Ampeg cab crossover boards blowing?

[fishtx]

I did a quick search but didn't find anthing specific on this, so here goes...

I have had to replace the crossover boards in two different Ampeg cabs now (never had to replace a crossover board in any other brand of cabinet). Has anyone else had problems with the crossover boards blowing in their Ampeg cabs?

Note these were both in USA made Ampeg cabs (a PR410-hlf and a 610hlf)...

Just curious if this is a known issue. Thanks!

 

[projectMalamute]

What is it that's failing?

 

[fishtx]

the horn crossover...on both cabs has failed.

on one cab (the 410), it I completely turned the crossover off, it worked and sounded fine...but when I dialed in the horn...it sounded like I had blown the horn it'self...first I replaced the horn thinking thats what I had done...but it turned out to be the crossover.

on the other cab (the 610), it sounded like I had a blown speaker...no matter where the crossover was set...after replacing the crossover it now works fine...

 

[will33]

If you turned the horn (tweeter) completly off that could've burned the Lpad. When you turn the adjustment down, it causes the Lpad (dial) to absorb all the power that would've normally been going to the tweeter. If you don't want to hear the tweeter, turn the Lpad down but not completly off, allow the tweeter to absorb a little of the power (to help dissipate heat). Technically it will still be playing but will be playing so much quieter than the woofers it likely won't be noticed.

 

[ashtray]

Say - what happens if you just unplug the tweeter and leave the wires just wrapped up, but in the cab? (my tweeter doesn't have a volume knob for it)

 

[billfitzmaurice]

Say - what happens if you just unplug the tweeter and leave the wires just wrapped up, but in the cab?

Depending on the topology of the crossover the lack of a load could blow your amp. Aside from that, no worries.

have had to replace the crossover boards in two different Ampeg cabs now (never had to replace a crossover board in any other brand of cabinet).

You should never have to replace a board. OTOH blowing a cap, coil or resistor on the board is no more a rarity than blowing a component on a board in the amp, where you also would usually replace the blown component rather than the entire board.

 

[Bassmec]

Christ you are showing your age.
Today the accountancy watch word is "modular!" you know an amp, a cab.
Telling someone that the problem actually may be as little as $0.75 to repair is downright old fashioned thinking.
Next you will be telling people things like tweeters can have their diaphragms replaced and the cardbord bits in speakers can be replaced with repair kits and such like!
This information is now top secret chaps as the department of homeland security has deduced that loudspeaker adhesives are far too dangerous to be carried in any part of an aircraft traveling abroad.
This is not so on domestic flights I understand.
See the following exert from a letter by sound speaker repair:
"It is illegal for us to ship flammable adhesives over seas.
It is stated at the beginning of the auction that the glue will not be shipped outside the U.S.
"Do to D.O.T. regulations, kits shipped outside the U.S. will not include glue."

We are sorry for any inconvenience this may have caused you.


SoundSpeakerRepair.com
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Tucson AZ, 85705
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Bill don't you know there's a war on Chap, Lose lips ETc. Mums the word eh!. don't want Jonney foreigner getting hold of glue and stuff doesnt bear thinking about.
Toodle Pip and all that rot. Fairfax

 

[rstansfield64]

I had crossover go bad in a PR15H. I just bypassed the crossover and wired straight from the 1/4 input to the 15" driver. I never used the tweeter anyways.

 

[fishtx]

Depending on the topology of the crossover the lack of a load could blow your amp. Aside from that, no worries.
You should never have to replace a board. OTOH blowing a cap, coil or resistor on the board is no more a rarity than blowing a component on a board in the amp, where you also would usually replace the blown component rather than the entire board.

Thanks Bill...I should have stated more clearly. I know it was a component on the board, and that could have been replaced, but it's easier to just pull the entire back panel and replace it than to troubleshoot the board to component level to repair (at least for me). I did do a visual inspection of the board and didn't see anything obvious. I kept the old crossover and will look at it at some point to see if I can just replace the bad component. I will then have a spare board assembly..

The replacement crossover assembly is relatively inexpensive (like $35), and the guys at Loud have been easy to work with. My real question here was "is this common to Ampeg cabs?".

