Blown Ampeg crossover?
Christine Dobbins
We are a very loud band. Our bassist uses a G&L L2000 into a newer (1999 or
so) Ampeg SVT3, and that into an Ampeg PR410HLF - the big 4x10 with the horn
in the middle and ports on the bottom. We play out between one and five
times a month, which isn't professional by any means, but enough so our gear
gets moved around a lot. Everybody's stuff is starting to look a little
rough around the edges.
Last year, she blew the horn in the cab (a Fostex 025H27, 1" VC, 150W), and
we replaced the diaphragm on the recommendation of the guy at the Bass Place
in Tempe, AZ. It worked fine for a while, until a couple of weeks ago when
we started having problems again. It's a crackly, rattling sound that goes
away when you disconnect the horn or turn it all the way down on the back of
the cabinet (but then, of course, you lose that high end spank as well). We
bought another diaphragm, installed it and are still getting the same sound.
I pulled the tweeter from the SWR workingman's 15 we have, and tried it in
the Ampeg cabinet and the rattling sound was even worse. Just to be sure
(after exceeding its power rating), I reattached the tweeter to the
workingman's 15 and could not get any kind of rattle out of it, no matter
how high I cranked the high end and transparency knobs. So, this leads me to
believe that the problem is originating with the crossover. Has anyone had
the same or a similar experience with Ampeg, or for that matter, any other
crossover where the lower speakers sound fine but the horns/tweeters sound
blown? Is the crossover even the problem, or is there something I'm
overlooking?
I know this was a little long, but I wanted it to be descriptive.
Todd H.
> Okay, here's the situation...
>
> Last year, she blew the horn in the cab (a Fostex 025H27, 1" VC, 150W), and
> we replaced the diaphragm on the recommendation of the guy at the Bass Place
> in Tempe, AZ. It worked fine for a while
This is key. It worked fine for a while after the new compression
driver. Through whole practices even. Hrmm.
> , until a couple of weeks ago when we started having problems
> again. It's a crackly, rattling sound that goes away when you
> disconnect the horn or turn it all the way down on the back of the
> cabinet (but then, of course, you lose that high end spank as
> well).
So reducing power to the horn makes the signal and the noise go away.
Was the noise the same as you got when the horn blew at first?
> We bought another diaphragm, installed it and are still getting the
> same sound.
New diaphragm now this time doesn't fix it. Makes you wonder if the
first replacement was a red herring. I could have just as easily been
some other variable that changed during the replacement. Temperature,
cabinet position, different cord being used, who knows.
> I pulled the tweeter from the SWR workingman's 15 we have, and tried
> it in the Ampeg cabinet and the rattling sound was even worse.
At least now we're consistent. :-)
> Just to be sure (after exceeding its power rating), I reattached the
> tweeter to the workingman's 15 and could not get any kind of rattle
> out of it, no matter how high I cranked the high end and
> transparency knobs.
Ok, workingman 15 horn not the problem. Probably the new compression
driver is fine to.
> So, this leads me to believe that the problem is originating with
> the crossover.
Rattling or cracking from a passive crossover in a speaker cabinet
would be unusual. There's simply not much to go wrong there, and
there really isn't an obvious failure mode that could switch enough
current or swing enough voltage to cause crackly. Debris in the
potentiometer rattling around with the low frequency driver shaking
the cabinet is the best hypothesis I could lodge in that scenario.
While you've done some excellent diagnostic work, there are several
more likely components that I can't tell we've eliminated yet.
Have we ruled out instability in the amplifier itself? Have you
tested the same cabinet with another amplifier? Have you tested the
same setup with another bass? Is the same instrument cord involved by
chance? When I hear crackly, I first suspect a cord, then a bad
potentiometer or loose connection in the instrument or preamp.
Quickly you could get down to possibly isolating a problem with the
cabinet...or eliminating it as a source of the problem.
Happy troubleshooting!
--
Todd H.
http://www.toddh.net/
Christine Dobbins
Thank you for your responses.
To answer your questions...
> > , until a couple of weeks ago when we started having problems
> > again. It's a crackly, rattling sound that goes away when you
> > disconnect the horn or turn it all the way down on the back of the
> > cabinet (but then, of course, you lose that high end spank as
> > well).
>
> So reducing power to the horn makes the signal and the noise go away.
> Was the noise the same as you got when the horn blew at first?
Yes. It's the same sound, really nasty.
>
> > We bought another diaphragm, installed it and are still getting the
> > same sound.
>
> New diaphragm now this time doesn't fix it. Makes you wonder if the
> first replacement was a red herring. I could have just as easily been
> some other variable that changed during the replacement. Temperature,
> cabinet position, different cord being used, who knows.
Well, like I said, we've played out a bunch of times on the new driver, in a
lot of environments and at a lot of temperatures. We've even moved to a new
practice facility. She was having problems with the Speakon to 1/4" adapter
on the back of her amp a few weeks ago, just before we started hearing these
driver problems. She got rid of that and is now just running 1/4" to 1/4",
but using the same speaker cable. However, I'm reluctant to think that it's
the speaker cable (although I will try it out this evening) because the
crackly sound goes away when the driver is either not connected, or turned
down all the way.
