TASCAM 48 grounding issue

  • Thread starter Thread starter lo.fi.love
  • Start date Start date
lo.fi.love

lo.fi.love

Functionally obsessed.
Hey folks,

I'm doing a quick post here to get started - I'm at work right now and I can't spend too much time on this at the moment - but I will follow up more when I get home tonight.

I've discovered an intermittent hum in my signal chain and I discovered my 48-OB to be the source. This only happens occasionally, though: With the same configuration (everything patched the same way, the same equipment powered on or off, nothing changed), it will sometimes go away in an hour or so. This has to do with my audio equipment, and not with anything else on this circuit, as best as I've been able to determine.

The 48 has a two-pin power cord, and presumably there is a chassis ground that I could get to. Provided that I can determine that the 48 is the true cause of this hum, what can I do to resolve this problem?

I'm really confused because I'm using mostly the same equpiment as I always have, the only (and main) differences being that I'm now using my M-520 mixer instead of the M-30 mixer that I was using before, and I now have all of my outboard gear racked on two steel equipment racks.

Does anybody have anything to add here? Any comments? I'll post more information when I get home, since this whole grounding issue seems to be fairly complex.

Thanks!!
Jeff
 
Are you getting the same problem with your M-30 connected to the 48?
 
My M-30 is in pieces right now... I pulled it apart to clean out a short in one of the faders.
 
I should also mention that everything in my project studio is connected to one single outlet.
 
i'm also curious as to the 48's grounding, as I was surprised to see it was two prong with no external ground point when I got mine, long shot but if you recently rewired maybe check you don't have any power cords running parallel to audio cords?
 
lo.fi.love said:
My M-30 is in pieces right now... I pulled it apart to clean out a short in one of the faders.
Click to expand...

Try to get the M-30 into service to see if you're getting the same problem. That would be my first thing to do. The way it looks to me is that the recent switch to the M-520 started the whole hum issue. Is that the only thing you've changed?
 
cjacek said:
Try to get the M-30 into service to see if you're getting the same problem. That would be my first thing to do. The way it looks to me is that the recent switch to the M-520 started the whole hum issue. Is that the only thing you've changed?
Click to expand...

For the most part, yes, it's the only piece that's changed. However, I did move all of my outboard gear to two steel racks. I imagine this has some sort of impact but I'm not sure what.

Edit: Sorry if this is confusing. The M-520 is the only new piece of gear to be introduced. Now, what's confusing is that I'm not sure what to do with the grounding terminal on the PS-520. I connected it to a grounding pin receptacle on my power strip via 16-gauge speaker cable to see whether this helped at all, but there was no noticeable change / only a negligible difference.
 
Hi,

2 suggestions,

Steel racks, I always mount the gear using nylon screws and a nylon washers behind the rack item ears. I then check with a meter to see if I have the earth lifted between the rack gear and the rack. I have had untold trouble with rack gear earth loops that come and go.

Run an earth cable (10 amp wire or larger) between the recorder chassis, mixer chassis and monitor amp chassis, lift and attach and see where (if) the hum goes away, remembering to earth to an unpainted part i.e a screw attaching to the chassis.

Let me know how you went.

Cheers

Alan
 
You may be getting a chassis ground loop in the new racks. The only way to check that would be to unrack everything and who wants to do that???

Are you positive the outlet you have evrything connected to is well grounded? Do you have a power distribution unit with a ground fault indicator on it?

I'd start with making sure the mains ground is good (see if you can measure voltage across the hot side of the receptacle and the ground), and if that is good then leave your rigged up ground wire in place for the PS-520 (and BTW that is pretty much what I did...broke a ground prong off of an old extension cord and soldered it to a piece of 14AWG solid core wire, attached the free end to the lug on the PS-520 and stuffed the end with the prong in an available ground receptacle on my power distribution unit).

Do you have any isolating washers in place on your rack screws? If you need some I have (literally) thousands...if you need some, PM me. They are #10 nylon shoulder washers, use two per screw (one in between the rail and rack ear and the other between the ear and the screw head). I've never had a hum problem.

Another idea...take some free wire and run from the ground lug on the PS-520 just for a test to the chassis of the 48...hum go away?

Measure for voltage between the PS-520 and the 48 chassis...might not tell us anything but it might be interesting.
 
Geez, thanks everyone for the suggestions!

So, I need to do all of this in stages. I'm first going to use the nylon washers (I have plenty, but thanks Cory!). I'll see what that does. I imagine this one single task could take the rest of my free time tonight, so I'll post back once it's done.

I've got a lot of trial and error ahead of me...
 
sweetbeats said:
You may be getting a chassis ground loop in the new racks. The only way to check that would be to unrack everything and who wants to do that???
Click to expand...

Well, I'm doing that. It's an inexpensive measure: the screws, washers etc. are relatively cheap. I'm reinstalling everything to make sure that there is no metal-to-metal contact on my rack. I'm doing this with washers, sort of making a sandwich of screw-head > washer > equipment rack ear > washer > rack rail. Adhesive-backed foam discs/pads between rack chassis. I'm getting a powered screwdriver this time, though... my hands were sore after installing everything with hand tools!

Are you positive the outlet you have evrything connected to is well grounded? Do you have a power distribution unit with a ground fault indicator on it?

