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Millett "Starving Student" hybrid amp - Page 390

post #5836 of 6815

What kind of bolts and nuts should i use to mount the heatsink to a chassis?

 

 

post #5837 of 6815
Quote:
Originally Posted by juntom10 View Post

What kind of bolts and nuts should i use to mount the heatsink to a chassis?

 

 


Anything as long as you don't tie the MOSFET tab to the chassis (ground). You can use Beezar's mounting kit, which includes everything you need and has an insulator and a thermal pad.

 

http://beezar.com/catalog/product_info.php?cPath=30&products_id=60

 

  • 4-40 x 3/8" Socket Head Cap Screw - SAE black steel
  • #4 Flat Washer (2) - 18-8 Stainless Steel
  • Aavid high-temp, rigid polysulfide glass-filled shoulder washer
  • #4 Lock Washer, Stainless Steel, split-ring
  • 4-40 Steel Nut
  • Bergquist adhesive-backed thermal pad (no grease required)

 

post #5838 of 6815
Quote:
Originally Posted by Aflac View Post




Anything as long as you don't tie the MOSFET tab to the chassis (ground). You can use Beezar's mounting kit, which includes everything you need and has an insulator and a thermal pad.

 

http://beezar.com/catalog/product_info.php?cPath=30&products_id=60

 

  • 4-40 x 3/8" Socket Head Cap Screw - SAE black steel
  • #4 Flat Washer (2) - 18-8 Stainless Steel
  • Aavid high-temp, rigid polysulfide glass-filled shoulder washer
  • #4 Lock Washer, Stainless Steel, split-ring
  • 4-40 Steel Nut
  • Bergquist adhesive-backed thermal pad (no grease required)

 


I was wondering how to put the original heatsink on the case (the one that you have to solder). but i guess i can just use ones that were used for pcb kit (square looking heatsink), and use parts that you listed above... 

To do that, i need to get a metal panel.

Hmm actually this project is getting more interesting...

Everything is new to me (i was building kits before), and kind of excited to make my own version.

Yesterday, it took me 3 hours to make BOM for 12AU7 version with parts that i want to use...

Now it is time to order parts, and need to find materials for the casing :)

 

post #5839 of 6815

I'm attaching the BOM that i made for 12AU7 version.

 

Of course you can change parts to ones that you like.

 

BOM for 12AU7.jpg

(I realized i can not attach the .xls file....so i took a screen shot lol)

 

By the way, I have some questions.

 

For capacitors, can i use whatever capacitors that have higher capacitance and voltage stated in the list?

 

Also, lets say i need 680uF, 63V capacitor, can i use 2 of 680uF 50v capacitors in series?


Edited by juntom10 - 4/26/11 at 11:23pm
post #5840 of 6815
Quote:
Originally Posted by juntom10 View Post

By the way, I have some questions.

 

For capacitors, can i use whatever capacitors that have higher capacitance and voltage stated in the list?

 

Also, lets say i need 680uF, 63V capacitor, can i use 2 of 680uF 50v capacitors in series?


You can probably use higher values, but realize that there is more to capacitors than values.

That doesn't mean that there will be any benefit from it. And different caps sound different.. Power caps should have low ripple, and stuff like that.

 

When you put two 680uF caps in series, you'll double the voltage capability, but you'll loose half the capacitance.

 

So, you'd need two 50v 1360uF caps in series to have over 63v

 

post #5841 of 6815

OH! that makes sense!

 

Thank you for the answer! :)
 

Quote:
Originally Posted by nullstring View Post




You can probably use higher values, but realize that there is more to capacitors than values.

That doesn't mean that there will be any benefit from it. And different caps sound different.. Power caps should have low ripple, and stuff like that.

 

When you put two 680uF caps in series, you'll double the voltage capability, but you'll loose half the capacitance.

 

So, you'd need two 50v 1360uF caps in series to have over 63v

 



 

post #5842 of 6815

Today, i received the package from digikey.

 

I was so happy looking at parts haha...

 

but one sec.

 

???????????????????

 

what is this?

 

wow....ugh...ugh..

 

.

.

.

 

I didnt know i ordered this enormous toggle switch...ugh

 

it looks cool. but bit bigger than i thought lol (i didnt check the size when i was ordering it)

 

I was bit wondering why this costs 6 bucks....

