New Millett Hybrid Maxed Amp - Page 428

The PCB assembly is done.  Now on to the casework.  For those who have finished the MOSFET-MAX, any tips/tweaks/tricks regarding the casework you can suggest?  For a little background, I am using the standard Hammond case from the BOM and plan to integrate the grubDAC onboard.

When I did mine, I mounted two RCA jacks on the left side of the rear panel, one above the other. That caused interference with the Grub, so I would recommend

that, if you're also installing RCA's, you mount them side by side above the Grub.

Hello Everyone,

Very new to DIY Audio, just ordered some parts for a Hybrid Maxed Amp that I plan using at work.  I'll probably get most the little stuff before the PCB board gets here, but I'm taking the chance to organize my work bench.  I'll post some build shots as I move along, and I might have a few questions, but for now I'm just saying hello.

A little background: I've got a master's in aerospace engineering, so I've had some past courses in electrical engineering and basic circuits.  I've had to break out the text book and freshen up a little.  I don't plan on making any deviations from the design, but the engineer in me is curious what each part of the amp does.

I guess that's it for now.

Quote:

Originally Posted by bwshockley 

Hello Everyone,

Very new to DIY Audio, just ordered some parts for a Hybrid Maxed Amp that I plan using at work.  I'll probably get most the little stuff before the PCB board gets here, but I'm taking the chance to organize my work bench.  I'll post some build shots as I move along, and I might have a few questions, but for now I'm just saying hello.

 

A little background: I've got a master's in aerospace engineering, so I've had some past courses in electrical engineering and basic circuits.  I've had to break out the text book and freshen up a little.  I don't plan on making any deviations from the design, but the engineer in me is curious what each part of the amp does.

 

I guess that's it for now.

Welcome! It's an awesome build. Definitely one of the most fun I have done (though not that many), and in the end, you really feel like you've accomplished something! Are you going BJT or Mosfet?

What build do you guys recomend for the HD800, Mosfet, BJT's, Caps??

Thanks

Quote:

Originally Posted by scootsit 

Welcome! It's an awesome build. Definitely one of the most fun I have done (though not that many), and in the end, you really feel like you've accomplished something! Are you going BJT or Mosfet?

I was going with MOSFET.  However, I'm not knowledgeable enough to know which I should lean towards.  I don't have headphones for this yet.  I've been using cheap things that technically work, but will purchase a nice mid-range, closed-back, over-the-ear set for work.  Maybe the ATH-M50(s)?

Any recommendations on either head phones or MOSFET v. BJT?

Quote:

Originally Posted by bwshockley 

I was going with MOSFET.  However, I'm not knowledgeable enough to know which I should lean towards.  I don't have headphones for this yet.  I've been using cheap things that technically work, but will purchase a nice mid-range, closed-back, over-the-ear set for work.  Maybe the ATH-M50(s)?

 

Any recommendations on either head phones or MOSFET v. BJT?

Impedance of the ATH-M50 is 38 ohms.  If you stay with low-impedance phones, the MOSFET-MAX is absolutely the best bet.

One thing you should try to do - order the Toshiba JFET's from http://www.bdent.com  I used to make up and sell a matched quad, but my supplier ran out of the 2SJ74's.  BDent has them at a reasonable price for someone building an amp, but they're way too expensive for me to re-sell that way.  You can read up on the AMB-JFET mod to the MOSFET-MAX here (near the bottom of the page):

http://www.diyforums.org/MOSFET-MAX/MOSFET-MAXhistory2.php

Details on how to mount them are here:

http://www.diyforums.org/MOSFET-MAX/MOSFET-MAXmosfets.php

These can make a huge difference in the response and linearity of the MOSFET version at QB2 and QB3.

The MOSFET-MAX really shines with low-impedance phones, but will do a pretty good job with high-impedance, too.  The limitation is the tubes, but a a pair of 12AE6's will ensure enough voltage swing for the higher-impedance phones.  The key is that the Class A bias on the MOSFET output buffer is at least 125ma and can be pushed to 150ma or more (carefully).  If the phones will use it, it has the capability of supplying perhaps 1-1/2 Watts.   The BJT MiniMAX version is best all-around, but is really optimized for size, convenience, and the custom-machined case.  On the other hand, the full-sized V1.2 MAX PCB offers the flexibility of the onboard DAC and more flexibility with the cap sizes.   I usually steer people toward the MOSFET-MAX for low-impedance and toward the MiniMAX if they want to try all phones and are looking for a complete kit.

Quote:

Originally Posted by tomb 

Impedance of the ATH-M50 is 38 ohms.  If you stay with low-impedance phones, the MOSFET-MAX is absolutely the best bet.

 

One thing you should try to do - order the Toshiba JFET's from http://www.bdent.com  I used to make up and sell a matched quad, but my supplier ran out of the 2SJ74's.  BDent has them at a reasonable price for someone building an amp, but they're way too expensive for me to re-sell that way.  You can read up on the AMB-JFET mod to the MOSFET-MAX here (near the bottom of the page):

http://www.diyforums.org/MOSFET-MAX/MOSFET-MAXhistory2.php

 

Details on how to mount them are here:

http://www.diyforums.org/MOSFET-MAX/MOSFET-MAXmosfets.php

 

These can make a huge difference in the response and linearity of the MOSFET version at QB2 and QB3.

