At least there's no pin 1.
I frankly don't see that this as wildly different from an XLR. Hum, noise, and other EMI incursion issues seem better or no worse than the other two commercial pre-amps I have. I could have used LEMO or mini-XLR's and been more religious, they might help with a better shielded cart.
Last edited:
It's only pin 1 on XLR connectors. But the basic shield problem applies to all shielded cable connectors, be they XLR, RCA, 'DB9, 15 or 25' or whatever.
A new Jim Brown PowerPoint, start at slide #108.
http://k9yc.com/KillingRXNoiseVisalia.pdf
A new Jim Brown PowerPoint, start at slide #108.
http://k9yc.com/KillingRXNoiseVisalia.pdf
Last edited:
Yeah, that is too simplified for hi-fi audio. Some audio interference may go unnoticed with the sound quality on a ham rig even if RX interference is low. The priorities are different. The RF interference sources can be high enough to force the need for pin 1 to chassis even if this is at the expense of benign interference sources.
Thanks, the second reason I ask is that I have commercial examples of both ways and the differences in a relatively benign environment are not night and day. I do have a test bed a few miles away in Needham MA., an antenna farm where no car radio I have ever owned has passed the gauntlet.
With all the pin 1 throwing hands up in horror there is an interesting point here (that is not explicitly covered in the Whitlock papers, which is that the phono is battery powered and as such does not need a ground connection therefore there cannot be a ground loop.
This then links to the question of correct practice for grounding the screening of battery powered phono stages. Normal practice would be to ground via the first mains powered unit, but if things are differential and balanced then in theory you could just float the battery powered part.
thoughts?
This then links to the question of correct practice for grounding the screening of battery powered phono stages. Normal practice would be to ground via the first mains powered unit, but if things are differential and balanced then in theory you could just float the battery powered part.
thoughts?
Preamp chassis should be connected to preamp ground at least, so that it is an effective shield. If not fully balanced and isolated this would imply the chassis was connected to the cable shields, through whatever routing was used.
I don't see any benefit to isolate a battery phono preamp from signal cable shields. The purpose of such isolation is to prevent LF ground currents from flowing, but no LF ground currents can flow from a normal tonearm in the first place.
We can take advantage of the fact that we don't need to break or reject LF ground loops, by giving the preamp a uniform shield. I think it would be fine to have inputs and outputs next to each other with all RCA shields going straight to chassis. This would allow a full faraday shield and let RF currents skin around the outside of the chassis without entering it. RFI on downstream equipment could probably be handled with ferrite beads.
I don't see any benefit to isolate a battery phono preamp from signal cable shields. The purpose of such isolation is to prevent LF ground currents from flowing, but no LF ground currents can flow from a normal tonearm in the first place.
We can take advantage of the fact that we don't need to break or reject LF ground loops, by giving the preamp a uniform shield. I think it would be fine to have inputs and outputs next to each other with all RCA shields going straight to chassis. This would allow a full faraday shield and let RF currents skin around the outside of the chassis without entering it. RFI on downstream equipment could probably be handled with ferrite beads.
Battery power
A warning, I wasted some time on this. Apparently those USB battery packs are mostly intended to charge cell phones and have a shutdown threshold. The Silent Switcher (and a low enough power circuit) does not have enough standby current draw to keep the battery on. This will frustrate you, not all of them do it (or the threshold varies). Luckily 40mA or so at +-15 translates to 240mA from the battery for me but only when fully populated. Cute fix below.
https://www.dorkbotpdx.org/blog/paul/battery_pack_load
A warning, I wasted some time on this. Apparently those USB battery packs are mostly intended to charge cell phones and have a shutdown threshold. The Silent Switcher (and a low enough power circuit) does not have enough standby current draw to keep the battery on. This will frustrate you, not all of them do it (or the threshold varies). Luckily 40mA or so at +-15 translates to 240mA from the battery for me but only when fully populated. Cute fix below.
https://www.dorkbotpdx.org/blog/paul/battery_pack_load
Last edited:
BTW Patrick I did not burn out the SS, just the lab brick.
Another obvious warning, don't use spare stereo jacks as +- supply connectors they reverse and short in sequence as you plug them in hot.
Have you got my email re AD797 ?
Patrick
Yes, haven't gotten around to answering.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.