FirstWatt F1 Gathering materials

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Guys,

I've decided to try building the FirstWatt F1. I've put together a BOM based on the schematics in the service manual. This is my first attempt to build an amplifier so I had a few questions which may seem rather naive to the experts ;)

PowerSupply capacitors : Do I need to buy any particular brand/quality what should I look for?

Resistor/Capacitors in the input path (r1-r4, c1,c2) I'm assuming that you need to put high quality resistors capacitors here? Again any recommendations on brand/quality/source or what should I be looking for?

MOSFETS: I've been reading some of the posts here about the importance of matching FETs. How many do I need to purchase in order to be able to get a matched set? for example to match the 2 IRFP240s do I need to buy 4, 6, 8?

Thanks in advance,

--Chris
 
The one and only
Joined 2001
Paid Member
I used the Panasonics from Digikey.

The resistors are RN55D type 1% except for the 3 watt
resistors, which are also Panasonic from Digikey.

I matched the devices to .01V, and the two P channel are
matched to the two N channel. If you match to .1V for Vgs
you can trim the Sources resistors to get the offset down to
the 50 mV spec without much difficulty. If necessary, I usually
trim the P channel Source resistors, as that has little effect on
the gain figure.

I would probably buy 2X to ensure matching, and the single
current source N channel can be the odd device out of match.

:cool:
 
Mr. Pass,

Thank you for responding so quickly. I've went ahead and put together a 95% BOM for the project. I have a couple more naive questions ;)

The PS Toroid : will a 250VA Avel 18V+18V work? I believe on another F1 thread the person was using a 300VA toroid.

The Line capacitor in the PS: The schematic shows ".0033 LINE", I'm assuming its 0.0033 uF, so a BC Components 0.0033UF 275VAC X2 should work?

C3 and C4 : Are there any particular ratings required for these capacitors?

I'm planning to use a 3RU rack mount chassis with heatsinks on both sides and 1/2 of the back panel. I should be able to get aproximetly 5.25"x40" of area for heatsinks.

I have a complete BOM except for the mentioned capacitors and heatsinks, with your permision I'd like to post it here for anyone else interested in the project.

Thanks again for all the help :)

--Chris
 
DIY_newbie,

>> The Line capacitor in the PS: The schematic shows ".0033 LINE", I'm assuming
>> its 0.0033 uF, so a BC Components 0.0033UF 275VAC X2 should work?

A 3.3 nanoF at 400 V AC {Style Orange drop} check for the noise level
and the position of the transfo ...

>> C3 .. C4 : Are there any particular ratings required for these capacitors?

For these 15 000 microF about 35 volts service, 85 or 105 degreeC ; 3000 hour
mini ; computer type with low ESR ; good panasonic's TSUP or TSHA series
Nichicon VR or PW series

>> The PS Toroid : will be a 250VA Avel 18V+18V work?
Attention the F1 draws 100 watts by channel and with a coeff of 2/3
that goes to 250 to 350 VA for a stereo amplifier...
Look for a "audio type" for better quality ...

Good luck. :)
 
Alain Dupont said:
DIY_newbie,

>> The Line capacitor in the PS: The schematic shows ".0033 LINE", I'm assuming
>> its 0.0033 uF, so a BC Components 0.0033UF 275VAC X2 should work?

A 3.3 nanoF at 400 V AC {Style Orange drop} check for the noise level
and the position of the transfo ...


I'll look into these.

Alain Dupont said:
>> C3 .. C4 : Are there any particular ratings required for these capacitors?

For these 15 000 microF about 35 volts service, 85 or 105 degreeC ; 3000 hour
mini ; computer type with low ESR ; good panasonic's TSUP or TSHA series
Nichicon VR or PW series

I apologize for not being clear, I meant C4 and C5 on the channel schematic. The 220uf and 1000 uf capacitors near the current sources.

Alain Dupont said:
>> The PS Toroid : will be a 250VA Avel 18V+18V work?
Attention the F1 draws 100 watts by channel and with a coeff of 2/3
that goes to 250 to 350 VA for a stereo amplifier...
Look for a "audio type" for better quality ...

