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
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.
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.
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.
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?
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?
not sure how you come to the conclusion that "all burst into oscillation"... mine don't, i just checked.
again, i would like to offer to look at some oscillating boards and measure them and publish the results here, plus a couple ideas i have to resolve the issues. PM me....
You must be joking. 5.2nV/rtHz noise (best case, can be up to 8nV/rtHz) plus the 150 ohm input resistor, that's about 6nV/rtHz (ignoring the servo contribution). Marginally good for MM.
If by 20dB you mean a transformer in front of this preamp, then that's not an apple to apple comparison with the Paradise. Try DC connecting those extra 20dB and see where your offset (and the LF fluctuations) are going. And I haven't even considered the temperature offset drift.
BTW, OPA177 has not less than 25uV offset. You do the math for 80dB DC gain. This would be a job for a chopper stabilized opamp (Vos<1uV) but then you definitely don't want such around a MC.
Sorry, wrong assumption based on Take5's successful build. In fact i only learnt about this peculiarity tonight. My arm is wired balanced and even though i used a single shared raw dc supply i never had the issue he describes. But it was surprisingly easy to duplicate. I should probably try a common ground point at the PS ground for the input ground return.
Improvements are being developed as we type
Thought-controlled arm helps amputeesMy thought controler arm (and fingers) was typing that, but that will change also http://www.eetimes.com/electronics-news/4059143/Fraunhofer-shows-thought-controlled-typing
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