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Millett "Starving Student" hybrid amp - Page 437

post #6541 of 6786

Hi those boards ship worldwide for $3.00 for up to 2 boards

 

if you want more than two I can quote

 

cheers

FRED

post #6542 of 6786

Thanks for the help guys its coming along nicely.  I had to switch most of the caps from 63 to 100v as that is what my local surplus electronics shop, HSC, had on the shelves and could only find an 100k stereo POT as opposed to the 50k Pot specified in the diagram.

 

SO I am wondering what changes I need to make inorder to accomodate this ie. changing resitors R16 and 17.  When the Pot is turned all the way there will be a 50k resistor impeding the signal.  SO I am guesing I should just leave the 50k resistors and the 100k pot will just attenuate the signal faster than the 50k.  Can anyone shed some light onto this?

post #6543 of 6786

A pot is only a resistor voltage divider. The voltage at the output is a ratio of where the wiper is in respect with the total rotation range. The pot can be 10k, 50k or 1 Meg, it doesn't change anything. The only thing that changes is the load the DAC sees.

 

Adding a 50K resistors before a volume pot virtually lengthens the resisting surface by 50K. Say you have a 50K pot that you never go over half its rotation range. Adding a 50K resistor before pushes that useless half outside the rotation range (not really on a log pot, but you get the idea). It's effectively stretching the first half of the pot across its whole rotation range. The value isn't important, you chose it after experimenting with your system until you find the right value. It depends on the voltage out of your DAC and the voltage your headphones need.

 

Personally I went with the largest knob I could fit to the enclosure instead of attenuating the signal with resistors. I find this a cleaner solution to the same problem.

post #6544 of 6786

I'll just drop this here...

 

post #6545 of 6786
Looking pretty schmexy...
You've decided on a design now then? Well keep us posted.

I'm still going round in circles with mine due to budget concerns... I have a plan but it'll cost about 120€, so I'm going to try to get some work done right after my exams so that I can get on with it. smily_headphones1.gif
post #6546 of 6786
Quote:
Originally Posted by KimLaroux View Post

I'll just drop this here...

 

 

Are those CCS boards I see right beside the tube sockets?

post #6547 of 6786
Quote:
Originally Posted by the_equalizer View Post

 

Are those CCS boards I see right beside the tube sockets?

 

Yes. biggrin.gif

 

They are the same tail CCS as in the SOHA II. I also built a voltage multiplier like the SOHA's, which you can see between the AC inlet and the audio inputs. Now, the tubes run on a 165 V rail and the MOSFETs on a 25 V one.

 

I'll start a new thread once I'm done to share the story of this project. It's not really a MSSH now anyways, so I'll need to rename it.

post #6548 of 6786

just ordered my tubes and sockets to go along with the pcb from fred_fred2004.

 

Trying to finish my BOM from mouser but would like some input about a switch and fet heat sinks. I have some ebony from another project so I'm going to case this amp up with that. I'm going to use a big 1.5 inch alum knob and I'm looking for a good looking switch to match that. I'm also looking for those curved heat sinks ive seen used, but Icant seem to find them on mouser.

 

Thanks

post #6549 of 6786
Quote:
Originally Posted by KimLaroux View Post

 

Yes. biggrin.gif

 

They are the same tail CCS as in the SOHA II. I also built a voltage multiplier like the SOHA's, which you can see between the AC inlet and the audio inputs. Now, the tubes run on a 165 V rail and the MOSFETs on a 25 V one.

 

I'll start a new thread once I'm done to share the story of this project. It's not really a MSSH now anyways, so I'll need to rename it.

Nice job on your amp. CCS with tube can stress filaments if not carefully done. I assume you are using something like:

http://www.cavalliaudio.com/diy/soha%20ii/main.php?page=design/opdesign

post #6550 of 6786
Quote:
Originally Posted by alphaman View Post

Nice job on your amp. CCS with tube can stress filaments if not carefully done. I assume you are using something like:

http://www.cavalliaudio.com/diy/soha%20ii/main.php?page=design/opdesign

 

I am using the tail CCS as shown at the bottom of this page: http://www.cavalliaudio.com/diy/soha%20ii/main.php?page=design/ipdesign

 

The only difference with mine is instead of having it powered between the negative rail and ground, I power it between ground and the 25 V rail.

 

I paralleled the triodes and use a single 7.52 K cathode resistor instead of the mirror. The tubes are powered from a 160 V rail.

post #6551 of 6786
Quote:
Originally Posted by KimLaroux View Post

...It's not really a MSSH now anyways, so I'll need to rename it.

 

Super Starving Student? MHSSS?

post #6552 of 6786
My vote would be for : 'This amp came in over budget, but who's counting? Hybrid Student amp' biggrin.gif
post #6553 of 6786

I totally lost count of the money I poured into this project. I stopped counting somewhere around 500$. I don't really feel like going back and do the sum... rolleyes.gif Though this was a learning project which went trough many redesigns and tweaks for the sake of experimenting and learning. So I'd consider the money more like tuition fees than project costs.

 

I think I'll simply name it 12AU7/MOSFET hybrid, or something. It's not a commercial or published DIY project so I don't really care if it remains nameless. I may draw and share the final schematic at some point, but it may be useless. This whole project was designed around a 30-0-30 transformer I salvaged from an old stereo amp. Buying such a transformer for a high voltage hybrid may not be the smartest idea. If you count in the price for the voltage multiplier, I bet it'll end up being the same price as a high voltage transformer designed to power tubes. And then there's the problem that I didn't design the schematics, the amplifier is a patchwork of schematics from already published DIY projects and datasheets. I simply did the math to make all these schematics work with the voltages I managed to get out of the transformer.

post #6554 of 6786
... Mines gone/going the same way! But yeah, I've learnt so much from it. I know have a (hopefully) final design idea taking shap that I'll be able to build after my Baccalaureat.
post #6555 of 6786

This is a LONG thread, and many may not have the time to trudge thru it all. Not a bad time, methinks, to post an UPDATED schematic and BOM.

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