F5 Turbo Builders Thread

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#2,501
P3 in the F5T V.2 Schematic

I'm wondering how to find the best operating point for P3 in the schematic. Yes I know Nelson spent a few words in his F5T article but without an oscar
and having only multiple multimeters I have o idea what level will be the best 😕

Or is just a matter of listening to the sound quality?

Any recommendation how to handle it without a graphical test equipment?
 
#2,505
hi mallard.
Hear's my take if I'm wrong ,,,,,,sk170 and j74 have different gain curves,causes distortion, close if matched but not exactly the same(all other parts have a variance to them too),P3 adjusts the total of the 2 curves,sorta like towards one or the other,to get it as correct as it can be ,you need a thd analyzer,but I have set P3 to the middle,and kept up with whitch way it is turned and have noticed that the bass goes a little thin one way and fatter the other,Your choice for that!JUST my 2 cents.... no analyzer ,put it to the middle or remove it from the board,and be happy!
I like the way these amps sound !!!!Happy Listening.
NS
 
#2,509
Toroidal and Voltage rating of PSU caps for F5T v.2

I'm currently thinking about the setup of my F5T v.2 PSU.
My plan is to build a dual mono setup with 2 separate toroidals.
I have two questions where I'm not 100% sure about:

1. What power level should each toroidal have? I was thinking about 2 times min.800VA to max 1000VA... btw. I will buy from TOROIDY based in Poland.
2. What voltage rating should the capacitor bank have? Is 40V enough or is better to use 63V to be on the more expensive and safe side?

Some advise is very appreciated! Thanks in advance!
 
#2,510
Mallard said:
I'm currently thinking about the setup of my F5T v.2 PSU.
My plan is to build a dual mono setup with 2 separate toroidals.
I have two questions where I'm not 100% sure about:

1. What power level should each toroidal have? I was thinking about 2 times min.800VA to max 1000VA... btw. I will buy from TOROIDY based in Poland.
2. What voltage rating should the capacitor bank have? Is 40V enough or is better to use 63V to be on the more expensive and safe side?

Some advise is very appreciated! Thanks in advance!
Click to expand...

How many output devises on each channel, how much current are you going to run per devise, what rail voltage are you shooting for?
If you list that stuff, we can help determine the VA rating, cap voltage.

In my opinion, you can't have too much VA rating, so you should buy as big a transformer as you can afford or have space for. If you are running 32 volt rails, 40 volt caps is a good place to be. I have very stable voltage here and I run 32 volt rails on 35 volt caps, but there is no room for error.

Rush
 
#2,511
Rush said:
How many output devises on each channel, how much current are you going to run per devise, what rail voltage are you shooting for?
If you list that stuff, we can help determine the VA rating, cap voltage.
Click to expand...

The secondary of the toroidal will have 24V, so I'll run 32V on the amp circuit.
How much current I will run on the output devices? The peak current is 38Amp as I learned in the f5T documentation. But I gues this will surely depend on the heat dissipation.
The chassis I want to use is the big 5U from diyaudio shop.

Regards, Mallard
 
#2,514
Mallard, "How much current do you intend to run?" refers to idle current not peak current. In most cases with these amps idle is the operating point of concern because that's where the current will be for most listening.

I haven't built my F5t going into a 5u case but the specs are 0.28C/W per heat sink section. Theoretically you could dump around 90 W per section and 2 sections per side. From what I've read that's optimistic. I think 140-150 W per side will likely make them as hot as you'd want domestically. As Walter said, 2x is minimum transformer VA rating but 3-4x will run cooler with less chance of mechanical hum. I haven't decided my final layout but 2 500 VA Antek transformers fit comfortably side by side across the front of the case.
 
#2,515
Bob, my target is to bias each channel at 2Amp... at least

What is the price of these Antek transformers?



BobEllis said:
Mallard, "How much current do you intend to run?" refers to idle current not peak current. In most cases with these amps idle is the operating point of concern because that's where the current will be for most listening.

I haven't built my F5t going into a 5u case but the specs are 0.28C/W per heat sink section. Theoretically you could dump around 90 W per section and 2 sections per side. From what I've read that's optimistic. I think 140-150 W per side will likely make them as hot as you'd want domestically. As Walter said, 2x is minimum transformer VA rating but 3-4x will run cooler with less chance of mechanical hum. I haven't decided my final layout but 2 500 VA Antek transformers fit comfortably side by side across the front of the case.
Click to expand...
 
#2,516
Mallard said:
Bob, my target is to bias each channel at 2Amp... at least
Click to expand...

Maybe this is the silly question ofthe day

Why turbo with only 24 V trafos and 2 A bias?

I am doing that with standard cascoded and 2.6 A on twins
Dissipation is about 45 W on each mosfet living about 5W margin from the
50W maximum recommended by Papa

IMO if I ever feel the need to go Turbo (not with my actual room size) I would use a minimum of a 32+32 V traffo
 
#2,520
Do you have a recommendation regarding the source resistors @ 2Amp ? I don't understand why 0.5Ohm are suitable to drive 2 Amps...

A general question for the F5T builders out there. What current is a reasonable value for the v.2 given the 5U chassis?

Thanks for your help guys!

AudioSan said:
then you need to modify the amp a little bit. source resistors with less resistance or a third output pair. or drop the diodes in paralell with source resistors.
Click to expand...
 
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