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New Millett Hybrid Maxed Amp
Jul 13, 2010 at 9:43 AM Post #6,106 of 6,727


Quote:
tomb said:
Actually, the CA2 and CA9 position have the most to do with preserving bass from the basic input signal/source.  It's a question of keeping all there is, or taking some away.  This can happen with the wrong bypass cap at CA9 (don't use Vitamin Q's, there, for instance), or if CA2 is too small (<1000uf).  Either the ES 1000uf 16V or the Elna RFS Silmic II at 1000uf and one of the voltage ratings listed in the previous post is best.  For CA9, you should just use Wima MKP10's.
 
As far as bass at CA7, it's strictly controlled by the RC-circuit cutoff frequency formed with CA7, RB14, and the impedance of the headphones.  1000uf should take care of everything down to 4 ohms, assuming you use a 22R at RB14.
 


 
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Thanks Tomb,  I guess I got confused when i was reading last night.  I do have Wima MKP10's in CA9 but used a Panasonic FM 1000uf in CA2.  Maybe I will look into getting a better option for CA2 then.  Looks like digikey has the Elna in stock [size=small]604-1111-ND[/size]
 
Now that I have it all working I'm play mode to see what changes what :)
 
Jul 13, 2010 at 10:12 AM Post #6,107 of 6,727


 
Quote:
aalelan said:
Thanks Tomb,  I guess I got confused when i was reading last night.  I do have Wima MKP10's in CA9 but used a Panasonic FM 1000uf in CA2.  Maybe I will look into getting a better option for CA2 then.  Looks like digikey has the Elna in stock [size=small]604-1111-ND[/size]
 
Now that I have it all working I'm play mode to see what changes what :)
Click to expand...


Yeah, that's the perfect cap to use at CA2 for the MOSFET-MAX.  However, please note that once you're using 1000uf at CA2 anyway - the changes to a true boutique cap will be subtle back there, at best.  The most noticeable changes are at CA7.  Still, it's probably worth the investment if you're looking to incorporate the best tweaks.
 
Focus on tubes, too, if you can - that's where the biggest changes are made, once you have the proper caps in the proper positions.  There's a huge variance in the quality of Millett-type tubes.  The quality can't be tested on a tube tester, either, so it's more of a pot-luck, tube-rolling type of thing, even though all the tubes you might be trying are the same designation, for instance.
 
 
Jul 13, 2010 at 11:43 AM Post #6,108 of 6,727

 
Quote:
tomb said:
 

If you're building a MOSFET-MAX, you're already using 1-1/2" tall heat sinks and locating the PCB in the bottom slot of the recommended Hammond case.  This allows you to alleviate the only issue with Elna RFS Silmic II's: their very-large size.  IMHO, there's no reason to use anything else than an Elna RFS Silmic II, as long as the rating is sufficient and there's sufficient room.  They are as good as Black Gate NX's without the break-in and the high cost (now add rarity!).  What's not to like?
 
Use the 1000uf Elna RFS Silmic II at 16V, 25V, or 35V for CA2 L/R - all available and stocked at DigiKey.  Use the 1000uf Elna RFS Silmic II at 35V for CA7 L/R.  Handmade Electronics also stocks some of those sizes.
 
Stay away from KZ's - their natural "etchiness" combines badly with the detail of the MOSFET diamond buffer and borders on constant sibilance. (I speak from experience.
wink.gif
)
 
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Thanks for the information, Tom! Just to make sure, are there any drawbacks to using a cap rated at a higher voltage than recommended? For instance, if I use a 1000uF 50V cap at CA2 and CA7, will there be any negative consequences?
 
Jul 13, 2010 at 7:38 PM Post #6,110 of 6,727
 
Another MOSFET lives!
 
100_2118.jpg

 
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This shot shows the interference between the back PS cap (2200uF/35V) and the test point. I simply
loosened the cap and bent the tip of the point a bit.
 
100_2117.jpg

 
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Tube LED's are the violet ones from Beezar. They look nice with the top off, but don't really show up
when it's all buttoned up. I may change them to red. Power LED is the color-change also from Beezar.
 
Jul 13, 2010 at 7:48 PM Post #6,111 of 6,727


Quote:
aalelan said:
I have gotten lost on what a good bias point is for the MAX-MOSFET  Running the PS at 27v  and tubes at 13.5v  what should I do the FET's at?  I'm currently running at 180mv..
 
