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Old 7th January 2013, 06:46 PM   #901
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Quote:
Originally Posted by sq225917 View Post
I'm putting each channel of mine into its own case and the two psu's into another. Any suggestions. i think I might build a couple of DDCR tonight.
Maybe to save on cost of external case you can consider making internal sub enclosure in cooper as I have done on MY Paradise
But with 2 suplies you will have no problems and by experience Hessener board design is realy good and pick up from poor screaning is realy low if any

One thing I wuld look at is TT cable configuration as same use Cartridge return as grounds I reviered mine for ballanced (4 separate cables from cart + super duper ground) and had no problems.

PS wait till tomorow for purchase of Psu components
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Old 7th January 2013, 06:51 PM   #902
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Originally Posted by Bksabath View Post
Maybe to save on cost of external case you can consider making internal sub enclosure in cooper as I have done on MY Paradise
But with 2 suplies you will have no problems and by experience Hessener board design is realy good and pick up from poor screaning is realy low if any

One thing I wuld look at is TT cable configuration as same use Cartridge return as grounds I reviered mine for ballanced (4 separate cables from cart + super duper ground) and had no problems.

PS wait till tomorow for purchase of Psu components
In the case of the earlier mentioned schema (6 wire connection) I would propose to use a 3rd shielded cable, outside is chassis ground, inside is signal ground.
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Old 7th January 2013, 06:54 PM   #903
PMA is offline PMA  Europe
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Any ideas how to encase the input devices together?
Multiple transistor chips in one case, like dual transistors.
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Old 7th January 2013, 07:09 PM   #904
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Any ideas how to encase the input devices together?
Gilbert O'Sullivan - Matrimony (HQ) - YouTube ?
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Old 7th January 2013, 07:18 PM   #905
Waly is offline Waly  United Kingdom
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In 2008 I was asked to design a MC preamp. It was completely DC coupled. There was a small-lot production of that phono preamp, like 50 - 100 pcs. None of the preamps produced had problems with DC offset fluctuation, in other words all were stable and output DC offset voltage was like 1 - 2mV or less, depending on ICs used.
I would ask for the schematic, but I am sure you are going to say it's not available, since this was a commercial project.

Even for 50uV input offset (which is very good) and 60dB gain @ 1KHz (that is, 80dB at LF) you are at a 500mV output offset. Make it 40dB gain at 1KHz (usually not enough for MC) and it's still 50mV. It's of course possible to trim down the offset to mV, but then you are in the same situation as with the Paradise.

So at least have the decency and post your MC pre specification and topology, otherwise you may be suspected of being just another business self-promoter.
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Old 7th January 2013, 07:23 PM   #906
PMA is offline PMA  Europe
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I would ask for the schematic, but I am sure you are going to say it's not available, since this was a commercial project.
This
Preamplifier for MM cartridge
+ 20dB gain in front of it. The servo connected as in the schematics.

I do not need any self-promotion, for I make money in plasma spraying. Now I am only offering open projects and advices.
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Old 7th January 2013, 07:35 PM   #907
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Tightened up the servo with a 150k in parallel to the 1M. Predictably the offset range went down by almost an order of magnitude but the infra low frequency "breathing" remained. I don't know if this counts as infra-low-freq oscillation or there is some other name for it but it's real and while it can be reduced in magnitude the underlying mechanism remains.

I would guess that airtight cases and low beta input transistors will minimise the amplitude of the "breathing" but isn't there some more elegant way to deal with it?


As i got curious about all the compulsory grounding schemes i did bring the two input grounds together and was rewarded with some real fireworks on the scope. It cannot sync to it, or maybe it oscillates over a whole range of frequencies, who knows?

Some time ago i remember sharing some general prejudice towards ground planes in analogue circuits instead of proper star ground. Could all these issues be related entirely to this?
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Old 7th January 2013, 07:37 PM   #908
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Tightened up the servo with a 150k in parallel to the 1M. Predictably the offset range went down by almost an order of magnitude but the infra low frequency "breathing" remained.
There should be nothing like that. If yes, it indicates a serious flaw.
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Old 7th January 2013, 07:43 PM   #909
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PMA, as no one else seems particularly interested in this subject, could you not take a peek at the circuit and share some insight?
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Old 7th January 2013, 07:47 PM   #910
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1st UHF oscillations must be excluded. But I understand it is very difficult for it needs sophisticated equipment. So I appeal on authors of the project to check one of the flawed boards, e.g. yours.
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