Hissing Noise

[Donald Wormuth]

Ok, I've got a 1980 Washburn Force ABT B-10 when I pull active knob. Not there when passive. I get a hissing sound that is there always. Whether I'm playing or just sitting there its fairly loud. Not so loud that you can hear it over playing. It's there whether I am touching strings or bridge. I'm not sure what it might be. Possibly a shielding issue? Any ideas as where to start?

 

[RSBBass]

Cool bass but its 40 years old and some of the components in the pre-amp may be slipping out of tolerance.

 

[Donald Wormuth]

Cool bass but its 40 years old and some of the components in the pre-amp may be slipping out of tolerance.

It's an awesome bass I got it for free. I had a house fire and my stuff all burned so i was asking around to musician friends if anyone had a used one for sale. There was but nothing I could afford at time. A co-worker heard me talking to someone on phone, next day he brought it in and just gave it to me. You wouldn't happen to know anything about the pickups in it? I can't seem to find any info on them. They are stock.

 

[bobdabilder]

Pictures of a bass help people remember better

 

[Killing Floor]

+1, if you can remove the cover plate so we can see the electronics it might help.
Shielding is always a good idea. But if it doesn't happen when passive that may not be the issue.
Sometimes constant hissing is a sign that Sonic Youth has reunited but I don't think they'd be in your house without you being aware of it so let's focus on the preamp.
Lastly, good battery?

 

[Donald Wormuth]

Pictures of a bass help people remember better

 

[bobdabilder]

You have nice coworkers.

 

[Donald Wormuth]

+1, if you can remove the cover plate so we can see the electronics it might help.
Shielding is always a good idea. But if it doesn't happen when passive that may not be the issue.
Sometimes constant hissing is a sign that Sonic Youth has reunited but I don't think they'd be in your house without you being aware of it so let's focus on the preamp.
Lastly, good battery?

+1, if you can remove the cover plate so we can see the electronics it might help.
Shielding is always a good idea. But if it doesn't happen when passive that may not be the issue.
Sometimes constant hissing is a sign that Sonic Youth has reunited but I don't think they'd be in your house without you being aware of it so let's focus on the preamp.
Lastly, good battery?

+1, if you can remove the cover plate so we can see the electronics it might help.
Shielding is always a good idea. But if it doesn't happen when passive that may not be the issue.
Sometimes constant hissing is a sign that Sonic Youth has reunited but I don't think they'd be in your house without you being aware of it so let's focus on the preamp.
Lastly, good battery?

 

[Donald Wormuth]

View attachment 4207384 View attachment 4207390 View attachment 4207392

 

[Donald Wormuth]

Pictures of a bass help people remember better

i posted some farther down thread

 

[bpc]

I would replace those electrolytic capacitors. That's the black cylinders. If you are comfortable soldering then it is quite easy. Electrolytics can break down over time. Their values are written in the side. Be sure to get replacements with the same voltage value. Larger voltage ones will work but will be larger and may not physically fit.

But before that, you didn't say, is the battery new?

 

[dwizum]

Any ideas as where to start?

Check for snakes?

The LF442CN op amp on your preamp looks like it's more tailored for low power consumption than good performance or low noise. This may just be the way it is. Hissing that's always there is not environmental in nature, shielding won't help. It's usually because of poor performance from the chip on the preamp and/or poor component selection.

Replacing electrolytic caps won't hurt but it feels like a bit of a shot in the dark to me. If you really love this bass it might make sense to just put a good preamp in it. There are OK preamps on eBay for pretty cheap these days (i.e. the Tone Monster products). Or solder your own, there are a handful of very good designs floating around this forum and most of them cost $5-10 to put together.

 

[bpc]

feels like a bit of a shot in the dark to me

Agreed. Was my best shot though.

 

[Donald Wormuth]

I would replace those electrolytic capacitors. That's the black cylinders. If you are comfortable soldering then it is quite easy. Electrolytics can break down over time. Their values are written in the side. Be sure to get replacements with the same voltage value. Larger voltage ones will work but will be larger and may not physically fit.

But before that, you didn't say, is the battery new?

Yeah I am comfortable doing that. I have an associate's degree in electronics engineering. I've done a lot of that I've even built my own boards for stuff. My teams capstone project we built our own pinball machine. My job was to build controlboard for the counters and the ball holder. I used to have my own function generator, Oscope, every testing equipment you could imagine. But I came down with cancer. And my health insurance dropped me. Had to sell everything to pay for treatment. probably have some in my tool box. Had started building a compressor pedal before I got I'll. Any suggestions on how much larger? On those caps.

 

[bpc]

Any suggestions on how much larger? On those caps.

No, I meant use the same values to avoid them being larger.

As @dwizum says, it is a shot in the dark but it is cheap (free if you've got the parts llying around) and easy as you know how. If changing the capacitors doesn't help then a new modern pre-amp is the solution. You could also just run it in passive mode to avoid the issue.

Let us know how you get on with it.

Sorry to hear about your health issues. Your story makes me very grateful for our NHS here in the UK.

 

[dwizum]

If you're trying to save on cost and have good PCB soldering skills, you could make your own preamp! There are a variety of designs out there that need less than $10 in parts, some of them have threads on this forum. If you're interested but don't know where to start, post here or shoot me a PM. I have pcbs for 4 or 5 designs and would be happy to send you one, along with a parts list.

 

[byacey]

Excessive hiss is usually the result of too much gain and not enough signal- ie. SNR, and another possibility is the input impedance isn't optimized for the impedance presented by the pickups.

If the pickups are passive, you'll want to aim for an input impedance of at least 500K to 1Meg, or higher. A fet input opamp would be the best choice here. If they are active pickups, a bipolar transistor input tailored for a low source impedance will yield the least noise. Should the pickups be active, any external preamp will now also be amplifying the self noise of the preamps built into the pickups. When too many gain stages need to be attenuated to keep the signal down to a usable level, the noise accumulates with every subsequent amplification stage.

The battery and caps have little to do with this noise, unless some of the coupling caps are completely open. I would be willing to bet it's just poor design or the wrong application for this preamp.

 

[byacey]

Yeah I am comfortable doing that. I have an associate's degree in electronics engineering. I've done a lot of that I've even built my own boards for stuff. My teams capstone project we built our own pinball machine. My job was to build controlboard for the counters and the ball holder. I used to have my own function generator, Oscope, every testing equipment you could imagine. But I came down with cancer. And my health insurance dropped me. Had to sell everything to pay for treatment. probably have some in my tool box. Had started building a compressor pedal before I got I'll. Any suggestions on how much larger? On those caps.

I wouldn't touch the caps until you find out exactly what the problem is. Many problems have been created by people arbitrarily replacing or "upgrading" parts when not necessary.