Thanks!
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You should boost them up to 275mV, if you can stand the heat.  Unlike the BJT's, the MOSFETs will get better and better, the more current you feed them.  I regularly run mine at 125ma (~275mV)
 
 
Jul 13, 2010 at 7:54 PM Post #6,113 of 6,727


tomb said:
 Focus on tubes, too, if you can - that's where the biggest changes are made, once you have the proper caps in the proper positions.  There's a huge variance in the quality of Millett-type tubes.  The quality can't be tested on a tube tester, either, so it's more of a pot-luck, tube-rolling type of thing, even though all the tubes you might be trying are the same designation, for instance.
 
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This is REALLY good advice. I was surprised at how much tubes vary the sound. I guess it is the mechanical nature of their construction. I have had two sets of tubes, seemingly identical, perform completely differently. Also, learn how to spot microphonic tubes. TomB taught me how to recognize that condition (whereas part of the tube internal touches the glass and starts to "ring") and how to tolerate it, attempt to fix it or chuck it. In the pictures I show above, the left tube, marked RAYTHEON is slightly microphonic. Not enough to make a difference, but, microphonic nonetheless. The right tube is completely fine. Welcome to the wonderful world of tubes! :wink: am I getting rid of that tube? Nope. Sounds great at the volume I listen too.

jk
 
Jul 13, 2010 at 8:02 PM Post #6,115 of 6,727
YEAH Funch!

I have been waiting for this post for a while now, you have been suspiciously quiet! :wink:

Looks great! You drill work is superb. Far superior to mine!

So, what do you think? Enquiring minds want to know.

Details, details please.

jk

 
Jul 13, 2010 at 8:19 PM Post #6,116 of 6,727
tomb - Thanks for the nice words.
 
Jake - Thanks. The drill work took FOREVER, but was worth it. To get the holes as accurate as possible,
 
I placed the template on each panel and used a spring loaded punch to dimple it. Then I used my pin vise with
 
a small bit just to start and dimple the hole. After that, I went back with the largest bit that would fit in the
 
pin vise to enlarge the dimple. That way the bit for the final drilling won't wander, and will put the hole in the
 
exact correct location. BTW, I used the drill press for the final drilling. I still botched the two rear holes over
 
the PS heat sink, but you have to do a second look to see it. The final step was to used a hand countersink
 
tool to clean up each hole.
 
100_2122.jpg

 
Impressions to come later.
 
Jul 13, 2010 at 10:27 PM Post #6,118 of 6,727
Looks Great Funch!!!  I need to make up my mind how I want to do my casework for mine..
 
OK, OK... I have taken a baby step up I moved them to 220mv, I will scoot them up a little at a time over the next few days.
 
I'm trying to talk a guy at work in to getting a set of AGK K701's so I can try them out on this!  I think he kinda wants to, its just going to take a few nudges :)
 
This is just like when I rebuilt my Corvette, every time I look at it I think "well I could do this....."  what have I got myself into!?!?
 
AA
 
Jul 14, 2010 at 12:41 AM Post #6,119 of 6,727


Quote:
jdkjake said:
You even drilled the right tube bushing!!

Your the man Funch. Awesome attention to detail.

jk
 
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Actually, it's called being terminally anal!  I did try to run it up and down
 
the drill bit on the press, and tried to file it, but it's too tough, so I had to
 
use an Xacto knife to carve it away.
 
Jul 14, 2010 at 6:57 PM Post #6,120 of 6,727
Scratching head here..  Playing around here at my desk and I figured I would check my voltages.. my FET bias had droped about 12mv from last night so I tweaked it up again..  then I checked my tubes, left was at 16v!! and the right was at 14v..  I got the right back down to 13.5 but the left will not go down at all for some reason..  I checked the PS output and it was at 24!?!  so I check the AC side of things and the wall wart is only putting out 22.8v  where it was running at almost 27V loaded up.  The most I can get out of the PS adjusting the 1K is 25.4v
 
Everything seems to be going whacky on me, any ideas??
 
EDIT: just to note the wall wart is the 50va one from Beezar, so it should be plenty hefty enough.
 
AA
 
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