I'd start with making sure the mains ground is good (see if you can measure voltage across the hot side of the receptacle and the ground), and if that is good then leave your rigged up ground wire in place for the PS-520 (and BTW that is pretty much what I did...broke a ground prong off of an old extension cord and soldered it to a piece of 14AWG solid core wire, attached the free end to the lug on the PS-520 and stuffed the end with the prong in an available ground receptacle on my power distribution unit).
Click to expand...

I did the multimeter test.. a friend suggested this on Sunday. It was fine, within acceptable tolerances and everything. I use two of these... there's a little red LED labeled "Protected", but I have no clue what that actually means. Maybe no-one does :)

The strange thing is that there isn't really anything else on this circuit. It has one outlet in my bedroom, one outlet in my room mate's bedroom, and it powers the lights in our closets. BUT, this place has a really shoddy electrical system. That's how it is in Oakland... cheap housing and unresponsive, greedy landlords who make illegal/unprofessional "repairs". I'm sure there's got to be something else sharing this circuit. Hell, we couldn't even find the breaker box for a couple of days last year, when we had the power out in 2/3rds of the house... I'd swear they wired the place with spaghetti instead of copper...

Anyway, long story short, I'm really considering an isolation transformer, in addition to getting a power conditioner. That is a LOT of money, but I'm starting to realize that it might be necessary.


Another idea...take some free wire and run from the ground lug on the PS-520 just for a test to the chassis of the 48...hum go away?
Click to expand...

I will try this.

Measure for voltage between the PS-520 and the 48 chassis...might not tell us anything but it might be interesting.
Click to expand...

I will try this, too, just out of curiosity.

Man, this is all really tedious and frustrating, but I'm still somehow enjoying all of this. Maybe I should post in the "Why Analog?" thread and write, "Because it makes me think!" :)
 
Heheheh...

Jeff, are your washers the shoulder type that ensure that the rack ear cannot touch the screw at all, or are they just nylon flat washers?

Start with the power conditioner. I have a Monster PowerPro 2500 and I've been REALLY happy with it. I need another one though.

Keep us posted...if the electrical is shoddy that isn't a good thing, BUT it was fine before, so hopefully one of the measures will work.

Good luck!
 
sweetbeats said:
Jeff, are your washers the shoulder type that ensure that the rack ear cannot touch the screw at all, or are they just nylon flat washers?
Click to expand...

I have two kinds. One is sort of a cup (with the open part facing toward you, as you're looking at the rack) and the other is the flat kind. What specifically are you talking about? Can you give an example?

Of course, I'll post more as I figure this out. I'm waiting for 600 RCA plugs to arrive in the mail this week, so the next 2-3 weeks will be dedicated almost exclusively to wiring and troubleshooting/hum-hunting.
 
Like these...the smaller part goes inside the rack ear hole so there's no way for the screw threads to touch the rack ear at all, and plus they help to properly position the unit.
 

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sweetbeats said:
Like these...the smaller part goes inside the rack ear hole so there's no way for the screw threads to touch the rack ear at all, and plus they help to properly position the unit.
Click to expand...

OK, I see what you mean. Where do you think I could pick these up locally, i.e. what chain retailer would have these?

Or, failing that, approximately how many extra do you have? I think I might need quite a lot. Maybe upwards of 100.
 
I have thousands, Jeff...black nylon #10 shoulder washers.

PM me.
 
I actually use nylon bolts for rack gear as well. Also protects the gear from rack rash.

I use an isolation transformer followed by a large UPS for incoming power. This gets rid of almost everything in the power supply. Also check that the house is earthed correctly, you may have to put down an extra earth stake to get a good earth.

Another idea I looked at for power was to use large truck batteries followed by an inverter (large) as the power supply, the truck batteries are charged by a battery charger from the mains. This not only gives you clean power but also acts as a UPS (uninterruptible power supply). Does cost a bit to set up but is completely clean, if you get keen you could charge the batteries from a solar panel during the day.


Cheers

Alan.
 
so

sweetbeats said:
Heheheh...

Jeff, are your washers the shoulder type that ensure that the rack ear cannot touch the screw at all, or are they just nylon flat washers?

Start with the power conditioner. I have a Monster PowerPro 2500 and I've been REALLY happy with it. I need another one though.

Keep us posted...if the electrical is shoddy that isn't a good thing, BUT it was fine before, so hopefully one of the measures will work.

Good luck!
Click to expand...

So those types of power conditioners really do improve noise? Is it a noticeable difference or just peace of mind? Ive always been curious about them because ive always had weird electrical related problems and noise/hum/etc.
 
If the mains ground is bad or nn-existent and/or you have system ground-loop problems, no power conditioner will take care of that. Depending on the power conditioner it is varying degrees of peace-of-mind to real filtering and protection. I feel a little safer that my gear will be protected from a lot of mains line issues and RFI garbage, but nothing cleans your power like an isolation transformer.
 
Update:

I've wired EVERYTHING together. My cable-making adventure has finally ended. Now, I'm hunting and eliminating hums.

The signal coming from the 48 is still the problem. I connected a 14 gauge solid wire from the tape deck to the PS-520 ground lug and... no real difference. I have hums on a few channels. Not all the channels, but a few. I took the DBX NR out of the chain and I can tell that the noise is coming from the tape deck itself.

What's more interesting is that I found continuity between chassis and the racks, using my multimeter. I thought I had avoided this with the shoulder washers but it appears to not be so. My next step is to see what happens when I ground everything together.... I will ground the racks to the PS-520 ground lug, and then make a connection from the ground lug to a ground pin receptacle on my power conditioner. I will post back after I try this.
 
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