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Jon L

First Watt F5 clone. Just bought

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the Rawsonte First Watt F5 clone off Agon. He immediately removed the listing as soon as I paid, so I don't have a photo, but I can't believe I caught his ad exactly when he put it up and got it :)

I plan to drive various things with this 25 watter, including HE Audio He1.2b electrostats, Sennheiser HE60, and my various speakers.

Offical F5 photo

f5ju9.jpg

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I plan to drive various things ...including HE Audio He1.2b electrostats...
First of all, congrats, should be nice.

Secondly -- I don't remember if you've posted impressions of these, have you?

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Damn, I always get a kick when I see those kleinhorns :eek:, incredible, single driver... I think they could be used as tree houses in the off-season

Hope to hear more about the amp once you get it.

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Damn, that's nice! Nice cases on those... wonder where he gets them?

and how he sells these so darn cheap. MSRP on F5 is technically $3K!

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and how he sells these so darn cheap. MSRP on F5 is technically $3K!

easy, look at the part cost :) You can get a kit for $26 per channel.

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easy, look at the part cost :) You can get a kit for $26 per channel.

But not including the chassis, toroid, binding posts, etc?

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But not including the chassis, toroid, binding posts, etc?

yeah... you get my point though. It's a very simple amp, as all the first watt designs are.

Add in $80 or so for a Plitron toroid, $50 for binding posts, $10 for IEC inlet, $12 for XLR jacks, and $200 for a chassis and you're still well under $500.

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Is there actually a kit though?

The F5 is supposed to be offered through the Pass DIY store some time "soon". Not clear if it'll be a kit or just a bare board though.

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The F5 is supposed to be offered through the Pass DIY store some time "soon". Not clear if it'll be a kit or just a bare board though.

NP will be offering the boards only for the basic schematic, not the more advanced balanced versions that people are building. The kit I'm referring to can be bought at tech-diy from Jack:

Tech DIY Company Store

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point being:

A.) buying black market DIY stuff is lame.. I wonder why he removed the Audiogon listing so quick...

B.) the reason he charges less than the MSRP is because there is not much to it when you don't have to design the circuit just copy someone else's ideas.

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These are probably the photo's from the add.

1219711802.jpg

1219711801.jpg

1219711800.jpg

Looks reasonably well built if a bit untidy.

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Looks reasonably well built if a bit untidy.

He must of really lowered the power output on that to get away with those heat sinks... or it's going to cook.

Ask swt61 about the heat sinks I'm using. :)

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How many watts is the full-spec version supposed to dissipate? I'm guessing that chassis would be good for maybe a hundred or so, but with the output devices clustered at one end like that you wouldn't get uniform dissipation over the whole sink.

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How many watts is the full-spec version supposed to dissipate? I'm guessing that chassis would be good for maybe a hundred or so, but with the output devices clustered at one end like that you wouldn't get uniform dissipation over the whole sink.

F5 puts out 50 stereo watts... my guess is those heatsinks can do 20-30W total.. welcome to class A.

From the article:

"Heat Sinking

At 1.3 amps per channel, you will see idle heat dissipation of 62 watts. To keep the

temperature rise of the heat sink to 20 deg C. above the ambient temperature, you will

want a heat sink rated at about .6 deg C./watt for each transistor. An example of this

would be a chunk of finned aluminum, with a series of 2” fins attached to an 8” by 6” base.

You will need two per channel.

The output devices need to be intimately attached to the heat sink. The mounting surface

on the heat sink should be at least

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F5 puts out 50 stereo watts... my guess is those heatsinks can do 20-30W total.. welcome to class A.

Right you are, I sort of brain-farted on the class A part.

And ouch, I just caught the two per channel requirement. :eek:

Edited by n_maher

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Right you are, I sort of brain-farted on the class A part.

And ouch, I just caught the two per channel requirement. :eek:

yup, 0.6 C/W per transistor hence the pair. Trust me, this builder had to of lowered the rails or this could be another example of epic fail.

Also, everyone over specs what Papa recommends, as those strangely configured, non-conventional heat sinks he uses seem to have magical properties.

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F5 puts out 50 stereo watts... my guess is those heatsinks can do 20-30W total.. welcome to class A.

"50 stereo watts" = 25 watts per channel?

Reno HiFi who sells First Watt has F5 listed as 25 wpc..

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"50 stereo watts" = 25 watts per channel?

Reno HiFi who sells First Watt has F5 listed as 25 wpc..

yeah, stock idle heat dissipation is around 62 watts stereo. I have one channel running now on my bench and that's almost exactly what I got. I'm at around 22 C temperate rise above ambient.

Once you get it, I can help you measure it and you can figure out exactly how it's biased and what it's output is and when it leaves class A. I'd personally turn it on for 12 hours or so and measure the DC offset voltage before I hooked it up, but that's just me being paranoid. Nelson recommends a few weeks burn in before being sure the DC offset is in spec, and somehow I doubt the builder did this...

Another thing about buying on the "DIY-market" is that you really need a distortion analyzer to tune this amplifer, according to Nelson... that's the only way you'll get the specs posted, as he's been quite candid about that.

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