The clankiest, grindiest Class D head.

I'm surprised G-K gets so much love, but I suppose most use them scooped. Their EQ, when set flat, is slightly scooped & of course using the contour knob scoops it even more.
If you play with a lot of mid-range, like me, the G-K overdrive sounds horrifically solid state. I mean really awful.

Quilter is the answer, but don't be afraid to buy one of their Tone Block Pros.
I always played mine flat, which in a GK usually means bass at 10:00, treble at 9:00, and Mids at 1:00. You’re right, they are naturally a bit scooped, but I think they sound awesome with the mids bumped. Any contour knob on any amp I’m using stays buried in the zero range.

Uncle Hanky ain’t no spring chicken though, he likes what he likes, and if he says Peavey, then I say “more Peavey or GK.”
 
I'm surprised G-K gets so much love, but I suppose most use them scooped. Their EQ, when set flat, is slightly scooped & of course using the contour knob scoops it even more.
If you play with a lot of mid-range, like me, the G-K overdrive sounds horrifically solid state. I mean really awful.
Um, by 'flat' do you mean all knobs at noon? Because that's not 'flat' on a GK head.
So really all it takes is the ability to set the EQ properly.
If one leaves the contour knob all the way down, the scoop is (for the most part) non-existent.
As far as the overdrive goes, of course a solid state amps overdrive would sound...solid state.
There is a delicate balance between the input volume, boost, and woofer (master) volume to get GK growl.
And no, it's not ideal (I use pedals for my dirt) but I wouldn't call it awful.
Well, maybe...
But without true understanding of how those three knobs interact with each other, it is possible to get a less than desirable sound.
 
I thought it just sounded ok, then I got my ears cleaned. I came home & plugged in & thought it sounded horrific.
Luckily I'd just bought it from GC, so I returned it the next day.

I think they sound awesome with the mids bumped.

Not in overdrive.

You'd think the Fusion would take that SS bite off the sound, but it doesn't.
 
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Not exactly class d, but the GK RB 400 and 700 are some of the "growliest" heads I've played through. The RB 400 at 200 watts @ 4 ohms can really snarl when pushed, and with that wattage rating it's much easier to get it in the sweet spot than the RB700 with its higher wattage.

When I think of a Grindy bass tone I immediately think of the touch and go records, Jesus Lizard/Shellac/etc.. stuff.
Old traynors or GK stuff will get you there for sure.
 
I thought it just sounded ok, then I got my ears cleaned. I came home & plugged in & thought it sounded horrific.
Luckily I'd just bought it from GC, so I returned it the next day.



Not in overdrive.

You'd think the Fusion would take that SS bite off the sound, but it doesn't.
Meh, everyone has different ears, thankfully.

I'm not familiar at all with Quilter - their one bass amp does sound *very* mid-heavy, and I mean that in a good way. The depth and contour knobs instead of the usual BMT set up is interesting. I don't think there is a single dealer within a 15 hour drive of my house, so *I* won't be owning one any time soon.

 
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"Meh" is not what I was saying when I heard that Fusion MB 500 still sounded like a fully SS amp. Total letdown!

Aguilar & Quilter are not mid-heavy, they're just flat & everyone is used to scooped amps.

I skipped buying a Quilter Tone Block 201 last year, because I never could get the EQ to do what I wanted on the Tone Block 200 I owned prior.
 
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"Meh" is not what I was saying when I heard that Fusion MB 500 still sounded like a fully SS amp. Total letdown!

Aguilar & Quilter are not mid-heavy, they're just flat & everyone is used to scooped amps.

I skipped buying a Quilter Tone Block 201 last year, because I never could get the EQ to do what I wanted on the Tone Block 200 I owned prior.
Many *are* mid scooped when everything is set at 12:00, for sure. I suspect it’s a hangover from the Ampeg dominance of the bass amp market, but maybe not. But based on that being the norm, flat *is* mid heavy. But I get what you’re saying, I’m not trying to be argumentative. However, I’ve never had a problem getting any bass amp set to flat, by dropping the bass and treble like I mentioned and if necessary boosting the mids on the ol’ 3-band EQ. Many distortion, OD, and fuzz effects also scoop the mids, so if you’re setting a GK (or pretty much any bass amp, like you said they’re all scooped) to noon and either overdriving it or using an OD pedal, you’re definitely gonna be disappointed if you’re looking for a mid heavy tone. That’s why we have EQ.

