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roggom
PostPosted: 16 Nov 2010, 16:03 
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Location: Denver, Colorado
santik wrote:
so, you are saying that the MOSFETs should be as cool as possible in order not to induce distortion? and some FETs will definitely make this sound?

I have noticed that Mosfets found in power supplies IRF 530 630 and so forth will exhibit the quick hiss and also have a worse response curve. I am not 100% sure what is going on, just think it is something internal to the mosfet to prevent thermal runaway. If you are experiencing more than one hiss an hour then heatsinking is in order. It does not have to be fancy, I have used washers before.

For your power supply question download PSUD2 and design for least amount of ripple. http://www.duncanamps.com/psud2/index.html Some RC LC theory http://www.play-hookey.com/ac_theory/ps_filters.html

Now the only issue with low voltage power supplies is to really make them clean you will need very low value resistors, in turn they draw some current.

Other than that you can look up some 12v power supply projects by Ti Kan (AMB) http://www.amb.org/audio/sigma11/
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roggom
PostPosted: 16 Nov 2010, 16:22 
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smiki wrote:
I'm looking at the PCB image you provided (http://diyaudioprojects.com/Solid/12AU7 ... -Image.png) .

But seems to me there is an error with the C2 capacitor polarity (at the top).
The positive (+) pin should be connected to the cathode (pin no. 3 of the tube) not the GND trace as the image shows.

Same error is on the component layout image and eagle BRD file.

You are correct, got a little happy in eagle with the flip button. It will get updated but may take a while.

Welcome to the boards.
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santik
PostPosted: 16 Nov 2010, 20:17 
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Joined: 18 Sep 2010, 12:48
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roggom wrote:
santik wrote:
so, you are saying that the MOSFETs should be as cool as possible in order not to induce distortion? and some FETs will definitely make this sound?

I have noticed that Mosfets found in power supplies IRF 530 630 and so forth will exhibit the quick hiss and also have a worse response curve. I am not 100% sure what is going on, just think it is something intenal to the mosfet to prevent thermal runaway. If you are experiencing more than one hiss an hour then heatsinking is in order. It does not have to be fancy, I have used washers before.

For your power supply question download PSUD2 and design for least amount of ripple. http://www.duncanamps.com/psud2/index.html Some RC LC theory http://www.play-hookey.com/ac_theory/ps_filters.html

Now the only issue with low voltage power supplies is to really make them clean you will need very low value resistors, in turn they draw some current.

Other than that you can look up some 12v power supply projects by Ti Kan (AMB) http://www.amb.org/audio/sigma11/

the MOSFETs are heatsinked... and I noticed... if I fan the heatsinks... it gets cooler and sounds slightly better...

I am presuming the hissing does come from the power supply... I am thinking of making it away... I guess it is ripple in the supply... how do it away if it is ripple? I have 1000uf 50V capacitors in hand.

are you suggesting I put a very low value resistor at the power to remove them? in between the capacitors?
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jaki54321
PostPosted: 16 Nov 2010, 22:26 
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Ok guys i am an idiot... I bought polarized caps for the 2.2 uF caps(C1) and I was wondering, when they come in the mail, can I still use them? I dont want to have to buy more and pay more shipping for 60 cents worth of caps =| Stupid shipping lol
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roggom
PostPosted: 16 Nov 2010, 23:09 
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jaki54321 wrote:
Ok guys i am an idiot... I bought polarized caps for the 2.2 uF caps(C1) and I was wondering, when they come in the mail, can I still use them? I dont want to have to buy more and pay more shipping for 60 cents worth of caps =| Stupid shipping lol

No problem, just remember the (+) always faces the tube.

So as an input coupling cap the music signal comes into the (-) and out the (+)

Welcome to the board!
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roggom
PostPosted: 16 Nov 2010, 23:17 
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Santik,

My suggestion at this point is to purchase a used SMPS that exibits low ripple. It may take some trial and error. Go to a thrift and pick up all the 12 and 13vdc smps you can find. They usually are only a few dollars or pounds. Once you get that working.

Review the Neeets module I linked earlier and study chapter 3, it covers power supplies and filtering.

Once you have a grasp it will all come a little easier. Not that do not want to answer your question, just this is a learning experience. :up:
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santik
PostPosted: 16 Nov 2010, 23:26 
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Joined: 18 Sep 2010, 12:48
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yeah, I understand. Will do.

Will see what I can do and tell everyone what I did to overcome it! :D
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sknhd69
PostPosted: 17 Nov 2010, 08:57 
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Location: remote town, far east
hi, this is my first post [found the project via google] :mrgreen:
and this is also my first tube-based project :idea:

i've finished this project, it sounds great...but with some problem:
- too bright
- early clipping :(
- lack of bass :headphones:

i'm using Electro Harmonix 12AU7 and 4k7 resistor [instead 10k pot]
how to fix that problem? :up:

P.S: pic uploaded later :P
thanks :thumbsup:
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roggom
PostPosted: 17 Nov 2010, 19:04 
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sknhd69 wrote:
hi, this is my first post [found the project via google] :mrgreen:
and this is also my first tube-based project :idea:

i've finished this project, it sounds great...but with some problem:


- too bright Check the values of your coupling capacitors, they should be 2.2uF not .22uF. It is easy to confuse. Easy way to test is to put another higher value capacitor in parrallel with C1 (if electrolytic (-) to input (+) towards tube.-


early clipping :( What voltage do you have at the (+) of C3? Should be half of your supply voltage, if not increase or decrease the value of the plate resistor.



- lack of bass :headphones: again check the value of your coupling capacitors/i'm using Electro Harmonix 12AU7 and 4k7 resistor [instead 10k pot]
how to fix that problem? :up:

P.S: pic uploaded later :P
thanks :thumbsup:


Post pics when you have a chance thanks
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sknhd69
PostPosted: 17 Nov 2010, 20:52 
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Joined: 17 Nov 2010, 00:28
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Location: remote town, far east
roggom wrote:
sknhd69 wrote:
- too bright Check the values of your coupling capacitors, they should be 2.2uF not .22uF. It is easy to confuse. Easy way to test is to put another higher value capacitor in parrallel with C1 (if electrolytic (-) to input (+) towards tube.-


early clipping :( What voltage do you have at the (+) of C3? Should be half of your supply voltage, if not increase or decrease the value of the plate resistor.



- lack of bass :headphones: again check the value of your coupling capacitors/

Post pics when you have a chance thanks

yes, C1 is 2.2uF electrolytic [but the + goes to input and - to the tube :blush:] and it fries my laptop's soundcard :hot:

the [+] of C3 is 7.20v. is it means to use higher plate resistor value? :idea:

Pics: [sorry phone camera :mrgreen: ]
outside
Image

inside
Image
a bit mess ;)

freq. response attached :up: [tested using friend's tascam us-122]

cheers :beer:


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