Hifisonix X-Altra Mini II Line Preamplifier with Remote Control

Originally published in January 2022.

The Remote Control board optionally replaces the manual select control board to provide full remote control functionality on the preamplifier. The remote control board has a H-bridge output to drive a motorised ALPS RK27 or RK16 20K log taper potentiometer (5V at 100 mA) and is short circuit proof. Further, a mute LED is located at the top of the select control dial and illuminates the gap between the dial and the front plate RED when mute is active. The select is implemented with a rotary encoder. Modushop will supply the front panels with the Plexiglas IR sensor window should you decide to go for the remote control option (see further down on this page for the link to the housings). Additionally, there is a 12V trigger output (40mA max) with current limiting ie short circuit proof. The boards are supplied with the 32 bit ARM LPC1114 microcontroller mounted and pre-programmed so you have to mount the remaining components.

The remote control is a standard Apple TV remote. These cost £19.99 in the UK and they are available world-wide. By going down the Apple TV Remote route, I don’t have to worry about trying to supply remotes – you just order one from your local Apple store. They are slick, beautifully made and a perfect match for the ‘Mini II’.

To sync the Apple TV Remote with the X-altra Mini II, hold the Menu + Select button on the remote down for 6 seconds. You will have to repeat this 2-3 times to cycle the correct control code page on the remote. Once paired, no further syncing is required.

The X-Altra Mini II Remote Control Board with the microcontroller mounted and pre-programmed is avaiablle for purchase in the Shop.

Introduction

This is my new all analogue line level preamplifier. I built the first ‘X-Altra Mini‘ in 2009 while living in Japan. Since it really was a bare bones LM4562 preamp, I called it a ‘Mini’ to reflect the fact that it did not do much else other than select an input, amplify it by 14 dB and present it to the output. There was a very basic class AB headphone amp included. Two other line level preamps came along in the interim – the ‘SCA-1‘ a PGA2320 based design (2010 also while I lived in Japan) and then the ‘Symphony‘ in 2013/4 while living in Taiwan – both since scrapped off along with the original X-Altra ‘Mini’. In 2016 I did a commercial preamp, the Model 1501, featuring remote control, phono input, balanced output and up to six inputs. This preamp used and AD797 and a 10k level control Alps RK27 to achieve very low noise and low distortion. Fast forward onto 2021/22 and my fifth line level preamp has arrived, the X-Altra Mini II. I’ve stuck with the ‘Mini’ moniker to reflect the fact that all the modules are small and compact, making extensive use of SMD. This preamp is different to all the others because the boards, housing etc are all available for DIY constructors who want to build their own. The measured performance is very good and at the same level as any well engineered high end commercial unit.

Here is a PDF presentation overviewing the X-Altra Mini II PCB’s and mechanical layout (updated June 7 2023 )

PCB’s for this project are available over in the Shop. They are sold in bundles in various configurations, but you are also welcome to buy individual boards (these are also listed in the shop). If you don’t see what you want, just email me at bonsai(at)hifisonix.com.

Here is the BOM (Excel) for all the modules (updated  June 72023)

X-Altra-Mini-II-BOM-June 2023 (1)

You can buy a complete housing kit that includes the milled, laser printed front plate and the internal 3 mm base plate onto which the PCB’s are mounted) from Modushop here

Modushop X-Altra Mini II Housings

The housings are beautifully made and will give your finished X-Altra Mini II a professional grade finish.

The document below is the drilling template for the 3mm aluminium base board that comes with the Modushop housing kit and slides into the housing side panel slots internally. This means the exterior cover plates don’t have any holes drilled into them, keeping the overall appearance neat and clean. To use the template, print it to actual size on A3 and then mark just ONE of the corner holes for each of the PCB’s then use the actual PCB’s before assembly to mark off the remaining mounting hole locations. The diameter of all the holes in the base plate is 3.5mm. Don’t forget to deburr the holes. ATTENTION: THE BASE PLATE DRILLING WAS UPDATED 03 OCTOBER 2022.

You must  print the drilling guide out on A3 Landscape and select ‘Print Actual  Size’ in your printer dialog box.  If you select any other settings, the drill template will not be sized correctly.  The PCB’s mounting holes on the printout must exactly match up with the hole locations on the printout for all boards.