Good luck. :)

I just looked up the specs on the Avel here :
http://www.partsexpress.com/pdf/avelspecs.pdf

The specifications say that the 250VA is 93.2% effecient. Doesn't this imply that I should be able to pull (250VA / 18V) * 93.2% = 12.94 Amps? How do I convert this to a Wattage figure? Isn't this simply 18V*12.95A = 233 Watts? 15% overhead?

--Chris
 
Newb,

Forget those fancy shmancy calcs for the tansformer. They don't
apply to nuthin you're doing. You're pulling huge amounts of
current for tiny bits of the 60 Hz cycle. The 93% efficient means that at rated
power, the transformer is heating itself using 7% of the power
it's pulling at the primary, and 93% of the power being pulled at
the primary is making it to the secondary. So your calc is correct.
BUT, like I said, it doesn't apply to your situation, that calc is for
a RESISTIVE load, and your load is about as far from resistive as it could possibly be.

Our man Nelson has
a rule of thumb to provide a VA rating that is 4x the idle power.
So if the idle power of your F1 is for example 100W, you should
use a 400 VA if they come like that, or a 500VA. Forgive me
Master if I've messed up. If it's a question of 250 VA or 300 VA
go with the 300. It's gonna hum less, and it'll give more oomph to the supply. When in doubt, go bigger on the supply as long as it will fit in your box.

I used Nichicon Super Through (type KG), 22,000 uF, 2 per rail in my Aleph 2s. I'm sure you could be happy with one of those per rail for a small amp like an F1. Do you need 2 per amp or one per amp ? They're rare and you may have trouble getting them.

Also, on the FET matching, you need 2 pairs, no ? If so you'll get a better result if you match out 16 transistors rather than 8. But 8 might be OK. What are they, like $1 each or less ???

W.
 
DIY_newbie,

>> I meant C4 and C5 on the channel schematic. The 220uf and 1000 uf
>> capacitors near the current sources.

35 volts good quality Panasonic M series or Nichicon VR, PW series

>> Doesn't this imply that I should be able to pull (250VA / 18V) * 93.2% =
>> 12.94 Amps?

max is 6.94 amps for each secondary winding
But you are working on a class A ; and in this case we do not use full capacity of
the transfo ; we use a 2 or 3 coeff otherwise the heat noise, saturation etc will be present and so it's not a good idea to load the transfo more than 50 %

so for 50% load or even better 33 % load ... look at the Aleph-X excel datasheet
you will be able to draw 3.47 Amp from each secondary
Thats 3.47 Amp * 24 Volts = 83 VA * 2 channel = 166 VA max for 50 %
and these 166 VA are considered on full resistive load

The 6% lost in efficiency is somehow negligible here...
it's lost in magnetic filed, heat, copper loss, coupling between primary and secondary

PS: look at other examples of Nelson's design, Aleph series... for suggested VA

regards.

Alain.
 
Thanks for all the replys!

wayne325 said:
Newb,
Our man Nelson has
a rule of thumb to provide a VA rating that is 4x the idle power.
So if the idle power of your F1 is for example 100W, you should
use a 400 VA if they come like that, or a 500VA. Forgive me
Master if I've messed up. If it's a question of 250 VA or 300 VA
go with the 300. It's gonna hum less, and it'll give more oomph to the supply. When in doubt, go bigger on the supply as long as it will fit in your box.

I used Nichicon Super Through (type KG), 22,000 uF, 2 per rail in my Aleph 2s. I'm sure you could be happy with one of those per rail for a small amp like an F1. Do you need 2 per amp or one per amp ? They're rare and you may have trouble getting them.

Ok, let me see if I understand this. Each channel idles at 100W according to the service manual and its a stereo amplifier, so I need 400VA per channel or 400VA for the pair? I can't seem to find an 18V+18V with a rating that high. Does it make sense to use a toroid per channel? Avel makes a 160VA and 250VA with dual 18V secondaries. RE: PS Capacitors I plan on using the same panasonics Mr. Pass recommended in his first post.

wayne325 said:

Also, on the FET matching, you need 2 pairs, no ? If so you'll get a better result if you match out 16 transistors rather than 8. But 8 might be OK. What are they, like $1 each or less ???

