Ampeg BA 115 - busted power amp ?

[Gustav_over_net]

Hello,

Two days ago I was using my Ampeg BA115 HPT just fine.
Before upcoming gig I wanted to make sure my sound from DI out is set up nicely, so I plugged XLR from Ampegs Di out to my sound interface and played for a while.

I got the sound I was going for. It was a bit late and I wanted to play for a little longer, but also not to disturb neighbours, so I plugged a cable in headphone jack and plugged other end in another input in my sound interface.
No sparks, no loud noise, no nothin'. Amp just stopped working that second. No sound comes through when I play bas, neither to speaker, DI out, or to headphones.

Now when I turn it on, the main LED turns on but after a few seconds it slowly fades and goes dark. Timing of this matches, I think, Ampegs protection power up (amp was newer on 100% the second I turned the switch, it was always muted for a short moment and then went slowly up to match output with master volume dial)
Therefore I think its a problem with power section.
But is it really (headphone out does not work either, and it should use only preamp)? And if so, what exactly? Anyone else had similar problems? Or maybe preamp tube is damaged?

Things that may be relevant
- I did not unplug XLR cable before plugging another cable into headphone out
- cable from headphones went into HiZ powered preamp on sound interface
- both inputs on sound card were 48V since I recorded stuff with condensers that day and forgot to turn it off.

Thanks for any help or suggestions, especially if someone had this happened to them,
Gustav.

 

[LAPetrarca]

Hi.....

There's a thread here somewhere about an issue similar to this. I also experienced this myself.

There is most likely a power module in the amp head that is dead. It happened to mine a couple of years ago and, at that time, the Tech told me it was the single most common point of failure in class D amplifiers. I forgot what the repair cost me and it was still working as of a couple of months ago when I sold it.

 

[BogeyBass]

here is a schematic should be a good start

 

[DigitalMan]

Are you saying that you had an XLR cable from the DI output of the amp into your computers audio interface, and at the same time had a 1/4" cable from the amp's headphone output to another input on the audio interface?

 

[Gustav_over_net]

Hi.....

There's a thread here somewhere about an issue similar to this. I also experienced this myself.

There is most likely a power module in the amp head that is dead. It happened to mine a couple of years ago and, at that time, the Tech told me it was the single most common point of failure in class D amplifiers. I forgot what the repair cost me and it was still working as of a couple of months ago when I sold it.

Thats what I meant by writing about power section probably being busted
About that thread - I can't seem to find it, if you could throw me a link I would appreciate it.
If the problem is common that is good news, chances are it won't cost me an arm and a leg to fix this.
The thing is, Im not sure if we are talking about the same amp, I was almost sure that this combo is not a D class.

here is a schematic should be a good start

Thanks, if I read this correctly DI out seems to be in paralell with headphone jack, and it seems that connecting second disconnects first, although I'm not sure If I get this the right way.

Are you saying that you had an XLR cable from the DI output of the amp into your computers audio interface, and at the same time had a 1/4" cable from the amp's headphone output to another input on the audio interface?

That is correct. DI out was still connected when I connected headphone out to interface via 1/4" jack.
Did not think abut it to be honest, in the back of my head I had this idea that if master volume changes volume on DI out, and headphone jack disconnects power section, then using headphone out should also disconnect DI.
Given the effect, and that it was the last thing that I did before malfunction, I think I got this idea wrong.

Is that a common mistake that leads to my symptoms? If so, what is broken?
That would also be good news since I would much rather have this amp being busted by my stupidity than its lack of reliability

 

[BassmanPaul]

Sorry but it’s tech time!

 

[Gustav_over_net]

Sorry but it’s tech time!

umm, what?

 

[Crater]

umm, what?

What he's saying is that unless you have previous experience troubleshooting and repairing electronics, you'll be better off taking your amplifier to a qualified technician to get it repaired. If you can't read and make sense of the schematic that's posted you shouldn't attempt to repair your amplifier, in my opinion.

in the back of my head I had this idea that if master volume changes volume on DI out, and headphone jack disconnects power section, then using headphone out should also disconnect DI.

According to the schematic, NO. Plugging in the headphone doesn't mute the DI. In fact the headphone and DI outputs are in parallel, but with 270 ohm resistors in series with the DI outs. Plugging in headphones activates a muting circuit between the preamp and power amp. (That also means the left and right headphone outputs are OUT OF PHASE, because they're tapped right off the pair of op-amps used to drive the headphone output.)

Your amp is not class-D, it is a class A/B power amplifier with MOSFET power transistors.

 

[LAPetrarca]

Sorry but it’s tech time!

