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Old 11th February 2010, 09:07 AM   #1
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Default 12AU7 + mosfets

ok .... now you have to be nice to me please

i am no good with tubes and i am no goot with mosfets .....as my avatar say i am a 2SA1302 guy

so i have a load of 12AU7 tubes and a load of J352-K2221 mosfets ....so i found schematics in the internet for hybrid amplifiers like the one posted

----is this combination going to work ???
----is this an amplifier worth buliding ???
---- then again under the specific material is there any changes to be made ???

opinions please and some help

it will be a waste to have all these goodies unused

i am also open to other circuits so everything is welcome

thanks sakis
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Old 11th February 2010, 09:31 AM   #2
Zen Mod is offline Zen Mod  Serbia
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go to Borbely site , search for headphone amp .

ECC88 is good enough with Ub under 100V , but ECC82 certainly isn't

in case that you want to use 82's , you need much higher Ub and recalculation of entire circuit
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Old 11th February 2010, 09:36 AM   #3
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Hey Sakis,

ECC82 is a very unlinear tube needing feedback to work well.

To get the most of it you shoud go for something like 10mA/120-150V. Ie as Zen Mod states, it is not suitable here.

Maybe you can use it as input-device in a folded cascode driving an outputstage.

Last edited by revintage; 11th February 2010 at 09:40 AM.
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Old 11th February 2010, 09:52 AM   #4
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guys ....come one .... be with me now

i dont have neither ECC 88 nor ECC82 i have 12AU7 !!!! all of these work diferent and here is were i need help

then again i am not looking for a headphone amp and also the above schematic is something similar to elektor schematic that was published and working
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Old 11th February 2010, 09:54 AM   #5
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12au7=ecc82
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Old 11th February 2010, 10:06 AM   #6
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Quote:
Originally Posted by revintage View Post
12au7=ecc82
i am sorry i think that this is not correct ...12AU7 is similar to ecc82 but not the same


then again if i am wrong and these tubes are the same what about the rest of the circuit ( since its supposed to be copy of the working elektor circuit )

and also what about my mosfets ???? are these mosfets switable for this application ????

regards sakis
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Old 11th February 2010, 10:26 AM   #7
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Q1 and Q2 are drawn wrong and additionally are npn on the drawing. They should be PNP . Q4 is also incorrectly drawn .The type numbers however are correct. You plan to use IRF9540 and IRF540 ...correct ?
You need to have a relay to connect to the headphones. While power up and down the output voltages can swing up to the supply voltage causing some damage or destroying the phones .

Why don't you sim the circuit and see what you get. However as the 12AU7 ( ECC82 ) is not very linear the way you want to use it ,even if you can get distortion figures down, it might not sound as clean ( very subjective) as an inherently linear tube like the 6DJ8 or 6922 . But then you might never notice the difference unless you compare them side by side. If you just have the
12AU7 just go ahead and build one using it. Don't forget to use a delayed relay switch on and instant disconnect on power down. Or just plug in phones after 30 seconds or so after power on and disconnect phones before power down.

OR for testing use a back to back 470uF caps between phones and amp. That will protect it from dc . If they are good caps it might not be too audible in the signal path. I've found some Samwha elco's quite decent.
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Last edited by ashok; 11th February 2010 at 10:29 AM.
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Old 11th February 2010, 10:35 AM   #8
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If you check the curves you should run the ECC82s on just above 1,2mA to get Ug -1V. Doubt it will be a good solution though.
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Old 11th February 2010, 12:03 PM   #9
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i'm interested in seeing how that amp performs,it's a very interesting crcuit.jer
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Old 11th February 2010, 03:32 PM   #10
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Can't find the more recent drawing I was wanting to post, but this is close.
I think the only difference, I had a +/- supplies and servo details completed
in the other... In newer version the output cap would not be needed. I'll
keep looking for it, its probably on my other PC.

Maybe an outside the box idea?
Here we see 50% UL feedback into the 12AU7 plate.
I've never built it, only sim. But in sim, this trick seems to work just fine.

I think my reasoning for the 50% plate swing was to keep the plate
voltage from dipping too low, but still allow a full voltage output.
M1 then has a synthisized Mu twice that of the feedback triode.
Its been a long time to remember all the details.
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Last edited by kenpeter; 11th February 2010 at 03:44 PM.
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