 

[billfitzmaurice]

The replacement crossover assembly is relatively inexpensive (like $35),

That's very inexpensive, so much so that it does raise the question as to whether the components, or for that matter the entire crossover, might not benefit from upgrading.

 

[fishtx]

That's very inexpensive, so much so that it does raise the question as to whether the components, or for that matter the entire crossover, might not benefit from upgrading.

Yep...I am looking at the invoice right now. I was a little under what it actually cost. The price was $38.72 for the assembly, and that was for the entire assembly (ie the mounting plate, 1/4 jacks, speakon jacks, crossover board and db adjustment knob...thw whole assembly.

so maybe that's the problem i've been experiencing right there...cheap components being used.

 

[billfitzmaurice]

so maybe that's the problem i've been experiencing right there...cheap components being used.

And/or not enough of them. I have no idea what they use, but IMO a crossover should be that, a crossover, not a high-pass filter. A minimal crossover would employ a second order lowpass on the woofer and a third order high-pass on the tweeter. The component count would be three capacitors and two inductors. Using even moderate quality components you could easily spend $25 on them alone, not including the rest of the peripherals.

 

[projectMalamute]

And/or not enough of them. I have no idea what they use, but IMO a crossover should be that, a crossover, not a high-pass filter. A minimal crossover would employ a second order lowpass on the woofer and a third order high-pass on the tweeter. The component count would be three capacitors and two inductors. Using even moderate quality components you could easily spend $25 on them alone, not including the rest of the peripherals.

I just took apart an ampeg SVT410HE. It was a 3rd order high pass filter for the tweeter, 10's run full range. I think. Two capacitors in series, an inductor running from between the capacitors to the other side of the driver. 10's went right to the input jack anyway.

If you are crossing over at 5K do you really even need the low pass for a typical 10" bass speaker? Seems like it would be pretty well rolled off on it's own.

edit:

Ampeg actually says the crossover frequency is 4K, but still...

and found a picture of the same circuit:

I've omitted the L-pad and fuses, otherwise looks just like that. However, both of the capacitors are of the same value in this thing. None of the calculators/recipes I've found seem to give me that, seems like one of em is always 3 times the value of the other.

 

[billfitzmaurice]

If you are crossing over at 5K do you really even need the low pass for a typical 10" bass speaker? Seems like it would be pretty well rolled off on it's own.

Yes, but even 4kHz is too high, as tens don't do squat off-axis above 3kHz, leaving a hole in the response. I only run tens to 2.5kHz.

None of the calculators/recipes I've found seem to give me that, seems like one of em is always 3 times the value of the other.

Yep.

 

[Jerrold Tiers]

Yes, but even 4kHz is too high, as tens don't do squat off-axis above 3kHz, leaving a hole in the response. I only run tens to 2.5kHz.

Yep.

That's very broad as a statement......... you might want to re-consider.

One of the 15" Ampeg speakers (older Eminence versions) will happily "go" to 5 khz, and does rather well as to dispersion as well...........

Plus, many small horns get their efficiency by directing much of the sound forward, without a particularly wide dispersion...unless specifically designed for that. So the combination may be better matched than you think.

I don't like tweeters anyway, they seem to be about buzzy non-musical stuff, particularly if there is any clipping involved. I'd prefer the natural rolloff of a good cone for most purposes in bass, and all guitar use.

A a hi-fi industry rule of thumb, your statement isn't a bad one, but there are always exceptions.... and the instrument amp biz isn't the hi-fi biz.

 

[billfitzmaurice]

One of the 15" Ampeg speakers (older Eminence versions) will happily "go" to 5 khz, and does rather well as to dispersion as well..

I'd only believe that if I saw a polar plot to back it up. It's not impossible, but exceedingly unlikely. An EVM 12L is pretty happy to 7kHz, so long as you're not bothered by a ten degree dispersion angle.

I don't like tweeters anyway, they seem to be about buzzy non-musical stuff

If there's an octave or more wide hole between where the woofer leaves off and the tweeter begins that's certainly the case. The vast majority of cabs would be far better served with a midrange driver rather than a tweeter.

instrument amp biz isn't the hi-fi biz.

True, but that doesn't mean one should have to settle for poorly engineered products just because 'they're only instrument amps'.