Koch KB2500 Limited Edition

Hmm, I just found my old review of the KB2500 LTD. I just read it again and I guess I can give a more elaborate review of this amp. :)

Oh, and excuse my bad English in the other review.. ;)

So, all the features in my other review still stand, but here are some additions to that.
- The amplifier comes with 6550 power tubes. It is possible to switch to EL34 as I mentioned above, but the amplifier must be modified for that... We only found out when we tried to install EL34! After some calls to the Koch factory, they remembered why we failed. By changing one little component inside, the range of the bias control can be enlarged! After this procedure, the amp accepts 6550 AND EL34.

My amp is now a little harder to bias without specialised equipment, but this is not a problem.

Also, I noted that the amplifier would deliver 200W with EL34 right? NOT TRUE! I was falsely informed last time. The amp still delivers 300W with EL34.

Now that I have also heard some other full-tube amplifiers I think I can make a good comparison between those and by that have a better insight in the good and bad sound-qualities of this amplifier.

- It is very 'tidy' for a tube-amp. It is very clean, open and clear. Compared to other full-tubes like the Ampeg SVTs, Ampeg V4BH and Orange heads it is very hard to get to a heavy overdrive or full distortion. Ampeg's for example have more 'rumble' or 'grit'.
Off course it is possible to use the built-in overdrive, but it only delivers pre-amp overdrive. I have not yet succeeded in getting a Ampeg-like gritty overdrive from this amp.
- The eq is very discrete, but not extremely powerfull. It is more usefull for adding nuances than changing your entire sound.
- Changing the amplifier to EL34 did change the sound! It has nog a little more low-mid and sounds a little more 'round'. You might say it has taken the sound more towards the Orange AD200 I guess. It sounds a little more rock'nroll/blues/jazz now compared to before.

I did not have any problems at all since those tubes broke as you can read in my other review.

If you have a problem (like 'why don't these EL34 respond to the bias control?') you can call and they'll find the answer. Eventually I even got to speak to Dolf Koch himself!

I also went to the factory last month to get my amplifier modified for EL34. The people there were very kind en helpfull!

I stay with the 9 I gave earlier! Incredible amplifier! I like it even more with EL34 in it! Compared to other full-tubes it is lightweight, but when you hear it... It sounds like it weights a 1000 pounds!

Before I start, I appologize if my English isn't perfect.

This is a limited edition full tube bass amplifier. It can deliver up to 300 watts RMS of power into 4 or 8 ohm. First, let me make one thing clear: on the inside, this amp is EXACTLY the same as the Eden VT300b, I have an email from the Koch company to confirm. Koch designed and produces the VT300 for Eden Electronics but also made a limited amount of 16 amplifiers for itself --> the KB2500 Limited Edition. I should also note that the KB2500 Limited Edition is NOT the same as the KB2500 (normal edition)!!! Allthough the names are allmost the same they are not very alike! Koch also played a part in de design and production of the Sadowsky SA200, which resembles the VT300 and KB2500 Limited Edition al lot, but is not exactly the same.

Let me go through all it's features one by one:

- There were 16 of these beasts made, I have serial number 910100006, so I assume I have No.6. :)
- Full tube, it can take 6 6550 or EL34 powertubes.
- 300 Watts into 4 or 8 ohm when equiped with 6550 powertubes, 200 watts if equiped with EL34.
- Three pre-amp tubes (I don't know what types right now, but I believe 2 are 12ax7 or similar and one other type)
- Switchable between 4 or 8 ohm with a small red switch on the back. The switch is not easy to move, because it is a little sunk into the amplifier body. I must be carefull not to cut my finger because the metal around it is sharp. The positive side of this is that the switch will never be moved by accident. Just impossible!
- Passive and active inputs
- Switchable overdrive. There is a red push-button on the front panel to engage it. (also by footswitch, I'll come to that later) The overdrive works together with the gain. Unfortunately there is no level control for the overdrive, which is one of the things I miss on this thing!
- 4-band passive EQ: 60Hz, 250Hz, 800Hz, 6KHz (on/off switchable by footswitch only)
- active tone control: bass and treble
- Master volume
- Built in Limiter/compressor (on/off switchable by footswitch)
- Standsby switch
- Lighted power switch
- Will work with 100, 115 or 230 VAC (with proper fuse)
- Effectloop (serial)
- Tuner out
- Pre/post swiDI-out (xlr) with groundlift and level control
- One Speakon speaker-output (NL4) and two Jack (TRS?) speaker-outputs
- Silent fan (always on, but very silent)
- Not rackmountable, it is build in a very thick wooden housing with tholex on the outside. A bit heavy, but 'sound'. There are metal corners and two rubber straps on top.
- Weighs a lot, but not as much as a Ampeg SVT (and that's VERY important!!!) The weight of this thing is do-able. The straps on top help a lot! I guess it would weigh about 25kg, but I'm not sure.
- Bias controls are inside

The footswitch
- 5 button footswitch with indicator lights and metal housing
- Mute to tune
- overdrive on/off
- eq on/off
- Compressor on/off (well, actually it is limiter on off) It keeps the poweramp from overdriving at higher volumes. So actually it is usable as some sort of poweramp-overdrive in live-situations, allmost like a driveboost. At home I use the pre-amp overdrive, live, I use the compressor on/off to make it growl!
- Damping high/low. This is a very special feature, it controls how the incoming signal from the speakers is handled. To me, it was explained like this: The poweramp sends a signal to the speakers to move (lets say) forward, but after this, the speaker tends to move back to it's original position. A high damping prevents this hard, a low damping prevents this to a lesser extent. Low damping sounds smoother and more vintage, high damping more modern and tight! Most full-tube amps only have low damping, so compered to those, this amp can sound more tight and modern in the low-end.

I give it an 8 because it misses the level control for overdrive (the sadowsky had that!) and the compressor is actually a limiter with no controls other then on/off...

I use it with a Ibanez BTB1005E ol with stock Bartolini pu's and pre-amp. This goes straight into the Koch. The Koch powers two Eden Nemesis speaker-cabinets, one 2x10 and one 1x15. I also tried this amp using Eden D410xlt, D210xlt and Vanderkley 2x10 and 1x12.

The sound from this amp is very warm, but more clean then an Ampeg SVT for example. It is also more tight, especially with high damping! It also sounds VERY powerfull, I never had to turn the master up above a quarter!!! And I play heavy rockmusic! VERY loud! It really gives that low-end that puts you UNDER the guitar, so I can always hear myself!

The overdrive is a very good sounding natural tube-overdrive! Very nice! Combined with the compressor at higher volumes it can go to a terrible growl!

The EQ is very silent, I can turn all knobs all the way up without extra hissss coming fron the amp (the only extra hisss I hear comes from my bass/cable!). Also, whatever I do with the EQ, it always sounds beautyfull, so the eq is very usable!

A 9, because nothing is perfect, but otherwise... ;)

The tubes broke down on me once, but this was not the amps foult (the previous owner put in some cheaper tubes). Next to this, it is a tube amp, but it seems very desent!

Koch is helpfull, they answer emails and I can phone them! I had some questions about this amp and they helped me with it!

A beast in sheaps clothes! It is LOUD but more thight than an SVT! Nothing is perfect, but the sound on this baby! WOW!