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Old 5th May 2015, 04:33 PM   #1
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Default For those with finished, playing Pearl 2 Phono preamps

What sort of measurements are you getting on your unit? I am still tweaking mine, but I show a little DC offset measured at the output jacks, P1 lets me get close to zero, (on the "0") test point, not the outputs) but it drifts around a bit. I get approx 1.6 across R6, and the 21 volt spot is about a 1/2 volt low, so close.

I am concerned a little with the drift on the "0" test point, but what really bothers me is the DC. I measured it at the RCA output jack, red probe stuck in it and the black probe on the collar of said RCA jack...I assume this correlates to "on the pads" which I took to mean the pads on the board that the RCA outputs are connected to? It seems the DC offset should be zero with no wiggle room, not sure how to remedy this. At what point is it safe to hook up for a test listen?

I am told if after adjustment I am measuring voltage at the "0" test point, the mosfet is likely shot, and mine is drifting a bit...

Thanks for any comments,

Russellc
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Last edited by Russellc; 5th May 2015 at 04:37 PM.
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Old 5th May 2015, 05:27 PM   #2
lafish is offline lafish  United States
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I measured a stable zero at the test points, I plugged it in and heard absolutely nothing. Meaning it was so quiet I wondered if it was working at all. But then I put on an album and it was wonderful. Give it a try. It sounds even better after 24 hours.
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Old 5th May 2015, 05:32 PM   #3
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Originally Posted by lafish View Post
I measured a stable zero at the test points, I plugged it in and heard absolutely nothing. Meaning it was so quiet I wondered if it was working at all. But then I put on an album and it was wonderful. Give it a try. It sounds even better after 24 hours.
I do not have a stable zero. Must address this first! Thanks for the response!

Russellc
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Old 5th May 2015, 08:10 PM   #4
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Of more concern is that I am measuring a few milivolts of DC on the output jacks. My F-5 as we all know, has no caps and I am concerned about hooking it up until I am clear. I have PM'd a few people who originally had the same problem. Passing through the pre amp (BA-3 pre) may have sufficient capacitors to block anything before the power amp, and I guess B-1 does too (as well as my tube preamp) but I want to feel comfortable with this "measured dc"....I am probably measuring it wrong or something silly like that.

Russellc
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Old 5th May 2015, 08:59 PM   #5
Zen Mod is offline Zen Mod  Serbia
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what's DC offset , specifically ?
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Old 6th May 2015, 12:34 AM   #6
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what's DC offset , specifically ?
Well things are improved after a discovery. After leaving it shut let it stabilize around 0-1 mV. taking the top off or breathing on it, and it will fluctuate from 5-12 mV, quickly stabilizing once top is put on or you stop breathing on it. sealed up, it would go 0-.1 or .3 mV, but if I moved any air around or let a breath out over the vents, it might go 3-7 stabilizing once all was still.

I still cant get the test point to stay at zero, no matter how much I piddle with P1 but several builders have experienced this and they let it play on. If it sits still and sealed up, it stays 0 to less than one mV. (output offset, not P1 test pad) Any movement or breathing on case will get you up to 3-5 mV. removing the top and getting busy fanning around can get you 12 mV for a sec or two. I was working UNDER A FAN last night for crying out loud.

Unless you think it unwise, I think I will hook it up to my beater 6230 JBL power amp and see what happens.

Thanks for the response, appreciating any input.

Russellc
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Last edited by Russellc; 6th May 2015 at 12:39 AM.
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Old 6th May 2015, 12:41 AM   #7
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By "test pad", I mean that spot on the board that says "adjust P1 for 0"

Russellc
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Old 6th May 2015, 02:02 AM   #8
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What a comedy of errors.... I hooked it up. It was dead silent. But no music came out. I stared at this contraption with total disbelief. Nothing? Yup, then I saw the Umbilical cord not attached to the Pearl. New hope. Powered all down, reconnected everything and music sort of, but high pitch white noise and distortion. Then I remembered the required zobel for my SAE 1000. I'll do that later, I have another headshell for the Unitrac with either a Ortofon or Shure mounted...that will be easier just to see if it works...

Russellc
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