agedhorse

It might be a coincidence, but it's also just as likely (maybe more likely) that you prefer the voicings that were more common in the older designs. Preamp (and speaker) voicings have evolved a lot in the 40 years that I have been designing products and this has been driven primarily by changing player preferences along with changes in music styles. One of the best examples of this that I can think of (off the top of my head) is the Darkglass models, they are what the industry refers to as "Euro-modern hard rock/metal" and is quite different from products we used to offer in our lines (Carbines and Strategy/Prodigy) which were American hard rock/metal oriented. The Euro tone evolved from the American tone as the music itself evolved. Because class D wasn't available (in practice) when these older products were developed, they were by default class AB. When Darkglass revisited this theme with their approach, class D was available and a practical option so that's the direction that they went. The appear to be very successful for those players seeking that voicing. I did test a Carbine preamp with a class D power amp, it was close enough that nobody was really sure which power amp they were listening to when testing... but that voicing was becoming less and less popular so the decision was made to evolve the Subway line into something that followed the evolving tastes. In no way does it make you wrong for preferring the amps that you like, but there's a lot more involved than just the amp class.

I’m not going to get into those specifics here.

There are all kinds of dynamics and voicing modifiers that go into a preamp design. The Streamliner that was mentioned earlier was very much about voicing and dynamics and sounded/felt totally different from the Shuttles even though they both used the same power modules. There’s a lot more to how an amp sounds/feels than just the power amp design (which can also be designed in ways to exploit or reject a particular aspect of tonality and feel.

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How are the pre’s “very similar”? Change one or two component and the voicing can change wildly. Unless the preamps are IDENTICAL, you aren’t comparing power amps, you just think you are (which is where confirmation bias comes into play) Now if you were to say that you preferred one amp over another without insisting that it’s due to the class of power amp, I can totally appreciate that.

I have done double-blind tests regarding which preamp players prefer (not just my designs) and it’s ironic that what many players are convinced they like ends up not being what they chose when they couldn’t see it. This is why double-blind testing is come, to remove the effects of confirmation bias. I have designed some very high powered class AB amps back in the day, well received in the pro touring world, but today’s better class D designs are every bit as good when mated to the identical preamp.

Failure and overheating is not a class D issue, it's a "poor design" issue. I haven't had any of these issues with any of the class D amps I have designed, going back over 15 years.

Of course the powered speaker is class D with a SMPS

In some cases they are identical. I have designed both bass amps and touring pro audio powered cabinets using the same modules.

Class C is not a viable topology for audio signals, not in any way. ALL amps must have a power supply transformer in order to pass safety standards everywhere in the EU and just about everywhere else in the world as well.

Kris needs to put him in touch with Rich. Rich will be able to help him. There is another problem that’s causing these symptoms. It could be a failed bias supply, a short from grid to cathode in one of the tubes, a screen to grid short in one of the tubes, etc. Correctly identifying the cause is essential to a proper repair.

He can always e-mail our service manager Rich, he will know who to contact in the UK/EU. The speaker muting relay stuck in the mute position is unlikely (very unlikely) to cause a set of power tubes to fail.

That’s not uncommon for OEM valves, some manufacturers purchase them unlabeled or labeled with a code only. This is especially true if they have an arrangement to test/screen all parts and return those that don’t part their test criteria.

Yes, but a lot of bass player tonal expectations have changed as well as a need for more low frequency extension without sacrificing articulation. Of course HPF's have been used on bass channels in the studio and in live sound for decades, so IMO it's not a fad but an evolution in response to evolution.

I was addressing your comment about 3 year old amps and tubes, you suggested being more worried about caps. I now see that you also mentioned old amps.

Preamp tubes/valves when designed reasonably are typically good for a lifespan pf between 7,500 and 10,000 hours with some that will make it to 15,000 hours and some failing earlier. I see so many perfectly good tubes/valves replaced without any consideration that what's being installed may in fact have higher failure rates due to infant mortality (first ~200 hours) On a 3 years old amp, capacitors aren't even barely "broken in". Typical lifespans when designed/selected properly runs in the 15,000 - 30,000 hour range, but I have some that I have seen well beyond that. I have however seen a lot of damage from folks who think a capacitor change-out is a maintenance item that should be done every 10 year or so (fueled by a bunch of bad information on the internet).

My comments were general in nature, all heavy components need to be securely mounted regardless of how they are used. I would not recommend using tape to mount a component that's likely to get hot.

That's classic damage from a hard fall (either shipping or a gigging load-in/out gone terribly wrong). There are cracks in the baffle, the baskets are clearly distorted at the mounting screws and it's likely that there's more damage that is not yet uncovered. If the top 2 drivers are damaged, it's common for there to be more drivers with damage. This is a older, heavy cabinet without the value (IMO) to justify repairing (or replacing) the baffle, and drivers (even if only 4 drivers are damaged). When the cost of a proper repair exceeds the value of the cabinet, it's time to look at other options. Regarding reconing, there's no way a pro recone shop would recone a speaker with a distorted basket, the chances of success are very low and nobody wants to warranty (and eat the cost) of a repair that they know is not right. If the cabinet works ok for his application as is, I recommend leaving well enough alone. The less it's moved around, the better. As soon as you start taking it apart it's almost certain that it won't go back together without bigger problems than he has now.

I did post but the post is gone. That’s due to catastrophic damage from a fall, bending the sheet metal. I am working with the op already on this.

Yes, this is sometimes done for mechanical reasons (especially with surface mount components, which obviously doesn't apply here). Smaller components have lower individual mass combined with a lower center of gravity.

It still needs to be mechanically secured or damage to the leads and/or PCB will result when the cabinet takes even a minor tumble. Most 20 watt parts have bumps in the bottom for this purpose, most 10 watt parts do not, and don’t need it with FR-4 PCBs.

When using heavier parts (like 20 watt resistors), provided the smaller part is properly specified, I see more mechanical damage from the larger parts being not well secured to the PCB. With the larger resistors, they must be mechanically secured in addition to being soldered. All it takes is the cabinet falling over to cause such mechanical damage.

10 watts will be plenty, multiply the (~25W) RMS power rating of the compression driver by~ 1/3 (the ratio of 4.7 ohms / 8 ohms) and you will see a maximum power dissipation of about 8.25W, which is pretty much the absolute worst case that the resistor will see. In actuality, given the crossover frequency and the power spectrum density for bass guitar, it will be about 1/2 of this value. I have used this formula and approach in commercial speakers for decades without any problems.

None of the Subway amps require a load to operate safely.

Distortion and square waves don’t obliterate speakers any more than an undistorted signal of equivalent RMS power, and in fact is easier on a speaker mechanically. A square wave of the same peak voltage as a sine wave has twice the thermal power but the same mechanical power. This is probably the root of most misunderstanding about the topic. Now peak power is something entirely different, a sine wave always has a peak power that’s double the RMS value, it’s purely two ways of using math to describe the same thing.