Starting a First Watt F3 build and need some help

Marsfrogie

Member
2008-02-14 12:24 am
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.
 

Marsfrogie

Member
2008-02-14 12:24 am
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
 

Marsfrogie

Member
2008-02-14 12:24 am
This is what I had in mind. How hot do yours run? Have you measured? Thanks for the link!

f3heatsink.jpg
 

Marsfrogie

Member
2008-02-14 12:24 am
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.
 

Babowana

Formerly "jh6you". R.I.P.
2006-07-13 4:23 pm
www.aheadamp.com
Marsfrogie said:
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.
 

Marsfrogie

Member
2008-02-14 12:24 am
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?
 
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