamp into a cheap amp and pair of speakers, then poke around in the amp with a wooden chopstick to see if I can change the nature of the noise.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline bgf

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Re: beepre right channel hum
« Reply #14 on: July 23, 2021, 08:57:44 AM »
so capacitor tied in at voltage check point 36 and 37 when moved up and down changes the hum.
brent fauss