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Nelson Pass F3 amplifier help wanted
Nelson Pass F3 amplifier help wanted
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Old 31st August 2017, 02:42 AM   #1
russell66 is offline russell66  Australia
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Default Nelson Pass F3 amplifier help wanted

Hello
I am wondering if anyone can help me fix this amp. I have a limited understanding but it seems pretty simple. I understand the transformer, then there is what I think is a PSU with various caps and then the Amplifier circuit. The black resistors on the top are smoking when it's switched on. Someone has replaced one channel at one point with different resistors which seems to work ok. I have replaced 3 resistors also but still got the same issue. I would like to put it in a better chasis and perhaps improve some parts if needed. Boards and that sort of thing are available cheaply from China and it would seem better to buy something than spend money on finding the problem as that is expensive. Thats if I knew what to buy. I tried to post some pics but couldn't so i made a short video. Thanks for any help.
Heres the video link.

YouTube
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Old 31st August 2017, 03:03 AM   #2
2 picoDumbs is offline 2 picoDumbs  Australia
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What are the black resistors connected to?
Post a circuit diagram circling the parts on the diagram that are giving you trouble.
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Old 31st August 2017, 04:36 AM   #3
russell66 is offline russell66  Australia
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I don't have a circuit diagram or know how to get one. I think it is a standard pass circuit.
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Old 31st August 2017, 05:33 AM   #4
Gyuri is offline Gyuri  Hungary
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It is most probably a ZV9 on Veteran's PCB.

http://www.firstwatt.com/pdf/art_zv9.pdf
Attached Files
File Type: pdf implantation ZV9.pdf (36.3 KB, 42 views)
File Type: pdf zv9_schema.pdf (31.2 KB, 45 views)
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Old 31st August 2017, 05:38 AM   #5
Rodeodave is offline Rodeodave  Austria
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Nelson Pass F3 amplifier help wanted
This is not a Nelson Pass F3, it's a Tim Rawson rip off.

First Watt Clone f3 by Tim Rawson - Audio Asylum Trader

No wonder it's not working.
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Old 31st August 2017, 08:49 AM   #6
russell66 is offline russell66  Australia
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Pretty sure Tim based his work on the design that was made available to the DIY community by Nelson Pass and it does look just like that one so I'm thinking that's it.
Do you know the circuit diagram or is the one in the above post accurate.
Perhaps just to clarify because I think your onto something.
If its a Tim Rawson rip off that suggests its a copy of a Nelson Pass F3 which means it is an F3 build by Tim. If it's not an F3 and it's a Tim Rawson rip off, then that means its a Tim Rawson's own design which means I won't find the circuit in the Pass F3 arena. Would you know which of those is accurate? I'm sure it's the first in which case it is an F3. Thanks
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Old 31st August 2017, 09:54 AM   #7
2 picoDumbs is offline 2 picoDumbs  Australia
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Take a close up photo and circle the offending components.
Use photobucket to embed the images
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Old 31st August 2017, 09:55 AM   #8
2 picoDumbs is offline 2 picoDumbs  Australia
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If you live in Melbourne I can come and look at it for you.
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Old 31st August 2017, 10:27 AM   #9
Dennis Hui is offline Dennis Hui  Canada
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Nelson Pass F3 amplifier help wanted
Looks like Peter Daniel's F3 board. For example, see here:

F3 PCB + Lovotech 1016

There were a number of group buys for this pcb so you should be able to find out more.
You can also download the f3 schematics and visually check how well it matches your pcb.

Should also add that if it is a Peter Daniel pcb is should be very close to the published schematics, but
with some minor changes like removing the led and maybe adding some bypass cap.
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Last edited by Dennis Hui; 31st August 2017 at 10:42 AM. Reason: Led
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Old 31st August 2017, 10:44 AM   #10
2 picoDumbs is offline 2 picoDumbs  Australia
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I compared the pcbs.
They are similar to Peter's pcb but there are differences.
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