>
> > I pulled the tweeter from the SWR workingman's 15 we have, and tried
> > it in the Ampeg cabinet and the rattling sound was even worse.
>
> At least now we're consistent. :-)
>
> > Just to be sure (after exceeding its power rating), I reattached the
> > tweeter to the workingman's 15 and could not get any kind of rattle
> > out of it, no matter how high I cranked the high end and
> > transparency knobs.
>
> Ok, workingman 15 horn not the problem. Probably the new compression
> driver is fine to.
We think so too. Unfortunately, before I tested the new driver, I put the
old one in the package and wrote "blown" on it, meaning we can't take it
back (sometimes we all do dumb things).
>
> > So, this leads me to believe that the problem is originating with
> > the crossover.
>
> Rattling or cracking from a passive crossover in a speaker cabinet
> would be unusual. There's simply not much to go wrong there, and
> there really isn't an obvious failure mode that could switch enough
> current or swing enough voltage to cause crackly. Debris in the
> potentiometer rattling around with the low frequency driver shaking
> the cabinet is the best hypothesis I could lodge in that scenario.
>
> While you've done some excellent diagnostic work, there are several
> more likely components that I can't tell we've eliminated yet.
>
> Have we ruled out instability in the amplifier itself? Have you
> tested the same cabinet with another amplifier? Have you tested the
> same setup with another bass? Is the same instrument cord involved by
> chance? When I hear crackly, I first suspect a cord, then a bad
> potentiometer or loose connection in the instrument or preamp.
Well, we ran the head into an older peavey cabinet (I don't know the model)
with 1x18" and 2x10" speakers and were getting some nasty distortions two
months ago or so. But other than that, we haven't really run the head
through any other cabinet recently, or the cabinet with any other head. All
our friends in bands use combo amps, so we don't really have the resources
to try out a lot of different stuff.
>
> Quickly you could get down to possibly isolating a problem with the
> cabinet...or eliminating it as a source of the problem.
>
Reading the additional symptoms I have listed in this reply, it seems that
there is some evidence that the head is malfunctioning, not the cabinet.
However, it just seems strange that we wouldn't hear any rattles or crackles
through the 10" speakers, but only through the horn. One thing I have not
tried that I also thought of was to connect the ampeg horn to the tweeter
leads for the SWR. I doubt I will hear anything, but at least then, I will
be positive sure the horn is not the problem.
Thanks again for your insight, and I look forward to hearing any additional
comments you might have.
Andrew Cooke
[...]
> Rattling or cracking from a passive crossover in a speaker cabinet
> would be unusual. There's simply not much to go wrong there, and
> there really isn't an obvious failure mode that could switch enough
> current or swing enough voltage to cause crackly. Debris in the
> potentiometer rattling around with the low frequency driver shaking
> the cabinet is the best hypothesis I could lodge in that scenario.
You know more electronics than me, but couldn't it be the capacitor in
the crossover? It could be doing nasty things at higher voltages
(volumes), but behaving OK at lower voltages. I don't know anything
about crossovers, but old electrolytic caps in power supplies can be
responsible for horrible (and intermittent) crackling noises. Would
there be an electrolytic cap in a crossover? Do other constructions
fail in similar ways?
Doesn't explain the first failure, but perhaps that really was just the
horn going bad.
Just a thought,
Andrew
PS There's also a usenet group called something like
sci.electronics.repair, which is supposed to be useful (never used it
myself).
mark@xush
Active ones? I've heard that kind of distortion from active electronics
when the gain is pushed too high...crackle thru the horns...
sorry if I'm overstating the obvious here.
mark
xush studios
"Christine Dobbins" <chdo...@worldnet.att.net> wrote in message
news:4VAG7.177591$W8.59...@bgtnsc04-news.ops.worldnet.att.net...
Todd H.
>
> Well, we ran the head into an older peavey cabinet (I don't know the model)
> with 1x18" and 2x10" speakers and were getting some nasty distortions two
> months ago or so.
Hrmm.
> Reading the additional symptoms I have listed in this reply, it seems that
> there is some evidence that the head is malfunctioning, not the cabinet.
> However, it just seems strange that we wouldn't hear any rattles or crackles
> through the 10" speakers, but only through the horn.
If the noise being generated is high frequency primarily, the
crossover by its very design would route that high frequency noise
only to the horn. For instance, you never hear much hiss through your
10" speakers I bet.
> One thing I have not tried that I also thought of was to connect the
> ampeg horn to the tweeter leads for the SWR. I doubt I will hear
> anything, but at least then, I will be positive sure the horn is not
> the problem.
> Thanks again for your insight, and I look forward to hearing any
> additional comments you might have.
I might be tempted to take the amp to your local ampeg dealer and plug
into a brand new cabinet that's similar to yours. That would also be
diagnostic.
Todd H.
>
> You know more electronics than me, but couldn't it be the capacitor in
> the crossover? It could be doing nasty things at higher voltages
> (volumes), but behaving OK at lower voltages.
