Newbie - How much damage did I do?

[oops i did it again]

Hi all. Thanks for being out there.

Disclaimer: I like to tinker and have no training in electronics. So I'm sorry if any vocabulary in this post is dead wrong. Also, I did this on an amp I got for a hundred bucks. I'm dumb, but not dumb enough to try this on a nice amp.

So here's what happened. I've attached a picture of the current status in case it helps.

I have a Bloc 80B bass amp from sometime in the 80s. It was making an awful buzzing/rattling noise on low pitches. I opened it up and discovered that:

1) the tab that connects the wires from the cone with the wires from the amp had come loose from the metal frame of the speaker. I assumed it was banging against the cone and making the noise.

2) one of the wires from the cone had snapped, probably when I pulled the speaker out.

I soldered the wire back together and wrapped it in electrical tape. Then I glued the tab back in place with epoxy. It was very ugly, but when I put the amp back together and played it the rattle was gone. Mission accomplished.

But there was a little distortion on the bottom end when the volume was up high, and a pretty loud hum when the amp was on with no instrument cable plugged in. It reminded me of the sound of an ungrounded turntable. So I decided to open it up again. At which point:

the soldered wire came apart again, thanks to my crappy soldering skills. I resoldered it, then wrapped it in tape again.

The hum was still there. I noticed that the tab I'd glued back in place had originally been connected to the metal frame around the speaker cone. I thought maybe those were supposed to be connected as a kind of ground. I grabbed some copper wire that came with a light fixture and tried to connect the two pieces. I fiddled around connecting the snapped tab to different parts of the metal frame around the speaker cone. Sometimes the hum went away. It was difficult to get it away consistently. So:

1) I soldered one end of the copper wire to the metal frame around the speaker cone.

2) I held the other end of the wire to different parts of the metal tab. The hum went away.

3)I plunked a note on the bass (I suspect this wasn't a good idea while holding the wire in place, but there you go). It was very distorted and much quieter than it should have been with where the volume was set.

4) I looked at the copper wire. It was lying across both terminals (black and red) on the tab. "That's probably not good," I thought.

5) I took the copper wire completely off and plunked again. No sound from the amp. I turned it off and back on. It came on, but was still badly distorted.

5) I plugged some headphones into the amp and plunked once more. Same distortion through the phones.

That's the story. Does anyone have any idea of how bad this is and whether it's possible to repair? I'm afraid I've turned a pretty decent home repair into a fried circuit board.

Thanks for reading all this, and for any help you can offer. It's a long post, but I wanted to get all the facts out there.

Thanks,
Pete

[Enzo]

Hi Pete
Where are you?

Look up speaker reconing for someone in your area that does that. Take your speaker to them and have them repair the damage.

The tiny ultra-flexible wires from those terminals back down to the cone are called "tinsel wires." Looks like you need a new terminal strip and replaced tinsel wires. if the speaker otherwise works, you may be OK. They may have to remove the dust dome and replace it to get at the tinsel wire terminations, don;t know. The dust dome is the thing in the center of the cone.

The reconer will be able to tell you if the rest of hte speaker is OK or not, and what would have to be done to it, and what the cost would be.


And if you have no local reconers, you can always send the speaker to one.

[Jazz P Bass]

I have zero experience with this amp.
Some amplifiers have short circuit protection built into the output stage.
The output stage drives the speaker.
If this amplifier does not have the protection, you just may have toasted your output stage.
The fact that it is not blowing fuses is a good sign.
Then again, the distortion you hear may be the speaker.
I think hum went away, when you where touching things with the wire, because you where grounding out the output. (BAD THING)
The fact that it hums & now it is distorted tells me it is time for a trustworthy tech to have at it.

[oops i did it again]

Thanks, guys. I was afraid I'd done something unpleasant. @Jazz P Bass, it actually doesn't hum anymore. The only sound that comes out is distorted bass. If that changes your opinion...

Honestly, it sounds like it's time for a professional to look at it (and probably tell me the repair will cost me more than I paid for the amp). Thanks again!