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Severe distortion problem with new active bass

S

Sunim Koria

Apr 8, 2008
7
0
#1
Hi guys, so here goes:

I bought my first active bass yesterday (Yamaha RBX series) and I absolutely love it - great action, nice, full and punchy, and most of all very clean sounding too; no noise whatsoever!

However, I had a band practice earlier on today at some dedicated rehearsal rooms, and the bass just totally turned into something else. Firstly, it distorted like crazy - the distortion becoming more severe the harder I picked the strings. Secondly, the bass almost took on the personality of a passive bass with really faulty wiring - the sound abruptly cuts out when the pots are turned to full, the pots themselves crackle too, most controls are rendered useless, and the tone generally becomes intermittent and unpredictable. There was no mains hum or static noise though.

I immediately thought it was the battery (still being the one supplied when I bought the bass), so I replaced it with a new one but it did not help at all. I also tried different inputs on the amp (active+passive) and also going through the line-in of the PA but it was still the same. I didn't have a DI box at hand to try. Now that the bass was unplayable, I wound up looking like an idiot for most of the rehearsal by "playing bass" on a standard six-string electric that happened to be lying about.

Frustrated by all this, I took the bass straight back to the dealer after the rehearsal and told them the problem. They proceeded to test the bass out on several amps, checked the wiring etc., and guess what? It was absolutely fine! The bass played well through everything - no noise/distortion or intermittence, just a really nice, clean, full sound! The wiring and electronics all seemed to be in pristine condition, no dry contacts, loose connections etc. and all the controls worked perfectly. It was as just good as it was on the previous day when I bought it. The guy at the store couldn't say much about it, and I was totally baffled, and so I ended up looking like an idiot once again.

I got home and tested it on my own rigs and it still played to perfection. I even tried shaking the bass violently whilst it was connected to see if it was an undetected wiring issue, but the bass has no problems whatsoever as far as I can tell.

My guess is that the problem is at the place where I rehearse - the building has an known issue with grounding and electrical isolation and it is primarily due to the fact that there is an active train line running several feet directly above it. Most of the amplification equipment there emits a strange UFO-like sound when the gain is turned up.

Although, to my belief all active circuitry on electric guitars/bass have an isolated ground, but is this really true? Would there be a suitable workaround for this problem by using a ground-lifting device of some sort? My main concern is that the same issue would resurface if played at a certain venue with the same electrical problem, and most times I don't have the convenience of taking a back-up instrument.

I will greatly appreciate it if any of you guys can throw some light on this matter.

Many thanks,

SK
 
#2
The problem is not your bass. It's probably the amplification setup where you practiced. The preamp gain is probably too high in the system, and, given the already hot output of active basses, pushed it to hard clip.

Did you try turning down the volume on your bass when you were there?
 
#3
Do you have any power conditioner in your rig??
Otherwise you might wanna try a Furman 3 filter (#amp depends on how many watt your amp head has) power conditioner and see whether the noise is still there... =)
 
#4
Thanks a lot for the replies guys. I really don't think it was a gain staging problem as I did try turning down the volume on the bass, but all it did was give me exactly the same distortion artefacts at a lower level. Also a simple gain problem wouldn't interfere with the controls of the bass like it did in this case.

I currently haven't got a power conditioner for my rig, but I will certainly look into it.

As a workaround for a situation like this, would you think it would alleviate the problem if I "digitized" the output from my bass when sending it to the amp? ie. putting it through a digital effects unit, or some other kind of simple A/D->D/A convertor?

Thanks again,

SK
 
#5
You could, I suppose, try putting it through a compressor.

Sunim Koria said:
Thanks a lot for the replies guys. I really don't think it was a gain staging problem as I did try turning down the volume on the bass, but all it did was give me exactly the same distortion artefacts at a lower level. Also a simple gain problem wouldn't interfere with the controls of the bass like it did in this case.
Click to expand...
If the gain was high enough, it could. (ie. The entire signal spectrum down to noise level would be boosted to clip, though that is unlikely since it's about a 60 to 70+ dB boost we'd be talking about.)

It might be ground loops in the electrical connection.
 
#6
was this the rehearsal space rig or your regular rig? was it your own cords?,
start simple, maybe borrow the guitar players rig for a minute and try the higher strings, use your own cord, straight no pedals, add things in, if everythings cool on that it rig, it's the rig.
 
#7
Sunim Koria said:
My guess is that the problem is at the place where I rehearse - the building has an known issue with grounding and electrical isolation and it is primarily due to the fact that there is an active train line running several feet directly above it. Most of the amplification equipment there emits a strange UFO-like sound when the gain is turned up.
Click to expand...

Sounds like bad power to to the gear, which is probably why it's distorting. The voltage is probably low and dirty.

Sunim Koria said:
Although, to my belief all active circuitry on electric guitars/bass have an isolated ground, but is this really true?
Click to expand...

No. Active instruments isolate the pickups from being loaded down by the cable and amp, but the ground is not isolated.

One of my active basses has a signal that's so hot it distorts my Roland mixer, even if I turn the padding down on the channel.
 
#8
The only thing I was using which wasn't my own gear was the amp and the PA. I was not going through any pedals at all, even though I had a Boss compressor at hand. I will try absolutely every alternative I can the next time I rehearse there.

Although the power to the gear there might be dirty I don't think it's low - a lot of synths with "hot" outputs are going through the PA with no distortion whatsoever, and I got exactly the same kind of distortion when I moved from the amp to the PA. I also forgot to mention in my previous posts that I tried tapping the battery compartment and the amp/PA picked up a loud crackle with each tap, sounding like a very loose wiring connection in the bass.