^ this.

 

[Gustav_over_net]

What he's saying is that unless you have previous experience troubleshooting and repairing electronics, you'll be better off taking your amplifier to a qualified technician to get it repaired.

Yeah, that's kinda what I felt he was saying.
I asked about the cause of the problem, probable damage and maybe costs of repair from someone with similar experience or just knowledge about this. Pretty straight forward questions if you ask me.
So then when someone drops by and writes "if it's broken it needs fixin' boy", -what?- is al I can ask really.

If you can't read and make sense of the schematic that's posted you shouldn't attempt to repair your amplifier, in my opinion.

I got right that DI out and HJ are in parallel didn't I ?
And also, I did not write anywhere that I want to repair this myself, so I don't know what leaves that impression

Plugging in the headphone doesn't mute the DI
Plugging in headphones activates a muting circuit between the preamp and power amp

So does this mean that if I plug headphones then DI will still be unmuted, cause thats what I am getting from what you wrote? COuld this damage anything?

Your amp is not class-D, it is a class A/B power amplifier with MOSFET power transistors.

Cool, so I know my hardware after all But that also means I am not getting any closer with answers :/

Thanks for all the replies so far, if anyone knows anything more let me know.

Gustav.

 

[BassmanPaul]

Gustav, meaning no disrespect, but when someone asks what could be wrong they ARE looking for a solution. That solution is not something that can be garnered across the internet. Add to that, iMHO, if you had the skills required to repair your amp you would have done it without asking for help from us. Thus I suggested a trip to a tech before you attempt a repair that you might well make worse. Folk who do tech work often come across units that an owner has done a botched repair. Often times that attempt increased the repair bill by a factor of ten or so.

 

[Gustav_over_net]

Gustav, meaning no disrespect, but when someone asks what could be wrong they ARE looking for a solution. That solution is not something that can be garnered across the internet. Add to that, iMHO, if you had the skills required to repair your amp you would have done it without asking for help from us. Thus I suggested a trip to a tech before you attempt a repair that you might well make worse. Folk who do tech work often come across units that an owner has done a bitched repair. Often times that attempt increased the repair bill by a factor of ten or so.

Now that I think about it, it may have actually looked like I was preparing to fix this myslef even thou I did not specifically state that.

I have a gig coming and I am also going skiing this week, so time is somewhat important.
Therefore a brief evaluation of what might be wrong, to know if its repairable by tech within a given amont of time and also if it won't exceed value of the amp itself, seems like a super reasonable question.
And besides that I just like to know what goes wrong when something isn't working, most importantly how much of my own fault is in this.

And its not like "how could anyone know anything about YOUR specific malfunction". Its not like I went skydiving with this amp or sth , I just plugged cables in them holes.
There are tons of cases when something is poorly designed, or parts known to fail in some conditions, and its all to be gathered form no other place than the internet. Are you sure this is not the case?
Even people writing that they have never experienced this with their amp, and they tried plugging both cables (which I do not recommend at this point), would be information. But so far I got nothing.

Still, thanks for replying and your time BassmanPaul
Gustav.

 

[Crater]

Using the headphones and DI at the same time shouldn't cause any problems. The headphones will not mute the DI. It's possible that using headphones will using the DI could affect the tone out of the DI, but it shouldn't damage any amp components. I don't think you connecting the DI and headphone at the same time directly caused this, I think it's an unfortunate coincidence. If the problem was only with the power amp section your DI and headphones would still work. The fact that the power light won't stay on makes me think your problem is in the power supply.

 

[agedhorse]

There's something about this amp that might be responsible for your symptoms.

First, does the DI work without the headphones plugged in?

If you try to use the headphones into a mono sound card input that ties tip to ring on the plug, you will get no output because tip and ring are out of phase (reversed polarity) and they will sum to zero.

Second, phantom power shouldn't matter if the schematic is correct.

If the red power LED dies out after turn-on, it has nothing to do with the protection as it monitors the low voltage power supply output only.

In this case, I suspect that your failure has nothing to do with what you did, and the first suspicion I would have is an intermittent power switch. Try switching it back and forth (with amp unplugged) to see if maybe the moving contact assembly is hung up. Otherwise, it's time for a tech to take a look at it, it should be an easy amp to service provided the tech is really qualified.

 

[Gustav_over_net]

Using the headphones and DI at the same time shouldn't cause any problems. The headphones will not mute the DI. It's possible that using headphones will using the DI could affect the tone out of the DI, but it shouldn't damage any amp components. I don't think you connecting the DI and headphone at the same time directly caused this, I think it's an unfortunate coincidence. If the problem was only with the power amp section your DI and headphones would still work. The fact that the power light won't stay on makes me think your problem is in the power supply.

