Strange on-board preamp noise

Ro(c)kBass · #1 07-20-2011, 04:04 PM

I have a Yamaha TRB-10005 gone bad: it makes a funny squealing noise. When I plug it in the noise starts at a very high frequency and very quietly. With time the frequency of the squeal decreases and it becomes louder. The noise is almost as loud as the sound of strings played. Also the normal sound is a bit distorted. The noise sound like a computer generated sine-wave.

Do you have any ideas what is the problem and how to fix it?

What I know so far:
- The selection of pickup does not affect the noise therefor it probably is not the source of the noise.
- Using different cables and amps does not affect the noise either.
- Volume knob normally brings the noise down.
-The three band EQ knobs have some effect on the noise but nothing unexpected.
- I also noticed that if I leave my bass unplugged for a longer period of time the speed of noise frequency decreasing is slower and if the bass was plugged in recently it is faster (up to 3 times).

You can listen to the noise in the attached recording. At the beginning of recording I mute the strings, select both pickups, set all three EQ knobs to 0 and volume all the way up. I plug in the cable and let the noise become louder/lower. After I play some notes I turned the EQ knobs: first I boost for second or two than I cut and finaly put it back to 0; starting with hi, then mid and finally using the bass EQ knob.

berwick63 · #2 07-20-2011, 04:14 PM

I couldn't tell you the answer, but thats a sweet noise, haha

Kind of reminds me of a Pop Fly in NES Baseball.

_chrispy · #3 07-20-2011, 07:26 PM

Have you tried to change the battery? my TRB makes a similar noise but not as loud when the battery is going flat.

Funkinthetrunk · #4 07-20-2011, 08:36 PM

Quote:

Originally Posted by _chrispy

Have you tried to change the battery? my TRB makes a similar noise but not as loud when the battery is going flat.

WOW....try changing the battery, like he said.^

SGD Lutherie · #5 07-21-2011, 10:43 AM

Yep, change the battery.

Rob22315 · #6 07-21-2011, 12:52 PM

If it's not the battery, it sounds to me like a resistor or capacitor has gone bad causing the circuit to oscillate because whatever's changed in the preamp has caused the feedback to increase a lot. Most likely a capacitor experiencing a significant decrease in internal resistance. The guitar sounds distorted because the opamp is being driven into clipping range as a result.

That sound is the same sound made by an old radio shack kit lie detector I used to have. The circuit would oscillate in proportion to the resistance of the skin of the person being tested - the more you sweat (lie), the higher the oscillation of the detector. My guess is the frequency of the oscillation is changing slowly over time because the bad part is either heating or charging or both, which in turn changes the feedback in the circuit.

Just a hunch . . .

Funkinthetrunk · #7 07-21-2011, 06:16 PM

Quote:

Originally Posted by Rob22315

If it's not the battery, it sounds to me like a resistor or capacitor has gone bad causing the circuit to oscillate because whatever's changed in the preamp has caused the feedback to increase a lot. Most likely a capacitor experiencing a significant decrease in internal resistance. The guitar sounds distorted because the opamp is being driven into clipping range as a result.

That sound is the same sound made by an old radio shack kit lie detector I used to have. The circuit would oscillate in proportion to the resistance of the skin of the person being tested - the more you sweat (lie), the higher the oscillation of the detector. My guess is the frequency of the oscillation is changing slowly over time because the bad part is either heating or charging or both, which in turn changes the feedback in the circuit.

Just a hunch . . .

Dude...why did you have to go all technical on us.

Rob22315 · #8 07-21-2011, 06:19 PM

Can't help it. I r an engineer. BTW its probably the battery

Ro(c)kBass · #9 07-25-2011, 02:20 PM

Thanks for the replays! It turned out the empty battery caused the noise after all. It was my first guess too, so I changed it but apparently the one I carried as a backup in the bass case was also empty. After your replays I changed it for a brand new battery just in case and the noise is gone