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HH K150 Keyboard Combo

Despite their wide range of stage equipment, HH haven't, up to now, had much to offer the keyboards player. This has changed with the recent introduction of the K80 and K150 which are available both as discrete mixer-amplifiers ('heads') and as combos.

For this review, though, we'll be concentrating on the larger and higher powered K150 combo.


This model has 4 input channels, the first of these being the 'bright' input (with a slight peak around 1.5kHz) favoured for certain electric pianos. Each channel features switched routing to a common FX send-return socket and a shared 7-band graphic EQ, no dedicated equalisation (ie. for individual inputs) being provided. There's also an internal spring-reverb, and each channel sports a couple of pots to control the FX send and reverb levels. The other control on each channel is, of course, the input gain, but it differs from most in being active. This means that rather than attenuate away excess level from an amplifier stage with a (fixed) gain of x30, say, the pot directly adjusts the gain of the front-end circuitry. The overall effect is to make it easier to set the controls so as to avoid distortion when injecting high level signals.

Moving across the front panel to the other side of the graphics, there are reverb and FX returns, an output peak (clipping) LED, plus two jacks; one for headphones, the other for reverb and FX footswitching. The connection here is with a stereo socket, so you can use a dual footswitch with a single plug, and three core lead. Returning to the headphone socket, this disconnects the speaker outlets when in use, and is ideal for tuning up or practice.

Compared to some HH instrument amps in the past, this one is generally sparse and devoid of Sci-Fi controls - the immediate impression is of a musicians' workhorse yet without looking unattractive. Instead of gimmicks then, we find a couple of sensible extras on the rear panel. First, a balanced output for DI purposes - not exactly a new idea, but a facility that should be seen more often in view of the cost of a good DI box. Second, a Bi-amp socket. This is a line level, 'low frequencies only' feed to a separate bass power amp ('slave'). The clever bit is that inserting a jack plug here also removes all the LF content from the K150's speaker output socket - so this unit becomes the mid/treble amplifier. You then hook up appropriate drivers, ending up with a 2-way active (or Bi-amplified) keyboards stack.

In addition to these novel features, there's a pair of send/return jacks, a line level (slave) output, and two speaker outlets, one being used up by the jack plug from the combo's speaker enclosure. The 18" bass driver is loaded with a large vent, which suggests that it's tuned to augment the lowest bass notes, rather than higher up. This unit is partnered with HH's well known ring-radiator horn tweeter, or 'bullet', as it's more conveniently known. With the two drivers excelling at their respective ends of the spectrum, output in the midrange deserves attention, and accordingly, a silvered centre-dome on the 18" speaker offers some balance in this region.

Front panel features.


Whether using a keyboard or a rhythm box, it was easy to set up a range of tasty sounds with the graphic EQ and a touch of reverb; even with the EQ switched out, the sound was acceptable, indicating an essentially smooth response. (The rhythm box was particularly revealing - in general any system that sounds correct on percussion will also excel on keyboards, and the K150 falls into this category). However, in some instances, there was a definite lack of bite on keyboards, and as one would expect from the combination of drivers employed, the high midrange is slightly recessed. This is a pleasant departure from the usual state of affairs, and is readily rectified by a slight adjustment to the EQ's 2kHz slider.

Whilst on the topic of EQ, it's good to see that the instruction manual advises against ragged settings like 60Hz @ +12dB and 150Hz @ -12dB. Instead, it sensibly advises that you set up gentle curves. On the other hand, it's suggested that the graphic could be useful for room equalisation, which is really not on with only 7 bands - even assuming room EQ to be a valid technique in the typical live environment.

Alas, the graphic controls don't have centre click-stops, so it's hard to quickly set all the knobs to 0dB, especially when you're adjusting from above, on a dark stage. Of course, you can hit the 'graphic send' pushbuttons, always assuming you can see them, but that's not quite the same thing as zeroing the graphic's sliders. Fortunately, there's little audible effect when the knobs are slightly askew about the central position, but HH should consider fitting sliders with centre click-stops in future.

The reverb had a relatively small range of useful adjustment, especially with percussive sounds, where over most of the higher gain settings, it became too 'twangy'. This is a common problem with combos, being due in part to high level bass vibrations reaching the springline, but some judicious damping and improved shock relief would be advantageous. The headphone output scores well on sound quality, and it was also easy to drive high impedance headphones at high SPLs. Although this can be a danger to one's hearing, it's an improvement over insufficient level - many headphone outputs only offer sensible power into low impedance cans.

