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Millett "Starving Student" hybrid amp - Page 436

post #6526 of 6806

Connect them across the tube heaters. There is only 13 V across them, so you don't need a high power resistor. And since this voltage is already at the sockets, you don't even need to add any wires. Win-win.

post #6527 of 6806

Quick question, Currently I have the amp build on a wood case, but since it's not very well build because it was my first time, I'm planning on redoing it on a metal case.

Can someone tell me what do I need to watch out for while bulding on a metal case? The mosfets already have an insulator for the heatsinks but what about the rest of the parts that will be screwed to the metal case?

post #6528 of 6806
Quote:
Originally Posted by Amatsu View Post

Quick question, Currently I have the amp build on a wood case, but since it's not very well build because it was my first time, I'm planning on redoing it on a metal case.

Can someone tell me what do I need to watch out for while bulding on a metal case? The mosfets already have an insulator for the heatsinks but what about the rest of the parts that will be screwed to the metal case?

The case being metal isn't a big deal, everything that connects to it will be grounded and in the end your case will be grounded also, the only thing you really need to worry about is shorting the circuit by accidentally touching a solder joint or stray wire to the case. The only thing that gave me any problems was the MOSFETs, I had to brush liquid black tape on the connectors because the leads were a lot longer than the insulators I used. But other than those everything should mount directly to your case. 

post #6529 of 6806
Quote:
Originally Posted by jarscar View Post

The case being metal isn't a big deal, everything that connects to it will be grounded and in the end your case will be grounded also, the only thing you really need to worry about is shorting the circuit by accidentally touching a solder joint or stray wire to the case. The only thing that gave me any problems was the MOSFETs, I had to brush liquid black tape on the connectors because the leads were a lot longer than the insulators I used. But other than those everything should mount directly to your case. 

 

Only two pages back:

 

Quote:
Originally Posted by KimLaroux View Post

I believe your grounding scheme is not efficient enough. It's kind of a common problem here, as it's usually a first project for most of us. You have to think of the ground as a return path for different signals, and not as a "neutral" point where everything gets nullified. Ground is nothing more than the opposite of the power rail, after all. A perfectly silent tube amplifier uses a balanced wiring for V+ and Gnd throughout the amplifier, with proper decoupling at each stage.

 

The voltage you get at any single point is in reference to the ground at the other side of this point. If that ground point is noisy, the end result is the same as if your V+ was noisy.

 

Power supply grounds are noisy. Signal grounds are sensitive to noise. Therefore, make sure the power return paths are not going across your signal return paths. 

 

This is why the first recommendation most people have is to tell you to use a Star Ground. Connect all your return paths to a single point. Connect this point to the power input jack using a single wire. Connect the star ground to the chassis at a single point, making sure no current flows trough the enclosure. This is not a car, it's an audio device. The enclosure should be used as nothing more than a shield.

 

I had to rebuild my whole amplifier many times to learn all that. Now it's dead silent.

beerchug.gif

post #6530 of 6806
uote:
Originally Posted by KimLaroux View Post

 

Only two pages back:

 

Yeah and I fixed my grounding scheme, all my problems had to do with a daisy chain grounding. I no longer have  any noise at all, and I didn't directly ground my parts to the case, but l didn't insulate them from the case either, the ground of the RCA jacks for instance connect to the nut which screws directly to the case. I didn't mean to speak out of turn I was just trying to tell him he wouldn't fry a tube or anything by mounting to a metal case.

post #6531 of 6806

I love this. I'm thinking of building the 12AU7 version. Man, the price of valves have gone up in the last year or so (I usually get guitar amp valves).

 

I have a question about integrating a power supply within the box. Is this recommended? If so, which power supplies do everyone use? Does the star ground to chassis go back to main unput plug or GND of PSU output.

 

Also, regarding the Cisco power supply, there are plenty on ebay, but don't have the exact part number, however they are 48V 0.4A. Is that fine too?

 

-sanguinicus

post #6532 of 6806
Quote:
Originally Posted by sanguinicus View Post

 

Also, regarding the Cisco power supply, there are plenty on ebay, but don't have the exact part number, however they are 48V 0.4A. Is that fine too?

 


The minimum is 48 volts, 0.38A, so 0.4A is enough to get it up and running.

post #6533 of 6806
Dumb question. How do i ground this? Like I have a capacitor going to ground
post #6534 of 6806
Quote:
Originally Posted by audi0lurker View Post

Dumb question. How do i ground this? Like I have a capacitor going to ground

the minus pin from your power supply connector is the ground...google  "star ground" There can be local grounds connected together and ran to a central star ground. Look at "star ground" on google images too.


Edited by vixr - 5/31/13 at 5:06am
post #6535 of 6806

Hi guys 0/ I’m new to the forum so be gentle please J .

I’m just in the process of finishing Pete’s Might Midget, just a matter of casing up and getting it to my friends to hook up to his many boxes that beep and make pretty patterns on the front, I think they are called oscillators , not sure lol. Anyway I love the idea of the starving student but I have searched for a supplier of the toobs in the uk and can’t find anyone so far. When I search on eBay I get suppliers in the US and these “5 Tubes 10GF7A, 6Z106J10, 19DQ3, 6Z10/6J10, 6CG36BW3” . I’m not a toob expert is there an alternative toob because it looks like they will cost nearly £10 each if I get them from the US and that really defeats the object of the low cost amp ?

post #6536 of 6806

Well, there's been mention that the market has been depleted of 19J6 valves. There's a few on eBay but they cost a fortune and it can't be garaunteed that they are matched; they aren't sold in pairs. Many users here have had much success building a variation with 12AU7 valves and their variants. I've just finished my BOM for a 12AU7 one.

 

And the thing with the pretty patterns, I think you're referring to an Oscilloscope :)

 

See here for the variation: http://www.diyforums.org/SSMH/SSMHvariants.php Or, have a look back through the 400+ pages haha.
 

post #6537 of 6806

Thanks for that .. just looked and its still going to be £9 each for the valves.. rip off Britain same ones in the US £3 ! Think I'll build an O2 instead :(

post #6538 of 6806

Why don't you just ship them from USA? I live in Australia and I'm looking to USA for valves...

post #6539 of 6806

Wow, thanks for the great idea. I'm hoping to try my hand at it soon and can't wait to see what the results might be! I just hope I can find all the items as it seems everyone is jumping on your awesome idea.
 

post #6540 of 6806

If it helps, Fred_fred2004 made some circuit boards for the linked 12au7 design. I am currently waiting on the shipping since he is located in Australia but he is selling them at a great price and still has some left. 

 

http://www.head-fi.org/t/664191/starving-student-pcbs/15#post_9503650

 

That's the post. He mentioned he still has a few left if you are interested. Let me know if you have any issues with the link.

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