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Schertler David & Jam

Acoustic Instrument Amplifiers
Published April 2016
By Bob Thomas

Schertler David &  Jam

Schertler are no strangers to the art of amplifying stringed instruments, and their latest designs don’t disappoint.

Schertler, founded in Switzerland in the early 1980s by bassist Stephan Schertler, may well be better known these days for their innovative acoustic instrument pickups than for the wide range of instrument combo amplifiers and sound-reinforcement systems that they market. This reputational discrepancy may have arisen back in 2003, the year that Schertler launched their classic acoustic-instrument combo amplifiers, the three-channel Unico and the two-channel David. These appeared to have been designed specifically to match Schertler’s Dyn and Stat transducer systems, thereby ruling them out of consideration by many musicians, myself included.

In 1999, Schertler acquired a stake in the Italian company SR Technology. In the course of time, SR Technology not only became the manufacturing facility for the David and the Unico, but also brought to market a substantial range of acoustic-instrument amplifiers and sound-reinforcement systems under their own name. SR Technology’s Jam series of acoustic-instrument combo amplifiers bore a certain family resemblance to their Schertler stablemates, although their input channels were set up as on-board mini-mixers that not only could accept a range of inputs, but also could also be pressed into service as small PA systems, in which role my own Jam 400 has often served over the years.

In 2012, Schertler acquired SR Technology in their entirety, and the Jam series are now sold under the Schertler name, with the SR Technology brand being focused on active loudspeaker systems for the live-sound, installation and hi-fi markets. This move has been accompanied by a change in Schertler’s overall business model, whereby the Schertler and SR Technology brands are now available through a network of selected business partners at whose showrooms prospective customers can try out and purchase products at the same price, with free delivery, a 30-day money back guarantee and a three-year warranty, as offered on the Schertler web site.

In early 2015, Schertler launched the first in a new range of acoustic-instrument combo amplifiers, the Giulia Y, and that has now been joined by the two models being reviewed here: the David and the Jam. Like the Giulia Y, these new models take their styling cues from the original Giulia, first seen in 2013, whilst their controls and features seem to me to be somewhat of a melding of Schertler’s original David and Unico with SR Technology’s Jam series.

Let’s Get Physical

Since the David could be regarded as a feature-light version of the Jam, rather than describing both their anatomies in full, I’ll use the Jam as the reference and point out the differences between it and the David.

The three-channel Jam is the larger and heavier of the two, due in part to its use of an eight-inch woofer rather than the six-inch version fitted to the David. Both feature a one-inch dome tweeter and both are bi-amplified: the Jam has 150W driving the woofer and 50W on the tweeter, while the David’s amplifiers deliver 70W and 30W, respectively. The front-ported cabinets of both amplifiers are made of high-quality plywood and both are available in either a wood finish with a cloth speaker–grille cover, or in a more roadworthy dark grey painted finish with a metal grille cover. The units’ electronics sit in steel chassis that wrap around the top rear of their cabinets, with the input channels on the top and a large heatsink on the back. The chassis are recessed into their cabinets so that both the channel controls and the heatsinks have a measure of protection from impact.

The first channel in both amplifiers is designated as the instrument input, and is presented on an unbalanced TS jack socket. A button (preceded on the Jam by a polarity switch that is absent on the David) provides 10V DC power for electret microphones, and this is followed by the channel preamplifier’s gain control, which allows you to optimise the incoming signal level to obtain the best signal-to-noise ratio whilst preventing distortion. If you get a bit too enthusiastic, an indicator LED will illuminate to let you know that your signal is approaching distortion.

This is followed by the Warm switch, which inserts a filter that damps the higher frequencies in order to produce a warmer sound when a bridge-mounted pickup is being used on a violin, viola, cello or bass. A three-band EQ section comes next, with a fixed mid frequency on the David and a 300Hz to 3.3kHz mid sweep on the Jam. Next is a reverb send to the on-board solid-state reverb that, on the Jam only, also feeds an aux out jack. The final knob for channel 1 is an output level control.

On both models, the heatsink and controls are recessed into the cabinet, to provide some degree of protection from knocks and bumps.On both models, the heatsink and controls are recessed into the cabinet, to provide some degree of protection from knocks and bumps.The next channel is identical on both models, and is set up for microphone or instrument signals. Microphone input is via an electronically balanced XLR, with switched phantom power that, for some strange reason that lies far beyond the meagre limits of my understanding, supplies only 24V. I really don’t understand this choice, as I can’t be the only person in the world who gigs with 48V phantom-powered instrument microphones (DPA 4099) and preamplifiers (Baggs Para DI). The remainder of the channel (on both models) is identical to the David’s first channel, except that the Warm switch is replaced by a rotary resonance control. This governs a variable-depth notch filter that can be switched between 150Hz or 240Hz to reduce the possibility of feedback due to an instrument’s body resonance.

Of the two, only the Jam has a third channel. This is a dedicated microphone input on XLR and is again supplied, quite incongruously in my personal opinion, with switched 24V phantom power. The rest of the channel features — gain, three-band EQ with mid-sweep, reverb send and overall volume — are identical to those of channel 1 on the Jam.

