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First Watt F7 review
First Watt F7 review
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Old 16th June 2017, 10:51 PM   #971
Zen Mod is offline Zen Mod  Serbia
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Papa already did something as that - putting sole 0R1 in rail for Iq measurement purpose (Vfet Amp? ) ............ there is also slight possibility of little influencing THD spectra that way , accent on "little"

however , even if power resistors are 5% or so , setting Iq with same (percentage) accuracy is good enough
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Old 17th June 2017, 12:00 AM   #972
oreo382 is offline oreo382  Canada
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Quote:
Originally Posted by vdi_nenna View Post
What does this mean?



Maybe if the CRC resistors are matched. What happens if they are not? These resistors are 5% tolerance normally.
wouldn't it be better to measure all resistors in CRC and find the value? I don't even think I have a DMM that can read a .47 properly.
If your crc is like the normal one, both boards positives off one side and both board negatives off the other side you can't adjust each board individually very well.Both boards bias adjustments are the sum going thru each r in the crc.This is where the 0.1 ohm in each board positive rail helps. You can adjust each board for bias and offset more accurately
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Old 17th June 2017, 12:12 AM   #973
wdecho is online now wdecho  United States
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Nice progress. Still tho a perf board assly without heatsinks and only One channel doesn't read as giving reassuring Sound quality judgements.
Not saying that it ain't exquisite.
Just wondering ...How ? can you tell.
OR? is that merely some in process piccie
It was installed on a heatsink before firing up along with the other channel. Picture was taken before being installed on heatsinks. The heatsinks have been installed in wood box with PS section that I call my test chassis. If I cannot live without a build I take the heatsinks from the box and build a proper case and PS section. This may be one of those builds. It is that good.

I have since had reservations about picture and have asked to have it removed since the F7 is a commercial product being sold but as it is not built from an official schematic I did not think Nelson would mind. And since I have not shown the underside I thought it would not hurt posting a picture.

I can say this try at duplication of a F7 sounds mighty fine in the lines of the V-fet but this statement is only from memory. I have not done an A/B comparison as yet. I can say that this build had some of the best square waves between 20 and 20K hz of any of my builds. I am very satisfied with the results. None of this could have been possible without Nelson revealing the concept of improving the F5 with fewer parts using lateral mosfets and employing PCF. I do not believe he will object with a solder slinger giving it a go. I bought ECX10 laterals being that the ALF's are no longer available.
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Old 18th June 2017, 01:50 PM   #974
tpark is offline tpark  Canada
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My builds always use separate power supplies for each channel and I had forgotten about using a single supply for both channels. I still think that is the place to measure the bias current.
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Old 18th June 2017, 06:54 PM   #975
Nelson Pass is offline Nelson Pass  United States
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You can always use the .1 ohm resistor while adjusting, and
remove or bypass it later.
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Old 19th June 2017, 01:41 PM   #976
vdi_nenna is offline vdi_nenna  United States
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What about using a 10A DMM ammeter? Just bridge the power supply and amp PCB?
Too dangerous?
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Old 19th June 2017, 06:36 PM   #977
Nelson Pass is offline Nelson Pass  United States
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I never use it. I like to put 0.1 ohms in series somewhere and watch the
voltage drop and that way I never blow the hard to replace fuse on the DMM.
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Old 19th June 2017, 07:08 PM   #978
vdi_nenna is offline vdi_nenna  United States
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Roger that...
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Old 23rd June 2017, 03:09 PM   #979
generg is offline generg  Germany
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With this nice explanation from Nelson here

25W Class A amp with Lateral MOSFETs


you can check if your build fulfills the 2dB pos feedback.

In my Spice try I had to choose for the sense resistor a value around 0R6 to get the right pos feedback.
But in my Spice work no ALFS, but SJ162 and SK1058.

The voltage value with an 8 Ohm load has to be 1.26x bigger than the value without the 8 Ohm load.

Does anyone have the parameters for the ALFS?
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Old 23rd June 2017, 05:27 PM   #980
Zen Mod is offline Zen Mod  Serbia
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they're supposedly same as 2SJ/SK , if I remember correctly
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