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New Millett Hybrid MiniMAX (what happened to this thread?) - Page 121

post #1801 of 1944

Hey guys, quick question about the tube bias.

 

When I turn the amp on the bias is ~14.5 V. It takes about an hour to get down within good levels. This is normal right? Nothing for me to be concerned about?

 

Also, this amp sounds absolutely awesome with my dt880s, and my new hd650s are coming today and I cant wait to hear them. Thanks tomb, for helping me out.

post #1802 of 1944

That sounds all good, Bob.

post #1803 of 1944

I figured. I just like to be cautious.

 

HD650s are here. Sounds fan-freaking-tastic.

post #1804 of 1944

Great to hear, Bob!  As Beefy confirmed, it takes about an hour or so before the bias quits dropping.  What you describe is perfectly normal.  Those 12AE6's make a good pairing with Sennheisers.

post #1805 of 1944
Quote:
Originally Posted by tomb View Post
Those 12AE6's make a good pairing with Sennheisers.


Ain't that the truth!

post #1806 of 1944

Sorry if I'm reviving an older thread, but I just finished my Minimax (connected to a grubDAC)--sounds amazing!

I had some problems drilling out the tube sockets but tomb helped me out (I ordered his kit).

I had a fun time building this amp; thanks for a great kit and amp. Here are some pics:

 

IMG_4335.JPGIMG_4366.JPGIMG_4402.JPG

post #1807 of 1944
Quote:
Originally Posted by nate911 View Post

Sorry if I'm reviving an older thread, but I just finished my Minimax (connected to a grubDAC)--sounds amazing!

I had some problems drilling out the tube sockets but tomb helped me out (I ordered his kit).

I had a fun time building this amp; thanks for a great kit and amp. Here are some pics:

 

IMG_4335.JPGIMG_4366.JPGIMG_4402.JPG


Nice work, Nate!  Those are great pics with the tube lighting, too!
 

post #1808 of 1944
Quote:
Originally Posted by nate911 View Post


Sorry if I'm reviving an older thread, but I just finished my Minimax (connected to a grubDAC)--sounds amazing!




Never feel you need to apologize for resurrecting a build thread with a new build.

It is always a great day when a new amp comes to life! Congrats!
post #1809 of 1944


 

Quote:

Originally Posted by tomb View Post

 

Nice work, Nate!  Those are great pics with the tube lighting, too!
 


Thanks! Yea I snapped some good pics, beautiful amp and case.

 


Quote:

Originally Posted by jdkJake View Post



Never feel you need to apologize for resurrecting a build thread with a new build.It is always a great day when a new amp comes to life! Congrats!


Indeed, thanks!

post #1810 of 1944

Getting a weird DB bias with my latest build - can't set DB bias on one channel lower than 135mV, while the other one I can set normally to 80mV.  I think the soldering job is fine, but I didn't match the transistors very well.

 

Perhaps the PN4392 is burned, otherwise, the 2K trimpot inline with 100R is still too high...  Maybe the CSS transistors are poorly matched, but I wasn't expecting it to have such crazy results...

post #1811 of 1944
Quote:
Originally Posted by FallenAngel View Post

Getting a weird DB bias with my latest build - can't set DB bias on one channel lower than 135mV, while the other one I can set normally to 80mV.  I think the soldering job is fine, but I didn't match the transistors very well.

 

Perhaps the PN4392 is burned, otherwise, the 2K trimpot inline with 100R is still too high...  Maybe the CSS transistors are poorly matched, but I wasn't expecting it to have such crazy results...


You're correct.  Miss-matched transistors are not going to prevent you from turning down the bias below 135mV and the CCS transistors are not going to have an effect on this (unless they're 5088's or something really weird).  I suspect something else is going on - bad trimmer, bad PN4392 as you suggest (although that implies zero bias), or maybe you misplaced a resistor.  It should be easy to compare with the good channel, just be very methodical.  It's almost like proof-reading our own essay paper: it's really hard to see our own mistakes (assuming that's it, that is).  Let us know what you find. smily_headphones1.gif
 

post #1812 of 1944

BTW, I was planning on making a bigger announcement (with some SASE freebies from Beezar), but I've started supplying 1.15K and 11.5K resistors for the CCS (RA8 and RA9 - L/R).  It brings the CCS current down to 0.565ma and cuts the distortion in half.  IMHO, the difference is easily noticed in the listening.  I never thought that little bit of change (the original MiniMAX was 0.650ma) would make that much of a difference.  However, after working with Dsavitsk's Torpedo prototype over the last year, he's taught me that small changes in the CCS can have a big effect.  I've tested with RMAA extensively, before and after - with old CCS and new CCS currents, and the 1.15K/11.5K resistors make a real difference.\

 

 

EDIT: Dang, I thought I clicked to edit the post above.  Oh, well ...

post #1813 of 1944

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

post #1814 of 1944


 

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

post #1815 of 1944
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
 

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