gold aero db45 phono stage output DC offset - diyAudio
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Old 9th January 2015, 09:15 AM   #1
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Default gold aero db45 phono stage output DC offset

good day guys.
i just got this phono stage to fix and wonder anyone here have the circuit for it ? it have about 14vdc offset at it output . anyone ever have this problem ?
thanks
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Old 9th January 2015, 09:37 AM   #2
Mooly is offline Mooly  United Kingdom
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Should be an easy fix even without a circuit. Is the offset on one or both channels ? If both then look at the PSU and a missing rail. If it uses opamps then check the supplies on the opamp pins.

If by chance it were single rail then there will be capacitor coupling at the output and a falling DC offset would be normal if the preamp lacked any termination resistor on the output.
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Old 9th January 2015, 09:46 AM   #3
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Originally Posted by Mooly View Post
Should be an easy fix even without a circuit. Is the offset on one or both channels ? If both then look at the PSU and a missing rail. If it uses opamps then check the supplies on the opamp pins.

If by chance it were single rail then there will be capacitor coupling at the output and a falling DC offset would be normal if the preamp lacked any termination resistor on the output.

Thanks Mooly.
it offset on both channels . it doesn't use opamp but have a regulator SK10058 on the PSU . i believe it is dual rail supply . i suspect the reg to be at fault so i will check this first.
cheers
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Old 9th January 2015, 09:53 AM   #4
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If you post a picture of the internals we might be able to offer some more clues. I can't trace that regulator as a device type...
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Old 9th January 2015, 10:26 AM   #5
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If you post a picture of the internals we might be able to offer some more clues. I can't trace that regulator as a device type...
Thanks Mooly.
me too i can't find much info's on this device .i will post some pictures soon
cheers
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Old 9th January 2015, 11:36 AM   #6
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Originally Posted by Mooly View Post
If you post a picture of the internals we might be able to offer some more clues. I can't trace that regulator as a device type...
here is some pictures of the PSU and the preamp.
let me know if you see anything's suspect .
the black/white pair is the output ,
Cheers
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Old 9th January 2015, 07:12 PM   #7
Mooly is offline Mooly  United Kingdom
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I'll be honest, I'm struggling to piece that together. It looks more like a single rail design going off the central common ground and how it looks.

Silly question... have you actually tried the preamp ? or is it just the offset that is bothering you ? which if it really is 14 volts is the problem of course.

If you load the output with say a 100k does the offset fall ? A single rail amp with an "open ended" (not terminated) coupling cap would show such an offset because the DVM doesn't draw enough current to load the output side of the cap down and allow the cap to charge.

Hard to believe it would be like that but have to ask

The two green caps on the power board. The underside should give a clue as to the configuration. If they are in series then the centre connection will probably be ground and as such connect to the main audio ground. Check by measurement to confirm. If so then does each cap have an equal voltage across it, say 18 volts or maybe a bit more.

I can't place the IC. The 00 looks more like DD to me in the picture. There is a LDD058 device and that is reg but its a 6 pin oddity for cell phones and the like.

Did I say it would be an easy fix Its one of those things you need to be able to spin around in front of you to see the underside as well as the top of the boards to suss the configuration.

You need to determine what the PSU arrangement is first, dual or single rail and those caps are the first clue. Check that all the large electrolytics have voltage across them. If some have none (or maybe even reverse biased) then that would point to a rail being missing in a dual rail set up.
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Old 9th January 2015, 07:17 PM   #8
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On the power board...

Are the red and yellow wires joined ? What DC voltage is on each of those ? Does the black wire of those three connect to the main audio ground ?
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Old 10th January 2015, 01:30 AM   #9
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On the power board...

Are the red and yellow wires joined ? What DC voltage is on each of those ? Does the black wire of those three connect to the main audio ground ?
Hi Mooly.
the all 3 wires red/yellow/black are separate . the yellow wire go to audio ground on the signal chassis . the black and red is supply B+ to the signal chassis . it look like the rail is down on one .
i measure 28.8v on the red wire and 14.6v on the black wire .
there i think the SK10058 is at fault but i can't find any infomation's on this device . the two green filter caps indeed in series .
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Old 10th January 2015, 01:37 AM   #10
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Chinese cross-references (the only ones I could find) give RC4195 as an equivalent, or perhaps just another code, for SK10058. It is a dual tracking, fixed +/- 15V regulator. Don't ask me how 2 fixed regulators can be deemed dual tracking but the location is at least consistent with regulators.
RC4195 datasheet, RC4195 pdf, RC4195 datasheet pdf, Fixed 15V Dual Tracking Voltage Regulator
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