Problem with SM-900. Hum at playing passive instruments at passive input

[mroku91]

Hi! I've got a problem wit my SWR sm-900 (prefender). I have music man sr5 and passive fender precision. And i have twoi inputs in preamp in SWR (active/passive)

Music man sound excellent on both inputs. No hum no noise, no overdrive, just like my line 6 variax guitar).
When i plug passive instrument into Active input- it's ok.
But when i plug passive instrument to passive input i hear sond of bass + hum whitch sounds the same all the time - it doesn't change when i move my guitar. When i turn the volume knob to 0- hum is gone.

Hum appears when i just plug any cable to passive input (even if i touch the ground by my finger). There isn't any hum when i plug calbe into active input.

I have tried other cables and passive guitars and it was always the same. I've changed Tube in preamp to brand new one too.
Could somebody help me?

[JimmyM]

you're assuming that just because it's passive that's the problem. could be a problem with the bass that's unrelated to passive/active. what kind of bass? what are your settings on the amp and bass?

[mroku91]

I have got music man sringray5 93' (active) and 83' Fender precision Elite (without preamp) it's all passive. I haven't got any problems with it while i was playing eden wtx-260 and when i plugged it into my audio interface.
I plugged passive washburn electric guitar to sm900 and result was the same as with Pbass.

Tip: i can reduce the hum with turning volume pot on my pbass to zero. hmmm...

Here is a little record of this noise:
http://www.sendspace.com/file/74m11s
1.PBass into active input with boosted gain on preamp (to set the volume to the same level as in passive input)
2.Pbass into passive input (turning knobs in bass volume, tone)

[BassmanPaul]

If the hum disappears when you turn your bass volume to zero the problem lies with the bass. You should think about shielding the passive bas's conrol cavity and also under the pickups. Carvin sells a neat little kit with self adhesive copper foil quite cheaply.

Paul

[mroku91]

I have shielded my bass very exactly with copper tape. i've also plugged the split coil straight into the output jack, the hum was still there! Notice that everything was ok when i plugged Pbass to Eden WTX-260 (no hum). Are you still sure that problem is with the bass?

[msquared]

The problem is with the bass. The difference between active and passive, as far as the amp is concerned, isn't going to make that kind of hum. Shielding will do a lot to eliminate hum but can never get rid of 100% of the problems, which is why humbucking pickups (like the one in your SR5) were invented.

A lot of what causes hum is the environment. Where in the room you're standing, what the wiring situation is in your bedroom or on the stage, proximity to televisions or other electromagnetically noisy devices, all of this stuff will cause your single coil bass to hum. Do you have any dimmer switches on the same circuit that the amps are plugged into? Does the hum change when you move around the room or turn a different direction?

Regarding the differences in your amps, it is likely that the Eden's gain setting is far lower than the SWR's and that it was making up the signal in the amp stage, and that the hum is just much quieter for that reason. Differences in EQ settings on the bass and the amps can also account for this.

[mroku91]

As i sad my bass is well shielded. The main hum doesn't change when i'm movin my guitar. And it doesn't change when im standing closer or further from a amp. What can be wrong with the standard precision bass? I plugged pickups straight to a jack and it doesn't help, so the wiring is ok. Can it be problem with the pickup? The is absolutely no hum when i plug passive bass to active input nad boost volume level as in passive

[lbwdog]

[quote=msquared;8956326]

The problem is with the bass. The difference between active and passive, as far as the amp is concerned, isn't going to make that kind of hum. Shielding will do a lot to eliminate hum but can never get rid of 100% of the problems, which is why humbucking pickups (like the one in your SR5) were invented.

..............all of this stuff will cause your single coil bass to hum.

The P Bass is humbucking. (two split coils)

Mroku91; You say it does this with a passive Washburn guitar? Have you shielded this guitar as well as the P Bass? If so, you could have caused a grounding problem in both.

If not, there might be a bad ground on the amp's passive input jack. Try another passive Precision Bass to see if it still hums, if so, you'll need a tech to look at the whole problem.

[lbwdog]

[quote=lbwdog;8958662]

Originally Posted by msquared

If not, there might be a bad ground on the amp's passive input jack.

I'm thinking this may be the problem. The only difference in the passive and active inputs are, the active jack has a pad to reduce the level at input, but otherwise they're parallel.

[mroku91]

washburn wasn't shielded but hum was the same. Yes there is some extra hum depending from where am I am standing etc. but the main hum doesn't change and appears with both passive instruments with and without shielding.

Recorded on MMsr5:

http://www.sendspace.com/file/4fg6pi

1. Cable in active jack without bass and touching ground (no hum)
2. Cable in passive jack without bass and touching ground (hum)
3. MM into active input (no hum)
4. MM into passive input (no hum)


Co i can say:
-passive bass into passive input HUM----
-passive bass into active input NO HUM
-active bass into passive/active input NO HUM
-reducing volume on passive instrument plugged to passive input eliminating hum
-Cable with nothing connected and plugged into passive input HUM----
-Cable with nothing connected and plugged into active input NO HUM
-hum on DI out and on the speaker out too
-passive instruments are not causing problems on other preamps
-passive instrument is well shielded by copper tape
-I've tried other cables and other instruments

[lbwdog]

I saw another thread where you said the input jacks had been replaced? Check for bad solder joints.
http://www.talkbass.com/forum/showth...t=#post8888439

[mroku91]

I have sent amp to my friend who has repaired it but as you see, he didn't. I plugged ground from passive jack to ground in active jack and it didn't help too.


I took off battery From my music man so there was no "active" mode, and there was no hum in passive input. I connected ground to the strings and touched a cable from MM humbucker by a tip of jack connector and i have heard clean passive tone without any hum... so maybe it'ss problem with my pbass... (sorry for my english)

[mroku91]

I borrowed another passive guitar from friend and again..hum. So 3 guitars giving hum just in passive input. It must be something wrong with the amp.


Here a liitle video:
http://tinypic.com/player.php?v=opoj75&s=5
View My Video

[BassmanPaul]

Or you are in a noisy environment and all three passive instruments are responding the same way.

Paul

[mroku91]

I'm living in that room for 8 yrs. I had david eden wt600, ashdown amb evo 500, gallien krueger, ampeg b2r etc. there was no problems with passive instruments As you hear in the video the noise is existing event nothing is plugged to the cable.

[BassmanPaul]

If I just plug a cable into any of my amps there is noise. The cable needs to be terminated for lowest noise.

Paul

[msquared]

Since you apparently feel that the information you've gotten thus far is worth exactly what you've paid for it, perhaps it's time to take your amp to an expensive repair shop and see what they have to say about its bustedness.

[craig.p]

How do I say this delicately... You won't be the first person to fight hum problems on that particular amp. It's not your bass. http://reviews.harmony-central.com/r...WR/SM-900/50/1

[mroku91]

Thanks for help friends I'll send sm900 to good repairman

[mroku91]

finally repaired! There was problem with ground on jack inputs