 

and now i know lol

 

haha

 

After i receive wires and pots that i've ordered, ill start building!

IMG_1753.JPG

post #5843 of 6815

So I came across another DIY project that integrated nicely with my starving student amp.  http://www.head-fi.org/forum/thread/198828/the-hissbuster-for-sensitive-headphones  I was looking for a way to tame the gain for sensitive/efficient headphones, and this does the trick.  I used the resistor values for a -20dB attenuator with my Ultrasone HFI-780s.  To give you an idea, that brings the volume control from ~9:00 to 1:00 on the pot at normal listening volume. (minimum with the pot speced out in the BOM is around 7:00.  You just make this up, and put it between your output caps and your headphone jack. 

 

The parts I used (and their mouser part #'s)

1x 3PDT switch (108-1M31T1B1M1QE-EVX)

2x 27 ohm metal film resistors .5W (660-MF1/2LCT52R270J)

2x 3.32 ohm metal film resistors .5W  (660-MF1/2DCT52R3R32F)

 

I was looking for a good way to decrease the gain, while still keeping the option for a high gain mode for headphones like my buddy's AKG K240 Studios which require the volume pot to be up half way anyway.  

 

You can see by the original schematic that the layout is pretty simple, but I incorporated it all onto the back of a switch to keep things tidy inside the amp.  I originally only used a dpdt switch, but that created a 3.3 ohm load in parallel with the headphones when the attenuation circuit wasn't active (and I figured that using up current=less than ideal).  I included a paint drawing in case to help visualize what I did.  I mounted this switch on the back of my amp, and when i want a -20dB attenuation on the volume output, I flip the switch.  If I want full output, I flip it the other way.  This seemed to me like  a better solution than increasing the input resistance well over 100k ohms just to get some attenuation on the output.  (Also this eliminates any trace of hiss (however small) on the output.  I haven't seen this mentioned in this thread before, but I have seen people trying to reduce gain to bring the volume pot out of the poor tracking area and increase volume pot turn usability.  This solution worked very well for me and I hope someone else finds this useful.

 

attenuator.png

 

post #5844 of 6815
I just stuck a DPDT switch on R16 and R17 (from the PCB schematic).
post #5845 of 6815

With my headphones I had too much gain even with the input going through 50k resistors.

post #5846 of 6815

Is that implemented at the output? I tried using a switch on R16/17 but it doesn't work well. I could use something like this. Can this be used in a breakout box?

post #5847 of 6815

Yes, it goes on the output.  On my drawing, the "input" to the attenuator comes from the output capacitors, and the "output" wires go to the headphone jack.

 

Edit: It could absolutely be implemented in a small box (or even in line possibly without a switch).  I chose to put my inside the amplifier though so it was all self contained.


Edited by DarkTiger892 - 5/7/11 at 9:03pm
post #5848 of 6815

To clear something up.

the 50k resistors in series with the pot do not attenuate the signal at all

 

If you need to lower the volume, put a resistor in parallel with the pot.

 

ignore me

ignore me
Edited by nullstring - 5/12/11 at 12:56pm
post #5849 of 6815
Quote:
Originally Posted by nullstring View Post

To clear something up.

the 50k resistors in series with the pot do not attenuate the signal at all

 

If you need to lower the volume, put a resistor in parallel with the pot.


What? They have some effect on volume, and that's attenuation if I think I'm using the word correctly... I have 50k/150k resistors (R16/R17) hooked up to a switch which I use as a "gain switch", although it's not terribly effective.

 

post #5850 of 6815
Quote:
Originally Posted by Aflac View Post
Originally Posted by nullstring View Post

To clear something up.

the 50k resistors in series with the pot do not attenuate the signal at all

 

If you need to lower the volume, put a resistor in parallel with the pot.



What? They have some effect on volume, and that's attenuation if I think I'm using the word correctly... I have 50k/150k resistors (R16/R17) hooked up to a switch which I use as a "gain switch", although it's not terribly effective.

 


Yeah, I think something's mixed up here.  Resistance in series with the pot will most definitely attenuate the signal.

 


Edited by tomb - 5/10/11 at 10:54pm
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