Well then, at least I did not breake it.
I got the idea of how it works backwards so thanks for clearing that up.
That suspicion about power supply is also useful info.

Thanks for your patience Crater
Gustav.

 

[RyanOh]

I bought a BA-115 very cheap over the weekend knowing it was broken and hoping I could fix it myself. After a couple YouTube videos and searches, I opened it up...nothing obvious. I quickly realized it's tech time. There are too many possible issues and none of them I could fix.

I'll either have a fixed combo amp or a 15" speaker enclosure. Good luck on yours!

 

[Gustav_over_net]

There's something about this amp that might be responsible for your symptoms.

First, does the DI work without the headphones plugged in?

DI does not work.
Regardless of my actions the led indicating "power on" dies a moment after switching on the amp.

If you try to use the headphones into a mono sound card input that ties tip to ring on the plug, you will get no output because tip and ring are out of phase (reversed polarity) and they will sum to zero.

I also tried with simple headphones (ones I used before with this amp) but still no sound.

If the red power LED dies out after turn-on, it has nothing to do with the protection as it monitors the low voltage power supply output only.

That is good to know.

In this case, I suspect that your failure has nothing to do with what you did, and the first suspicion I would have is an intermittent power switch. Try switching it back and forth (with amp unplugged) to see if maybe the moving contact assembly is hung up. Otherwise, it's time for a tech to take a look at it, it should be an easy amp to service provided the tech is really qualified.

Thanks a lot for this info, I only have "universal radio-tv-all electronics" repair shops in my town, this would mean they may be up for this job.

Thanks agedhorse I will try with switching first thing tomorrow, thou even if it works I think someone should do a check before i gig with this amp again,
Gustav.

 

[Gustav_over_net]

Good luck on yours!

Thank you very much

 

[BogeyBass]

usually opamps dont go bad too often but if a phanthom power did cause damage if the opamp or maybe decoupling cap actually did fail in a closed failure. it would be a short and that would drag the 15 volt +/_ power supply probably down to 3/6 volts. I would start by just doing voltage tests on the 5532 ic opamp for the balanced out and a voltage test on the opamp for the headphone amp output. likewise any decoupling capacitor on the way out from those stages. any dc would have been blocked by a decoupling capacitor but say they are using 16 volt caps then 48 volt phanthom might have peeved one off a little lol if for whatever reason that happened, technically it shoudlnt but yah never know. and it pooped out in a short or closed state. also there is decoupling capacitors for the power supply rails on the opamps and usual practice is to keep those rather close to the opamp. so check them for visual damage. their little tin butts will be visibly slightly swollen if your lucky youll visually see the damage. so again if they are only decoupling those 15volt rails with bare minumum 15/20 volt cap they might failed too. need look at op amp data sheet and test voltage from transformer center tap ground point. and voltage directly at pin of the opamp +/_ power pins and see what those rails are for the little time it stays on

 

[agedhorse]

usually opamps dont go bad too often but if a phanthom power did cause damage if the opamp or maybe decoupling cap actually did fail in a closed failure. it would be a short and that would drag the 15 volt +/_ power supply probably down to 3/6 volts. I would start by just doing voltage tests on the 5532 ic opamp for the balanced out and a voltage test on the opamp for the headphone amp output. likewise any decoupling capacitor on the way out from those stages. any dc would have been blocked by a decoupling capacitor but say they are using 16 volt caps then 48 volt phanthom might have peeved one off a little lol if for whatever reason that happened, technically it shoudlnt but yah never know. and it pooped out in a short or closed state. also there is decoupling capacitors for the power supply rails on the opamps and usual practice is to keep those rather close to the opamp. so check them for visual damage. their little tin butts will be visibly slightly swollen if your lucky youll visually see the damage. so again if they are only decoupling those 15volt rails with bare minumum 15/20 volt cap they might failed too. need look at op amp data sheet and test voltage from transformer center tap ground point. and voltage directly at pin of the opamp +/_ power pins and see what those rails are for the little time it stays on

Or, a little knowledge makes somebody just dangerous enough to get hurt or to damage their otherwise repairable amp beyond repair.

You are grasping at straws here. The phantom blocking caps are clearly labeled as 50V, if there was something dragging the supply down it's unlikely to be obvious unless it's smoking smelly hot, and without some test equipment and the knowledge to use it, especially safety knowledge as the amp will need to be powered up for most testing purposes, your suggestion is IMO not a safe one for the OP.