IGS Audio Pure Tube Channel_ENG

Written by Emiliano Girolami on . Posted in Gear, Recording

A new pre-amp has joined the group in the IGS Audio catalogue. It is framed in a one rack unit of a 19” chassis. It uses vacuum tubes as active elements and it is built with the usual high quality we know from IGS Audio. The unit is promising, let’s go check it’s performances.

di Emiliano Girolami



The look (and the feel) is really vintage with big knobs and switches, quite enough space for fingers to operate and with a clear layout which makes everything clear without asking for the user manual. The front panel starts (from left) with an high impedence input followed by four big (backlit) white buttons for HiZ, Mic/Line, +48V and Phase adjust. The gain is tamed via a coarse switch with six positions to go from 10 to 60dB in steps of 10. Fine tuning is possible via the following stepped trim which is capable to go from -5dB to +5dB allowing to continuosly cover all the gain range from 5 to 65dB. Going further to the right there is a nice orizontal VU meter followed by the red jewel and the power switch.


On the back we have the fuse holder, the IEC power line socket, a switch to adjust the line voltage to adapt the unit to various standards and two XLR connectors for Input and Output. Between the connectors there are the tubes which are accessible without opening the box. This arrangement helps for maintenance or tube replacement and to reduce the thermal stress of the unit. The installed tubes are  one 6N1P-EW and one 6N2P-EW but the Pure Tube Channel allows for experimentation since it can use also  6B23P, 6BC8, 6BZ8 tubes which can be easily tested by the user.


The circuit has a Class A topology with Carnhill input transformer and Edcor output transformer. The use of capacitors in the signal lines have been kept to minimum to optimize the performance and guarantee a uniform frequency response from 20Hz to 20KHz (response remains under a good 0.2dB range)

The test

At the early stage of electronics, before the introduction of the solid state transistor in the market, tube audio amplifier were designed for the sake of cleanliness and true response. The Pure Tube Channel follows this philosofy. However the technology limits (mainly tubes and transformers non linearities) generate a very special response if stimulated in the proper way.

Working with the controls and choosing in the right way the source, it is always possible to find the sweet spot which adds something to the signal without being intrusive making things simply better. It is probably something related to the even harmonics slightly introduced by the unit but the result is that everything coming into the Pure Tube gets out much better than it was.

It is a combination of detail, fast transient response, capability of heavy bass handling and a sort of easiness in working with mids and highs which are always present but never harsh. This thing equally happens from the Mic/Line as well as the HiZ inputs. It is as difficult to describe as impossible to deny.

With male voices it is better to use solid state, condenser, transformerless mics. With the acoustic guitar the result is always better than expected. Electric guitars are treated very well with all the nuances and colours. As D.I. Device for guitars, bass and keyboards the Pure Tube is second to none. This preamp has the extraordinary capability to be, in the same time, warm and faithful yielding to good results always in few tuning steps.

In the two next videos you can listen to the IGS Pure Tube Channel. In the first one (Monnalisa by Ivan Graziani) it is used for the acoustic guitar. In the second video (Crown Blues by Emiliano Girolami) we have used the preamp for vox, electric guitar and bass.

In summary

The IGS Pure Tube Channel is one of the few devices wich we think we can spend the word “outstanding” to describe it. It is very useful for every application thanks to its capability to remain faithfull while adding character with a class of its own that we rarely have found out there.

The price is more than appropriate if related to the performance. Don’t let it go and consider the possibility to buy a couple!

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