Looking for help with Pass F5 mono's in Salt Lake City area - diyAudio
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Old 29th January 2015, 12:30 AM   #1
erpiii is offline erpiii  United States
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Default Looking for help with Pass F5 mono's in Salt Lake City area

I built a pair of mono blocks and can't seem to get them working. Please PM me if interested, thanks!
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Old 29th January 2015, 02:36 AM   #2
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So what's the problem?

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Old 29th January 2015, 06:08 AM   #3
Zen Mod is offline Zen Mod  Serbia
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..... they aren't XS300 ?

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Old 29th January 2015, 06:55 AM   #4
erpiii is offline erpiii  United States
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Mr. Pass,

I wish I knew what was/is wrong... I built these in 2011 and have had them sitting around since. I installed the Q1-2 transistors incorrectly and it failed the light bulb startup and scorched r2.

I've looked at them every time I've parked in the garage for the last 4 years. I decided today that I was either going to pitch them in the garbage or I was going to try to get them working. I ordered and received new transistors in 2011; I installed them today. This was no easy feat because of the design of the amplifiers; the reason why I have been avoiding it. After the installation I put it on the bulb tester and the bulb (100w) glowed briefly and then went out. I removed the bulb tester and tried to bias one amp. I'm pretty sure I zeroed the pots but I'm not getting any readings on the outputs for dc offset or the output resistors as I turn the pots. I really don't have a deep knowledge about circuits, just enough to make me dangerous. I breezed through the process of making the B1 preamp, so I was hoping the F5 would be a similar experience; not so. At this point, I don't know if I damaged other components or how to trouble shoot the existing ones on the boards. It may be best, at this point, to try and salvage the heat sinks, bus bars and torodials for another design.

Best regards,

Eddie
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Old 29th January 2015, 02:53 PM   #5
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how far have you turned the pots? they need a lot of turns to get any reading over the source resistors.
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Old 29th January 2015, 03:07 PM   #6
juma is online now juma  Germany
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erpiiii,
please read carefully the whole F5 manual:
http://www.firstwatt.com/pdf/prod_f5_man.pdf
to understand how this very simple circuit works. After that the measurements will begin to make sence. Check you power supply, the values and orientations of all parts. Also, check if semiconductors are faulty or not (burned resistor usually means that something else in the circuit died too, usually a semiconductor).
High resolution pictures of PCBs and wiring will help.
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Old 29th January 2015, 07:16 PM   #7
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Quote:
Originally Posted by erpiii View Post
I decided today that I was either going to pitch them in the garbage or I was going to try to get them working.
Neat design, Eddie! Don't give up on them!
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Old 29th January 2015, 07:35 PM   #8
6L6 is offline 6L6  United States
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I'm going to be in SLC (well, Park City, but still a lot closer where I am right now) Tomorrow, Sat and some bit of Sunday. I'll happily help if we can meet up somewhere, or you bring the amps to me.

I'll pack some extra DMM. You really need 3 to bias one properly.
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Old 29th January 2015, 09:16 PM   #9
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You are a most generous guy, Jim.

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Old 29th January 2015, 09:19 PM   #10
6L6 is offline 6L6  United States
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Not really... I've 2 days where I'm condemned to sit in Park City with nothing to do but ski and eat... so meeting somebody new and helping with an audio project just makes it sound like more of a perfect trip!
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