F5Turbo Illustrated Build Guide

[Zen Mod]

biasing of output mosfets is referenced to rails;
with that approach , you'll have difference between rails for front end and ..... back end

so , no , not good idea

see- there is no such thing as stupid question ......

 

[coolnose]

Thanks ZM , will have to work on the wiring then...

 

[esprit]

They are???

Place diodes on same heatsink as Mosfets.

I strongly suggest cascoding if you use 32v rails.

Would you suggest retro fit cascode, for existing F5t, with 32 volt rails.
Regards

 

[dewdrop]

Yes. For ease of mind and the longevity of your JFETs.

 

[paul141263]

Many thanks Guys, as I've said before I'm a complete novice, but I do have the help, of a pass 5 builder who built his amps some ten years ago. They sound amazing.

Thank you for your help and advice.

Paul

PS he's on it

 

[coolnose]

As stated before I am planning the PSU wiring on my F5T build, so far I have seen 2 "methods":

1: Wiring the FE board and the OP boars directly to the PSU (1 connection each)

2: Daisy-chaining, that is wiring the FE to PSU and then from the FE to the OP boards.

Question: IF daisy-chaining wouldn't it be better to connect the OP boards to the PSU and the chain the FE to the OP boards ?

I "think" the higher current in the OP boards should be connected first, at least this is what I have seen in other design (audio, but not power amp).

Thanks in advance,

Max

 

[recepky]

Hi friends
i have completed my f5 turbo project but couldnt set the bias. I ran out of trimmer turns. Dc offset is 1.8mv and didnt change during bias. Source resistor voltage stayed 0mv. Mosfets did not heat up.

I designed the amplfier two monoblocks each standard 50watts f5turbo. Fe board stuffed like cascoding. Each amplifier has its own 600va tansformer with +-35 volt dc unloaded.

 

[6L6]

Did you get any bias at all?

 

[recepky]

no

 

[recepky]

here is the pics

 

[recepky]

this is the mess i am dealing with

 

[Sangram]

Voltage across JFET source resistors (10 ohm)?

 

[recepky]

Voltage across JFET source resistors (10 ohm)?

hi sangram
do you mean R3 and R4? near the P1 and P2

 

[6L6]

First doublecheck your wiring, you've got a lot that's the same color, it's easy to make a simple error.

Also verify that the cascode transistors are installed properly.


Is there a fan in that case? You will absolutely need one, those heatsinks are incredibly undersized for passive cooling.

 

[recepky]

First doublecheck your wiring, you've got a lot that's the same color, it's easy to make a simple error.

Also verify that the cascode transistors are installed properly.


Is there a fan in that case? You will absolutely need one, those heatsinks are incredibly undersized for passive cooling.

Dear 6L6
I checked the cabling will check again.
yes I have a 12 cm fan backside.


Did you mean by cascade transistors Q7 and Q8


They are Toshiba A1145Y and C2705Y



I am not sure about their orientation, did flat surface must look outside?



pls see the pic below (flat surface of the transistors looks inside)

 

[Sangram]

hi sangram
do you mean R3 and R4? near the P1 and P2

I don't have that PCB or a view of the schematic, so part numbers are difficult to decipher.

 

[6L6]

I suspect the Cascode transistors are in backwards. Check the datasheets and the pinouts.

 

[recepky]

Dear 6L6
Since i am not cascoding (no paralel output boards for now) should i consider cancel those cascode transistors and short Q7 and Q8) if yes how can i short?

 

[6L6]

Cascode needed because you have 35v rails.

 

[wijgers]

crackling sound during warm-up

Hi all,

I've some issues with my F5 turbo V2. All is playing very well, however I've strange crackling sound during warm-up on the left-side channel.

It is only the left channel, Power supply feeds both channels, so I can conclude this is not the issue. Right channel is playing silent and after warm-up also the left channel is silent.

Is there anyone who can tell where to start looking te remove this crackling sound. I thought of going over all solder-joints, however is this the right approach?

Nils