[tomb]

Quote:

Originally Posted by ujamerstand /img/forum/go_quote.gif Nice! You can even switch between the bantamDAC and some other source! Is it in the same foot print as the minimax?

Um ... no - the MiniMAX is about 1/3 smaller - no room for a BantamDAC or GrubDAC on one of those.

 

[ujamerstand]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Um ... no - the MiniMAX is about 1/3 smaller - no room for a BantamDAC or GrubDAC on one of those.

Ah, okay. I just assumed because the layout looked familiar.

 

[tomb]

Quote:

Originally Posted by ujamerstand /img/forum/go_quote.gif Ah, okay. I just assumed because the layout looked familiar.

Yep. The history is that the MAX came first - a splendid design from cetoole that was a "MAXimum" upgrade from the old Millett Hybrid. Literally hundreds of MAXes were built over the last few years.

The MiniMAX was a return to one of the original MAX prototypes that started out with a smaller board sized for the Lansing case. I talked cetoole into re-designing that PCB so that we could offer a smaller version of the original MAX that used a Lansing case (my avatar is the first working prototype of the MiniMAX). While we were at it, we designed the custom-machined and silkscreened Beezar/Lansing case that people have become familiar with as the MiniMAX. Finally, we did extensive testing/re-design to get the onboard power supply to a level of DIY-competitiveness with regard to ripple and noise.

By that time, the MAX PCB was obsolete. So cetoole started on an updated design, using the MiniMAX power supply design and making use of the extra room afforded by the larger MAX PCB to implement an onboard BantamDAC (now includes the GrubDAC, too). It's taken awhile, but we went through a couple of iterations to solve the input sourcing relay arrangement. What you see above is the final production version that will go on sale at Beezar shortly.

We see the MiniMAX continuing because of the excellent case and refined total package that it represents. Plus, using BJT's as the output diamond buffer - it's as good as it can get (the MAX can do no better with BJT's). However, the larger MAX board allows the use of a Hammond 1455T1601 case, which can accomodate 1-1/2" heat sinks. This is enough for the high-bias needed for MOSFETs in the diamond buffer. So, MiniMAX - custom case and BJT diamond buffer and MAX - onboard Bantam/GrubDAC and MOSFET diamond buffer. At least, that's the way we'll be recommending the choice between the two.

Hopefully that gives you some of the history if you weren't familiar with it. Of course, you can read all of this and more on the History pages of the MAX, MOSFET-MAX, and MiniMAX websites.

 

[soloz2]

No, it's larger than the miniMax.

 

[Lou Erickson]

I was just wondering about this! It looks like a perfect headphone amp for the office. If I can find a case big enough to wedge a hard drive and little USB hub into as well, it'll be perfect. One USB cable to work's computer, let it play music through the DAC in the box... Mmm.

Very shiny, Tom!

Now, all I have to do is get a couple of these OTHER projects done first.

 

[BoilermakerFan]

Quote:

Originally Posted by Lou Erickson /img/forum/go_quote.gif I was just wondering about this! It looks like a perfect headphone amp for the office. If I can find a case big enough to wedge a hard drive and little USB hub into as well, it'll be perfect. One USB cable to work's computer, let it play music through the DAC in the box... Mmm. Very shiny, Tom! Now, all I have to do is get a couple of these OTHER projects done first.

There are USB hubs that are small enough to fit in the extended Hammond case and there are other cases with similar sized footprints that are taller so they will easily accommodate a USB hub. Add a 16-32Gig thumb drive with FLAC files and you're set.

 

[tomb]

I've updated the BOM to include the new parts required for the V1.2 PCB (now on sale). Note that the PS is almost identical to the MiniMAX, but a different parts selection is used for a couple of items to support the higher current of MOSFETs (our recommended diamond buffer for the MAX as opposed to BJT's on the MiniMAX).

BOM on the MOSFET-MAX website:
MOSFET-MAX BOM
(The MOSFET-MAX website will become the primary reference for the V1.2 PCB.)