 

The MOSFET-MAX really shines with low-impedance phones, but will do a pretty good job with high-impedance, too.  The limitation is the tubes, but a a pair of 12AE6's will ensure enough voltage swing for the higher-impedance phones.  The key is that the Class A bias on the MOSFET output buffer is at least 125ma and can be pushed to 150ma or more (carefully).  If the phones will use it, it has the capability of supplying perhaps 1-1/2 Watts.   The BJT MiniMAX version is best all-around, but is really optimized for size, convenience, and the custom-machined case.  On the other hand, the full-sized V1.2 MAX PCB offers the flexibility of the onboard DAC and more flexibility with the cap sizes.   I usually steer people toward the MOSFET-MAX for low-impedance and toward the MiniMAX if they want to try all phones and are looking for a complete kit.

I think I will stick with the MOSFET-MAX version right now, since that is the direction I have already set out on.  I ordered a matched quad set of the Toshiba 2SJ74BL & 2SK170BL from AMB.org and a pair of 12AE6's from you (I think), Tom, along with the v1.2 PCB and other recommended items.

Thanks much for the response.  Getting very excited to start my first DIY AMP.

Can the Millett Hybrid MAXed be made into a Balanced configuration - two of everything?  If so will the double the voltage swing for the higher impedance phones - the HD800s specifically?

Also - can you replace the caps with Black Gates or V-Caps?

Quote:

Originally Posted by preproman 

Can the Millett Hybrid MAXed be made into a Balanced configuration - two of everything?  If so will the double the voltage swing for the higher impedance phones - the HD800s specifically?

 

Also - can you replace the caps with Black Gates or V-Caps?

Yes, Head-Fi user "Pabbi1" built one like that several years ago.  There is also no restriction on which brand of caps you use.

EDIT: Corrected "Pabbi1" username.  Also, here is the link to his post of the "FrankenMAX" as he called his balanced version:

http://www.head-fi.org/t/233941/new-millett-hybrid-maxed-amp/2670#post_3518367

Unfortunately, it looks like the pics are gone.

Quote:

Originally Posted by tomb 

Yes, Head-Fi user "Pabbi1" built one like that several years ago.  There is also no restriction on which brand of caps you use.

 

EDIT: Corrected "Pabbi1" username.  Also, here is the link to his post of the "FrankenMAX" as he called his balanced version:

http://www.head-fi.org/t/233941/new-millett-hybrid-maxed-amp/2670#post_3518367

Unfortunately, it looks like the pics are gone.

Thanks,  yeah the pictures are gone.  I've bee trying to find some compressions of this AMP (balanced or unbalanced) Compared to some of the balanced chimerical amps like the Woo Wa22 and or any other amp it can be compared to.

Is a balanced MHM OTL or Transformer coupled?

Quote:

Originally Posted by preproman 

Is a balanced MHM OTL or Transformer coupled?

Unless you count the walwart, there are no transformers in any of the Millett Hybrids - MAX, MiniMAX, MOSFET-MAX or even the Starving Student.

Speaking of the walwart power supply, I'm looking into alternatives.  I'm not a big fan of blocky, outlet hogging converters, convenient as they are.  I was looking into a different input source without by passing the the two 2200uf capacitor bank or voltage regulator.  I was wanting something that is pretty much self-contained and found the Mean Well EPS-35-36 (http://www.meanwell.com/search/eps-35/default.htm).  It has an adjustable output voltage of roughly 32 to 39 volts DC at 1A.  I'd simply replace everything forward of the power from CR1A on the board, tune it to roughly 33 volts and continue to use the built in voltage regulator to send 27VDC to the rest of the board.  The EPS-35-36 can be had for around $15 online from what I've been able to find.  They are 3" x 2" x 1".  Not exactly small, but not huge either.  Other than moving the bulk for the walwart to inside the amp case, can anyone see a reason this wouldn't work?
 

Quote:

Originally Posted by bwshockley 

Speaking of the walwart power supply, I'm looking into alternatives.  I'm not a big fan of blocky, outlet hogging converters, convenient as they are.  I was looking into a different input source without by passing the the two 2200uf capacitor bank or voltage regulator.  I was wanting something that is pretty much self-contained and found the Mean Well EPS-35-36 (http://www.meanwell.com/search/eps-35/default.htm).  It has an adjustable output voltage of roughly 32 to 39 volts DC at 1A.  I'd simply replace everything forward of the power from CR1A on the board, tune it to roughly 33 volts and continue to use the built in voltage regulator to send 27VDC to the rest of the board.  The EPS-35-36 can be had for around $15 online from what I've been able to find.  They are 3" x 2" x 1".  Not exactly small, but not huge either.  Other than moving the bulk for the walwart to inside the amp case, can anyone see a reason this wouldn't work?
 

Wouldn't moving the transformer into the case and that close to the tubes introduce noise?

I did something pretty simple with a regular Millet (not the Max). I got a transformer from radioshack, and put it in a small, vented box. I then basically used a sigma25 (the draw of the Millett is lower than the Max), and boxed those separate from the amp itself. With the size of the input caps, you could probably just put a transformer in a small box that is still separate, but doesn't crowd the outlet, and have all of the regulators, etc on the main board. My thoughts, but I am far, far, far from an expert!