A guide to building the Pass F4 amplifier. - Page 12 - diyAudio
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Old 15th October 2013, 09:40 AM   #111
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Hi Guys, 6l6 Jim has convinced me to build the F4 as it seems he really likes it, and have started ordering parts.....

I found a small supply of original 74BLs from a friend and he will try to match, he asked me to find out how they should be matched tolerance, as matched quads or matched pairs.

What would be the proper matching levels for these fets? I assume only a pair per channel need to be matched, not a quad.

Thanks again to Jim for his help in helping me sort out my F5 bias....

Cheers, John
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Old 15th October 2013, 12:34 PM   #112
6L6 is offline 6L6  United States
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For the F4, the Idss of the J74 should match the Idss of the K170. Idss of 7.0-9.0 would be about ideal.

There is no place where you need a matched pair of J74 in that circuit... If you were building an Aleph J you would, as the input stage uses a matched set of J74 as a differential pair.

What preamp will you use for the F4?
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Old 15th October 2013, 12:58 PM   #113
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Thanks Jim 6l6, of course, for the F4 will ask for matched idss of 7 to 9 for the j74 and k170 is noted. He told me he thought he could match to idss of 3.

I will use the BA3 as a preamp for the f4 as discussed and will ask for similar matching as above for that.

I meant to say earlier for the Aleph J as a differential pair, what matching would I need?

Have ordered parts for all these projects now, F4 BA and Aleph J.
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Old 15th October 2013, 01:12 PM   #114
6L6 is offline 6L6  United States
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I hope he means .3

The Idss on the Aleph should fall in about the same range; 7-9 being ideal, although the range is not as critical as the tight matching of the two J74's - they should be within about .1

So with a BA-3 front-end preamp,and F4 and Aleph J you will need (4) K170/J74 sets and (2) J74/J74 sets.
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Old 15th October 2013, 01:15 PM   #115
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thanks, will tell him. .3 it actually was.
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Old 4th November 2013, 09:32 PM   #116
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Default regarding matching for F4

Hi,
could you clarify regarding F4,as I understood 2SJ74 should be matched with 2SK170 with tolerance about 0,1? And one more question, should I match mosfets( IRFP240PBF,IRFP9240PBF ) somehow?

Regards,
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Old 27th December 2013, 11:34 PM   #117
RevMen is offline RevMen  United States
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At long last, I am ready to order parts and build an F4.

About the power transformer. Of course the Antek AN-4218 is discontinued, replaced by the AS-4218. But the AS-4218 is perpetually out of stock.

Is anyone aware of a suitable substitute from another brand? Or would it be a good idea to use the grossly oversized AN-6218?
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Old 28th December 2013, 02:09 AM   #118
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I would used the AN-6218 unless you could wait for new stock. A little overkill but the only issue is more size, weight and money. Still a better deal than other brands.
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Old 28th December 2013, 03:36 AM   #119
6L6 is offline 6L6  United States
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Use a AN-4220 and make sure you use 35V PSU caps. (which 99% of people do anyway...)
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Old 28th December 2013, 04:21 PM   #120
RevMen is offline RevMen  United States
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Thanks for the advice!
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