DS5R Phantom power supply hum

[Simon Taylor (staylor)]

I'm having hum problems either with my 5-pin cable or the DS5R itself.
 
I've narrowed it down this based on the following:
1.  nothing plugged into SVT4 Pro (amp), ah glorious sweet quiet with (normal) low-hiss.
2.  direct (1/4) output from Series II to SVT4 Pro, glorious sweet quiet with low-hiss
3.  5-pin from bass to DS5R, 1/4 cable (same as previous test) from DS5R bass (mono) output to SVT4 Pro and I get a nasty hum.
 
I've already adjusted the hum canceler pots for the space.  So, all I'm left with is the idea that either the DS5R is introducing the hum, the 5-pin cable is doing it, or something about the phantom AC power (as opposed to the battery DC in test #2 above) circuit is causing it.  Maybe some hum is normal??  If so, how much?  This is pretty nasty -- enough that with my amp turned up, I can hear ghost-beats as the fingered pitch interferes with the hum pitch.  Also, when I start to play with the Q settings, it gets even worse . . .
 
I hate nasty hum and electronic buzz with a passion, and I could possibly be accused of seeking the perfect quiet ambient sound levels.  I don't have enough experience to know whether I should be hearing this level of ambient hum/electronic buzz or not, but my gut tells me not.
 
I've read all the posts about using good instrument cables.  However, I don't think that is the problem here, since the 1/4 cable I use works just fine (no significant hum) when I'm running straight out of the bass (off batteries).
 
Any suggestions?

[Nate Pitts (cntrabssn)]

Simon,
 
Assuming the 5-pin cable is OK, try lifting the chassis ground connection on the DS5R using a 3 to 2 prong adapter plug. This should not cause any trouble as long as you have a chassis ground somewhere in your system. Lifting the ground has worked for me in the past. You might also want to check all of the jacks on the supply to ensure solid mechanical connections. Does the location/orientaion of the DS5R change the hum? If so, it's possible that something is inducing hum into it, e.g. the SVT4's power supply.
 
I hope this helps,
 
- nate.

[Simon Taylor (staylor)]

Nate,
 
So, do I understand correctly that lifting the ground connection means using a 3 to 2 adapter so the DS5R is now ungrounded (at least via the power plug)?  Also, I'm not sure what you mean when you say ...should not cause any trouble as long as you have a chassis ground somewhere in your system.  I don't have any special grounding.  Right now it is all just straight 3 prong power plugs into one simple $20 power strip.  Are you saying that as long as I have one of my units properly grounded and all the units (including DS5R with lifted ground) mounted to the rack, that this will be the chassis ground?  I.e., the ground (particularly for DS5R) is being carried by the contact between chassis of components and rack, right?  If I understand correctly, maybe another thing I could try to help would be to mount the DS5R and the SVT4 Pro in the same rack?
 
The DS5R is rack-mounted right now, so I haven't tried rotating it to see if the hum seems induced by some RF.
 
These are good suggestions.  If you can clarify about lifting the ground and chassis grounding, I would appreciate it.  
 
Also, I've been looking at power conditioners.  Can anyone advise whether the lower cost units (like Furhman units) provide good AC noise protection and whether this might apply to my situation?
 
Thanks!
 
Simon

[Nate Pitts (cntrabssn)]

Simon,
 
By lifting the ground, I do mean using the adapter to break the chassis ground connection normally made through the power cable. The cable shield between the DS5R and your amp will provide the path to ground. You need to have a chassis ground in your system for safety purposes. That way, your chassis won't become hot in the event of some sort of electrical fault condition. When your gear is rack mounted, the chassis are all connected mechanically as you mentioned.
 
I suspect that your hum is caused by a ground loop, so what we're trying to do is minimize the number of paths to ground.
 
I don't think you're running into an AC noise problem, but I'm not totally sure. When I ran into my hum problem, my DS5R was sitting on top of my SKB rack, but everything was plugged into a Furman PL-PRO. I'm not sure how the different conditioners compare, but I think it's a good idea to have one.
 
Man, I'm starting to realize how hard it is to keep my thoughts straight some time! I'm trying to keep my posts brief. Anyway, try the ground lift suggestion, and let us all know how it goes. We'll try to move forward from there.
 
Good Luck,
 
- nate.

[Paul Lindemans (palembic)]

Hi Simon,
 
I don't have a power conditioner (yet) but our guitarplayer in one band uses one in his neck. It's a Gemini (I have no other specs) and over here in Belgium rather cheap: about 120?. He says that it does the job very well and at about 1/4 of the price of the higher classified brands.
 
Paul

[Paul Lindemans (palembic)]

LOL! Youre typing too fast Paul: neck = rack

[Simon Taylor (staylor)]

Thanks Nate & Paul!!  I've got a rehearsal tonight in our studio space and will try these suggestions.
 
Simon

[Simon Taylor (staylor)]

er, the Peabody's Monster studio, that is.  Peabody's Monster is the band I'm in here in Juneau.

[Ron Wickersham (rjw)]

Hi Simon,
 
you're correct that the system should be as quiet when externally powered as when it's running off batteries.
 
here are some troubleshooting suggestions:
1) plug the system together with the 5-pin cord and power supply and with the hum happening. turn off the power switch on the rear of the DS5R.  if the hum is only present with the power supply on, then there is something wrong with the power supply. but if you get no change in the hum, the problem is in the cabling.
2) in the Series I or Series II electronics when you turn the selector switch to standby, the signal leads are shorted to ground, so what you hear is all cabling noise.
3) also in the Series instruments, if you plug a cable (or even just a plug) into the 1/4 inch jack, the instrument will be powered by the batteries.  so in this case you can listen to the instrument fully operational using the 5-pin cable and the jumper to the amplifer, but powered by the batteries.  
4) so powered by the batteries but using the normal cabling, you can turn the power switch on the DS5R on and off to see if running the power supply (albeit not using it) makes any difference.
5) and indeed you can remove the AC power cable and see if having the unit grounded thru the power cable makes a difference.
 