As Parabolic Box suggested, I'm 90% sure this has got something to do with a ground loop problem that my bass can't seem to handle. I'm going to try and convert the bass signal to digital and then back to analog to see if I can override it.

The other 10% of me thinks that the pickups are picking up some kind of EMI from the train lines above (don't know how far-fetched that sounds?), but I'll try plugging a pair of earphones straight into the output jack when I'm next there to confirm whether or not the problem is coming from "within the bass".

Cheers for all the responses guys, I really appreciate it.

SK
 
#9
Sunim Koria said:
The only thing I was using which wasn't my own gear was the amp and the PA. I was not going through any pedals at all, even though I had a Boss compressor at hand. I will try absolutely every alternative I can the next time I rehearse there.

Although the power to the gear there might be dirty I don't think it's low - a lot of synths with "hot" outputs are going through the PA with no distortion whatsoever, and I got exactly the same kind of distortion when I moved from the amp to the PA. I also forgot to mention in my previous posts that I tried tapping the battery compartment and the amp/PA picked up a loud crackle with each tap, sounding like a very loose wiring connection in the bass.

As Parabolic Box suggested, I'm 90% sure this has got something to do with a ground loop problem that my bass can't seem to handle. I'm going to try and convert the bass signal to digital and then back to analog to see if I can override it.

The other 10% of me thinks that the pickups are picking up some kind of EMI from the train lines above (don't know how far-fetched that sounds?), but I'll try plugging a pair of earphones straight into the output jack when I'm next there to confirm whether or not the problem is coming from "within the bass".

Cheers for all the responses guys, I really appreciate it.

SK
Click to expand...

Intermittent probs, you just gotta love 'em. I doubt that it's as complicated as all that. My money's on a loose connection or cold solder joint in the bass.
 
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#10
Thanks for the post, ggunn. I am certain there is no problem with the bass as such - I've tried everything to make sure it's not a wiring problem, by having the bass properly checked over and even rigorously trying to *make* the problem come back by throwing the bass about et al., but everything still holds. Also I doubt a problem with the severity of the one I experienced at the rehearsal rooms could totally disappear just like that - it actually did sound like the bass was almost beyond any electrical repair!

Cheers,

SK
 
#13
Sunim Koria said:
I also forgot to mention in my previous posts that I tried tapping the battery compartment and the amp/PA picked up a loud crackle with each tap, sounding like a very loose wiring connection in the bass.
Click to expand...

Well I think there's the problem right there. I had a wiring problem in one of my basses that had EMG's in it, and it was breaking up. I rewired it and that fixed the problem. It was an issue with the wire from the battery touching something it shouldn't have been! I've also had a very distorted signal when my plug wasn't all the way in a few times.

Sunim Koria said:
As Parabolic Box suggested, I'm 90% sure this has got something to do with a ground loop problem that my bass can't seem to handle. I'm going to try and convert the bass signal to digital and then back to analog to see if I can override it.
Click to expand...

Ground loops can only occur between equipment that is powered from the mains. If each piece of gear is plugged into a different outlet, they are often not on the same circuit, and you have a difference in ground potential from one piece to the next. When you patch them together, you get current from the higher ground potential flowing to the lower, and you get a ground loop.

There is nothing inside a bass, even an active one, that has a different ground potential than your amp... since that is where your ground reference is. If you plug your bass into two different amps using a Y cord, you might get a ground loop, but it still has nothing to do with your bass. This whole obsession with star grounding inside basses to avoid ground loops is a big myth.

That has nothing to do with what Parabolic Box was talking about... but I just wanted to mention it. ;) There could be bad grounds at the rehearsal space.

But if it's only your bass breaking up I would check the wiring in the bass. If you have a bad battery connection or a short, that will produce a lot of distortion, just like a weak battery will.

Have you tried a different patch cord?
 
#14
Thanks David. Well if the bass did have a wiring problem during rehearsal it has managed to sort itself out good and proper! I had a tech look over the wiring straight after the practice and absolutely no fault could be found. As I stated in a previous post, I've actively tried to make the problem come back to confirm that it was a wiring issue in the first place, but it all seems very robust and nothing sounds out of place. The cord that I was using in rehearsal works perfectly on my own rig, so I think that was definitely not the problem.

I'll just have to see what happens the next time I'm there!

SK
 
#16
Hello, I got the same problem a couple of weeks ago with a used Hohner B2A... It worked for an hour then... distorted sound...

I have tried everything : check voltage (9,254V), PA or bass amps, lower the volume, lower the internal preamp output gain pot, check all wires, check all solders...

The I finally removed the preamp and use it as passive. I was furious of these complicated active s*** and wanted to break the bass in a thousand pieces, and I am now looking for a best solution as the gas factory that was mounted in this bass.

I am thinking about a simple Noll PA1 booster without Eq correction, or maybe an EMC BTC control. Adios to any kind of system with more than 5 wires !

The best think I have done is removing the obsolete original preamp and its infinite wires which crossed the bass from side to side...

Please include a photo of the yam electronic board and wiring so we can all check the improvement of technology and ergonomy in modern basses...
 
#18
I used a Laney amp at the rehearsal, and also the house PA. My personal bass amp is an Ashdown and the bass is fine through that - through both inputs.

My current theory to the problem is that due to the bad electrical grounding of the rooms a significant amount of voltage is being sent through the ground, into the bass and disrupting the 9v reference voltage supplied by the battery via the TRS connector. After all, it is the ground cylinder on the cord which is used to activate the circuit, by connecting R + S to the same path. Please do let me know if this theory holds any water.

Many thanks guys,

SK
 

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