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Old 9th April 2014, 04:10 AM   #1
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Location: Spring Valley Lake www.fastlaneaudio.com
Default F5 good to go.

Hello, name is Dave. I am new to this forum, however I frequent regularly.

I could use some assistance from F5 builders.

I built my F5, and 1 channel biases normally and the other has low voltage across P1.

I caused this fault to occur, when I accidentally put R11 to ground.

So far I have checked component values, and replace a several fets, and I still can not bias potentiometer p1, I get a max voltage across R11 of 20mv, I should be getting 590mv.

I have not yet replaced the 2sk170 or 2sj74 - on order.

Any info would be helpful.

Thanks, Dave

Last edited by FastlaneAudio; 11th April 2014 at 04:36 AM.
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Old 9th April 2014, 04:35 AM   #2
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The build was going nicely until I botched it up.

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Old 9th April 2014, 05:51 AM   #3
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pull all semis out and test them

one by one
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Old 9th April 2014, 01:52 PM   #4
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Both the ZTX 450 and 550 are smoked, I suspect the 2sk170 and 2sj74 are toast as well.

I haven't tested a transistor since college. I had to lookup how to test them.

Thanks, Dave
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Old 11th April 2014, 04:34 AM   #5
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Default F5 good to go.

Removed and tested the 2sk170 and 2sj74, both good. Started checking resistor values, none are burnt, but R11 measures 1.3M ohms, That might be an issue for a .47R.

Replaced the resistor and re-biased the amp. All is working properly, sounds great except for a low level hum that only occurs with my preamps connected - some sort of ground loop I suspect.

During biasing, I had an oscilloscope on the output, and was clear the trace was cleaner biased at 1.2mv. however my instructions mention biasing close to 0mv. In the end, I stopped tweaking at 0.4mv. Checked temp at both heat sinks, approximately 125 deg F.

Listening test, this amp has only been running 8 hours and sounds great. I have been running this amp on my personal speaker design ( The Yields). These speakers utilize an Audio Nirvana Super 10 full range driver from 200+.

Immediately I verified Mr. Pass's depiction of this amps characteristics, Bass is spot on, detail is amazing, and this amp is unforgiving of response spikes typically found in full range drivers.


Nelson Pass quote. "F5: Dynamic, accurate, a little unforgiving. On speakers with peaks in the top end, it will reveal as too bright and annoying.
On speakers with a slightly diminished top end, it adds a little sparkle,
this in spite of being flat out at
high as 500 KHz. Good control - if your speaker is a little boomy, it will tend
to tighten it up. Overall, probably the most neutral of the FW amps. It will
drive 4 ohm loads without particular issues. Oh, and it does sound very good."

I could not agree more.

Dave

Yield OB
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Last edited by FastlaneAudio; 11th April 2014 at 04:43 AM.
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