Can a faulty lead "Scream"? EDIT- no it can't. Preamp Problem.

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Petebass
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Can a faulty lead "Scream"? EDIT- no it can't. Preamp Problem.

Post by Petebass » 09 Feb 2018, 13:48

You'd think that after so many years and so many gigs that I would have seen it all right? Nope, I had a strange experience last night.

We were rehearsing for a gig tonight, it was going very well. Then all of a sudden, the bass amp starts screaming mid song. It was loud enough to make the whole band stop playing and look at me. It was high pitched, squelchy, and only lasted a second or 2. The it started doing it regularly, like once every song.

By process of elimination I narrowed it down to a particular instrument cable. Once I removed it from the signal chain, the bad noises stopped.

Is this even possible?
Last edited by Petebass on 10 Feb 2018, 15:40, edited 1 time in total.
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ozrider
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Re: Can a faulty lead "Scream"?

Post by ozrider » 09 Feb 2018, 14:22

Petebass wrote:
09 Feb 2018, 13:48
You'd think that after so many years and so many gigs that I would have seen it all right? Nope, I had a strange experience last night.

We were rehearsing for a gig tonight, it was going very well. Then all of a sudden, the bass amp starts screaming mid song. It was loud enough to make the whole band stop playing and look at me. It was high pitched, squelchy, and only lasted a second or 2. The it started doing it regularly, like once every song.

By process of elimination I narrowed it down to a particular instrument cable. Once I removed it from the signal chain, the bad noises stopped.

Is this even possible?
I've only had this happen due to a faulty (cracked) preamp circuit board. Used to happen when the bass got a bit cold, totally high pitch freaky sound.

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BazzBass
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Re: Can a faulty lead "Scream"?

Post by BazzBass » 09 Feb 2018, 17:29

maybe the cable turned microphonic on you?
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BassLine
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Re: Can a faulty lead "Scream"?

Post by BassLine » 09 Feb 2018, 18:00

At a theatre gig I had squealing in my bass amp & Comms headphones. I had taped down my power cable, Comms cable and bass lead right next to each other.
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Re: Can a faulty lead "Scream"?

Post by noplanb » 09 Feb 2018, 19:21

Oscillations can occur when an input (or output) has insufficient damping, ie has a much higher impedance than what it was designed for. An open lead is like an antenna - as we all know - and picks up buzzes and maybe local radio splutter. If you have partial connection - ie bad lead joint, fatigued kink about to break, oxidised plug and/or socket surface, then really high frequency hash can runaround a bit more and interplay between bass and amp output and input circuits(?) And an RF oscillation can then modulate itself into a audible range scream. (Well, its a pretty tale, if not exactly correct....)
So, yes, "maybe the cable turned microphonic on you"
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Petebass
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Re: Can a faulty lead "Scream"?

Post by Petebass » 09 Feb 2018, 23:30

Ok it's not the cable after all. It did it again during sound check for the gig. I swapped to the spare bass and no problems since. It's the bass! Ozrider, so you reckon preamp?
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Re: Can a faulty lead "Scream"?

Post by BassLine » 09 Feb 2018, 23:32

noplanb wrote:
09 Feb 2018, 19:21
Oscillations can occur when an input (or output) has insufficient damping, ie has a much higher impedance than what it was designed for. An open lead is like an antenna - as we all know - and picks up buzzes and maybe local radio splutter. If you have partial connection - ie bad lead joint, fatigued kink about to break, oxidised plug and/or socket surface, then really high frequency hash can runaround a bit more and interplay between bass and amp output and input circuits(?) And an RF oscillation can then modulate itself into a audible range scream. (Well, its a pretty tale, if not exactly correct....)
So, yes, "maybe the cable turned microphonic on you"
"I love it when you talk dirty to me!" 8/

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ozrider
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Re: Can a faulty lead "Scream"?

Post by ozrider » 10 Feb 2018, 00:07

Petebass wrote:
09 Feb 2018, 23:30
Ok it's not the cable after all. It did it again during sound check for the gig. I swapped to the spare bass and no problems since. It's the bass! Ozrider, so you reckon preamp?
Yup, that's what it sounds like from my experience, especially it was so sudden, not like you'd hear when you were getting feedback, it would just come on, this high pitched sound. I took it to a tech here in Perth and the guy said there was a crack in the circuit board and so he repaired it. I'm not really sure what he did to be honest, I just had to trust him, but it was fixed. Whatever it was, it was in the bass.

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noplanb
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Re: Can a faulty lead "Scream"?

