I'm developing a tube filter/buffer for use with a modified Sony XDR-F1HD (replacing its audio stage).
I've been looking around at new and kit buffers which I could quickly repurpose, and surprised to discover that all that I've looked at have IEC grounded A/C connection.
I figure that they do this for safety (if power transformer has failure, it could put A/C or HV on the chassis). But this wasn't done in the golden age of tubes, virtually all such equipment has no A/C ground. So is this because of improved safety standards, or low quality transformer and construction quality now?
It's a huge inconvenience for me. I have an exceedingly complex whole house audio system and I am constantly struggling to eliminate ground loops. It has come to this: only one component per interconnected system can have earth ground. Period. Everything else must float. I figure greatest risk is with power amplifiers, so those generally get the ground connection, line level gear gets ground lifted.
One way around this is to use small wall wart power supplies, as Musical Fidelity does with their X components. The small UL-listed AC transformer does not apparently need a ground connection (as it doesn't have one). Unfortunately, this does put a severe limit on available power and usually requires rectifying and complex voltage doubling and tripling circuits in the chassis itself (so much for getting the PS out of the unit).
Another way might be double insulation. The transformer itself should not be directly mounted to chassis, but indirectly through insulated washers, etc. Also all HV wire must be insulated. But it seems like typical Chinese manufacturers do not do this, and I have not yet found a buffer kit that takes this approach.
I've been looking around at new and kit buffers which I could quickly repurpose, and surprised to discover that all that I've looked at have IEC grounded A/C connection.
I figure that they do this for safety (if power transformer has failure, it could put A/C or HV on the chassis). But this wasn't done in the golden age of tubes, virtually all such equipment has no A/C ground. So is this because of improved safety standards, or low quality transformer and construction quality now?
It's a huge inconvenience for me. I have an exceedingly complex whole house audio system and I am constantly struggling to eliminate ground loops. It has come to this: only one component per interconnected system can have earth ground. Period. Everything else must float. I figure greatest risk is with power amplifiers, so those generally get the ground connection, line level gear gets ground lifted.
One way around this is to use small wall wart power supplies, as Musical Fidelity does with their X components. The small UL-listed AC transformer does not apparently need a ground connection (as it doesn't have one). Unfortunately, this does put a severe limit on available power and usually requires rectifying and complex voltage doubling and tripling circuits in the chassis itself (so much for getting the PS out of the unit).
Another way might be double insulation. The transformer itself should not be directly mounted to chassis, but indirectly through insulated washers, etc. Also all HV wire must be insulated. But it seems like typical Chinese manufacturers do not do this, and I have not yet found a buffer kit that takes this approach.
It is very difficult to do DIY double insulation, so safer to go for ground plus single insulation.
Anything metal which a user could touch must be grounded to the safety ground. In the old days safety was not taken so seriously. You just need to be careful, as you realise, to keep the safety and signal grounds apart except at one point. I think most people put this point in the preamp, if present. Other components should have a backup connection between signal and safety grounds, such as a big resistor or 35A bridge - the idea is to blow the fuse if there is a short, but otherwise not introduce a ground loop. There has been lots of discussion on this, so do some searching.
Anything metal which a user could touch must be grounded to the safety ground. In the old days safety was not taken so seriously. You just need to be careful, as you realise, to keep the safety and signal grounds apart except at one point. I think most people put this point in the preamp, if present. Other components should have a backup connection between signal and safety grounds, such as a big resistor or 35A bridge - the idea is to blow the fuse if there is a short, but otherwise not introduce a ground loop. There has been lots of discussion on this, so do some searching.
star grounding
I am privileged to own pre-1966 equipment that does not have safety grounded cases or three pin power cords. Thus I can easily implement tree gounding wihout having the device case ground-mesh of RCA cables-device case-safety ground-terminal strip-safety-ground-device case ground loops built in. In today's US economy where lawsuits are the only growth industry, anybody selling any AC powered device that is not either double insulated or having a safety grounded metal case, is a fool. Tubes really need a metal case to lose heat, unless you expose them to the air with plastic mesh or a fan. Having the preamp as the trunk of the grounding tree makes sense, because 1. you touch it a lot 2. the magnetic phono cartridge needs a grounded headshell as hum blocker and the ground wire runs from the turntable to the case of preamp. I have a tree grounded audio system, with the preamp having an additional safety ground wire from case to the power strip not installed by dyna, and the amp grounded to the preamp through the outside of the RCA cables. This is not ideally safe, as RCA cable outside is not a rated UL component for safety grounding. If I had a child crawling around that could touch the power amp, I would build a vented wood box around it. Since I never touch the power amp myself, only the plastic power switch, I don't worry about it.
Bands with large systems use modern equipment that has safety grounds on every component, and pro ones use "DI units" between every component, which is an op-amp setup that rejects common voltage signal (hum) else jensen transformer signal couplers. My one modern device, the CS800S power amp, has a grounded case and third pin on the power cord, and is causing a ground loop hum problem with the RA88a mixer. The CS800S is supposed to have op amp inputs with plus and minus hooked up to reject hum from the 1/4 phone jack ring. It doesn't work that way, probably somebody blew up the op amps by plugging a guitar amp in the "out" jacks which come from the output of the first op amps, so it only works with input to the "out" jacks. Thus the hum. I found out last night when the hum went a way when a stray RCA wire shorted both the mixer case, and the fan grill of the CS800S, eliminating the annoying hum. I'm going to have to repair the CS800S op amp circuit, and determine if the previous owner cut the case ground-power cord pin link inside the CS800S. Many amateur bands just cut the safety pins off their power amp cord and live dangerously.
I am privileged to own pre-1966 equipment that does not have safety grounded cases or three pin power cords. Thus I can easily implement tree gounding wihout having the device case ground-mesh of RCA cables-device case-safety ground-terminal strip-safety-ground-device case ground loops built in. In today's US economy where lawsuits are the only growth industry, anybody selling any AC powered device that is not either double insulated or having a safety grounded metal case, is a fool. Tubes really need a metal case to lose heat, unless you expose them to the air with plastic mesh or a fan. Having the preamp as the trunk of the grounding tree makes sense, because 1. you touch it a lot 2. the magnetic phono cartridge needs a grounded headshell as hum blocker and the ground wire runs from the turntable to the case of preamp. I have a tree grounded audio system, with the preamp having an additional safety ground wire from case to the power strip not installed by dyna, and the amp grounded to the preamp through the outside of the RCA cables. This is not ideally safe, as RCA cable outside is not a rated UL component for safety grounding. If I had a child crawling around that could touch the power amp, I would build a vented wood box around it. Since I never touch the power amp myself, only the plastic power switch, I don't worry about it.
Bands with large systems use modern equipment that has safety grounds on every component, and pro ones use "DI units" between every component, which is an op-amp setup that rejects common voltage signal (hum) else jensen transformer signal couplers. My one modern device, the CS800S power amp, has a grounded case and third pin on the power cord, and is causing a ground loop hum problem with the RA88a mixer. The CS800S is supposed to have op amp inputs with plus and minus hooked up to reject hum from the 1/4 phone jack ring. It doesn't work that way, probably somebody blew up the op amps by plugging a guitar amp in the "out" jacks which come from the output of the first op amps, so it only works with input to the "out" jacks. Thus the hum. I found out last night when the hum went a way when a stray RCA wire shorted both the mixer case, and the fan grill of the CS800S, eliminating the annoying hum. I'm going to have to repair the CS800S op amp circuit, and determine if the previous owner cut the case ground-power cord pin link inside the CS800S. Many amateur bands just cut the safety pins off their power amp cord and live dangerously.
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