Did you find there was a learning curve with the knobs on the Quilter?
 
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If you want to boost mids it's just guess work on the Quilter. I had to drop a Tone Hammer pedal in front of it to get a Terence (Geezer) Butler (à la Fairies Wear Boots) timbre out of it.
That will be my test for all amps going forward, how difficult is to pull off "Fairies Wear Boots"?

For me, the pinnacle of bass tone is Geezer's in "Warning", which I get on a clean MarkBass amp set to actual flat and a Joyo Orange Juice preamp pedal in front of it with Tone at 0, Drive up all the way, and Voice at 10:00. P bass with flats, Volume and Tone both around 8-9. I use it for a lot of stuff, but that's the song I stole it from.

I leave my amp settings there all the time, and change settings on preamp pedals and my bass, so I have a different pedal for different sounds - I don't have a "Fairies Wear Boots" one, but now I'm gonna have to see what I can scrounge up.
 
GK amps are not flat with knobs at noon, so that's no surprise. It's a disservice to yourself to treat any amp with the intention that noon= flat. The user manual will tell you what the +/- db gains are on an amp, and that can help get you closer. It's not necessarily easy to set amps flat without some type of analyzation hardware. For instance, Fdeck posted this years ago about an MB200 set flat...

Contour = Off
Treble = 10:00
Hi Mid = 2:00
Low Mid = 1:00
Bass = 10:00

Not a single knob is set to noon, nor does any knob reflect a scale of any kind. Some manufacturers prefer you to use your ears, and not your eyes to make adjustments. Need mids, move the bass and treble knobs left, and move the mid knob/s to the right.

My 1001RB II definitely isn't flat with knobs straight up, and neither is my Ampeg PF500. Also, I have a Blackstar guitar amp, and it too, is not flat with knobs at noon.
 
I also was not a fan of the Boost on the MB500 although it did help fatten up the notes, but I really like the Boost on the 700rb II. It is different and brings the magical pixie dust.

As for Geezer Butler, he is easily my favorite bassist and his tone on the Black Sabbath 13 album is definitely his best IMHO.
All of the playing on 13 is awesome, but honestly Ozzy’s vocals sound kinda tired, like he phoned it in. The rest of the guys are pounding it in.
 
GK amps are not flat with knobs at noon, so that's no surprise. It's a disservice to yourself to treat any amp with the intention that noon= flat. The user manual will tell you what the +/- db gains are on an amp, and that can help get you closer. It's not necessarily easy to set amps flat without some type of analyzation hardware. For instance, Fdeck posted this years ago about an MB200 set flat...

Contour = Off
Treble = 10:00
Hi Mid = 2:00
Low Mid = 1:00
Bass = 10:00

Not a single knob is set to noon, nor does any knob reflect a scale of any kind. Some manufacturers prefer you to use your ears, and not your eyes to make adjustments. Need mids, move the bass and treble knobs left, and move the mid knob/s to the right.

My 1001RB II definitely isn't flat with knobs straight up, and neither is my Ampeg PF500. Also, I have a Blackstar guitar amp, and it too, is not flat with knobs at noon.
Yep - and cut first, then boost if needed.
 
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By the by, I checked my cab. 600W. I was fairly certain I was correct, but I wanted to be sure.
34B33E56-5061-4AE5-9AA5-498D4A4D3AA9.jpeg
 
Going from those old Peaveys to a modern class D amp would be almost like going from a tube amp to class D. Completely different sound and response. My advice would be to get a spare Peavey (or three) if that's the sound you want. They shouldn't be too difficult to find for cheap. Something like a Standard 260D could probably work too. In fact, any Peavey bass/PA head from that era could work. They all have THAT sound. All of them are generally very reliable but they ARE getting a bit old. And when they DO fail it is (in my experience) often ICs that may be difficult to find these days. At least not something a local repair shop would have in stock. So that's something to consider too.