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First Watt F7 review
First Watt F7 review
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Old 7th December 2017, 12:46 PM   #1121
cygnus x1 is offline cygnus x1  United States
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Will do. Thanks for the advice.
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Old 7th December 2017, 04:34 PM   #1122
Nelson Pass is offline Nelson Pass  United States
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Quote:
Originally Posted by cygnus x1 View Post
I've seen here in several post where the 170/74 are not matched and the 74 is 20% larger IDSS...so if I were to order fets from Spencer, do I want matched or this miss-matched set. I would still ask for ch/ch match.
The slight mismatch in production F7's gives rise to a slight negative phase
2nd harmonic, which is the preferred signature.
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Old 7th December 2017, 04:51 PM   #1123
Michael Rothacher is offline Michael Rothacher  United States
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Old 20th December 2017, 07:16 PM   #1124
schubert is offline schubert  United States
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Originally Posted by 2 picoDumbs View Post
In mine J74 has the smaller idss. Hahaha
If you don't know exactly what you want it might be best to go with matched.
I tried mismatching with 2SJ74 having the smaller value (7.6mA compared to 7.9mA) and the result was too much bass with big speakers in my small room. It was fine in systems with small speakers or less than ideal bass response, though. I had the pot between the JFETs set at 17:5. I traded out the 7.6mA units for 10.2mA, and now the sound is nicely balanced for my room. There's still some tweaking to do, but the sound is basically the same minus some bass.
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Old 20th December 2017, 07:17 PM   #1125
2 picoDumbs is offline 2 picoDumbs  Australia
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Nice one
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Old 20th December 2017, 08:11 PM   #1126
vdi_nenna is offline vdi_nenna  United States
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I had the pot between the JFETs set at 17:5. I traded out the 7.6mA units for 10.2mA
Did you center the pot afterward? Should you? Just curious.
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Old 20th December 2017, 08:13 PM   #1127
2 picoDumbs is offline 2 picoDumbs  Australia
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Originally Posted by vdi_nenna View Post
Did you center the pot afterward? Should you? Just curious.

To many variables here.
You need a distortion analyzer, or rely on the ear.
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Old 20th December 2017, 08:17 PM   #1128
vdi_nenna is offline vdi_nenna  United States
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Yeah, that's right- Offset, bias, harmonics...lunar phases. I forgot.
Just happy to be listening to mine right now.
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Old 20th December 2017, 08:57 PM   #1129
Dennis Hui is online now Dennis Hui  Canada
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The F7-ish seems like a tinkerer's delight. I imagine it's fun to corroborate
what one hears with the distortion characteristics.
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Old 20th December 2017, 09:12 PM   #1130
Nelson Pass is offline Nelson Pass  United States
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Not like amps with lots of feedback, where all the distortion went away.

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