Magnetized AVC?

Discussions and experiences with user adjustable gaps.
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merlin el mago
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Joined: Fri Aug 15, 2014 2:48 pm

Magnetized AVC?

Post by merlin el mago »

All summer without listening music due to the hot temperature, few days ago connected to listen & my god the sound it's distorted like a vacuum tube gone, without bass & with cutoffs.

When I have time I will use my signal generator to see what happens with the signal trought the AVC.

I'm sure it's the AVC because used a 100K switched ladder attenuator & sounds good.

How to fix the issue?

TIA
Felipe
dave slagle
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Re: Magnetized AVC?

Post by dave slagle »

Hey,

There really isn't any possibility of the AVC to become magnetized or break. The two things that come to mind are a leaky cap putting DC on the core and a possible shorted turn (two pins shorted to each other). A DVM should help diagnose the first and a visual search might point to the second. Also noting the end to end DCR of the autoformer may give some info.

Is the problem happening the same in both channels?

What is the source driving the autoformer?

dave
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merlin el mago
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Joined: Fri Aug 15, 2014 2:48 pm

Re: Magnetized AVC?

Post by merlin el mago »

Yes both channels.

The source driving impedance is 867,2354 ohms.

DVM measurements:

Position att. Left channel Right channel
1 0R15 0R22
2 0R66 0R61
3 0R83 0R82
4 1R27 1R24
5 1R86 1R85
6 2R83 2R80
7 4R34 4R32
8 6R83 6R71
9 10R64 10R47
10 16R39 16R18
11 38R21 38R10
12 57R47 56R95
13 57R17 56R94

TIA for fast and kind support
Felipe
dave slagle
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Re: Magnetized AVC?

Post by dave slagle »

can you re-check you numbers?

the source impedance (867,2354 ohms) number does not make sense unless it rounds down to 867Ω

the measurements between steps 12 & 13 are the same which should not be the case. what is the DCR between 12&13 (at the switch and at the autoformer.

dave
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merlin el mago
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Re: Magnetized AVC?

Post by merlin el mago »

Yes 867 ohms.

DCR between pins 12 & 13 are 0R35 both channel at the autoformer, unfortunately a little bit complicate to measure at the switch.
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merlin el mago
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Re: Magnetized AVC?

Post by merlin el mago »

Could be dust at the switch?
dave slagle
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Re: Magnetized AVC?

Post by dave slagle »

it sure seems somehow pins 12 & 13 are shorted to each other. carefully retrace your wiring looking for an error. I am assuming it was functioning properly and then "broke at some point"? The fact that it is happening the same in both channels points to some external cause since it is unlikely that both channels would fail in the exact same way.

dave
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merlin el mago
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Re: Magnetized AVC?

Post by merlin el mago »

But the noise in both channels is in all positions?
dave slagle
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Re: Magnetized AVC?

Post by dave slagle »

I cannot think of anything within the AVC that could cause this.... The apparent short between 12 & 13 should not be there and it is highly unlikely that the problem is internal to the autoformer

dave
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merlin el mago
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Re: Magnetized AVC?

Post by merlin el mago »

With a new and better DVM measured again direct pin to pin at AVC:

Position att. Left & right channel
1 0R45 0R45
2 0R70 0R70
3 1R14 1R13
4 1R77 1R75
5 2R75 2R72
6 4R30 4R27
7 6R76 6R70
8 10R62 10R54
9 16R53 16R40
10 25R54 25R35
11 38R90 38R80
12 58R30 58R09
13 70R64 70R33
dave slagle
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Re: Magnetized AVC?

Post by dave slagle »

those numbers all look good.
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merlin el mago
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Re: Magnetized AVC?

Post by merlin el mago »

Yes thanks, now it's working ok, the problem was the lineamp.

Have a nice day Dave & thanks for support.
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