The X-Altra Mini II ‘BB’ Line Preamplifier – September 10th update

September 10th 2024 Quick Update. Here is a picture of the final X-Altra Mini II ‘Big Board’ with the remote controller board. Setting aside the wiring to the volume control and the headphone socket, all that is needed to run the preamp is a +-15V 5W regulated power supply. Testing and characterisation of the board will start in the next few days, and if that is ok, I’ll order a housing from Modushop and complete the preamp. After that, listening tests and then I will release it with BOM and write-up. Just to reiterate, here is what you will need for a complete remote-control preamp :-

Modushop X-Altra Mini II housing, 2 off 50 mm diameter control dials to accept 6mm shaft, 2 off control mounting PCB’s, one off main signal board with headphone socket adaptor PCB, 1 off remote controller board, one off PSU board and one off rear panel PCB (comes fully screened with all printing etc). 1 off ALPS motorized potentiometer RK27 (or RK168) log taper 20k, an Apple Silver Remote Control.

Please note: there will be a change to the internal mounting plate to accommodate the simplified assembly

Final feature set: 2 Off legacy level line inputs 350mV, 3 off 2V FS line inputs, 1 off MM phono input. 1 off 350mV record output with loop back; 1 off balanced line output, 2 off unbalanced line outputs; 1 off 2W into 32 Ohm headphone output; 1 off Trigger output +12V at 40mA max; Remote control of volume setting, input select and mute function using Apple Silver Remote.

Stay tuned for further updates!

August 18th 2024 Quick update. The new boards with the integrated MM phono amp stage have arrived and are partially assembled. Here is a quick pic.

July 22nd Update. The final version of the board has gone off for fabrication. In a few weeks I will start assembly of the main board and the new, updated remote control board. The board inter-wiring has been further simplified and the final step before releasing the PCB’s is to redesign the rear panel to make mechanical assembly even easier. If you recall, the original X-Altra Mini II was complex in this regard – the new board and mechanical assembly is altogether better. I hope to also be able to offer the preamp as a finished product in the hifisonix Finished Products store for those of you who want the security of a hand built and fully tested product! Further updates in August. Stay tuned!

June 10th Update. Board testing is complete, and it works as required and flawlessly with the Remote Control board (on the right-hand side of the picture below). All power to the remote board comes in via the 16-way ribbon cable, and the only other wiring will be as follows: –

mains into the PSU board from the rear panel IEC receptacle

+-15V to the main signal board (left hand board in the picture below)

2 off 2-core screened cable to the Alps motorized volume control pot

2 wires from the Remote Control board to the volume control pot motor

Thats it – very clean, simple wiring and a finished remote control preamp with 6 inputs and a top-notch spec.

May 16 2024 Update. Good progress today with component mounting. I am awaiting the remaining parts for the board from Mouser (TPA6120 headphone amp, THAT1606 etc). Once all the IC’s are installed, a basic signal integrity test will be done to ensure everything is working without any major problems. That should go according to plan, and the next step will be to install the relays (11 in total) and check that the remote controller board and the BB work together as a team! There is a second stage signal integrity test to make sure all the inputs are correctly assigned and the L+R channels are the right way around, and only after that can the input RCA receptacles be mounted. I then need to make sure the board mates correctly to the rear panel.

I have a simple linear PSU (rather than the original one which had a lot of functions on it that are not really needed given the BB is designed to only work with the remote controller), but that is really a separate part of this project and quick to turn around. I hope to begin the 1st round of signal integrity testing later this week, or over the weekend. Stay tuned for further updates!

4th April 2024 Update. The PCB has arrived back from the PCB house, so I will begin assembling the proto later today! The board is very compact (good for low noise) and as mentioned previously, incorporates all the functionality of the earlier X-Altra Mini II.

March 31st 2024 update. Well, the board layout is complete and has been sent off for manufacture. It’s very compact with all of the original X-Altra Mini II functionality packed onto one PCB. You will need very good SMD soldering skills to put this together, but the sound and performance will make it worth it.

Here are the preliminary specifications: –

Here is a view of the completed board layout: –

For a fully functioning remote control preamp, you will need the following:-

An X-Altra Mini II Remote Control housing from Modushop – pre-drilled, silk screened and with IR filter – about Euro 189

A ‘BB’ PCB as above

a Remote control PCB

A PSU +-15V

2 off switch mounting boards and a headphone socket mounting board

1 set rear panel gold plated and screened PCB’s – these from the rear panel, so you don’t have any drilling, filing etc to do

An Apple Remote (about 20 bucks from the Apple Store – don’t use the plastic cheapies off Amazon!)

Full details to follow in a few weeks after the first proto build and test!

March 23rd 2024 Update. Good progress – the board has been routed, so now its design rules checking and cleaning up to do. Here is a picture of the board: –

March 20th 2024 Update. A few X-Altra Mini II full feature line preamplifiers have been built, but not as many as I’d hoped. Although the finished product looks slick and uses an Apple Remote for control, I’ll be the first to admit it’s a beast to wire-up and test because it uses a lot of modules with lots of module inter-wiring. Interestingly, quite a few individual modules have been built, but I think builders are baulking at the complexity and expense of the existing design (about $190 for a set of PCBs and then another 185 Euros for a housing before tax shipping etc). To be sure, a commercial product with similar spec would cost a few thousand $.

I think it offers too many configuration options – most people just want 5 line inputs, a (optional) MC/MM input, a record loop, a few line outputs including balanced and a headphone output. This is exactly what the ‘Big Board’ aka BB delivers on one compact PCB.

The BB provides everything that the original Mini II does, but on a single board using the superb TI OPA1642 JFET input opamps and a TPA6120 headphone amp. It still however uses the original PSU, the original remote controller board. The phono board (MC and MM) will be an optional add-on, but if you dont need it, the phono input is linked on the PCB and you gain another line input. The BB is SMD, so builders will have to hone their soldering and tweezer skills.

Externally, the finished preamplifier will look exactly like the original X-Altra Mini II and provide the same functionality.

More updates to follow shortly! Stay tuned!