question about power supply

[goran]

I just wondering is it normal if you plug power supply into socket, connect it with amp, without bass and 5-pin bass cable plugged in, my power supply gives me a weird sound.
Even if I switch off bass, unplug it out of 5 pin cable, same thing, like a loud ground-lift sound?

thanks

[JimmyJ]

Goran,

You mean hum out of the amp yes?  Sometimes there can be some hum if the 5-pin cable is not "terminated" with the bass.  (Also, always leave the p/u selector switch in "mute" position or you will get quite a loud pop as you plug it in).

First try moving the power supply off the amp in case it's inducing hum in that way.

The power supply itself should not cause any hum so the next likely cause is that you have a ground loop going.  You can test that - disconnect the PSU from the amp and use the tip of the 1/4" cable to touch the metal of the PSU and the metal of your amp's input to see if the hum comes and goes.  Be careful because there may be some voltage differential between the two.  If linking the two chassis causes the amp to hum you definitely have a ground problem...

You're running at 220V there?  Is the Alembic power supply also 220V or are you using a step up converter?

Jimmy J

[goran]

Hey Jimmy, thinks a lot for reply... well since it would be hard for me to explain all that, I did a small clip so you can check it out. the clip is unlisted, so only people on this post can see it

What I forgot to tell you is that I am on 220V.

[JimmyJ]

Goran,

Thanks for the clip.  Now I understand what you are describing and will tell you that sometimes this happens to me also.  As long as it's clean and quiet with the bass plugged in I would say there is nothing wrong.

The reason for this is because when the cable is not "terminated" (plugged into the bass) it can act as a simple antenna.  That's why the hum shifts around as you move the wires.  Sometimes they can even become microphonic and tapping your foot on the cable will come through the amp as a thud.

Think about when you unplug a Fender bass at the bass end.  Apart from the noise of unplugging it, there will likely be some left over hum because the cable to the amp's input has no load.

Hopefully this is not a big problem for you.  You could try a shorter cable from the power supply to the amp input (that would make the antenna shorter).  Or just get in the habit of unplugging the amp end first - as you would with a Fender.

I've built mute switches into my rigs which short the input to avoid unplugging wires when everything is live.  Two pics below of a modified DI I use in the studio and a modified DS5 I carry when traveling light.  My two larger rigs have mute switches which leave the tuners in line...  You get the idea.  But on most occasions just unplugging the bass doesn't cause too much trouble (as long as the p/u selector on the bass is in standby).

That bass sounds nice!
Jimmy J

[goran]

Hey Jimmy,

wow that's a nice feature to have, mute switch. That thing doesn't bother me (the hum when I unplug the bass). I just had so much problems with power supply in auditorium where I played with orchestra, I almost wanted to go on batteries, but I realized that my jack is not mono, so had to bring my '66 jazz, but it doesn't have enough frets (I'm playing some written double stops). Do you sometimes have problem with power supply when there is bad power in auditorium? I was buzzing insanely with bass plugged in and that's where I found out about this hum when it's unplugged.

thanks

[JimmyJ]

Goran,

The orchestra stage is where any extraneous noise becomes very apparent!  If it was happening when the bass was on "standby" then it's a ground issue and there are a couple things to try...  If you are plugged into a DI box the first thing to do is flip the ground lift switch on that box.  Is the amp quiet when the DS-5 is unplugging from AC?  If your DS-5 has a ground pin on its AC plug try lifting that.  If not, try turning the plug around.  Same for the amp - ground lift if possible.  Some combination of the above should quiet a ground issue.

Your instinct to try battery power was a good one.  For that reason I recommend doing the mono mod on the 1/4" jack if you can, or at least making up a couple "summing" 1/4" cables for use in various situations.  The bass is not meant to run for long periods on batteries but there are occasions where it is just simpler to be able to plug straight into an amp.

