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Koch Amps ART-4502 Rackmount Poweramp

Electric Guitar Power Amplifier

  • 2 Channels
  • 2x 45 W Stereo or 1x 90 Watt mono
  • 12AX7 Tube per channel
  • Presence, depth, and volume controls for each channel
  • Two parallel mono jack outputs per channel
  • Selectable input signal (-10 dB/ 0 dB)
  • 19"/ 1 RU
  • Weight: 5.5 kg

Output power:

  • 90 W @ 8 Ohm (mono)
  • 70 W @ 16 Ohm (mono)
  • 2x 50 W @ 4 Ohm
  • 2x 45 W @ 8 Ohm
  • 2x 35 W @ 16 Ohm
4 customer ratings:
  • 5
  • 4
  • 3
  • 2
  • 1
4 / 5.0
  • handling
  • features
  • sound
  • quality
4 written ratings Read all reviews
Total
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Wow, Why is are'nt people buying this??

Angelus502, 10.11.2015
I've had about a month to mess around with this amp now .. And as there are no reviews online that I could find, I thought Id write an in-depth one and some updates to my findings...yep I've edited this review..mostly because it comes loaded with 2 x cheap China 12AX7's tubes which aren't great, and this amp responds very well to a tube change :)

But if you don't wanna read.. its one hell of on amp.. and if you want it to sound better, just change the tubes :)

So.. I was looking for another power amp for my second rig. I had a Harley Benton GP-400 in that rack, which sounds very good for the money, but the other gear is a step above, and I was looking for something much better. I wanted tube tone, but to avoid the cost of a $300AUD re-tube for a 50 Watt tube stereo power amp ( I've got way to much tube gear what with guitars and Hi-Fi), and this was about the top of my budget.

My options were..
Use Peavey classic 60 mono - Big heavy, more tubes.
A second hand Mesa 20/20 - The same money and wont do mono, and more tubes.
New ENGL 20 watts - More money and more tubes.
Marshall EL34 - I just dont like Marshall's as a general rule.
Rocktron Velocity 300 - Used are 2/3 the cost of new in Australia, Heavy, Solid State.
ISP Stealth - Class D??? hmmm ??? not rack mount.
Anything in a 80's Marshall Valve state, or Moss Valve etc - Still half the money and probably going to need re-capping.

You get the picture..either old, heavy, or lots of tubes. So I thought I'd take a punt on the Koch.. Hell it would cost me a small fortune to return from Australia, but I could always send it back if it sucked.

This amp is crazzy good. It does what it says on the box.. It sounds like a tube amp!

I bough the Koch while I was in the process of re-tubing my Peavey Classic 50/50. Out of the box it destroyed the Peavey 50/50 with old burnt out tubes.. Then I set up the Peavey with with a full set of new tubes - After some messing around with different preamp tubes I settled on some cheap JJ 12AX7's, 2 x NOS Mulard CV4024 (12AT7')s with Tungsol EL84's as the output tubes. Even though the NOS Mullards that I bought for a Hi Fi amp cost 3 times as much as current production tubes, I had to leave them in the Peavey because they just made her sing and scream :D And the Koch sounded flat :(

So I popped the lid on the Koch.. huge Toroidal transformer :D But sucky 12AX7's stamped "China" (very bad Mr Koch, you know you built a killer amp, does yours have China tubes in it?).. So I know anythings gonna be better than stock China tubes...

JJ cheap 12AX7s- a bit flat and lifeless, as they are.
EH 12AX7's- Boomy in the bottom end, and probably just boomy all over. Great preamp drive tubes though :D
Tung Sol 12AX7s' - mahh,,,, how do u say muddy, and a bit clippy, to much tube gain..:S
Grove Tube 12AX7's not bad at all, but one of my tubes is stuffed :S
NOS Mullard 4024 - Surprisingly after it made made the Peavey sing - good but a bit flat.
12AT7's Badged Peavy but must be 80's-90's stock that I pulled out of the Classic 50/50 - smooth, harmonic, it was the best of what I have, so there the tubes for now :)

Volume Wise.. Its loud.. I'ts 45 Watt per side tube amp kinda loud. It will drive 2 x 4x12's easy. It will probably spank the pants of a 200 watt per side class D amp for SPL's. Yes its loud enough.

