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tiroth 9th March 2005 03:12 PM

MOX active crossover buy
I'd like to float the idea of a MOX reorder, because there seems to have been some interest lately.

Option 1 - MOX v1.1
MOX is an active crossover prototyping system. Each MOX board contains I/O buffers, level adjustment, and low and high pass filters. The filters can operate in parallel or series (bandpass) and have adjustable frequency (20-20kHz) and Q. A single MOX board can handle 1st or 2nd order filters. All settings are made with jumpers. Input is balanced or single ended.
More pics at links below (large: 68k)

Jens Rasmussen created the layout for this board, as well as an excellant web page and manual. Info also available on my website. This board has been extensively tested in the earlier buy. The only problem identified was a parasitic capacitance issue that has been fixed with a new layout for this buy.

The MOX board is compatible with the DIP8 discrete opamp boards I developed, or any DIP8 dual opamp.

Boards needed for common configurations, stereo
1st/2nd order 2-way: 2
1st/2nd order 3-way: 4
3rd/4th order 2-way: 4
3rd/4th order 3-way with 2nd order BP: 6
3rd/4th order 3-way: 8

Option 2 - MOXlite
A "lite" version of MOX. This is not a prototyping board--it is for implementing designs that have already been prototyped. So, you give up the powerful adjustability of MOX, but you gain
  • Smaller footprint
  • Each MOXlite is equivilent to 2.5 MOX boards
  • 2 Parametric EQs
  • On-board regulators
The design goal for MOXlite was to create a small formfactor board that could easily be built into a gainclone or other amplifier to create an active speaker. No additional low voltage supply should be needed up to approximately 40V rails; a voltage-dropping resistor helps keep the regulators happy. A cheaper and more compact way to implement 4th order filters was also desirable.

Each board contains an input buffer, a hipass with parametric EQ, two hi/low/bandpass (one with parametric EQ), and regulators. The topology is identical to MOX. The boards are compatible with the DIP8 discrete opamp or any DIP8 dual opamp. Input is balanced or single ended.

Boards needed for common configurations, stereo
1st/2nd order 2-way or 3-way: 2
3rd/4th order 2-way or 3-way: 4

I am open to feedback on what changes people would like to MOXlite. I do not want to include everything but the kitchen sink though; the goal is lite and powerful, rather than a lot of features that many people may not need (or want to pay for). If you need a very powerful design, Jens has already created one and has made boards available.

Note that there are no level adjustments on board. This should be discussed. One motivation is that with a level adjustment comes a need for a buffer, and that means more board space for something that is just buffering. My reasoning was that this is going to be built into an amp, so just make the level adjustment at the input and the short signal paths eliminate the need for the buffer. Please give me feedback though on how you will use it. If the paths are short enough, it may be reasonable to add unbuffered trimmers, which would increase the board size only negligably.

Accessory - DIP8 discrete opamp
These small boards are used to create discrete opamps that are compatible with the standard DIP8 dual opamp formfactor. They use the excellant 2SK389 dual JFET, although they could be made to work with other transistors with some leg bending.

I still have boards left over from the original buy, so I do not plan to reorder. If you are interested, the assembly guide is here.

tiroth 9th March 2005 03:18 PM

The Plan
At this point, I am just trying to gauge the interest in making an order of MOX or MOXlite boards. Please respond in this thread or send me an email stating which boards you would be interested in, and how many. I am looking for an order of 100 MOX or 50 MOXlite to proceed.

Cost: $8 per board. This cost may be adjusted downward depending on the interest. (opamp boards are $5 for 4 dual opamps) Pretty colors (black? blue?) for PCBs are an option if there is interest. I will ship worldwide, $6/$9/$11 for USA/Canada/overseas.

Timing: I'll start taking preorders in the next week. Delivery to me to be mid-to-late April. I was able to turn all orders around within 3 days on the last buy.

Thanks and credits
  • Jens Rasmussen donated the layout and the excellent manual for MOX. He is not connected with this or the previous buy in any way, he is simply a generous individual. Thank you Jens.
  • Jens developed his layout from moamps' original MOX project. Thank you moamps for posting your project on DIYaudio.
  • The topology for MOX came from Nelson Pass and Pass Labs, who generously made the schematics available to DIYers. Thank you Nelson.
  • MOXlite is an adaptation of Jens' Active Filter One
  • I created the layout for the opamp and MOXlite
  • While they last, I still have free 1uF caps that Jens gave me to distribute. If you use them, please send Jens a thank you. :)
  • If this buy goes forward, a suitable donation will be made to support DIYaudio

Nisbeth 9th March 2005 05:02 PM

"MOX Lite" looks very useful indeed. I'm in for a handful of boards or thereabouts :)


moamps 9th March 2005 05:31 PM


Originally posted by tiroth
................If this buy goes forward, a suitable donation will be made to support DIYaudio..............
Just wondering... was that the case the first time round?


tiroth 9th March 2005 06:16 PM

Milan, I am afraid that was not the case for the last buy. I was not actually in the black on the day I shipped orders, due mostly to my ignorance of PCB manufacturing capabilities (skip scoring! :mad: ) and poor QA of the order by the salesman. I learned a lot from the experience though. :) Also, this was before the donation efforts were stepped up DIY, if you remember. EDIT: sent you an email, we can discuss offline if you wish.

JensRasmussen 9th March 2005 09:07 PM

Hi Tyler,

I have more of those 1 F caps if you need them.


Illusus 9th March 2005 09:16 PM

I'm in for a "handfull" as well.

moamps 9th March 2005 11:07 PM

Hi Tyler,

Thanks for explaining things in the mail. MOXLite seems like a good idea, although I may have one suggestion related to the PCB design.

I think that on the top side there should be a power ground track between + and -. Snubber caps (C10X) should be connected only to the power ground track (not the signal ground). The signal and power grounds must be connected only at the power supply's caps.


Illusus 9th March 2005 11:49 PM

I guess I should specify quantity to help you gauge interest.
I'd like 4 MOX1.1 boards...maybe some of the discrete op-amp boards as well, not sure about those yet.

tiroth 10th March 2005 02:57 PM

Feedback so far on MOXlite:

Grounding -- this could be a challenge, but I'll see what can be done. I'll post a mock up for comments.

Cap clearance -- I intended to have clearance for 5mm width caps for all filter sections. Jens has pointed out that I am probably short of this on a few caps. This should be easy to correct.

Milan has commented on the eponymous nature of MOX, which I feel is entirely appropriate due to the excitement his project engendered. ;)

Keep them coming. :)

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