Certainly possible.
> I don't know anything about crossovers, but old electrolytic caps in
> power supplies can be responsible for horrible (and intermittent)
> crackling noises. Would there be an electrolytic cap in a
> crossover? Do other constructions fail in similar ways?
Ah...good datapoint. I can add that I have seen non-polarized
electrolytics in crossover networks, so you may be on to something
here. Caps do go bad all the time, but I personally haven't run into
a crackling one, but then again, I don't do much repair or tinkering
anymore.
> PS There's also a usenet group called something like
> sci.electronics.repair, which is supposed to be useful (never used it
> myself).
There are some scary good people that debug this stuff for a living
over there. Highly recommended. Try a deja.com search of that group
for "crackling" and "speaker." Sam Goldwasser has an extensive
repair FAQ as well that's just incredible. Search for "electronics
repair FAQ" to find it.
Parke J. Shissler
Just a thought, and I may be entirely wrong here, but have you used
other instruments with this amp and experienced the same thing? If the
capacitor on the crossover could fail, it could equally be the capacitor
on the tone-control of the bass.
I just had a treble potentiometer replaced on one of my basses and was
experiencing the same type of crackling/popping, luckily it only
happened when I turned the control...but I can readily believe that the
vibrations of the bass itself could induce vibrations which could
trigger the problem as well.
Christine Dobbins
the SWR, ended up getting so trebly that my ears are still ringing - but no
crackle, no dirt whatsoever. So it's definately not the horn.
After that, I hooked the horn back up to the Ampeg cabinet, and swapped out
the speaker cable for one off my guitar rig, still heard the same crackle
and rattle. So, I hurriedly packed up the head and ran down to the Bass
Place, and hooked it into a very nice new Ampeg Classic 4x10 with a horn and
ports on the bottom, and got a very nice sound. I plan on recommending our
bassist check out that cab once she gets back in town.
So, that successfully eliminates the head, the cables, the bass, and the
horn. The only thing left in the signal chain is the crossover. I removed it
from the back of the cabinet, and I must say, it's almost as if Ampeg
anticipated the thing blowing out - the speakers all connect to the PC board
using a keyed connector (meaning it will only connect to the board one way
and one way only, unless you start breaking plastic) , similar to what you
might find if you were putting a PC computer together from component parts.
So, I popped that off and examined everything I could visually, and could
not find any kind of burn marks or any loose connections.
This leads me to believe that - lo and behold! - there's got to be some
debris in the potentiometer controlling the volume lead to the horn, either
that or it's gotten bumped the wrong way one too many times. So, Mr. H., you
were correct! I pat you on the back sir!
Okay, once again, much detail was added for the benefit of the archives or
anyone else who may have been following this thread. Our band just moved to
a new practice facility, as I mentioned previously. The new place is a
storage complex with gravel roadways between the rows of sheds. Our old
complex had newly paved roadways, and we have noticed a significant
difference in the amount of dust and dirt that accumulates on our gear in a
very short amount of time at the new place. If I knew better how to sew, I
would craft for myself and my band mates custom fitted dust covers for our
gear. My point is that it makes sense that some of this dust may have gotten
into the pot on the cabinet, making the disharmonious noises I have
described. Anyway, the Glenlivet and Guiness are really taking hold. I
should end this.
Rob Kloka
It's pretty easy actually.
--
-rob
O>
/(\)
^^
"Christine Dobbins" <chdo...@worldnet.att.net> wrote in message
news:mjJG7.163313. If I knew better how to sew, I
Todd H.
>
> So, I popped that off and examined everything I could visually, and
> could not find any kind of burn marks or any loose connections.
>
> This leads me to believe that - lo and behold! - there's got to be
> some debris in the potentiometer controlling the volume lead to the
> horn, either that or it's gotten bumped the wrong way one too many
> times. So, Mr. H., you were correct! I pat you on the back sir!
Thanks for the kind words, but are we celebrating prematurely?
We can jump up and down and feel like pros when you replace that pot
and it works without issue! Have we done anything to elminate a
capacitor on the crossover as the problem as Andrew suggested?
Or....get some electrical contact cleaner or poteniometer cleaner from
radio shack and give the pot a good soaking if you can. If the pot
sounds scratchy when you turn it, it becomes even more suspicous.
Best Regards,
Christine Dobbins
The problem was that one of the two filaments in the lightbulb was so very
slightly broken, so very slightly that you had to look at it directly from
the top of the bulb, very closely, under good light. I'd say the gap between
the two dangling ends of the filament was less than half a millimeter.
Unfortunately, it's a 28 volt bulb, and nobody we could find in town carries
something like that (athough after much searching, we found that Philips
manufactures a direct replacement, so we know it's out there, we just have
to order it). So, we threw a 12V automotive light with one filament in there
and it withstood our tests, although it sucks up a lot of tone. The sound
definately has less low end and less sparkle, but it's a sound, and a usable
one. We are going to practice on it tonight and see if it can stand up to
our rigorous demands.