My one concern was the Presence and Depth Switches rather than knobs. Some Control Knobs rather than switches here would be nice Mr Koch. But they'er not a problem.. when set to "Off" its, hmm how would I put it, they have that old school flat bland tone. Set to "On" and its mid scooped rock nirvana ( its not a huge EQ change though ). Its like the techs thought "Stuff it!!! here's where you need the EQ set bitches" and where its set is good, very good :)

What else... 1UR, not light but not heavy, 5kg I believe. Heat wise its good, fan is a little noisy for a fan when it kicks in, but hey that would only be a problem in the quietest of studios, no vents top or bottom so its not running hot. Also has 0db or -10db switch for pre amp or pedal input. And auto switching for stereo or mono depending on which cables you plug in.

I emailed techs at Koch for some advice.. they told me you need matching tubes for bridged mono. But you can use it as mono using only one side of the stereo output and then use 2 different tubes. Just dont connect a cab to the other output. My gut tells me Bridged mono results in a thicker tone than running one channel as mono. Scary I know for us old guys, but yep, they say its safe to run one side with no cab connected.

I did a lot of research on Koch amps as I had'nt heard of 'em before. What I found was they are generally very highly regarded and have great tone, I did find the odd quality problem, or a not happy customer, but my research suggested they are a high quality brand with good support.

It's a killer amp. Its plenty loud. Only 2 x 12AX7's which are far from light bulbs. Yeah it comes shipped with China tubes, but that's a 2 min with a screw driver job to fix. At the moment my Peavey 50/50 sounds better, but that is all due to having 2 NOS tubes in it. When I pull them out and put cheap 12AT's tubes in the Peavey then the Koch sounds better. I think some 7025 or ECC803 lesser gain modern tubes would probably go well in this amp if you don't wanna spend the money on NOS tubes.

Buy it, try it.. it does what it says on the box - 1UR, light, built like a tank, sounds like a tube amp.. if u want it to sound like a totally killer tube amp then change the tubes :D
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Total
features
quality
sound
handling

Well cooked!

Vincent5624, 15.07.2015
My guitar signal is processed by a Marshall JMP 1 preamp and by a Rocktron Intellifex. Both old but good parts. When I played so directly into the lectern, the world was right for me. In the live application, however, my old power amp did not provide enough of the treble, which makes my Strat with Cleansounds so right.
A 1 HE alternative was however difficult to find, until a friend made me aware of the company Koch.
Now I have the Art-4502 in the rack. "Only" 2x 40 watts roar me at the 9 o'clock clock so that I do not dare because of the neighbors to go to the whole.
The Potis work clean, and fully torn makes the amp almost no sound. Each channel has a toggle switch for bass and treble lift.
I would have liked Potis. The switches for the heights make noticeable the door to what I call Stratklingeln. Also the Teleperlt and twang, and the Les Paul now with slight strain the silky shimmer, which my old power stage (she would not be called here) probably not liked. The switches for the depths give warmth and pressure, but the overall sound remains differentiated. And the overall sound convinces me. The Dutch have cooked well.
After a while, however, the two fans speak up. Whispering I would not call that. This is already clear. In the Ü-Raum and on the stage but probably to sorrow.

Because of the post-strike, the power amplifier did not reach its destination for a long time.
Thomann therefore sent a second with a different service provider.
Very customer friendly !!!! Many thanks to the Thomans and Thofrauen!

-------- A few days later: The cook amp did not make it even in the Proberaum. After about an hour running at a quiet room volume, the Art 4502 turned off, only to be quieter and then no sound. Have the amp sent back and will first again use my old power amp. The one was always always: Reliable!
Since I am missing in the asterisks now a rubric: No star for application suitability!
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