Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › New Millett Hybrid MiniMAX (what happened to this thread?)
New Posts  All Forums:Forum Nav:

New Millett Hybrid MiniMAX (what happened to this thread?) - Page 122

post #1816 of 1944


 

Quote:
Originally Posted by tomb View Post

Yes - those are absolutely correct.  BTW, if you send Beezar an SASE - I'll send them to you for no extra charge.smily_headphones1.gif
 


Would this change in the CCS resistors also help the older BJT Millett Max, which I have? If so, I might take you up on that (typically) kind offer.

post #1817 of 1944


 

Quote:
Originally Posted by tomb View Post



Quote:
Originally Posted by MrDavis View Post


 

Quote:
Originally Posted by tomb View Post

Oops!  I knew I shouldn't have posted that from memory!  The distortion on the MiniMAX is improved by about 1/3 (still audible, IMHO).  The MOSFET-MAX's distortion is the one that's cut in half.  Regardless, major improvements either way with either amp.  Of course, the optimum loads still apply - MiniMAX is best for all-around and high impedance and the MOSFET-MAX does best with low impedance.smily_headphones1.gif

 

I'm still a noob at this, so I just want to make sure I'm ordering the correct resistors.

 

1.15 KOhms

http://www.mouser.com/Search/ProductDetail.aspx?R=RN55D1151FB14virtualkey61300000virtualkey71-RN55D1151F

 

11.5 KOhms

http://www.mouser.com/Search/ProductDetail.aspx?R=RN55D1152FB14virtualkey61300000virtualkey71-RN55D1152F


Yes - those are absolutely correct.  BTW, if you send Beezar an SASE - I'll send them to you for no extra charge.smily_headphones1.gif
 

 

I have to order a few more parts from you that I forgot to include in my last order.  I add it to the order notes section.  Thanks tomb.
 

post #1818 of 1944
That is interesting, on my MOSFET max I used The 1.13 and 11.3, should be sorta close....
post #1819 of 1944
Quote:
Originally Posted by H22 View Post

AThat is interesting, on my MOSFET max I used The 1.13 and 11.3, should be sorta close....


Within 2%. I would not worry about it.

Depending upon the tolerance of the resistors you used, you might be there already. wink.gif
post #1820 of 1944

I just finished soldering my Millitt Minimax. However, when I tried to turn the amp on for biasing the fuse blew immediately. I have checked al parts and solder joints and I do not seem to have any shortages or parts mixed up. I did however turn all trimpots 20 turns clockwise. Could it be a problem that I also turned the power supply and tube bias trimmers down? Should I turn these back up?

 

Thank you in advance, I’ll take some pictures when it is working (or when I need further help ;))

post #1821 of 1944

Try firing it up without tubes in. That cuts out the heaters and the buffer current should be way down low.

post #1822 of 1944

Thank you,

 

I will try this. If this works next steps would be:

 

Bias buffer

Put tubes back

Bias PS

Bias Tubes

 

right?

post #1823 of 1944

It's Alive!!!!

 

Changed the fuse for a 1.25A fuse and biased the buffer and tubes. Sound is delicious and very addicting.

 

Many thanks to Beefy and of course Tomb. His service and help are outstanding!

 

Will post pictures soon!

post #1824 of 1944

 

IMG_7210.JPG
Van Millitt MiniMax

 

 

IMG_7213.JPG
Van Millitt MiniMax

 

As promised!

post #1825 of 1944

I'm about to start mine - can't wait!

 

As I don't have a suitable AC supply (I'm in the UK), I'll be using a 32V 70W HP SMPS I managed to get for the bargain price of free - going to match transistors tomorrow and hopefully start the build this week. Very excited :)

post #1826 of 1944

Uhm... that might not be a great idea...

post #1827 of 1944

Could you elaborate? Voltage should be about the same 24V AC supply, so i'm planning to go into the regulator after the decoupling caps as per the schematic. Only change will be the rectifier section (DR1A jumpered, the rest unpopulated).

post #1828 of 1944
Quote:
Originally Posted by TomForshaw View Post

Could you elaborate? Voltage should be about the same 24V AC supply, so i'm planning to go into the regulator after the decoupling caps as per the schematic. Only change will be the rectifier section (DR1A jumpered, the rest unpopulated).


I'm not saying you can't do it, but there are a lot of factors to consider that may affect the proper operation of the amp.  A lot of it depends on whether you plan to utilize all those volts, or whether you plan on trying to regulate down to 27VDC, the recommended setting for the PS on the MiniMAX.

 

If you plan on using the 32V -

You only need a couple of volts from the LM317 to keep the voltage in regulation.  However, there is a physical limitation on the tube heaters.  Anything over 30V supplied to the amp circuit will lower the life expectancy of the tubes.  You'll need to resize R1 - there is a tweak page on the MiniMAX website with a graph that will show you how to do this: http://www.diyforums.org/MiniMAX/MiniMAXheaterResistor.php

 

Plus, I'm not sure how the LM317 circuit will react when fed from an SMPS.  It's quite possible that you'll be injecting a lot of high-frequency hash into the amplifier circuit that's not there with an unregulated, non-switching voltage source.  All of the filtering occurs before the LM317, so if you're bypassing all of that, it may adversely affect the sound quality of the amp. 

 

If you plan on regulating down to 27VDC -

Linear regulation is superior for sound quality.  However, it's very wasteful from an energy perspective and things get hot fast.  The 1" tall heat sinks used in the MiniMAX may not be enough to knock down the voltage that far.  Since the custom case is only 1" tall, that's your limit with the heat sink - but it may not be enough.


 

post #1829 of 1944

Thanks Tomb. I was planning on retaining the regulator - it sounds like the best way to go and a lot of thought seems to have gone into the design.

 

I just measured the SMPS - it's 29.8V unloaded - I suppose that may change when it's driving something, but if it's around there that would reduce the work somewhat that the regulator has to do - and the heat that gets burned off in the case. Hopefully 3V of overhead will be enough for the regulator - sounds like it might be pushing it a bit, but that can be adjusted later if it's not happy. 

 

Tempted to give it a try as it's what I've got on hand...

 

I'll check the supply on an oscilloscope, but there seems to be plenty of supply decoupling - although I'm tempted to retain CR3B as well to help block out a bit more of the potential high frequency noise.

post #1830 of 1944

dscn7616e.jpg

 

smily_headphones1.gif
New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › New Millett Hybrid MiniMAX (what happened to this thread?)