Both the David and the Jam have the almost obligatory (these days) stereo mini–jack input for playback from an MP3 player, smartphone or tablet. Since the Jam has an auxiliary out driven from its reverb sends, it also has a stereo effects return (summed internally to mono), with associated volume control. This return could also be used as an additional input for an external preamplifier, amp modeller or what have you. Whilst we’re on the subject of reverb, both models have a master reverb level control, but the Jam has the additional facility of being able to vary the reverb’s decay time.

Both amplifiers have a balanced XLR output, with its own independent level control. This is taken post the output insert point and pre the master volume and switchable 180Hz low-cut filter. Said filter enables you to eliminate low frequencies, which is especially useful if you are running with an active subwoofer connected to the unfiltered line out. The final switch on the front panels of both the David and the Jam mutes their outputs.

The preamplifiers of the David and the Jam are high-voltage Class–A designs with no integrated circuits and no negative feedback, an approach that I’ve come across more commonly in esoteric hi–fi units than in acoustic instrument amplifiers. More interestingly, from my perspective, the quarter-inch jack instrument inputs on both amplifiers feature a ‘bootstrap’ circuit that enables the input to automatically adapt its impedance to the source connected to it.Among the extras offered by the Jam compared with the David are a  polarity invert switch for channel 1, and an effects send and return.Among the extras offered by the Jam compared with the David are a polarity invert switch for channel 1, and an effects send and return.

Keep Your Schert On

Both the David and the Jam are, in practice, intuitive ‘plug in and play’ amplifiers. Setting the gain controls to the optimum levels presents no difficulty, as the overload LED gives you plenty of warning before distortion appears. With their EQs and notch filters set flat, both models deliver an accurate, clear and clean reproduction of the instrument and pickup connected. Despite the fact that both amplifiers claim the same 50Hz–30kHz (-3dB) frequency response, there is (as you might expect) a bit more air being shifted by the Jam’s larger woofer, giving it more apparent heft in the bass than the David.

The EQ on both the David and the Jam sounded extremely musical to my ears, and enabled me to tailor the sound of my instruments to my requirements. I tend to use amplifier EQ to sculpt the sound rather than to try to correct what I’m hearing, and I found that both amplifiers’ EQs worked well for me. I’m no big fan of static notch filters, but I have to admit that the David’s and the Jam’s variable-depth notch filters worked very effectively and didn’t appear to have too much of a negative effect on the sound of my instruments.

The Warm function’s high-frequency reduction was, in general, a bit too extreme for my personal taste, but I can understand how it could make an overly hard-sounding fiddle bridge pickup more listenable. However, it did produce a very acceptable jazz sound from an acoustic guitar fitted with a magnetic soundhole pickup, so the Warm switch would appear to have other potential uses besides taming scratchy fiddles.

On both amplifiers the reverb added a nice warm halo to proceedings, its restricted 200Hz to 10kHz bandwidth avoiding both muddiness at the bottom end and brittleness at higher frequencies. The Jam’s variable reverb decay time allowed me to tailor the reverb more closely to my needs, although I didn’t find the lack of that particular control on the David to be an issue.

The one thing that I did miss on both the David and the Jam was a way of connecting a dual-source pickup system to separate channels using (as I normally do with a blender) a simple stereo lead. Years ago, though, I made a stereo-to-dual-mono splitter box for my first stereo Gibson ES345 and, pack-rat that I am, I managed to find it without too much difficulty, enabling me to connect a piezo/microphone dual-source system to the first and second channels of either amplifier.

Something that initially threw me on the Jam was the three seconds that it takes after switch-on before its power indicator LED illuminates. Before I realised what was going on, I assumed that the IEC mains lead was faulty and had charged off downstairs to grab a replacement.

On another minor note, I found that both amplifiers exhibited a low level of background hiss, even with every gain control turned down. In addition, on the Jam only, turning up the mic/instrument channel gain introduced a 50Hz hum component, again at a very low leve. The source of this hum seemed to precede the channel EQ, as I found it could be reduced using the bass EQ. The overall level of background noise isn’t an issue with either amplifier in practical terms, however: it is barely noticeable at domestic volume levels, and even although the hiss increases as the master volume is turned up, it certainly wouldn’t be a problem on stage.


I really enjoyed playing through both the David and the Jam. Both sound good, are compact, easy to carry and intuitive to operate. The overall sound quality is clear, natural and open, making them ideal for small gigs or as instrument monitors when there’s a front-of-house PA system but no dedicated monitor engineer. From a purely personal point of view, I slightly preferred the David simply because of its physical size and the fact that I don’t need the Jam’s extra power — even though I did prefer the Jam’s slightly more solid bass delivery.

There is a fair bit of choice available in this price range at the moment, and Schertler will, I feel, have some work to do in order to compete effectively using their new hybrid distribution business model, especially given that, in the UK at least, there is currently only one partner showroom displaying their products.

Having said that, given the free delivery and 30-day money back guarantee that Schertler offer, if you’re in the market for a high–quality amplifier for your acoustic instruments you should audition either the David or the Jam. Both are more than worthy of being on your shortlist.


Competition to the David and the Jam at their price points is especially keen, and you’re going to be tempted by products from Acus, AER, Fender, Fishman, Marshall and Roland.

Published April 2016