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and now for something completely different part 3


kevin gilmore
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8 hours ago, thuytn said:

How hot does the heatsink get? Seems to me it's like 220-250mm long?

That power hole seems to be meant for the 12mm Bulgin-like switch...

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I have about 160mA bias atm and the heatsink is about 34 Celsius. Transistors are about 10 C higher. I'll push it a bit closer to 180-200 once it is all done to see if it makes any difference.

 

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3 hours ago, MASantos said:

I have about 160mA bias atm and the heatsink is about 34 Celsius. Transistors are about 10 C higher. I'll push it a bit closer to 180-200 once it is all done to see if it makes any difference.

 

Thank you. Seems much cooler than I thought.

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Hi Kevin, the 4 transistors around THAT340 are in different orientation, the THAT340 pnp C is to the following Tr E, while the npn is to C. which one is correct?

All ON brand MJE15030, 15031 that I used in the power output had oscillation, some Motorola were stable. Is the fT30 too high?

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Done! Neutrik 4 pin xlr mounted from behind with blind taps. all in all went well considering it was done all with a hand drill. No drill press around 😔

The on/off indicator led was mounted underneath the case, makes for a nice effect.

Quite happy with the result! Now the quest for a better streamer starts!

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I etched the board myself, am running the ZF.

I can only stop the oscillation by connecting a 500P to the B, C of the output transistors, smaller than 500P can’t stop the oscillation.

I may try to run the SS later to see the negative feedback will help the oscillation.

 

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  • 3 weeks later...

There are still missing parts but so far so good, transistors will be all mounted directly on the heatsinks. This is gonna be a dual chassis setup with custom cut heatsinks. I have some balanced headphone protector boards, not sure it’s worth adding the extra wirings... still waiting for Kevin’s ZF/SS switch board anyway.

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I also had the protector powered off the GRLV in my Dynahi. It worked fine but the Dynahi itself is very stable. I'm not sure with stock parts on the silkscreen, what's the dc offset trigger value? I know amb's e12 will do at 80mV.

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I always wonder what makes the CFA2 sound so good and makes me choose it over the dynahi every time. Does the magic lie in the current feedback topology or the triple darlington output stage?

just an idea - what happens if we parallel two or more sets of the triple darlington output for each CFA2 board? Would it be the more the merrier?

 

 

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  • 2 weeks later...
On 7/15/2020 at 4:46 AM, RudeWolf said:

A pair of 2sj109/2sk389. Sounds better that way and the DC is way more stable. I'll add that even with the THAT340 it sounded superb!

We cannot get  these 2SK109 and 2SK389 anymore, they are obsolete for a long time, all of them are fake from AliExpress.  

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