First Watt F7 review

[2 picoDumbs]

Oreo
You are in the same ballpark as me but I took it further.

 

[oreo382]

Try 11 ohms on the 170,9 ohms on the j74, 1 amp bias.Unplug the positive and negative supplies to the boards before adjusting the pot.

THATS WITH A 0.33 OHM pcf RESISTOR AS WELL.

 

[oreo382]

Oreo
You are in the same ballpark as me but I took it further.

How so,higher bias and different pot settings? My advice is from a sim with good models (temp compensated). They are close to what was actually measured by a friend of mine with one of those pc based programs and probe.
Not as good as a distortion analyzer which I would like to have.Then you're really cooking with gas

 

[2 picoDumbs]

Mine is quite a bit different in a number of ways but we are on same page here.

Mine is Sissy Turbo Version
Around 27V rails
double die lateral fets
1.7A Bias
Around 5 Ohms J, 15 Ohms K
Idss J around 7mA
Idss K around 9mA

Then tweak source resistance further on jfets using distortion analyzer to achieve around 0.05% distortion.

 

[vdi_nenna]

Mine is Sissy Turbo Version
Around 27V rails
double die lateral fets
1.7A Bias

Same league, different ball park.

 

[schubert]

THATS WITH A 0.33 OHM pcf RESISTOR AS WELL.

OK will do - thanks.

 

[Nag]

Dear Nelson,
We have missed fun/education reading article in 2017 on first watt web site. If possible please publish one article before end of 2017. We are greedy boys we will ask again in 2018.

 

[schubert]

Try 11 ohms on the 170,9 ohms on the j74, 1 amp bias.Unplug the positive and negative supplies to the boards before adjusting the pot.

I assume there's a good reason for 1.0A bias as opposed to 1.3 or 1.6A....?

 

[Nelson Pass]

Dear Nelson,
We have missed fun/education reading article in 2017 on first watt web site. If possible please publish one article before end of 2017. We are greedy boys we will ask again in 2018.

I've been busy, but I'll try.

 

[oreo382]

I assume there's a good reason for 1.0A bias as opposed to 1.3 or 1.6A....?

That bias gives about 20W/8 ohms @ 2% (like the FW F7).If you go with higher bias your PCF resistor will change as well as the jfet pot settings.

 

[schubert]

OK - you da man with the great sims, so 1A it is. Thanks

 

[NicMac]

Then tweak source resistance further on jfets using distortion analyzer to achieve around 0.05% distortion.

I adjusted so as to have 3rd harmonics 10dB lower than 2nd harmonics, and did not care for overall distortion (which I seem to remember changed relatively little).

My goto amp for almost a year now

Thanks Nelson!

 

[2 picoDumbs]

OK - you da man with the great sims, so 1A it is. Thanks

It can be anything you want, I suppose it depends on whether you want to copy or be original

 

[schubert]

Copy first, be original later - to taste. There's no intrinsic value to originality. Besides oreo is a lot smarter than I am!

 

[oreo382]

Copy first, be original later - to taste. There's no intrinsic value to originality. Besides oreo is a lot smarter than I am!

Actually I am just a backyard mechanic,Nelson is the smart one.He's left enough crumbs for us to get relatively close.

 

[Telstar]

Anyone made pcbs for this?

 

[2 picoDumbs]

I did mine on prototype board.
Purchased high purity fine silver solid core (0.7mm diameter) to make tracks. Much cheaper than I was expecting.
Digikey has some nice fr4 prototype pcb material.

 

[Nag]

10 Watt amplifier

Hi All,
In one of the thread Mr. Nelson posted below schematics for 5- 10 Watt output but without any specific values. I had taken resistance values from Sony fet diy.
except positive feed back it is almost identical to schematic provided in F7 document. I am going with input JFETS J113 & J175 and output exicon lateral mos fets. Can any one suggest values R1,R2,R3,R4,P1,P2,P3,P4,V- & V+. Output required 10watt.
Thanks,
Nag.

 

[2 picoDumbs]

This one does not have pcf.

 

[Zen Mod]

yeah

but it is having J113 and J175