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PostPosted: 06 Nov 2014, 22:35 
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Location: Winnipeg, CANADA
Hi Folks,

This is a project that I started long ago that was interrupted by a home move. The parts came back across my hands this year and with a lot of help from Walter of SAR Labs here in Winnipeg the DIY FirstWatt F5 Amplifier is finally complete!

The First Watt F5 Operation and Service Manual attached below shows the schematic of the amp.
Attachment:
First Watt F5 Operation and Service Manual.pdf

The only difference is that I used a separate power supply filter board for each channel.

Attachment:
DIY-FirstWatt-F5-Amplifier-Inside.jpg

The amplifier boards can be purchased from the store at diyaudio.com. For the transistor Walter used closely matched IRFP240/9240 pairs. The power supply boards are from chipamp.com. The rectifiers are MUR1560 and 15000 uF Nichicon capacitors were used. The transformer is a 400VA Antek with a heavy steel shield. I kinda went overboard in specking the power supply. :lildevil:

The chassis was purchased on eBay also some time ago and I have no idea what the writing means. I'm looking for ideas on how to cover up the writing on the front panel. I was thinking along the lines of an engraved brass plate like Mark uses on his builds. The photo below shows the FirstWatt F5 amp on the bench while I checked bias, DC offset and temperature. Once dialed in there is virtually no DC offset. The MOSFETs run about 26 to 28 degrees C above ambient temperature.
Attachment:
Bias-FirstWatt-F5-Amplifier.jpg

For the inputs Rhodium plated RCA jacks were used. I'll also want to get rid of the writing on the back plate. Any ideas?
Attachment:
DIY-FirstWatt-F5-Amplifier-Back.jpg

I've only had two listening sessions so far and let me say, this is a fine sounding amplifier. Works real good with a two way open baffle. I have yet to try the F5 amp with the Fostex horn speakers so I will save my comments until I have had more time with the amp.

Cheers


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PostPosted: 09 Nov 2014, 08:47 
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Hi Gio

F5 is nice and also the DMA enclosure, congrats :-)

I would like to have a F5 some day ...where did you purchase the F5 kits ? if ebay ...which shop ?


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PostPosted: 09 Nov 2014, 16:13 
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Hi Gio, Sometimes the lettering comes off with acetone. Usually the metal is anodized and is unaffected. Try it in a inconspicuous spot first.

Good listening
Bruce

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PostPosted: 09 Nov 2014, 19:35 
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Gio looks very pro. Should sound good.

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PostPosted: 10 Nov 2014, 18:12 
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Hi Kramme,

The boards were from a diyaudio.com group buy, and there more up to date boards now: http://www.diyaudio.com/store/amplifier ... s-208.html

The parts were purchased from http://www.tech-diy.com/Store/CloneKits.htm
However, it doesn't look like they have the F5 kits anymore.

Cheers

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PostPosted: 11 Nov 2014, 17:56 
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Hi Gio

Thanks for the info. Maybe this is what i'm looking for. all included for a stereo setup ( please verify ):

http://www.ebay.com/itm/2-SETS-DELUXE-F ... 27e4f01296


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PostPosted: 17 Nov 2014, 19:02 
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That looks like it would do. I always worry about the authenticity of the semiconductors when buying from unknown sellers. The PCB sizing is more along the lines of what is used in the FirstWatt amps and the extra length should allow you to get the MOSFETS closer to the center of the heatsinks.

Cheers

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PostPosted: 06 Dec 2014, 17:10 
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Gio wrote:
That looks like it would do. I always worry about the authenticity of the semiconductors when buying from unknown sellers. The PCB sizing is more along the lines of what is used in the FirstWatt amps and the extra length should allow you to get the MOSFETS closer to the center of the heatsinks.

About worry, i agree ( i've just got some fake 2SK1058 MosFets from china ...with wrong pinout :mad: ).

Thanks Gio, for info about placements on the pcs :up:


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