On the other hand, at low listening levels, there was excessive hiss (measured at less than 60dB, it could be 10 or 20dB lower), even with the gain controls set for optimum signal-to-noise ratio. Although to be fair, the hiss would probably not be over-prominent in view of the noisiness of some keyboards! Before purchase, then, it'd be a good idea to test out the headphones facility and assess the degree of aggravation if you anticipate doing a lot of quiet headphone work.

Rear panel connections.

Packaging and Mechanics

Musicians and sound engineers have always had strong feelings (both positive and negative) towards HH stage gear. To some extent, this is a reaction to their brash, 'forward', macho image. In recent times, this has mellowed, and along with Japanese competitors, the styling has gravitated towards that of UK professional audio. The K150 is a development in this direction, and put simply, it's a lot more pleasant to live with on an aesthetic level than some of HH's earlier creations.

Of course, HH's ideas as to who uses their gear has ramifications on the styling, so perhaps the recognition that most users are involved in Electronic/Funk/Jazz/Pop fusion rather than Heavy Metal mayhem has led to the welcome aesthetic refinements - Aswad, Fun Boy Three and A.C.R. being some typical professional HH users. But I digress: apart from the absence of click-stops on the graphics, the front panel layout is superlative. Moving onto the cabinet, both drivers are front mounted, and as the grille is easily removed, replacing blown drivers in a hurry should prove no problem.

On the rear of the combo, the flying jack lead from the speaker cabinet is long enough to reach a power amp laid on top of the combo - this is often handy for quickly checking the speakers if the combo goes dead for no apparent reason.

Like the external packaging, the internal layout is a major improvement - the infamous and unreliable HH wiring looms are largely vanquished; instead, money has been wisely spent on a well designed double-sided circuit board. For the musician, this should mean greater reliability, and if repairs are needed, it should also help to keep costs down, as access to the circuitry is so much easier.

Internal layout.


The input stages of the K150 use the NE5533 op amp, which is a dual version of the NE5534 low noise 'superchip', widely used in high grade UK pro audio equipment. Unfortunately, sections of the reverb and output circuitry incorporate 741s, an earlier and much noisier chip. This is okay so far as it goes, but doesn't help the poor noise performance on the headphones output, although to an extent, the noise problem appears to stem from a less-than-ideal gain structure. It's just a pity, that having used a good, low noise op amp for the front-end, the hiss is more prominent than it need be. The power amplifier is of the Bi-polar variety, which is odd in view of HH's commitment to MOSFET amplification. Nevertheless, the sound is devoid of any obvious shortcomings, and the power stages in HH instrument amplifiers do have an excellent record for reliability.


HH have clearly pulled their socks up: the K150 combo has been thoughtfully executed, and incorporates welcome improvements and elegant refinements from many angles. The main reservation relates to the graphic EQ. If you're simply equalising the speaker, that's fine, but given that many keyboards - even expensive ones - often lack EQ on their outputs, with a multi-keyboard set up, you've no control over EQ for each instrument - not even the most elementary bass and treble controls. Of course, it's not an insoluble problem. You can easily patch in a set of low cost EQ units (from, say, Turnkey's 'Accessit' range) between each keyboard and the K150's respective input. Or you could use a cardboard template to quickly reset the graphics for each instrument, assuming you're using them in a long sequence.

To finish on a more positive note, the K150's ability to make a cheap keyboard sound good was ample verification of the excellence of the speaker design, and with this in mind, the K150 is also well suited for use as a small and accurate PA.

So musicians who are looking for compact amplification with good low bass performance and near Hi-Fi characteristics should give the K150 serious consideration.

Recommended retail price of the K150 is £441.45 including VAT. Further information available from HH Electronic, (Contact Details).

Shortform data

Power: 150 watts into 4 ohms
(Note: because the combo speaker is rated at 8 ohms, you will only attain full power with an additional 8 ohm cabinet)
Input sensitivity: 190mV(-12 dBU)
Input impedance: 50K
Graphic EQ: +/-12dB @ 65, 150, 350, 800, 2kHz, 4kHz and 8kHz.
FX send/return levels: -10dBU

Previous Article in this issue

Rockman IIB & Ultralight

Next article in this issue

The Psychology of Music

Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.


Electronics & Music Maker - Oct 1983

Gear in this article:

Amplifier (Combo) > HH > K150 Keyboard Combo

Gear Tags:

Keyboard Amp

Review by Ben Duncan

Previous article in this issue:

> Rockman IIB & Ultralight

Next article in this issue:

> The Psychology of Music

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