Ampeg BA115HP buzzz

[drewl]

Dang, just wasted an hour swapping out what sounded like a bad tweeter on this ampeg combo, but the high frequency "buzz" is coming from the amp.
It's got a crossover and a rheostat to control levels to the tweeter, back it down buzz goes away, tweeter right?
BZZZT incorrect.

Front grill didn't want to come off-

Swapped tweeter, buzz still there-

Thought maybe it's the crossover so I
pumped another amp into it and it's fine.
Something in the amp.
I'll let you know when I find it to save you guys the same hassle.

[booj]

Is the buzz always there, or does it only buzz when there is a signal present?
If the buzz is always there, maybe it's a power supply component that needs a solder re-flow, or some loose component or ground connection.
If it only buzzes with a signal, maybe the jack is in need of a re-flow.
Either way it could maybe use some TLC, in the form of checking with a chopstick, cleaning all the jacks, connectors and controls, and re-flowing the heavier power supply parts and the jacks.

[drewl]

There's some clipping/distortion on the top half of the sine wave.
After reading some threads here, I checked the bias- it was at 0mv, so I set it to about 10mv across each of the .33ohm resistors (that is what they mean right?) and the distortion is gone.

I'll check it out when I get home from work, and will probably pull boards out, check/reflow pc board connections.

[AtomicMassUnit]

Is it definitely a buzz and not a hiss? Every one I've heard had a ton of hiss coming out the tweeter.

[drewl]

nah, it was a buzz that would follow the note and then fade out.
It was definitely the bias set too cold, it's sounding fine now.

[Jazz P Bass]

I am happy that you have it working.
What does not make sense is 'adjusting the bias hotter' fixed it.
Too cold of a bias (ie: Class B) will present extreme crossover distortion.
It was posted that the top half of the sine wave clipped before the lower half.
That is not 'crossover' distortion.
Any way, glad it is working.

[jrfrond]

It's a common malady with that POS. We've chased the ghost in several of them, and wound up replacing the amp PCB. It was cheaper and quicker. Ampeg has no answer for this issue.

[drewl]

The board physically doesn't look like a bad design.
Who knows what cheap metal they're using for the chassis, I'm seeing rust on alot of new amps made overseas lately.

Anyway, it looked like a crossover distortion, but on the top trailing edge of the sine wave on the output.
Thought I might be measuring the bias wrong, as I was getting no reading across any of the .33ohm resistors until I turned up the bias a bit.
I kept it on the low side, 10mv, just enough to have a nice clean output, didn't want to bias it too hot and have it come back blown up.

From what you guys are saying, it doesn't sound like this is a well designed amp.

Thanks.

[bstager]

I had the same buzzy noise whenever I played a note on my bass. Definitely the bias control. It acted like a dirty pot -- you know, like whenever a volume control gets scratchy -- only this pot controls the DC bias on the output FETs. With the amp off, I turned it back and forth a few times, which caused the "cold" bias to jump up to 50mV or so when I turned it back on, then I simply dialed it in per the specification (15-20mV). Soblem prolved! BTW, of course I checked the woofer and tweeter first. All was fine mechanically. This amp is NOT a POS! Very well built: heavy, die-cast tweeter, T-nuts on woofer, actual passive crossover on separate PCB inside cabinet. I love it!

[JimboS]

I just wasted an afternoon on one of these. Ordered a new tweeter, no change. Dived into bias adjustments - turns out there's a sweet spot between the amp sounding crap, and all the Fets blowing up. Went through about 8 of the little bastards,amp finally good; except for one note farting...
Turns out the buzz was the Lpad at certain frequencies -The wiper making poor contact sounds exactly like a tweeter crapping itself

[JimboS]

Errr, scratch that previous post. Soldering on the protection lamps was bad.

[dm4003]

Hi all, I'm new to the forum. I signed up because I have the same problem with my Ampeg BA-115 HPT. How would I check/set my bias? What equipment do I need, and where do I find the bias control on this amp? Thanks

[52 Bill]

Hi all, I'm new to the forum. I signed up because I have the same problem with my Ampeg BA-115 HPT. How would I check/set my bias? What equipment do I need, and where do I find the bias control on this amp? Thanks

Welcome to the place. What exactly is the problem with your amp? There are many reasons for amps to not work correctly and what fixed one amp may or may not fix another one.

Adjusting the bias on this amp is not something to be experimented with. If you mis-adjust it, you can cause major problems with the power amp and do some real damage.

[dm4003]

Welcome to the place. What exactly is the problem with your amp? There are many reasons for amps to not work correctly and what fixed one amp may or may not fix another one.

Adjusting the bias on this amp is not something to be experimented with. If you mis-adjust it, you can cause major problems with the power amp and do some real damage.

There is a buzz/hiss behind notes played. No noise without a signal though. It sounds just as others on this thread have described. I thought it might be the tweeter at first but I can tell it's not. There is also a loud pop from the speaker when the amp is turned off.

[Sound_Techs_United]

Solution to the Buzzing issue on the Ampeg BA115 hpt.

Dang, just wasted an hour swapping out what sounded like a bad tweeter on this ampeg combo, but the high frequency "buzz" is coming from the amp.
It's got a crossover and a rheostat to control levels to the tweeter, back it down buzz goes away, tweeter right?
BZZZT incorrect.

Front grill didn't want to come off-

Swapped tweeter, buzz still there-

Thought maybe it's the crossover so I
pumped another amp into it and it's fine.
Something in the amp.
I'll let you know when I find it to save you guys the same hassle.

DISCLAIMER:!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I am not a professional, I just tinker alot and I get results after many failed attempts. Make sure you all take precautions on how to make sure you do this safely and make sure you are not connected to an outlet. Do not kill yourself, and keep in mind that even if you are not plug to the wall outlet, amps do carry current via capacitors, which can harm or even kill you. Be advised! do this at your own risk. I am not responsible for you or any thing that may or may not happen to you. :!!!!!!!!!!!!!


Hey all, I am a repair maintenance tech at a rehearsal studio in Queens. I have noticed that Everytime I am looking for the solution to this issue with the buzzing I could never find the answer. So after many many attempts of fixing this particular amp here at the rehearsal studio shop. I came up with a couple of answers that have helped me to resolve this issue in the past. So here are some of the answers, (don't bother asking me technical questions, I'm just a repair maintenance kind of guy, not an electronics engineer)




1) You have a bad Bias Pot,
a) You can replace this pot, but before you do, first thing you can do that helped was just to bring the trim pot down. It may mean that your signal is too hot and is causing it to distort.
b) If bring the trim pot down does not work, then you may want to take needle nose pliers and squeeze the pot from underneath and the top. This actually has helped me a couple of times, because i am assuming it is because of all the rattling from the bass amp, that it may have messed with the internal part of the bias component. Sometimes squeezing it together will work.
c) Retouch the solder points of the Bias pot. Sometimes you will get cold points that just need retouching.




2) You have bad IC circuits
a) Believe it or not, I had bad IC circuits.. I believe the ones that solved my issue were the NE5532P ICS on the pre amp board and the power board. Replace them.

or

B) Retouch the them. It could mean that the IC chips are ok, they just have cold spots that need reflow.





3) Tweeter

a) Measure and see if tweeter needs replacement. I've personally never had to, but it is still an option.


Guys, thats it for now... If you wanna follow me on instagram... look me up.. Soundtechsunited.
Peace