Koch Classictone II-Twenty test by Gitarre und Bass

After 18 years, Dutch manufacturer Koch has revised its Classictone combo, which was then equipped with four 10″ speakers. However, the cabinet of the Classictone-II Twenty is no less spacious despite the single 12-inch speaker. With otherwise identical features, Koch offers the amp with either 20- or 40-watt power amplifiers.

As a special feature, the amps offer a recording output section, each with a jack and balanced XLR connector with frequency correction. In addition, an integrated load resistor (dummy load) allows the on-board speaker to be switched off even under full amplifier load, but should definitely remain connected.​

IMPOSANT
The mighty cabinet and the 22 kg live weight of the Classictone-II Twenty lead us to expect anything but a 20-watt combo. But we know that the cabinet and its volume influence the amp sound not insignificantly. 15 mm thick birch plywood forms the frame, in the corners of which four 4×4 cm square timbers provide increased stability. The tightly fitted, screwed rear panel and front were made of 13 mm birch plywood, each with trapezoidal openings.

Behind the front sits the actual baffle with the textile covering and the custom KochVG12-60 speaker, which is screwed four times from the rear and whose feed line is connected via plug-in shoes and amp-side via jack plug. The large spring reverb system was mounted in a tolex pocket on the bottom of the cabinet, the high-quality send and return cables meticulously laid with cable clamps and connected to the amp via RCA plugs with gold contacts.
​The cabinet, front and rear panel have been carefully covered with dark brown Tolex and visual accents have been set using black and gold piping. Eight screwed corner protectors made of sheet steel, four large rubber feet and a solid leatherette handle complete the case equipment. Velcro straps are available on the inner side panel to secure the footswitch and power cord during transport.

Shielded by aluminum foil, the amplifier chassis, which is bent from 1.6 mm sheet steel, hangs vertically from the rear panel on four threaded screws. Thus, tubes and transformers are aligned to the front, which requires dismantling the rear panel along with the chassis to change the glass bulbs, since the speaker magnet also obstructs access.

Inside the Classictone II-Twenty

​The cabinet, front and rear panel have been carefully covered with dark brown Tolex and visual accents have been set using black and gold piping. Eight screwed corner protectors made of sheet steel, four large rubber feet and a solid leatherette handle complete the case equipment. Velcro straps are available on the inner side panel to secure the footswitch and power cord during transport.

Shielded by aluminum foil, the amplifier chassis, which is bent from 1.6 mm sheet steel, hangs vertically from the rear panel on four threaded screws. Thus, tubes and transformers are aligned to the front, which requires dismantling the rear panel along with the chassis to change the glass bulbs, since the speaker magnet also obstructs access.
​All pots and connectors, standby switches and fuse holders are screwed to the chassis, four mini toggle switches are reliably soldered to circuit boards. The exemplary workmanship underlines the high manufacturing standards of the manufacturer. Briefly, I am confused, because Koch speaks of a three-channel amplifier, but the layout of the controls suggests a two-channel. Between the Clean and Gain controls I discover the small Gain/Boost switch, which allows the selection of crunch or high-gain sounds in the OD channel.

Top panel Classictone II Twenty

​Gain/boost and channel change can also be accessed with the included dual footswitch, suspending the function of the Clean/OD and Gain/boost switches. Two sturdy footswitches and bright red (Clean/OD) and green (OD/OD+) status LEDs are used in the robust sheet steel housing. The permanently connected supply cable with TRS jack plug is generously dimensioned at 5 meters.

The amp chassis offers three control surfaces, namely top, rear and bottom. On top we find input, channel select switch, clean volume, the OD channel with gain/boost switch, gain and volume pots, a classic passive 3-band tone control with bass, mid and treble for both channels (post-distortion) as well as reverb control, level and standby switch and a red pilot lamp as operation indicator.
​
Level switch? This three-way rotary switch, located directly in front of the power amp, replaces the familiar master volume pot with the positions Home, Studio and Stage. The rear panel provides a connection for an external speaker (8 ohms), a speaker on/off switch (dummy load), a balanced XLR DI out with ground lift switch and a jack line out (both with speaker simulation) as well as FX send and return (serial).

You have to bend down very deep - or put the amp on your face - for the lower connection panel, where Koch placed the sockets for on-board speakers, double footswitch and power cable, the holder for the HT fuse and the power switch. I would have liked to see the latter on the top, or at least on the back.

