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and now for something completely different part 3


kevin gilmore
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Hi Pars,

the latest revision v1.2 THD boards say BC546B and BC556B on them.

Regarding to the ZF and feedback resistor change it is for both around 2x, so 50k instead of 25k and 4.2k instead or 1.9k, basically what Paradoxper used. Important is that both modes match in volume - you may scope with 1kHz and match the 4.2k so that you get same volume in ZF-mode as in feedbak mode. This being said, I am still using 25k for feedback and 1.9k for ZF and only using the amp in ZF-mode.

As well as using the B-version sands from onsemi.

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1 hour ago, audiostar said:

Hi Pars,

the latest revision v1.2 THD boards say BC546B and BC556B on them.

Regarding to the ZF and feedback resistor change it is for both around 2x, so 50k instead of 25k and 4.2k instead or 1.9k, basically what Paradoxper used. Important is that both modes match in volume - you may scope with 1kHz and match the 4.2k so that you get same volume in ZF-mode as in feedbak mode. This being said, I am still using 25k for feedback and 1.9k for ZF and only using the amp in ZF-mode.

As well as using the B-version sands from onsemi.

As I recall, the one built by paradoxper that I fixed for tkam had a bit of difference in volume (not measured) between ZF and SS modes. Close, but not exact. It was close enough that it wouldn't have bothered me. I'll order B on-semi sand.

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6 hours ago, Pars said:

As I recall, the one built by paradoxper that I fixed for tkam had a bit of difference in volume (not measured) between ZF and SS modes. Close, but not exact. It was close enough that it wouldn't have bothered me. I'll order B on-semi sand.

This is why I use the original values from Kevin. 

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Hi, Guys, 

I'm working on my CFA2 project.

I've got a matching MJF15030/15031 question : How nice is the matching?

I had a Peak DCA-75 to match these two BJTs, the result is horrible. The hfe values of One bjt are most from 280-290, the other are from 70 to 120. It is seem not nice enough, right? 

So, how nice is the close enough matching of these two BJT?  May I need to buy more bjt to get nice matching?

 

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For many device series types, the N and P are not going to match well. If you can get more devices at a reasonable price, that is always best. Where are you purchasing these devices from? A known supplier? I guess my point is, are they genuine devices? A lot of fakes out there (ebay, aliexpress, dalbani, etc.)

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6 hours ago, Pars said:

For many device series types, the N and P are not going to match well. If you can get more devices at a reasonable price, that is always best. Where are you purchasing these devices from? A known supplier? I guess my point is, are they genuine devices? A lot of fakes out there (ebay, aliexpress, dalbani, etc.)

I got this DCA75 Pro from digikey. I think it can not be fake one. So, How close the two hfe values of these 15030/15031 are? Can you give me some values as a reference?

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