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MAJOR Ampeg cabinet issues

#43
lbwdog said:
I could be wrong, but I don't think that spec is correct. To my understanding, the switch lowers the frequency before roll off to accommodate 5 stringers. 11db would be an extreme boost at 20 Hz.
Click to expand...

Not to derail the thread, but I found the Bob Gallien interview that explains the 5/4 switch.

How does the 5/4 string voicing filter work?

One of the biggest keys to making a great bass amp is the manner in which you roll off the low end because you really have to pay attention to the roll off rate and the way it fades. Nowadays, speaker systems can handle really deep bass sounds, but back in the day, they couldn't. At the time, everyone was playing 4-string basses so the demand for producing lots of really deep bass was not there. For example, the 800RB doesn't produce a lot of low end response, but it has just enough to accommodate the frequency range of a 4-string bass. That amplifier is not going to work all that well with the B-string of a 5-string bass due to the bass frequency roll off that begins gradually at around 100 Hz and then really falls off quickly at 40 Hz.

The 5/4 string voicing button is something that has been added to our amps in order to extend the roll off of the bass frequencies produced by 5-string basses. This is not just simply a bass boost button which works like a graphic equalizer, and it isn't a feature that was conceived by a sales department which decided it would be a good idea to add for marketing purposes. Our button doesn't boost anything. It extends the roll off of the low bass frequencies which don't begin falling rapidly until around 30 Hz. If you are playing a 4-string bass and trying to replicate the classic sound of the 800RB, you will want to have this button out because the 800RB doesn't produce a lot of deep bass. If you are playing a 5-string bass, you will want to have that button pushed in. Some 4-string bassists will actually leave the button pushed in at all times because they want as much low end as they can get. This button solves a particular issue regarding the extended frequencies of 5-string basses, and at the same time, it permits us to bring our heritage with us as we move into the new era of amplification

Here's a link to the whole interview.
[Invalid or Expired Link Removed]
 
#45
If I were in your place, the first thing I'd do once I got the cab back from repair would be to pull all the speakers and write down on paper exactly how they're wired. Also make note of any impedance markings on the speakers. Then compare to one of the many guides on how to wire cabs. The second thing I'd do would be to put all the speakers back and then do the battery test for common phasing among all four speakers. If you use a second cab, then do the same for that one and make sure its results match the results for the first.

You absolutely positively need this baseline, and you need to establish it on your own. Why? Because your cab is stuck in a non-trustworthy repair loop. Therefore, you must do this work, or someone you know and trust must do it while you are looking on. Half hour at most. On a difficulty scale of 1 to 10, this is a zero. After this exercise, you will have completely eliminated the cab as a possible source of the problem, outside of mechanical defects in speaker construction.
 
#46
lbwdog said:
I could be wrong, but I don't think that spec is correct. To my understanding, the switch lowers the frequency before roll off to accommodate 5 stringers. 11db would be an extreme boost at 20 Hz.
Click to expand...
I doubt there's any boost. By the description it takes the low cut filter out of the circuit. Said filter may well cut response at 20 Hz by 11dB when engaged. You'd get more deep lows, but long with them more below bandwidth thump noise that can easily damage drivers.
 
#47
billfitzmaurice said:
I doubt there's any boost. By the description it takes the low cut filter out of the circuit. Said filter may well cut response at 20 Hz by 11dB when engaged. You'd get more deep lows, but long with them more below bandwidth thump noise that can easily damage drivers.
Click to expand...

Did you take into your though process the boost may compensate for a sharp roll off, making the net effect at 20 Hz -7db instead of -18db? These are just random numbers and not the actual designed db per octave as I have no desire test and expose Mr. Gallien's formulas. :)
 
#48
Gosh....I certainly didn't intend to stir up all this controversy over an amp button, but was just pointing out what Mr. Gallien said himself about it.

Once again: Our button doesn't boost anything. It extends the roll off of the low bass frequencies. ( Bob Gallien,from post #43)
 
#51
laurie said:
The HLF is 4ohm, the GK700RB is 4 ohm as well. Everything matches, even with the old head. Has ampeg ever had a bad batch of cabinets with the worst wiring ever? If not I might be the first one to debate it.
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I have never had any problem with my 4X10 HLF and I have had mine for probably 6-8 years. Wiring is pretty much a no brainer in a cabinet. I'd maybe suspect something in the cross over, but thats a stretch. Still, to have a power outage and blow a cab is more than unusual especialy if the amp was fine.
 
#52
Has the OP tried using a new thicker gauge speaker wire. A wire with a short or gauge problem will cause the speaker to blow under prolonged use. Not sure if it affects the damping factor in the amp or just overheats the driver but I have had this happen a handful of time to bassbins over the years.
 
#53
rovito said:
Has the OP tried using a new thicker gauge speaker wire. A wire with a short or gauge problem will cause the speaker to blow under prolonged use. Not sure if it affects the damping factor in the amp or just overheats the driver but I have had this happen a handful of time to bassbins over the years.
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A speaker cable with a short cannot damage a speaker as the short takes the speaker out of the equation.

If the speaker cable has too low a gauge it will reduce the power getting to the speaker leading to power loss, nothing else.

Damping factor is something that is built into the amplifier output stage by the topology used.

Paul
 
#54
BassmanPaul said:
A speaker cable with a short cannot damage a speaker as the short takes the speaker out of the equation.

If the speaker cable has too low a gauge it will reduce the power getting to the speaker leading to power loss, nothing else.

Damping factor is something that is built into the amplifier output stage by the topology used.

Paul
Click to expand...

Wasn't looking for an argument. Just telling what I have seen first hand. Just last year we blew a bassbin at a low volume gig. Checked the cables and sure enough one of the screws backed out of a banana plug and the wire was just resting on the on the terminal. Reset the screw and no problems since. Again I have seen this a handful of times with wires breaking at the solder joint and just touching enough to make sound... Worth a try to check the cable.
 

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