For those of you that want to use individual X-Altra Mini II PCB’s in your own projects, here are the PCB dimensions for all the modules

Listening Tests

I conducted listening tests using an Oppo BD103 CD player and an external phono source (X-Altra MC/MM Phono EQ Preamp published in audioXpress Feb and March 2021) for all three vinyl recording assessments and on one of the vinyls, I also listened to the X-Altra Mini II internal MC/MM EQ preamp board. The discrete line stage is open with a fantastically smooth sonic signature that is quite different from the AD797 commercial preamp, despite both preamplifiers measuring well under 10ppm distortion and with measured hum and noise at or below -120 dBV ie inaudible. The measured X-Altra Mini II spot noise floor is c. -140 dBV and so it is exceedingly quiet with no discernible hiss from the speaker tweeters. The -3dB bandwidth of the Model 1501 is c. 200 kHz while the X-Altra Mini II is 130 kHz. I have to point out that my hearing is not that of a young person – but HF is just one part of the overall listening experience with things like imaging, bass extension, midrange articulation etc playing equally, if not more, of an important role.

I used my kx2-Amp (class A 15W RMS, 28 Watt peak class A) and Dali Oberon 5’s, B&W 703 and KEF LS50‘s to do the listening evaluation and the smooth, open sonic signature is consistent across all three speakers. The X-Altra Mini II brought the venue and the artists into my listening room unlike any of my previous system setups. The imaging is absolutely outstanding on the X-Altra Mini II – one of my go to test CD’s for this is Fourplay’s eponymous CD that features fantastic left to right width and back to front sound stage depth. This of course has a lot to do with the speakers and the recording, but if the electronics are subpar in any way, they will not support the illusion that the sound is not coming from the speakers themselves – you really want to be able to close your eyes and not be able to point to a speaker source but rather individual instruments laid out left to right and front to back. The top end is ultra smooth and silky with no hint of sibilance. This is the first discrete JFET line level design I have done, and I think the JFET front end plays an important part. I also listened extensively to Chick Corea’s (RIP) ‘Super Trio’  CD recorded in 2005 by Chet Himes and Bernie Kirsh. This is a superb live recording with great bass extension and a wonderful soundstage and lots of excitement and sonic fireworks on display which was faithfully conveyed by the X-Altra Mini II.

For the vinyl assessment, I listened to three recordings – ‘Ella Fitzgerald Sings the Irving Berlin Songbook’, and two Chick Corea recordings from the 1970’s – ‘Mad Hatter’ and ‘The Leprechaun’. Out of the three, the Ella Fitzgerald recording is the best (I’ve written about it here). On the Ella Fitzgerald recording, the X-Altra Mini II conveyed the sense of weight in the lower registers with an effortless, open sound in the mid-range and top octaves, especially noticeable on brass. Images were precisely placed on the sound stage, extending well beyond the edges of the speakers and a long way back behind them. On this particular recording, I also listened using the X-Altra Mini II MC/MM preamp board and whilst not quite in the same league as the stand-alone X-Altra MC/MM preamp, the overall sound was nevertheless superb and remarkable quiet for an opamp based MC preamplifier. The Chick Corea recordings don’t really lend themselves to trying to assess sound and stage tonal quality in the same way the Ella Fitzgerald recoding does. They however are exciting recordings with a lot of propulsive bass, ethereal vocals (courtesy Gale Moran) and drum kit fireworks from the inimitable Steve Gadd. The preamp conveyed the excitement of the recording with great pace, attack and timing.

A few words on the headphone amplifier are in order. The X-Altra Mini II uses the HPA-1 class A headphone amp and my iteration has the OPA1642 dual JFET opamp (although you can also use an LM4562 or NE5532 as discussed in the HPA-1 write-up) driving a MJE15032/33 push-pull output stage biased at 90mA into class A (180mA peak class A current), so it will deliver 1.75 W in class A into a 32 Ohm pair of headphones. I use 12 year old Audio Technica ATH AD900 ‘Air’ headphones I bought in Japan which are not particularly bassy but have the best imaging, midrange and top end I’ve heard bar the Stax tube driven electrostatics – they really are quite special in my view. Through the phones, the preamp retains its open, smooth sound, again without any hint of harshness or sibilance in the top registers. Since the headphone amplifier output impedance is very low, the bass is crisp and goes much deeper than is the case with large diaphragm, open back headphones driven from high impedance resistive dividers. The dedicated, low impedance output headphone amp makes a huge positive impact on the sound.

The addition of two unbalanced (one main and one auxiliary) outputs in addition to a pair of balanced outputs means that with this preamp, I can now have both my power amps (kx2 and Model 1721) along with the sub bass permanently hooked up without recourse to cable swapping or special split cables – so it’s really convenient. The kx2 drives the Dali Oberons and the KEF LS50’s, and the Model 1721 the B&W 703 with the sub bass switched on with the KEF LS50’s.

As always, I am on hand to help you get your build up and running.

The picture below is of the ‘Classic’ version of the X-Altra Mini II.