F5 power amplifier

[tinitus]

I dare not say this, but are lowest resistance fore power up
I thought it was the other way round, that lower resistance would give higher bias

[alazira]

Hi,

Looking at the picture of Cviller's board for P2 I can see that if you use the 3266W (offset legs) then it will short/tie together the wiper (pin2) with pin 1. In this case, to start with zero ohms you will indeed have to turn it completely clockwise to start and bias by turning counter-clockwise. I built my first F5 with Cviller's board, but apparently used an in-line style and oriented it with pins 2&3 together, so that was why I remembered starting with it completely counter-clockwise and biasing it by turning clockwise. I should have been more careful with my advise.

On Peter Daniel's board he has a little symbol on the board for the screw so that you will orient it with pins 1&2 tied together, so you will zero it by having it turned completely clockwise.

I'm very sorry about that. Hopefully no one has melted their amp.

[Zen Mod]

Originally Posted by tinitus

I dare not say this, but are lowest resistance fore power up
I thought it was the other way round, that lower resistance would give higher bias

it's everything in Papa's pdf

[udailey]

What!!! five and a half thousand posts and its IN A PDF!!

[enochRoot]

actually, there is a mark on cviller's board as well to indicate orientation. it would have pins 1&2 tied. but in the assembly manual photo, he has it the opposite direction (pins 2&3 tied). i know this as i just soldered one channel up yesterday

[alazira]

Originally Posted by tinitus

I dare not say this, but are lowest resistance fore power up
I thought it was the other way round, that lower resistance would give higher bias

Hi,
Beftus has already quoted from the "initial adjustment" portion of the F5 manual, so it indeed is true. It does say in another area that "This 3.6V DC value is necessary to bias the power MOSFET's Q3 and Q4 into conduction."

[tinitus]

Originally Posted by Zen Mod

it's everything in Papa's pdf

It does actually say to set pots at minimum using ohmmeter

[Zen Mod]

Originally Posted by tinitus

It does actually say to set pots at minimum using ohmmeter

yeah ..... speaking of greedy boyz .... and teeth sharpening in threads

[tinitus]

Originally Posted by Zen Mod

speaking of greedy boyz

Thats me, and i LOVE my growing collection

[alazira]

Well,
I get home and I look inside my first F5 with Cviller's board and see that it is a W style trimpot, so I'm thinking "what the fudge?" It was made with a tech-diy kit and the website lists a bourns 3266W.

I look inside my parts bin and see that I have an extra one. I notice that unlike the picture I pulled off the internet, this one shows the pins labeled the otherway! Perhaps one is a counterfeit or mistaken art?

Just to confirm, zero ohms achieved in the completely counter-clockwise position.

Perhaps the best thing to do is make one of the following, set to zero, and place in the R3&R4 positions, leaving the P1&P2 positions empty (no jumpers).

I'm going to read a book now (Just started "Drood" by Dan Simmons)