Another tip is to keep cables as short as possible.  If you make up some 1/4" summing cables, maybe 2 meters would be enough...  The DS-5 to amp cable should also be short so you don't have coils of extra wire there.  Even the 5-pin, if you ever have the opportunity to make one or have one made, think about making a short one for the times you are sitting near your amp.

But if the pickups are hearing the noise - quiet in "standby" but noisy when on - then that's a different issue and a bit more complicated.  Some rooms - even some large halls - have so much electromagnetic junk flying around that it is difficult to find a quiet spot.  Our Alembic's large single-coil pickups hear more than your average pickup.  That's why they sound so great but also why they "hear" everything.  Always try pointing the neck in different directions to see if there is a quieter position.  Sometimes I end up pointing the headstock towards the audience. 

It is nice to have those extra frets!  Funny side story; Fender made a 5-string bass in the mid-60s with a high-C string.  But instead of extending the instrument's range they chose to make the fingerboard shorter with only 15 frets so E-flat was still the highest note!  Silly!

Jimmy J

[goran]

Yea, I know that 5 string Fender... that was silly.

So when I have bass on standby I have no interference, all quiet, but when I turn it on I have a a problem, I think it's the power in auditorium. The amp is quiet when DS-5 is not plugged in. I wish my DC-5 has a ground lift, really think that would do the difference.

I've tried smaller cable, flipping the ground lift on DI switch (but amp is quiet without even flipping it). I also realized that if I turn bass so pickups look up it gets even worse, I know I have older Alembic that doesn't have an upgrade for that broadcast noise. But this is first time I've had that problem, so no big deal. If it happens in near future I'll just use the batteries for one show.

Just one more question, I was looking for this info on forum but seems I can't find it: do I really need to do stereo to mono on Alembic or I can just do that with some kind of cable that goes from stereo to mono? And what that cable is called?

I'm really bad at technical stuff, so I would need for someone good with all that technical stuff, so I let him do something inside my bass. I'm not sure if I trust anyone with a soldering thing to go inside my bass, because I'm not able to do it myself so I feel that no one can  )

Again, thanks you so much for this.

Goran

[StephenR]

I also have an older Series bass that has never had the electronics upgrade. For the most part it is not a problem.

Here is a link to the FAQ about how to re-wire the stereo jack for mono output. The thread contains a link to an illustrated PDF. If you take the bass to a tech to have the work done the PDF will show him/her exactly what needs to be done. It isn't terribly difficult if you have basic soldering skills.

http://club.alembic.com/index.php?topic=270.0

There is also a thread about building a stereo to mono cable.

http://club.alembic.com/index.php?topic=275.0

Hope the links are helpful. If you have additional questions after reading them ask away, sure someone will be able to answer them.

[goran]

Thank you so much Stephen!

[JimmyJ]

From your description I'm afraid you are dealing with RF interference.  A ground problem would hum even with the bass in standby.  Most likely if you tried running on battery power you would still have the same noise problems at that location.  So I don't think it's your DS-5 or even the building's power.  But there must be unshielded power lines, transformers, or bad light dimmers nearby which are transmitting this interference which your pickups are hearing and amplifying.

The mod that Ron at Alembic came up with to make the instruments quieter really does help.  But it involves hand-tuning the preamp board while mounted in the instrument to optimize noise rejection.  That means the work has to be done to each individual axe in Ron's shop at Alembic HQ and as you can imagine there is quite a backlog of instruments waiting for his attention...

Things you can do in the meantime? ... Turn the bass left and right until you find the quietest position.  Turn off the boost switches and maybe roll off the LP filters as far as you can stand.  Consider putting a volume pedal or even a noise gate inline before the amp to keep it quiet when not playing. 

Sorry you are experiencing this difficulty but you are not alone, especially here in the Alembic forum!  These are the things we deal with to get that SOUND.

Jimmy J

[goran]

Thanks, yep, volume pedal s doing the job...but this is the first time I'm having the problem... usually it's good, I'm not worried