Purple Audio Sweet Ten Picking up hum from nearby power str

I've not had it with any 500 series racks or supplies, but I have with many other types of gear. Sometime I've even had to turn the offending piece 90 degrees to get it to go away. Isn't electricity fun?!?!?!?

drbill...thank for the reply! Do you think another make 500 series chassis could possibly behave different in my set-up?

It's hard to know. I'd look to make sure you have your electrical and wiring dialed in first. That said, in fully "analog", old school (console, tape machines, much outboard, etc.) this would not be an uncommon problem. Electrical, hums, ground noise, upper harmonic noise etc., can often be very tricky to analyze and fix. Sometimes it's something simple, other times, like I said - voodoo.....

Can you take the lid off the rack Power unit?

If you can, check and make sure that it, the lid, is making electrical contact with the rest of the chasis.

You can do the same with the Sweet 10.

Sounds like a shielding issue.

What happens if you put just a regular power strip next to the preamps?

Is it all units in the rack? Just one?



Just reread what you wrote... the rack Power strips are producing an audible hum?

Did some more troubleshooting. Swapped out hte power conditioner for another older one I had and the hum was reduced. However, I also bypassed all of the power strips and went down to floor strips I had which didn't completely eliminate it either, but was about the same as when I used the older strip mentioned above. What's most intriguing to me is that the humm is louder when the unit is completely powered off. After it goes through a slow power off sequence, the hum comes in louder than when it's being powered!

As a final test I compared the hum against a Heritage Audio OST-4 box I have and had none of the hum...obviously it's not milometers from a rackable power strip, but in my ind it's either the specific unit I have or the construction of the Sweet Ten model itself. Gonna call the vendor and get another brand chassis sent out to test in the same position. I liked the PA ST cause it has internal power and ability to expand into a summing mixer. But alas, got the rest of my preamps coming Wednesday, so it's more important to me to have something that isn't finicky!

To me sounds like a system problem, not a specific sweet 10 problem. But without testing and being there, it's impossible to tell. I'd be willing to bet your next sweet 10 does the same thing.

No a Star config is much more involved than that. But glad it works, cause that's all that matters. In my new install I did NOT implement a proper star ground implementation but I had clean power and built all power and wiring literally from the ground up.

Why would the hum increase when the power is off. Don;t transformers need electricity to output sound?

The power transformer in your conditioner creates an electrical field.  

Any adjacent transformer picks up some amount of that field.  Induced hum.  In the old days the recommendation was at least 3 feet away from any audio transformer, and transformers were usually much more heavily shielded back then than they are now.  Those CAPI and HA output transformers are not themselves shielded.  Any casing fully surrounding them is then their shield.  That may be an integral part of the 500 module, it may just be the case they are mounted in.  Likely not much difference in the shielding qualities of one companies metal enclosure over another.  

A transformer coupled audio amp can be turned off but connected to a monitored input, and induced hum will be present, no power or amplification required.  

One possibility.  

What are you not telling us about how the CAPI and HA were used previously?  In a different 500 rack mounted in the same place?  Or also new?  

A lot of equipment will hum MORE when turned off but monitored. I can think of many I have that have no audible hum when powered, yet significant amounts when powered off. This is different from the induced hum I've speculated on.  

I've got power conditioners for all different manutfacturers in my racks - ETA, Furman, Juice Goose, and a couple of others. No issues. But I've got my wiring and power issues sorted.

Re:

1. - Yes, degrees of hum ARE acceptable. The amount is up to you, If you put ENOUGH gain on something, you will pull in all kinds of crap. Deciding how much is "OK" is a personal decision. My method of testing :
- Bring in a mastered CD track into your DAW. Make sure it exits your D/A conversion @ full scale. Go thru your normal monitoring. Turn up the monitor control room volume until it is so loud you want to scream. Stop the music, raise it just a little more. Is it quiet? if so you're OK. My method when using a console with clients, etc.was to bring a CD player into a stereo channel on the console, hit "0VU", turn the CRM up to WIDE OPEN with power amps attenuated all the way down, and then gradually raise the volume on the power amps until I didn't EVER want them any louder. Is it quiet? OK then, move on. No one ever blew my monitors after that, and properly calibrating the room first kept me from chasing demons that didn't need to be chased.

If you raise your CRM monitoring 50dB above normal listening levels you'll have all KINDS of $#@! coming out your monitors. All of it will most likely never be heard if you have your CRM calibrated properly.

2. As mentioned above, no issue with rack mounted power strips here. You've got something else going on beyond "the normal" I think.

EmRR, this is indeed the case. The hum goes away when the rack/preamps are powered. Obviously for teh purposes of recording that is great and means no hum will be recorded, but still something I'd look to address if possible. Can you speak on the aforementioned scenario?

One thing I have gotten in the habit of doing is cleaning the paint off around a few of the top/bottom cover screws of any gear. I then test it with a DMM. This makes sure that the whole case is fully grounded to itself. It's solved a few hum issues on its own.

I also have one of those same Furman strips, and stopped using it because of the protection circuits self noise.