W.

Thats the plan to get like 8 of each type so 24 total devices and match the best

Alain Dupont said:
DIY_newbie,

>> I meant C4 and C5 on the channel schematic. The 220uf and 1000 uf
>> capacitors near the current sources.

35 volts good quality Panasonic M series or Nichicon VR, PW series

Heading over to Mouser/Digikey to start looking now ;)

What do you think of using a single 250VA for each channel Alain?

Thanks again guys!

--Chris
 
Disabled Account
Joined 2002
DIY_newbie said:

. . . 400VA for the pair?

. . . match the best


Yes, you are right. I use 800VA, but it's overkill. I have chosen that big because I have often disappointed with maker's power rating.

Match the best. Even if difficult, don't be disappointed. If we read the original article carefully, there is an easy DC offset-killer. Who is Nelson . . . ? He is not bad at all. Actually, I have used unmatched MOSFETs. Having used the DC offset-killer, I have managed the offset less than 30mA. Don'y worry . . . clever DIYers will assist you.

Regards
jH

PS
F1 will not make you disappointed. ;)
 
Alain Dupont said:

PS: At this point draw the enclosure and try to place the transfo(s)
you'll get a better view of the final F1 you want.

Forgive the primitive nature, but I ran home at lunch and sketched 1/2 of it while driving ;)

Toroids are 4.5" diameter 2" tall 250VA types :) I have the placed horizontally with the PS board above them, the other option is to place them vertically and the PS infront? The heatsinks are 10 3.35x5.25" eachh heatsink is 0.8C/W and I plan on mounting one power mosfet to each heatsink, how does this sound? Chassis is a 3RU rack mount 16guage steel black anodized.

F1_sketch.jpg


--Chris
 
Hmm

Torioid = 2"
Transformer bolt = 1/2"
Top + Bottom = 1/4".

Total space left = 2 1/2" that should be enough for the power supply board..

The other option is placing them vertically. But how do you mount a vertical toroid? do you strap it down through the center to the floor with a u-bracket? I can't mount it to the back since the input/outputs will be there..

Just got a quote on the heatsinks. $367 cut.. not too bad, gives me about 24-26 heatsinks enough for 2 F1s :) Each heatsink is rated at 0.8 degree C / Watt.

Another question, how do i mount the heat sinks? To the outside of the side/back panels? how do you guarantee good thermal transfer between the mosfet->sidewall->heatsink? Do I cut holes in the sides/back so that I can mount the mosfets directly to the heatsinks?

Thanks!

--Chris
 
DIY_newbie,

>> Do I cut holes in the sides/back so that I can mount the mosfets
>> directly to the heatsinks?

Better remove about all the lateral sides to install the heatsinks ; and absolutly
bolt the MosFets to the heatsinks... {using mica and grease or good thermo pads}

For the heatSinks take a look at Conrad HeatSinks ; and check ThermaFlo

http://www.conradheatsinks.com/welcome.htm
http://www.thermaflo.com/index.shtml

Regards.

Alain.
 
Thanks for those links Alain,

The thermaflow E1387 looks promising : a 5.25"x9.97" section can disipate 100W of energy with a 34 degree C rise over ambient. It would be nice since I would only have to have heatsinks on the sides and not the back panel leaving more room for connectors. Is this sufficient power dissipation?

http://www.thermaflo.com/bin/exdata...25&LengthUnits=in&SearchButton1=Change+Length

--Chris
 
Noob,

A delta of 34 is about as high as you want to go. That will
give you a temp of about 55C in the winter - approaching 60C
in the summer if you keep your apartment at 80F. Keep in mind
also those are free air figures and not stacked.

Just looking at those dimensions, that looks like a reasonable
size for the power you have to dissipate.

You can use a tiny bit of thermal grease or silicone thermal pads.
Check the transistors - if they are the same as the ones in the
Aleph, then they are electrically isolated so you don't have to
worry about electrical isolation. You must bolt the transistors
directly to the heatsink. Else much melty melty.

:bigeyes:
:bawling:
:hot:
:confused:
:cannotbe:
 
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