agedhorse

It depends on the size of the piezo crystal and how it’s implemented. Many passive piezo pickups are just fine driving a 1M input impedance and can sound better under that load.

This is a VERY complicated subject, and the blanket statements that are being made by the marketing materials have 3 distinct differences that are quite vague and misleading. 1. There is a difference in the general ratings between the PowerCon and SpeakOn connectors because the applications are very different. Since the PowerCon is used on the AC primary, specific clearance and creepage values have been updated in the new IEC 62368- standard. Since the SpeakOn is used on the secondary side of the AC system, the clearance/creepage values are not the same issue as on primary applications. On the AC primary side connectors, there is an additional need to be able to break the current without arcing since in the event of a subsequent short circuit, the available fault current (and power) is many times higher than on the secondary, which impacts PowerCon differently. Since Neutrik manufactures mating PowerCon cord sets, they must be compliant as well and that's a different matter entirely. How Europe handles the mating SpeakOn plugs is yet to be seen, but my feeling is that it's more bark than bite since Europe is already flooded with Chinese knock-offs of all kinds of products requiring certification (and for good reason) without any meaningful consequences to the violators AND there is a willing market of consumers focused on cheap rather than safe. 2. On the SpeakOn connectors, specifically the chassis jacks, since the chassis cutout is so large, AND because on a typical bass amp the speaker signal is classified as a potential ignition source PIS3, the housing material must have a specific flame spread rating of UL 94V-0 which is a VERTICAL spread rating and much harder to meet than the older UL 94HB which is HORIZONTAL and what the older housings were made from. The same applies to the older version of some (but not all) PowerCons. This requires different molding materials for the housing of the jack, though sometimes the older jacks can comply based on the specific application and lack of proximity to other PIS components, or by component testing. This is application specific and both the determination and the testing is convoluted. 3. On the SpeakOn specifically, changes in current ratings were also made, updates to both the continuous and duty cycle rated currents which are used in the application of designs under the new IEC 62368-1 safety standard without the need to do additional testing of the connector. Also, the speaker application rating is based on both short current (for contact current density) and long term under the audio power derating requirements, so while the contact rating may be 15 amps RMS, on the older connectors which are rated as continuous, the new connectors are rated for higher contact current density, but use 50% duty cycle rather than continuous. The new connectors specifically address contact robustness for very high pro audio power amps, not like what we see in bass amps. Much if this is addressed within the finished amplifier's certification procedure, it's a long and VERY expensive process. For example, on our guitar amps (we don't use 1/4" jacks for speaker outputs on the bass amps), most 1/4" jacks do not need to be V-0 rated due to their locations within the amp, but the speaker jacks do because the signal is at PIS2 or PIS3 levels. We had to separately approve the jacks we use to insure that they met the flame spread rating before they could be used in a location requiring this protection. This is one of the many reasons for the delays in certification approvals in Europe. We have many amplifier models and many components that needed to be evaluated and in a lot of cases tested separately before being tested in the finished amplifier because they are custom parts.

With a low powered speaker, a strong motor and just a couple mm of VC overhang, it’s possible to make a very efficient driver using a 4” coil and a tighter than average gap.

Be sure to use SpeakOn cables with genuine Neutrik plugs. Some knock-offs can damage the amp’s jacks.

It’s not due to the difference between class AB versus D. That’s a false premise to start with.

Turn the gain/volume up!

Correct, it’s the most common configuration, and a player would have a reasonable expectation that the head can be operated on top of a cabinet.

Not much safer given the plate voltages are fairly close.

Yup, this was also suggested Saturday on your TalkBass thread asking for help on the same amp... post #19. You could at least have the courtesy of following up there with your resolution IMO.

Maybe not, no way to know without a little more troubleshooting. The good news is that we do still have the newest PH 10" driver (8 ohms) in stock.

At this point, we don't know if any of the speakers are damaged yet. We do know that one is (very) incorrect.

Sorry, I wasn’t feeling well for a couple of days and missed this. First, a professional service technician that made that kind of mistake (substituting a 4 ohm driver for an 8 ohm driver in a 410 needs to hand in any credentials he may (or may not) have. That’s a bone-head error in judgement, just like choosing a BP-102 which is about the worst driver I can think of for that application. The original vendor for the earlier PH cabinets went out of business, the parts for those drivers are no longer available. The closest match to the drivers in your cabinet is the Legend CA-10 (8 ohm), and the drivers are wired series-parallel. Note that wiring so the polarities are correct is essential. If you need a diagram, message me and I will get it for you. This is why I always recommend verifying that the cabinet you are buying used is really what you think it is, I see folks get burned all the time.

A piece of heavy carpet might help, but some of this is going to be caused by the acoustic coupling between the speaker’s acoustic output and the top diaphragm of the riser. A high pass filter is one tool that may help, a parametric eq is another tool, turning down a bit might help too.

The GX-5 is an easy amp to repair for a qualified authorized service center. They have also proven to be extremely reliable over the past ~20 years or so. I don't recall any of the ~100 GX series amps that I had installed ever failing, they were at least as reliable as the RMX amps, but in a smaller (shallower) package. That said, the reduced cost of manufacture of some new amps can make them less costly to purchase in some cases.

Which model?

Why wasn't it repairable? Any authorized QSC service center should be able to service this. It's certainly not a self-repair type device, but it was never intended to be a DIY service device with the technology involved.

How are the secondaries attached to the bridge rectifier? Theres a lot of sloppy wiring and terminations showing in the picture.

With that wiring, I would be wary of intermittent short circuits that load down the secondary.

Not necessarily, it depends on the designer's intent and ability.

How would you propose to change the impedance matching by re-biasing? Bias does nothing to the high reflected impedance LxdV/dT effect.

Hold on a minute, 5A is plenty more than enough for an 800 watt amp (especially if it's SMPS/class D). If you were to do then math, with an 80% efficient amp (typical for a quality SMPS/class D), the IEC safety regulations calculate the input power as: (rated audio power x 1.2) x 0.125 duty cycle, so for an 800 watt amp this would be 120 watts mains input. Now if you wanted to use a higher duty cycle than the minimum (I typically use between 33% and 40% myself) to account for overdriving the power amp or high levels of compression, the calculation would be (800W x 1.2) x 0.40 = 384 watts input. Now divide by 230V and you get 1.67 amps which is EASILY handled by a 5A cordset (with the correct fuse for protecting the cord).

Well stated.

Not necessarily, some tube amps are fairly sensitive to output stage loading. A 50% mismatch could result in double the L(dI/dT) voltage which can over time (or immediately) break down insulation in the output stage.

No, some tube amps are particularly sensitive to a higher impedance load, because the reflected impedance to the tubes an primary of the OT can cause ringing and larger than expected voltage spikes which can damage OT’s, tubes and in some cases arcing between the pins of tubes.

There are companies that have no problem supporting 15-20 year old class D amps as well, making them non-disposable. it depends on the company and not the technology used ime.