agedhorse

I worked as production manager for Robin on a new project less than a year before he died. Brilliant, intense and a classic example of burning the candle at both ends. Very, very sad.

I show around +/-56V

Actually, voltage, current, impedance and power are directly related and can not be separated. Double the voltage into the same nominal impedance and the power quadruples, that's non-negotiable. Power factor, or the phase angle between the voltage and current doesn't really matter because it applies equally to both situations. Power = Voltage squared divided by the nominal impedance. The reason the power quadruples when the voltage doubles is due to the squaring of the voltage. Bridging carries the risk of one of the two speaker conductors being accidentally connected to ground. Because the output of the amp is not ground referenced, grounding either terminal can damage the amp. Some amps are designed from the ground up to be bridged, these are generally fairly tolerant of real world loads. Some amps bridge as an afterthought, these tend to be more vulnerable. Many class D amps are designed using bridged topology, in part to improve the power supply efficiency when driving inductive loads. This is an important part of some of these amps.

No Genz Benz amp was ever a Fender designed or built amp.

Sorry, I will need to look in the archives.

There are multiple voltages, +/- main rails, +/-15V and +24V

On the amp, the channel 1 input sensitivity control should be set all the way up (fully clockwise).

There is almost no rare earth elements that are used for magnetic structures also found in other electronics (including semiconductors). The rare earth elements that are used for speaker magnets are also used in all kinds of motors, generators and actuators. These devices are found throughout industry, transportation and also within electronic products (such as vibrator motors, haptic actuators, etc.). The speaker industry competes directly with these other heavy hitting players in sourcing the material.

That's a (very) far cry from a square wave. On a sine wave (a fundamental with no harmonics) it looks more "spectacular" than it is, but on a complex (real world bass) signal, the signal is built up of varying amplitude sine waves comprised of the fundamental and its many harmonics. Because the amplitude varies by a large amount between component signal elements (which is what makes up the envelope of the composite signal), clipping affects only some of the signal.

A couple of things to try... Does it make this noise with either the 410 or the 115? What are the cabinet impedances? What are the amp's minimum allowable load impedances? Are you SURE your cabinets haven't been modified or repaired incorrectly? Different amp types have different protection circuits, some can cause the noise that you are describing.

0dB is nominal, the difference between dBv, dBu is not important here knowing the MOL is over 3V rms.

Bridging is about BOTH voltage and current. It's impossible to change one without the other, they go hand in hand according to ohm's law. The preamp has plenty of output available to drive the power amp. That's NOT the problem, no matter how some here keep trying without understanding the differences between "nominal input level", "nominal input sensitivity", "nominal output level" and "maximum output level". The ~3V rms maximum output level of the preamp is the same as +12dBu which is typical for a preamp like this with a nominal output level of either 0dBu, +4dBu or 0dBv. In pro audio, the maximum output level is typically extended to +26dBu, but that doesn't matter here. The nominal input sensitivity of the amp is 1.15V which is the same as +3.5dBu. Since the OP is able to get the output limit LEDs on the amp to flash, the problem appears to be AFTER the power amp (ie. speaker cable wiring, defective/damaged driver, cabinet wiring, or polarity issues within or between speakers), or is the result of grossly unrealistic expectations.

In parallel, you have 720 watts split evenly between 2 cabinets. 2 cabinets off of a single channel is 600 watts split evenly between 2 cabinets. I agree with Downunder, very few 15" drivers suitable for bass guitar are cable of 600 watts RMS for very long. Looking at their website, their largest bass cabinet (CL-115 large) is rated at 500 watts RMS. The other question is how the cabinets are rated. If those are thermal ratings, than you should be aware that mechanical ratings are generally less then thermal ratings. Often, it's impossible to know what the mechanical ratings are until it's too late. I think 360 watts per cabinet is a reasonable power level, and say the power handing is 500 watts, the difference between 360 and 500 watts is about 1dB. Since there are no sensitivity specs on their website, there's no way to calculate the net effect on maximum SPL.

Actually, there are plenty of good applications for a biamped sub/top rig but not in smaller venues (under say 1000 seats) and especially indoors. Outdoors, where there is little boundary reinforcement is one such application. The additional low frequency volume and extension makes up for the "almost free-space" losses. The alternative to this is substantial side fills or taking the IEM path (which loses much of the feel for the band). These are not casually slapped together systems, but a significant amount of thought (and money) typically goes into such a rig. What I usually see is some form of PA sub (JBL SRX-718's and 728's used to be pretty popular for this application but often it's more of what the sound company is already carrying) and a conventional bass cabinet top, crossed over between 80-100Hz. Sometimes, you don't see the sub cabinets so it may not be as obvious.

Have them look at it again, if the actual cause is not correctly identified, no repair or miraculous guessing is going to fix the problem. No, transistorized (and solid state amps in general) are no less reliable (and IMO much more reliable) than most tube amps.

The power amp will not show any indication with the input sensitivity controls down. The metering looks at the signal post sensitivity control. Unless he has a bridging cable that is wired differently than a standard SpeakOn, it will not be in bridge mode regardless of what the switch position is. That might have saved his speakers under the circumstances. This amp will bridge into 4 ohms, but it's more than enough power to destroy the speakers (based on what he posted on TalkBass. Best way to operate his rig is one cabinet per channel in dual mode IMO (and IME)

I will ask.

Most Genz Benz amps had universal primaries with 115/230V switches

It’s more common now, but wasn’t 20 years ago.

No, the schematic shows a 120V primary only.

The good news is that it's a 120V, 50/60Hz transformer so a step-down transformer will work just fine. That replacement power transformer in 230V is going to be an expensive part, and in a vintage amp will probably reduce its value to a collector.

Correct, there are multiple disadvantages to the 1/4” (6.35mm) jack. Aside from the above issues, as the power rating grows on a bridged amp, the sleeve/shell terminal which is a driven terminal and NOT grounded/earthed, the voltage grows as well and the voltage on the sleeve can be 70V above ground and 140V above the tip. Some safety agencies in some regions do not automatically accept the safe voltages of audio signals (specific class of output port) being different from a general supply port, which places the threshold somewhere in the 200-400 watt range depending on impedance.

Defective tubes do sometimes occur.

Replacing parts it the “hope” that it will fix the problem is akin to hosing down the amp with “miracle cure-all spray” and “hoping” it to be fixed. Without correctly identifying the actual fault, faith in a proper, effective repair is essentially “blind faith”. Follow up with them to get your amp properly fixed.

Next time, leave the nail varnish off, it's not needed with the split lockwashers and can cause huge problems when you can't get the nuts off and snap the stud of the standoff or strip the screw on the standoff trying. Profusion parts are genuine, yes they are more expensive than what you see from China and Hong Kong on eBay/Amazon but they aren't counterfeit either.