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What is causing this crackling I am hearing ?

The power amp in the Subway Bass 800D is NOT exactly the same as design as the Demeter.

Important differences are that the Subway amps are rated (with safety/EMC certifications) for operation of 800 watts RMS at 2 ohms, and has significantly different master section drive management and algorithms.

Assumptions can’t be made across different manufacturers, even if they happen to use the same power module.

I just read the TT-800 manual ( hint GAS attack ) and I appreciate all the technical explanations you and the Mesa team have given specially on the power amp, in the FAQ section of the manual, My buddy did ask Demeter to equip his older VTBP-201S with an 800 watt power amp and it does behave differently than the subway WD-800 I borrowed for almost 2 weeks. I had a chance to compare them side by side for a few days. The WD-800 and I am the subsequent amplifiers are definitely rooted in tube power designs

I think many of us old guys do not play loud to appreciate/differentiate the designs in the power section of modern class D amps vs powered speakers and the like or just adding a class D power module. Loud may not be your default operating mode but you should at least try it once. Of course be very mindful of your speaker capacity and setup.

Klos: comparable to Modulus?

Carbon fiber is plastic.
You can make things out of plastic that has short carbon fibers in it, but that is not at all what is being done here. Carbon fiber (as done in a lot of things, including bass necks) is a composite material - long carbon fibers (which can run the entire length of the neck, and can be oriented however the designer wishes), which supply the tensile strength and stiff ness, and a glue - epoxy or polyester resin, which binds the fibers together. It's a VERY different material than any simple plastic, and has far different properties.

Wood is also a composite material - it has fibers (cellulose, which can run the length of the neck, but which run the direction that they grew in the tree) and it has lignin - a natural glue, which binds those fibers together. Wood is lighter than carbon fiber - maple is about a third the density of a typical carbon fiber layup - for a carbon fiber neck to be a decent weight, it has to be hollow.

Both wood and carbon fiber are anisotropic materials - they have far different stiffness and strength along the direction of the grain than they across the grain. You can make a neck that will resist the forces of strings tied to them with wood or with carbon fiber. If you try that will plastic in the normal cross sections you would use with wood or carbon fiber, it won't work at all - it won't be stiff or strong enough. It will also be heavier than maple - plastic is about 67% more dense than maple.

Ampeg SVT 7 Pro Club

Interesting. I'll consider buying and trying another of the original fan if I plan to take it into the heat. As for at home practice, the concerns I had with these PC fans greatly diminished once I opened the amp right after playing and was shocked how cool everything was.
The overall impression of “coolness” is misleading, there are a number of specific components (different components in different designs) that are heat sensitive, which dictate the requirements for airflow (CFM, static pressure and direction).

When designing a (reliable) cooling system, thermal sensors are placed at multiple critical components to be sure they all track together.

Additionally, in some designs, there are also multiple sensors at key components that feed back temperature information to protection circuits. When these are used, it’s important that the cooling system doesn’t over or under-cool the sensors or protection circuits mistaking can occur (with disastrous results).

This is all part of a patent we were granted about 15 years ago relating to SMPS and class D cooling and duty cycle management.

Buzzzzzz

Sometimes this happens. My dingwall and my Stingray 5 are both generally dead quiet. But the Dingwall can be susceptible to powerline noise from cheap dimmers, and the Stingray 5 is not. There's one venue in town (playing there in two weeks actually) that has such bad powerline noise that I can't use the Dingwall. It's the only place around where I have that problem. Unfortunately for that kind of noise there's not much you can do, especially if it comes from cheap dimmers. Just bring a bass that you know is resistant to it, as your Sadowsky seems to be.

Sometimes the bass gear isn't what matters.

It's not the PA (though that helps)... it's the guy running it.

One local venue has a reputation for bad sound. Some say it's the equipment, some say it's the shape of the room (definitely not ideal). I saw a semi-name band there a few years ago. For the support band the sound was its usual mess. After they'd finished as the headline band were setting up, their touring sound guy (who looked like the bad guy from Prison Break if anyone remembers that!) stepped in, and kicked the house guy off the mixer. He pulled up the settings he'd dialled in at soundcheck, the band kicked in and sounded AMAZING. I watched the sound guy make a few tweaks during the first few songs and it just got better. The sound was cohesive but I could hear every instrument standing out perfectly. The house guy (who was shadowing him) was just owned, and I made a point of telling the touring engineer how much better it was, within earshot of the house guy! The band were pretty bad, but the sound was some of the best I've heard from a PA that had a reputation for being the worst in town. I just kept hoping the house guy was smart enough to snapshot those settings...

If the sound guy is good, then they'll make you sound good. If the PA is good, you'll sound as good as the sound guy makes you!
This, 100%.

About a month ago, I had a comment from FoH guy that the bass was too thin. Same Ray35 bass, same player, same FoH rig in the same large church. The difference was a much less skilled volunteer FoH engineer.

Quad Cortex - Neural DSP

Is anyone running their QC into a pa style power amp? I'm wondering how it fares with an amp that needs 0.775V? My QC is set now for normal mixing desk and instrument input on amps type levels, is it going to mess up all my presets if I want to sometimes run into a power amp instead of a normal bass amp? Am I better having a separate rack preamp? (Which I might do anyway for stage sound control).

Ampeg V4B into SWR 8x8

Just to be clear, you had 2 700 into 2 Henry cabs or do you mean 2 700's into one cab. How did you do that?
I used either 1 x Henry w/ 1 x GK 700rbii or 2 x Henry w/ 2 x GK 700rbii.

Used 1 when the guitarists used a half stack each with 120 to 150 watt tube heads and used two when they each used their 612’s.

What the absolute least amount of pedals you could get by with?

I could probably get by with an overdrive and a DI. But, the absolute least that I could use AND still be really happy with the tone....2 drive stages and a preamp. Others that make an appearance are compression, octave, fuzz and chorus.
Right now, a small board is too small and a big board is too big. So, I have space to work with. Sometimes I fill it, sometimes I have a lot of empty space.

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