Post by noplanb » 10 Feb 2018, 09:17

so you reckon preamp?
So good 'ol process of elimination says not the lead. To the preamp: yes - you can go looking with magnifying glass and bright light - amazing what you see when you get down to miniature level. Cracks on the board, dry joints and pad-edge discontinuities will do the oscillation thing.
Warning: Good hand-eye skill work requirement ahead.
Assuming soldering skills, use a conical point temp-controlled solder iron, and go looking for this stuff. When you find it, just redo the joint with a tiny touch of fresh solder.
Sunken joints
Image
Solder skip
Image
Dry joint
Image
Lifted pad (solder a tiny bridge wire between it and an adjacent pad - pushing lifted pad down at same time)
Image
Cracked joint
Image

Couldn't find a picture of a pad-edge break! These are usually camouflaged by the screen-print coating. All I can say is, if the boundary around a pad looks very 'high contrast' across where the track joins the pad, then give it a scrape-back and solder in a tiny wire to bridge the boundary.
This page gives some idea, although his is a bad one, after a component was removed:
http://billmaudio.com/wp/?page_id=204
Image
Its worth at least a look. PS, it's called "easter-egging"
Last edited by noplanb on 10 Feb 2018, 09:23, edited 2 times in total.
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noplanb
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Re: Can a faulty lead "Scream"?

Post by noplanb » 10 Feb 2018, 09:20

I love it when you
>sigh<
The techno-pedants lot can be an amusing one at times.... :rollno: :lol:
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Petebass
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Re: Can a faulty lead "Scream"?

Post by Petebass » 10 Feb 2018, 13:00

Oh man, if I start with the magnifying glass, I just know I'll end up having to force myself to refrain from just re-soldering every single joint to make sure I don't miss anything.

I guess I'll just crack it open and if there's something fairly obvious. If not, off to the local tech ......
* 2 Stingray 5's (one heavily modded), Ibanez SR805, Ashbory, + more...
* Carvin B1500, Epifani PS1000, Ashdown Superfly amps.
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BazzBass
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Re: Can a faulty lead "Scream"?

Post by BazzBass » 10 Feb 2018, 16:44

noplanb wrote:
09 Feb 2018, 19:21
Oscillations can occur when an input (or output) has insufficient damping, ie has a much higher impedance than what it was designed for. An open lead is like an antenna - as we all know - and picks up buzzes and maybe local radio splutter. If you have partial connection - ie bad lead joint, fatigued kink about to break, oxidised plug and/or socket surface, then really high frequency hash can runaround a bit more and interplay between bass and amp output and input circuits(?) And an RF oscillation can then modulate itself into a audible range scream. (Well, its a pretty tale, if not exactly correct....)
So, yes, "maybe the cable turned microphonic on you"
thank you or explaining what 'turning microphonic' means to us luddites :) all I knew was a failing solder joint turns it into an antenna picking up interference
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Re: Can a faulty lead "Scream"? EDIT- no it can't. Preamp Problem.

Post by bassface » 10 Feb 2018, 23:01

This sounds very much like what happened to my Musicman stingray.
.very simple cause/solution in the end.

viewtopic.php?f=5&t=21955

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Petebass
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Re: Can a faulty lead "Scream"? EDIT- no it can't. Preamp Problem.

Post by Petebass » 11 Feb 2018, 00:52

bassface wrote:
10 Feb 2018, 23:01
This sounds very much like what happened to my Musicman stingray.
.very simple cause/solution in the end.

viewtopic.php?f=5&t=21955
I just read through that thread and yes, it sounds like the same problem. Changing the battery clip is pretty easy, so I'll give that a go. However, I've only ever used Energiser 9v batteries, so I see no reason why the battery clip would ........ Hold up, I bought the bass used. Who knows what batteries previous owners have used!

Now I just gotta find time to pull the bass apart ........
* 2 Stingray 5's (one heavily modded), Ibanez SR805, Ashbory, + more...
* Carvin B1500, Epifani PS1000, Ashdown Superfly amps.
* Lots of DIY neo/lightweight cabs including one made from composites http://www.ozbassforum.com/viewtopic.php?f=5&t=2546

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Re: Can a faulty lead "Scream"? EDIT- no it can't. Preamp Problem.

Post by ozrider » 11 Feb 2018, 01:15

Petebass wrote:
11 Feb 2018, 00:52
bassface wrote:
10 Feb 2018, 23:01
This sounds very much like what happened to my Musicman stingray.
.very simple cause/solution in the end.

viewtopic.php?f=5&t=21955
I just read through that thread and yes, it sounds like the same problem. Changing the battery clip is pretty easy, so I'll give that a go. However, I've only ever used Energiser 9v batteries, so I see no reason why the battery clip would ........ Hold up, I bought the bass used. Who knows what batteries previous owners have used!

Now I just gotta find time to pull the bass apart ........
I'd forgotten about that thread... hopefully it's an easy fix Pete!

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