Starting a First Watt F3 build and need some help

[Marsfrogie]

Hello all. I'm getting ready to start a First Watt F3 build and have a few questions about some components. On a scale of 1 to 10 I would rate my knowledge of electronic components at a 3 so take it easy on me. I just want to make sure I'm not buying the wrong stuff.

For resistors I'm using metal film where possible, metal oxide for higher wattage resistors and ceramic where that's all I can find. Is this ok?

For the potentiometers I'm using these. Are these OK?

Family Rotary - Linear
Resistance In Ohms 5.00K
Power (Watts) 0.25W, 1/4W


Will this work for the inrush current limiter?

Family Inrush Current Limiters (ICL)
R @ 25°C 15 Ohm
Current - Steady State Max 3A
R @ Current 0.335 Ohm
Tolerance ±20%

Is this bridge rectifier ok?

Diode/Rectifier Type Single Phase
Voltage - Rated 200V
Current Rating 35A
Package / Case MB-35
Packaging Tray
Speed Standard Recovery >500ns, > 200mA

Thinking about using this transformer:
AVEL's Y23 series power
¤ Load Capacity: 160 VA ¤
¤ Secondary Voltage: 18V + 18V ¤
¤ Dimensions: 4.0" D x 1.7" H ¤
¤ Weight: 3.3 lbs. ¤

Probably will use a stepped attenuator for volume control. Hopefully it all works out ok. Seems a little overwhelming right now but these projects normally seem to come together with parts in hand. Thanks for any help and thanks Nelson Pass for your great contribution to the DIY community.

 

[MikeW]

You can get most of the parts from Digi-key or Mouser. You will need a bigger transformer >300 VA or 2 of the 160's. Get a CL_60 thermistor. I have extra if you need one.

 

[Marsfrogie]

http://cgi.ebay.com/18-18V-400VA-To...Z4660QQcmdZViewItemQQ_trksidZp1742.m153.l1262

How does this one look?

400VA 18+18Vac secondaries. Dual 115Vac Primaries.

I can't seem to find a CL60 thermistor on digikey. Does it go by another name?

 

[Marsfrogie]

I found the CL60 at digikey, Thanks.

 

[Marsfrogie]

Also thinking about picking up this heatsink and running a bandsaw through the middle. Seems like it would be almost perfect.

http://cgi.ebay.com/Heatsink-LARGE-...ryZ66946QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[Marsfrogie]

I have been making some more progress on getting all of my parts together. Picked up a 400VA transformer and tracked down the LU1014's. I decided that I'm going to build the heatsink out of some aluminum stock I have lying around.

On the F3 schematics it says that the R5 is matched to the JFET. How do I do this?

Also, how do I adjust the 5K trim pots?

One other question, on the stepped attenuator for volume control, I should match that to the output on the CD player correct? Which in my case is 50K.

Thanks

 

[MikeW]

http://www.passdiy.com/pdf/ZV9.pdf
The answer to all your questions are here.

Do not underestimate the size of your heatsink. The ones I have are 11 inches x 11 inches x 2.5 inch fins.

 

[Marsfrogie]

This is what I had in mind. How hot do yours run? Have you measured? Thanks for the link!

 

[Marsfrogie]

Bear with me here. I've been reading the Z9 manual but it only has 1 5K pot in the circuit. The F3 has two and one more IRFP240 than the Z9. Do I measure the drain on Q5 and then adust P2 until the drain on Q3 is half? I am rather confused and don't want to smoke anything.

Thanks for clearing this up.

 

[Nelson Pass]

The extra Mosfet in the F3 is the power supply regulator.
The extra pot is for trimming the gain of the current source.

 

[Marsfrogie]

Thanks for the reply although I'm not entire sure I understand it. (Newbie )

So adjust P1 so that the drain on Q2 is half of the drain on Q3?

And adjust P2 so that it reads 21V in front of C1?

Start these adjustments with the pot all the way counter clockwise?

 

[Babowana]

So adjust P1 so that the drain on Q2 is half of the drain on Q3?

And adjust P2 so that it reads 21V in front of C1?

Start these adjustments with the pot all the way counter clockwise?

P1 to read the 21V in front of C1 . . .
P2 to earn the best sound with your ears . . .
Doesn't matter. Just adjust to all directions. The amp will be still safe.

 

[Nelson Pass]

Best to assume the value of the pot will be close to that of
the resistor used in ZV9. Raise the value as much as you like,
but I don't recommend going more than 20% or so lower than
the stock value.

 

[dave_gerecke]

Hello Marsfrogie, Here's a heatsink that should do the job. Cut in half for two heatsinks. I bought one of the same from this seller last week. It arrived pretty quickly and it is as big as described.

http://cgi.ebay.com/Aluminum-heatsi...ryZ66946QQssPageNameZWDVWQQrdZ1QQcmdZViewItem


Peace,

Dave

 

[Marsfrogie]

Cheers! Thanks for the responses. I want to try to build the heatsink myself first just so I can say that I did it. If it doesn't work I'll end up purchasing one. It's looking like this is going to be one big heavy tank of an amp. The transformer that I got in was HEAVY!

One other thing. How does the voltage get from 2X18 to 46V input at the board? Is that the bridge rectifier doing that?

 

[Marsfrogie]

Check out this guy for heatsinks too. These are new and he will cut them to any length needed.

http://cgi.ebay.com/HEATSINK-ALUMIN...ryZ31489QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[MikeW]

http://www.firstwatt.com/downloads/F3-service-manual-sm.pdf

 

[Marsfrogie]

I have been going over that a lot. Is there something in particular that you want to say about it?

 

[dave_gerecke]

Hey Marsfrogie, the 2x 18v to 46v happens like this:

2x18v = 36v. This is the rms value of the transformer ac out wired in series.

36v * 1.414 (sq rt of 2) is the peak voltage you will get at the output of the power supply after the bridge rectifier and filter caps. This is actually around 50v. But after some various other losses in the diodes, etc. it will come out around 46vdc after filtering and before any regulation in the circuit. I'm not that familiar with the F3 circuit.

Peace,

Dave

 

[Marsfrogie]

Thanks!