-ron
 
(there shouldn't be any difference in the adjustment of the hum cancelling trimpots whether powered by batteries or the DS5R)

[Simon Taylor (staylor)]

Yesterday, I only had time to get the SVT4 Pro mounted in the rack before rehearsal.  I still have to try the lifted ground thing.
 
Also, thanks for the inside trouble-shooting information, Ron!!  I will definitely try those steps.

[Simon Taylor (staylor)]

Hey folks.  I finally got to sit down and do some testing on the power supply.  
 
I tried lifting the ground by plugging the DS5R into a 3 to 2 adapter.  That did not yield an observable result.
 
So, I moved on to Ron's tests:
 
1.  turn off power supply while hum is happening.
Result: all hum/buzz was gone.
 
2.  selector switch to standby
Result: with volume knobs up, this reduces the hum, but with vol knobs down, it's the same.  I infer from this that there is no difference since there is noise coming through even with vol knobs down and/or selector switch in standby.  When volume knobs are up it gets worse because the instrument is amplifying the hum along w/ everything else....phew, killed that horse!
 
3.  plug a 1/4 jack (no cable) into 1/4 output to force over to DC (battery) power, while using the 5-pin cable for audio path.
Result: no hum, sweet silence when the strings are not ringing and beautiful Alembic tone when induced in the standard fashion.
 
4.  running the power supply and not using it 1/4 SII out to 1/4 Ampeg SVT4 Pro in
Result: no hum, sweet silence identical to test (3)
 
5.  I'm not sure if I understand what you are saying for test number 5, Ron.  If you are talking about lifting the ground as Nate suggested, then I covered that above.
 
Anyway, it would seem from the first test that there is likely something wrong with the power supply.  Are there any further tests I can run before shipping it back to you folks??

[Ron Wickersham (rjw)]

Hi Simon,
 
1) this test should prove the 5-pin cable and the jumpers ok.
2) with the selector in standby, you shouldn't get any output or hum regardless of the settings of the vol knobs.  but the fact that you do, makes the 5-pin cable or internal wiring in the bass more likely than power supply problems.
3) normally quiet with the batteries would suggest that the power supply is the problem, but here we've got the unusual behavior in line 2.  
4) in rereading, i see my wording was ambiguous.  i was suggesting continuing to get the signal down the 5-pin cable and from the jack on the power supply to your amplifier, and seeing if turning the power supply on and off made a difference.  but in reading the results of your test, i think regardless it doesn't affect this situation.
5) i wasn't clear here either, it was just a suggestion following up on Nate's ground loop theory, so that turning on the batteries with a 1/4 inch plug but listening thru the 5-pin cable and jumper between the power supply and the amplifier, that you could hear the effect of a ground loop caused by the safety wire in the AC power cable because you can listen for any difference when the safety ground is present or not.
 
i can't say for sure where the problem is now.  my biggest concern is that you can still hear hum and possibly some signals even with the selector switch in standby.  it would be really hard for any failure in the power supply to cause this.  so i'm leaning to thinking that the problem is in the 5-pin cable or in the instrument.
 
should it be in the cable, it would be the shield is failing (usually this happens within 10 inches of the connectors since this is where flexing causes the most strain), or pin 1 on either end is not connecting to ground firmly.  usually a failing shield is pretty obvious as it makes a big change when you flex the cable even slightly, but have a listen with the rig set up so you're hearing the hum with the selector switch in standby and see if wiggling the cable causes any difference.  if it doesn't, then i would be suspicious of the central ground point in the instrument.  this point is the sleeve terminal of the 1/4 inch jack, which has a small flag terminal which we extend with a large buss wire.  a black wire from pin 1 of the 5-pin connector goes here as does the black wire from the selector switch.  a yellow wire from the ribbon cable supplies the ground for the circuit card, and it's also the common for the batteries - with one black and one red battery wire soldered there.  if these ground signals are not well connected to this point then this could cause the symptoms observed.
 
if you have access to an ohmmeter, you could connect the 5-pin cable to the power supply and with the pickup selector switch in standby and the mono/stereo switch on the power supply in the stereo position, insert a plug in the bass 1/4 inch jack on the power supply.  you should measure 0 ohms (a dead short) from the tip terminal to the sleeve.  the measurement with the plug moved to the treble jack should be the same.
 
if that shows more than one or two ohms resistance, then you could connect one terminal of the ohmmeter to the sleeve of the 1/4 inch jack on the instrument and probe the pins in the 5-pin connector on the instrument.  you should observe 0 ohms on pins 1, 2, and 3.
 
###
 
and finally, i'm not completely able to rule out a power supply problem.  if one of the two large capacitors in the power supply failed, then instead of having approx 2000 microfarads of storage, we would have only the 1.5 microfarads provided by the small bypass capacitors in the instrument.  this would cause a very big ripple current in the 5-pin cable and the wiring in the instrument, and might cause some amount of hum due to the small but finite resistance of the conductors.
 
###
 
one way to check the ground connection thru the 5-pin cable and it's connectors is to connect a wire from the sleeve on the 1/4 inch jack on the instrument to one of the 1/4 inch sleeves on the power supply while listening to the hum, to see if there is any difference when the wire is touched to the jacks.  if the 5-pin cord and connectors are ok, then there should be no difference when you add the independent ground connection between the instrument and the power supply.
 
let us know of any other observations or symptoms that might help definitively diagnose the problem.
 
-ron