B100R pop on shutoff

[mtlbasslad]

Hi all, back again thanks to admin tb.

The annoying noise at shutoff is rumored to be associated with the pilot light (at least on the Talkbass forum), where all I could get was "ignore it". Wish I could, but there must be a way (hopefully not including a relay) to prevent this ?

Let's see if I'm clever enough to attach the circuit diagram... (crossing fingers)

Cheers

[loudthud]

Wow, what a wacky power amp! Since there doesn't seem to be an effects loop, I'd like to know if the offending noise occurs when the Master Volume is all the way down?

[g1]

Disconnect it to test their theory. If the shut off noise goes away, it should be simple to find a different way to power the light.

[mtlbasslad]

@ loudthud - no, still pops with master at zero...

@ g-one - good idea... but "simple way" ?

Thanks both of ya

update - g-one, pulled a lead off the pilot light, no more 'pop'
Now, about that "simple way" ?

[52 Bill]

@ loudthud - no, still pops with master at zero...

@ g-one - good idea... but "simple way" ?

Thanks both of ya

update - g-one, pulled a lead off the pilot light, no more 'pop'
Now, about that "simple way" ?

Did you turn up the master again to test the pilot light idea?

[mtlbasslad]

@52Bill - yes sir I did, as an ex computer programmer I'm fairly logical & meticulous... (I like to think so anyway LOL)

Bonus, noticed one of the famous 'fallen off port tubes', so I used some latex caulk on both of them. Guess I should check out my other B100R (yes, I have two) for the same problem.

So, any kinda 'just put a (insert part here) between (insert where here) solutions' come to mind?

Hoping Enzo checks in soon, he has been so kind to me in the past.

I can't say it enough, how I appreciate the wisdom & the patience you people have. I salute you all.

[Enzo]

Oh, I am here, thanks for the kind word. I just didn't have anything to add, everyone else has already covered it.

[mtlbasslad]

Hi Enzo, you help so many people that you have probably forgotten helping me about 4 years ago with a Harmony H303 - but i haven't.

So I just have to live with this annoying noise? Seems a pity for such an otherwise great amp...

I know there is a relay-based solution to this, was hoping for something simpler (or anything). I get ugly looks from bandmates (never mind wife) when this happens. My (our) other amps don't do this, so I assume it's something particular to this circuit. Other amps these days are Joanie's GK, Ampeg J-12T(RI), Mesa DC3...

Hope you are well, up here we use amps as supplementary heating below -30 LOL

[loudthud]

Since the pop still occurs with the Master down, that eliminates any cause in the preamp. I looked on TalkBass and didn't see the thread there (please provide a link) but I did find one talking about how the pilot lights seem to burn out alot. Apparently they are a 28V incandescent bulb. The pilot light just plugs on to the PCB with some faston connectors, you can just disconnect one wire (don't let it touch anything else) to test if it is the cause of the pop. Be sure to unplug the amp from the mains while you are working inside.

[mtlbasslad]

@ loudthud - yes did that disconnect & the pop (more like a crunch) is gone. Appreciate your concern for my health, I'm not exactly a virgin LOL. I know what big caps can do...

It will take me a while to find the TB link, not much info there anyway. About the burnout, I seem to remember someone saying that bulb got 36v from the circuit (when I say remember, temper that with the fact that I'm almost 67...) Some also suggest it's an LED - some may be confused...

Just wondering what the interaction could be, curious minds (even old ones) want to know...

Cheers, Lorne

[J M Fahey]

I started incredulously reading about the "Indicator Light" problem ... a power on/off thump cause by a pilot light? ... that's crazy !!!

Then I noticed the huge 220 ohms 2W resistor in series with it and said WTF?

What on Earth do they use that needs so much power?

The schematic says nothing about it and I was about to suggest you to take some picture showing the mystery component.

Then I read the comment about the airplane specs 28V bulb (I guess an amateur Pilot specified it, no kidding) which of courtse will burn a lot with +40V rail, combined with vibration (bass combo).

I suggest you junk it, replace it by a clear high intensity red LED, rise padding resistor to 2K2 - 1W, and sleep like a baby.

By the way, I also suspect very poor grounding choice for that indicator, so run the grounding wire "floating", straight to PSU ground, the pad or area between both large filter caps C33/C34 .

No way it will pop after reducing current by 90% and properly grounding it.

I also suspect (never saw one in the flesh), that the original 28V bulb screws/bayonets in some kind of socket, with some crimped connections.
Them, or dirty socket/mating surfaces can also create a "prrrrttt" kind of noise ... which you will completely avoid by soldering the LED.

Try it.

[Enzo]

And aside from the cures, and I have to agree that an LED is probably the way to go, remember that unless I misunderstand, this is only a pop at turn off. In other words it doesn't happen while playing. I can appreciate it might be an annoying thing, but it is just a turn off pop. It won't hurt anything, and the audience will never hear it.

And I am also having a hard time coming up with an explanation why this bulb would cause any audible symptom.

[loudthud]

Here's the thread I found: Ampeg B100R (2005) power light bulb out - a DIY repair? | TalkBass.com

The thread has a pic of the pilot lamp assembly, you might have to be logged in to see it. I didn't see anything about a turnoff pop. Perhaps the bias is set wrong and the imbalance of the pilot light causes the +40V to collapse too fast. The pilot lamp assembly is simply a blue plastic piece with a 28V grain of wheat bulb glued in the end.

[mtlbasslad]

Thanks too all of you for responding, warms the cockles of me heart LOL (I'm Scottish, don't ye know)

Mr Fahey, I think you might have the solution here, kinda neat that it's coming from the other side of the world. Wish I fully understood your solution, I'm a bit over my head here...
If i understand correctly, bump up the resistor from 220 ohms to 2.2K and move the ground? Not sure what the ground issue is, can you elaborate? Any particular type of LED ? Also "clear high intensity RED LED" confuses me - perhaps because most pilot lights are red? In the Ampegs they are blue, but in this case it's a clear bulb in blue plastic holder. We live in the woods, an hour away from any electronic stores (Google Gratten Lake, Rawdon Quebec Canada J0k1s0) so it will take some time to source the parts. Then I will be able to try out new Weller soldering iron eldest son got me for Christmas. I will let you know how it works out.

@loudthud - thanks for hanging in there, there is another thread on TB about pop, shucks - I might have started it (memory is something I used to have more of)

@Enzo - glad you are here... don't want to seem like a whiner, but it really is disturbing when my 2X B100R rig shuts down since killing the volume does nothing...

I will faithfully report on progress,

Cheers, Lorne

[mtlbasslad]

@ loudthud - bias in a SS amp? now you are scaring me, I (pardon my ignorance) thought bias was in the realm of tube amps only (like the stolen '66 B15N & '65 fender Super Reverb I still cry about late at night) can you educate me? I'm old, but I can still learn...