Backpanel Classictone II-Twenty

​NOT A BIT QUIET
For the first listening I turn the (master) level switch to the home position as a precaution. The Clean Channel shows plenty of headroom, because with PAF pickup types and powerful string attack, the first tightening (break-up) can be detected on the scale of 0-10 at about 6, and that at an impressive volume. What does Koch mean by "home level"? If you turn up Clean Volume further, the distortion ends with a very subtle crunch, characterized by powerful but tight, never boomy basses, warm mids, crystal clear, airy highs and pleasant brilliance.

In general, the Clean control works extremely precisely and increases the input level completely continuously over the entire control range. The amp's impulsive response and outstanding dynamics allow you to turn Clean up full and leave any further tone shaping to guitar volume and/or attack. More effectively than initially expected, the passive tone control intervenes in the action, the individual sections even interact a little. Thus, the most diverse guitar types can be balanced without any problems.

In terms of distortion, the overdrive channel starts where Clean ends, namely in gain position 1 with a subtle crunch. From here, the distortion intensity increases with almost astonishing continuity over the entire gain range up to heavy rock rhythm or singing blues rock lead. As expected, the amp shows increasing compression, but even at the highest settings it still reacts extremely dynamically and conveys a pleasantly sensitive feel.

Power switch and connection, fuse, footswitch, int. speaker

​But it gets even better: I turn OD Volume to 1 - yes, to ONE - and the Classictone-II delivers almost the same characteristics and dynamics at bedroom level! Okay, not with the pressure of higher volume settings, but voluminous, fat and yet lively and transparent. Gradually the concept of the master level switch makes sense to me. Amps with conventional gain/master control sound at room volume - i.e. gain fully up and master down to emission compatibility - mostly characterless and expressionless, floppy and meaningless. Here, however, the power amp is always included in the sound by the master switch, since the master level cannot be lowered lower than "home".

The boost switch of the OD channel activates the third channel of the Twenty and at the same time adds a clearly audible boost of gain, even when the pointer of the gain control points to higher realms. Result: Creamy, homogeneous lead distortion, healthy compression, precise, detailed resolution, high assertiveness, sustain until the day after tomorrow, all this with manageably limited dynamics and, last but not least, surprisingly low ambient noise.

In view of the home level, I hardly dare to select Studio and Stage. But this is absolutely recommended when testing this combo - preferably with band level - because then the amp shows its qualities to the fullest. The reverb pot mixes the effect signal of the large spring reverb with the direct signal, i.e. it is connected in parallel. Thanks to the even control characteristic, the effect component can be finely dosed until it produces an intense, natural, homogeneous, warm and spatial sound with a healthy portion of brilliance and clean signal at full output.

The long decay time of the large system may not suit everyone's taste, but can be compensated by lower reverb settings. With its nominal level of -10 dBV, the non-switchable serial FX loop is compatible with both pedals and 19″ processors and is exceptionally faithful to the signal. Both recording outs, the balanced XLR as well as the jack output, deliver appealing speaker-emulated DI sound that requires at most slight (taste-related) corrections at the mixer. The DI sound deviates somewhat from that of the on-board speaker, as it doesn't sound quite as lively and airy. I can always live with it, and the recording and FOH personnel certainly can as well.

2x EL84 and 3x 12AX7 tubes 20 watts

The Verdict
With the Classictone-II Twenty, the Dutch amp manufacturer Koch once again makes a successful contribution to the popularity of small tube amps, which has been increasing for years. Although, in view of the housing dimensions, there can be no talk of small here, here the adjective "power-reduced" would certainly be more appropriate. And so it happens that the 20-watt combo not only looks like a big one, but also sounds like one. With voluminous yet differentiated, transparent and lively clean to high-gain sounds, the Twenty is tonally very variable and displays impressive dynamics and sensitivity at no less impressive volume.

On the other hand, the amp also masters the discipline of bedroom levels without losing its vital characteristics. Practical line/recording outputs, serial FX loop, very good sounding spring reverb and master level switch complete the equipment of the impeccably manufactured three-channel amp, which is also offered at a fair price.

PLUS

● Sounds & tonal flexibility
● Precision, response & dynamics
● Harmonic distortion character
● Master level switch concept
● low side noise
● Quality of components & workmanship
● price/performance

MINUS

● Access power switch
● Inconvenient tube change