Nelson Pass DIY F5 build

specialidiot

Break Glass, Smoke Lucky
I've had the parts together for this build for a couple of months and with a few audio related projects recently completed, its time to get to work on it.

The F5 is a Nelson Pass designed fully Class A using FET amplification and is purely direct coupled - the only caps in the box are in the power supply. It's a pretty straight forward build.

A full description by Mr Pass can be found at http://www.firstwatt.com/articles.htm

The article is summed up thusly:
Conclusion

So there we have it.

Nice little amplifier without too many parts.

It sounds great.​

The driver and power supply boards were purchased as part of a group buy on diyaudio.com and came from Denmark for $40 shipped. Torriod was sourced from Antek for about $50, electronic components are mostly from Mouser with a couple of stranglings found only on ebay.

I did my own mini group buy of the heat sinks sourced from Conrad in Austrailia. By financing the buy and selling most of them for a tidy profit on ebay, I was able to fund my pair.

The enclosure was a struggle for me, I looked all over for the right one and finally found it at diyenclosures.com. I got lucky and scored the last one prior to this particular model being discontinued. I received enough of a discount to purchase a nice gold anodized front panel too!

Over the last couple of days I've assembled the enclosure, drilled and tapped the heat sink, and cut out the sides so I can mount the FETs directly to the HS.

It is a simple enough build but I'm going to take my time with it. I should be able to finish it up in 6 - 10 hours of steady work.

Here's the enclosure assembled but I still need to drill mounting holes for the power supply PCB mount, the RCA jacks, binding posts, rectifiers, and torriod mounts.

I'm thinking of having the top panel powder coated in a black crinkle finish to match the heat sinks.

I'll add to this post as the build moves on.

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Boy, that's a nice chassis!

Cool stuff inside, too. :yes:

Hey, how do you tap a heat sink?
 
You know, I'm putting together a DIY room for the fest. You gonna have this thing running by the beginning of May? :D
 
Very pretty!

Thanks Ed - glad to hear that you are up and around, too!

Redboy said:
Boy, that's a nice chassis!

Cool stuff inside, too.

Hey, how do you tap a heat sink?

Not as difficult as your builds Nate. PCB stuffing and soldering is a piece of cake. I do have some head scratching to do for wiring up the torroid and rectifiers to the PS board.

The heat sink is tapped using a thread cutting gizmo inside an appropriately sized hole that you drill. Requires a soft hand, patience, and a lot of 3 in 1 oil.

illustration stolen from the intarweb
tapping-turn.png
 
Got my subscription on thread and will be following your progress. I have been restoring many of my keepers and have been contemplating an amp build of my own with some donor components I have. I had read the article by Nelson on the F5 last year and decided on building one. I am a big fan of his and have quite a few STASIS designed amps and receivers around the place.

Looks like you’re off to a good start and will be a definite looker when completed. Maybe I will get some things off the bench to get one going myself now.

Regards,
TB
 
It has a low amount of gain, otherwise, it's a fantastic sounding amp.

In case you didn't know already, they run HOT. After mine has been running for a hour or so, I can't keep my hand on it for more than 5 seconds.
 
In case you didn't know already, they run HOT. After mine has been running for a hour or so, I can't keep my hand on it for more than 5 seconds.

Yeah, that's pretty well documented in the GB thread.

Little secret, ejfud has one that is temporarily located in my mancave, so I've spent some time listening and taking advantage of it's Class A toastiness.
 
Sometimes I've seen copper "spreader bars" used in attempt to better distibute the heat from a relatively small area to a larger portion of the heatsink.

Dunno if that's merited in this case, but I thought I'd toss it out there since lots of heat was mentioned.

EDIT: Copper having roughly twice the thermal conductivity of aluminum.
 
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Sometimes I've seen copper "spreader bars" used in attempt to better distibute the heat from a relatively small area to a larger portion of the heatsink.

Thanks, I'll check with some of the engineers here at work to see if they have anything laying around.
 
Looks great Jeff!

Can I have mine back now, I really miss it.

My F5 clone really doesn't run that hot relative to my Aleph 5 clone.
 
Looks great Jeff!

Can I have mine back now, I really miss it.

My F5 clone really doesn't run that hot relative to my Aleph 5 clone.

You sure can. I can bring it over tonight, and help carry your big'uns upstairs.

Rick Vestal said:
Please PLEASE do tell where you sourced that chassis!

In the OP I stated diyenclosures.com, but he's quit selling except for what he has left. If you go over to diyaudio.com you'll find a lot of enclosures available.
 
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