Thanks for prompt reply. I appreciate that leaving the inputs open isn't a realistic scenario (will make up a lead into a low R / short dummy load and retest) but the contrast between the left and right input was interesting and is as you have stated.
Just improvised a very simple mu metal vertical screen between R out and L in using the grounding clips provided on the PCB. Significant reduction to the cross talk (inputs are left floating so worst case). Not sure how much further benefit can be achieved by a full can (with ventilation holes?) over the input section (as the ground clips permit), maybe not a lot.
Just improvised a very simple mu metal vertical screen between R out and L in using the grounding clips provided on the PCB. Significant reduction to the cross talk (inputs are left floating so worst case). Not sure how much further benefit can be achieved by a full can (with ventilation holes?) over the input section (as the ground clips permit), maybe not a lot.
A very interesting phenomenon.
Right now I'm running the RTX off an i5 quad core and a 20' USB cable. I didn't buy a cheap cable, but there may be issues that I wouldn't even know about. I'll have to do some experiments to check the cable length and its s effects on the measurement system.
-Chris
Right now I'm running the RTX off an i5 quad core and a 20' USB cable. I didn't buy a cheap cable, but there may be issues that I wouldn't even know about. I'll have to do some experiments to check the cable length and its s effects on the measurement system.
-Chris
Did a bit of guessing on likely coupling modes and did a a bit more improvising on mu-metal screening and seem to have eliminated the cross talk completely. It didn't require a complete can over the left input circuit. Would experiment more but don't want to risk any inadvertent shorts on a brand new piece of kit so until I make a proper piece of shaped mu-metal that I can secure I will remove my temp fix.
What is the part number for the shields?
I'm opening the unit for the official fix anyway, may as well install the shields, I understand the unofficial mod will invalidate the warranty, but no issue.
Please don't get too excited its currently two bits of roughly formed mu-metal just to prove the point (and it seems to have done that much) so pics would look pretty naff. I will need to spend some time fabricating a piece of Mu-metal that fits properly and which I would be happy to leave inside the unit knowing it isn't going to come loose and short something.
My experimenting is with no cables connected to any input / output. As such its a rather false test scenario for practical use but it can logically be expected (and does) expose the internal cross talk as the input circuits will be at their most sensitive to pick up.
No shields have been designed, so there is no shield part number.
I am not sure that Mu-metal is needed. I think that the majority of the crosstalk is due to capacitive coupling.
I will be making a template for the screen using aluminium (i.e. the side of a used beer can) before I cut into my limited stock of mu-metal so if that piece of aluminium works as well as the results I have achieved with mu-metal then its QED for capacitive coupling and wont have to use mu-metal.
The input impedance is high enough that very little current will be circulating so very little magnetic field to couple. The beer can should be fine. However aluminium is a real PITA to solder to. If something from this list would work it would be great: RF Shields | DigiKey
I use aluminium (beer can) just to make a template to get the shape right (its a bit of cut and try as its too awkward to access to measure up) but if I get the shape right it will just sit in the ground clips provided on the pcb so no soldering required so if aluminium works as an adequate (capacitive) shield then job done.
I certainly recognise that leaving the inputs floating is an unrealistic testing scenario so did a very quick test with a shorted input, there was a reduction in cross talk as expected but still there hence experiment with a simple shielding configuration.
Christmas Schedule
Hi Jens,
Just wondering what the plans are over Christmas regarding further orders? My RTX must be due soon for invoicing (#56) but it is summer holidays here and most businesses shut down for at least a couple of weeks but I don't know if that happens in your part of the world (definitely not summer there!). Should I expect a delivery in the next month? If so, I'll have to arrange for the neighbour to look out for it while I am at the beach (tough life).
Cheers,
Anthony
Hi Jens,
Just wondering what the plans are over Christmas regarding further orders? My RTX must be due soon for invoicing (#56) but it is summer holidays here and most businesses shut down for at least a couple of weeks but I don't know if that happens in your part of the world (definitely not summer there!). Should I expect a delivery in the next month? If so, I'll have to arrange for the neighbour to look out for it while I am at the beach (tough life).
Cheers,
Anthony
Just got the package. However, DHL still charged me $14 for their pre-paid tax service! (They were paying $53 for my tax and charged me $14 for that) With the T/T transfer, the total surcharge comes to $71. If RTX really want to do do business with end users, you got to offer more choices for customer, including payment method and carrier. Speaking of the pre-paid tax service, UPS is $3 and Fedex is free of charge here. It seems DHL is the most expensive, and for that reason I will never choose them as my carrier in the future.
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