Also, please note that the relay-delay circuit has been updated to use a 24V regulator and 24V relay, doing away with the old Zener diode, resistor, and one of the electrolytics. This simplifies the circuit allowing for more reliability and better performance. Transient voltage offset on turn-off is almost non-existent, while the parts have been sized to provide ~45 seconds at turn-on from a cold start. Note also the use of suppressor diodes on the relay-delay and the relay input switching. These will provide better long-term protection of the relay contacts than the old 1N4148's.

I haven't cased one up yet, but bias at 125ma has been steady for months (also on the older proto) with little sign of over-heating on the naked PCB's.

I haven't updated the DigiKey section of the BOM yet, but the Elna RFS Silmic II - 1000uf 16V at CA2, and 1000uf 35V at CA7 are what we're recommending for the signal path. These caps are available at DigiKey and elsewhere and sound every bit as good as Black Gates to me. Use of one at CA2 seems to provide as much bass as an ES, too - just sterling audio caps all the way around, it seems. KZ's at Mouser are a distant alternate.

 

[jdkJake]

Great news Tom!

Besides the Elna RFS, any other recommendations that deviate from the BOM?

Also, are there any plans on updating the casework templates or will the old versions still work with the updated artwork?

jk

 

[tomb]

Quote:

Originally Posted by jdkJake /img/forum/go_quote.gif Great news Tom! Besides the Elna RFS, any other recommendations that deviate from the BOM? Also, are there any plans on updating the casework templates or will the old versions still work with the updated artwork? jk

No, but really - the entire BOM for the MOSFET-MAX is a bit of a deviation from a BJT MAX - taller caps, JFET-input, MOSFETs on the output, higher current PF1. Then there's the entire relay switching in back and the updated relay-delay circuit - but all of that is on the BOM. Also, the punch-down block in back is very new and unique to the MAX series. We had to use that because of the lack of space back there, but the desire to maintain some sort of terminal block-like capability (as opposed to MOLEX pins).

As for the case, the templates should be very close. I'll have to check because the spacing is slightly different with the sinks up front. Plus, there's the need for the USB connector in back (a square hole).

I had planned on tying the Bantam/GrubDAC LED into a switch up front: one LED for USB connection (red) and another for USB connection and switch to onboard DAC source (green). This can be done with a simple DPDT up front.

And actually ... the plans are to use speaker binding posts in the back as an option - tied into the headphone jack up front (one of the reasons that large slot is in the back - to allow the wiring to come up from below. Those items will need to be detailed in the drawing templates as well, but that should be a simple change I'll take care of very soon.

 

[tomb]

By the way - I remembered that I do have the templates for the case already laid out. As I said, the changes are not very many. I just have to post them. So, I'll do that this weekend.

Also - just a point of interest, but I specifically requested gold flush on the pads instead of leaded - in keeping with the MOSFET-MAX color scheme. However, Imagineering told me that gold was only good for 6-8 months. So, that's why the new PCB is red and silver instead of red and gold. The expiration on leaded pads is in years, not months.

 

[MASantos]

Tomb, why the "notch" on the back of the board near the power supply section? Space for an IEC connector?

 

[BoilermakerFan]

Quote:

Originally Posted by MASantos /img/forum/go_quote.gif Tomb, why the "notch" on the back of the board near the power supply section? Space for an IEC connector?

Quote:

Originally Posted by tomb /img/forum/go_quote.gif And actually ... the plans are to use speaker binding posts in the back as an option - tied into the headphone jack up front (one of the reasons that large slot is in the back - to allow the wiring to come up from below. Those items will need to be detailed in the drawing templates as well, but that should be a simple change I'll take care of very soon.

The notch is to clear speaker binding posts in the stock Hammond chassis.

 

[tomb]

The notch is also there for using a Box Enclosure case, which uses no bezels. (I've had a couple of special color Box enclosures for a MAX for two years now and haven't used them.) Since the length of board = length of case, without the notch there would be no room for any wiring underneath - tip jacks, speaker binding posts, or anything else.

 

[amphead]

Great to see the Max going strong with the new rev. Kudos Tom/Colin!

 

[MASantos]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif The notch is also there for using a Box Enclosure case, which uses no bezels. (I've had a couple of special color Box enclosures for a MAX for two years now and haven't used them.) Since the length of board = length of case, without the notch there would be no room for any wiring underneath - tip jacks, speaker binding posts, or anything else.

Speakers? How much power can this new MAX deliver?