# '80s Yamaha bass amp



## Sketchy Jeff (Jan 12, 2019)

yesterday i picked up an old bass amp - Yamaha B100-115ii 

well, "picked up" is a bit of a euphemism, it's about the size of a doghouse and must weigh 120lb or more

not much for high end but low end loud and clean wow so as long as it can stay somewhere where it can roll around and no need to haul anywhere it should be good for the few dollars i spent

question is this - i played it for a while last night and every five or ten minutes it makes a sound as if somebody quietly belched into a vocal mic. i don't seem to be able to make it do that or change how often it does it. it's not loud but happens often enough that i might not want to use it live even if i did feel like loading it up to haul somewhere. it's louder as i turn the volume up but not proportional to how loud the signal is - the noise is slightly louder when the instrument sound is much much louder. the the building i was using it in doesn't have the most well grounded electrical system so it's possible the power is a bit dirty although my other equipment doesn't make similar sounds in there. anything ii should check into that might be causing that noise?

j


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## greco (Jul 15, 2007)

Sketchy Jeff said:


> ...well, "picked up" is a bit of a euphemism, it's about the size of a doghouse and must weigh 120lb or more





Sketchy Jeff said:


> ...it makes a sound as if somebody quietly belched into a vocal mic


Thanks for my laugh(s) for the day.

I realize the sound must be annoying but I could clearly imagine the descriptor "quietly belched"

I will be following your thread as these electronic troubleshooting threads interest me very much.


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## bw66 (Dec 17, 2009)

Congrats on a great find. I have a B50-115 which I love (as long as I don't have to move it - also a beast at around 75 pounds, no wheels).

I suspect that it is picking up electrical interference from something in your house that turns on or off periodically. Have you tried plugging it into a different circuit - preferably on the opposite phase from the one you're currently plugged into?


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## nonreverb (Sep 19, 2006)

Sketchy Jeff said:


> yesterday i picked up an old bass amp - Yamaha B100-115ii
> 
> well, "picked up" is a bit of a euphemism, it's about the size of a doghouse and must weigh 120lb or more
> 
> ...


Are the pots dirty when you turn them?


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## Paul Running (Apr 12, 2020)

Does it sound like this:


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## Paul Running (Apr 12, 2020)

Here's the service manual. You may wish to check the cal. on it first. There are 3 adjustments to calibrate this beast, all are on the MA board: bias, the null adjust and the waveform adjust.


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## Sketchy Jeff (Jan 12, 2019)

pretty much yes maybe a bit more low end and cut the treble


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## Sketchy Jeff (Jan 12, 2019)

nonreverb said:


> Are the pots dirty when you turn them?


It's not too bad. But they do crackle a little bit and like every piece of 80s gear stinks like stale cigarettes and pot. I want to get in there with some deoxit before I use it for anything else. I'm going to try that first before I dig further into the belching sound


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## Sketchy Jeff (Jan 12, 2019)

Paul Running said:


> Here's the service manual. You may wish to check the cal. on it first. There are 3 adjustments to calibrate this beast, all are on the MA board: bias, the null adjust and the waveform adjust.


Thank you sir. Calibrating it might be a little bit above my paygrade but I'll ask around and see what I can figure out.


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## Mooh (Mar 7, 2007)

Cool. I used '70s and '80s Yamaha bass amps back in the...well, '70s and '80s. Usually ended up replacing the speakers, but otherwise they took a licking. Wish I had one of them still.


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## Latole (Aug 11, 2020)

Thank's for the service manual Paul Running.
I was at Country Squier Motel, Armprior yesterday night

I would replace the 4 filter caps. They are cheap and old caps are probably dry


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## Sketchy Jeff (Jan 12, 2019)

bw66 said:


> picking up electrical interference


well you win the prize and i get to feel a bit dumb

the burping sound comes from my phone checking in with the internet

i'm an idiot because my other two old amps both do the same thing except with the EQ of guitar amps the sound is much higher frequency - a high buzzing sound - instead of the super low sound. i guess the difference comes from sending what i assume to be a sort of full frequency digital RF signal through EQ of the bass amp

so i was looking around for an answer that was already in my pocket

my newer traynor YCV doesn't do it unless the phone is sitting right on the amp case so i assume it's shielded better/differently than the '80s JC-55 and '70s' Peavey head cuz those older ones do it if the phone is within 15'

j


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## greco (Jul 15, 2007)

Sketchy Jeff said:


> the burping sound comes from my phone checking in with the internet.


Great that you now know the cause of the "belching".

The fact that you were walking around with the source of your problem in your pocket was good for another laugh. (Please forgive my warped sense of humour)


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## Paul Running (Apr 12, 2020)

Sketchy Jeff said:


> the burping sound comes from my phone checking in with the internet


Becoming a very common problem now both EMI and RFI, soon all amps will require Faraday shields surrounding all the electronics to suppress all these unwanted signals.


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## Paul Running (Apr 12, 2020)




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## bw66 (Dec 17, 2009)

Sketchy Jeff said:


> well you win the prize...


Even a blind squirrel...


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## Sketchy Jeff (Jan 12, 2019)

bw66 said:


> Even a blind squirrel...


here's a a rabbit hole for the blind squirrel to fall into

my old amps pick up noise from my phone and sometimes other sources but i know about it and got used to dealing with it. when i use them live it's not a big deal. i've never once in all the years i've played on stages had anybody say they enjoyed the show except for the ambient noise in the PA. I guess that's not quite true. I once had a combination of guitar cable and a Ross amp that would pick up the local country station loud and clear and that was a problem. 

for those of us of a certain age, part of the excitement of going to a show involves those few seconds when the house lights go down and it's all dark and then there feels like a hum of excitement in the air just before the lights go up because there is a hum of excitement in the air - it's the buzz of the sound guy turning the mains up. And then if you stick around after the show and people leave and you think it's quiet in the room and then there's that thump of the PA amp getting turned off and after that it really is quiet in the room so you can hear your ears ringing and the event is over and it's time to go home.

if you listen to some really great live albums one thing that jumps out is how much sound system noise there is. one of my favourite albums live or not is the Brazilian singer and guitar player Geraldo Azevedo's live album Ao Vivo. It's really quiet arrangements and you can hear the big crowd singing along with him. The PA hum is incredible but in its way it adds to the vibe rather than detracting from it and they use it as part of the arrangement for the live tracks

Here's the opening track from the evil overlords at spotify






i guess this isn't really amp repair technical discussion except for whether or not to worry about the different thumps and buzzes that older gear puts out

j


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## Paul Running (Apr 12, 2020)

Gotta love those hums and buzzes, it removes the sterility, adding realism...ideal is too simple.


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