F5 power amplifier

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#4,641
F5 build

I just completed my F5 build. It sounds fantastic! Interesting how the description of the F5's sonic character has been so accurately described on this forum!! It reveals layers of the music that were blurred with other amps. I am using the amp to drive the midrange and tweeter horns in a klipsch KLF-30.
 
#4,642
For the CL60's in the power supply: I used two with a small cap between them as in the F4 power supply. I didnt use one to ground but it seems a fine idea.
The power supply worked well and the thermistors did their job. I have 120VAC.
Yes, its 2 for 120VAC and one for 230/240.
http://www.firstwatt.com/downloads/F5-om_sm-080527.pdf
Last page details that.


4.7k thermistors in the amp are just what they are spec'd. 4.7k. I think it had to be an NTC (negative temperature coefficient). So that means as temp goes up the resistance drops.
Here is one that should work
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=BC2313-ND
Cheap and cool looking.

Uriah
 
#4,646
Babowana said:



Two CL60 for 110/120Vac
One CL60 for 220/240Vac
As a key point, think about the double (surge) current in case of 100/120Vac . . .

🙂
Click to expand...


BABO,

AndrewT is right, he said "it's one CL60 for each parallel 110/120Vac primaryl"

Key words are " each parallel 120/120Vac"

AndrewT:

Papa disagrees with you on how many are needed for a 220Vac application. See below.

Ron
 

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#4,647
it's ohm's law at work.
a 300VA 110/120Vac transformer will require a maximum of 2.6Aac when working at full rating.
A CL60 in series with the 110/120Vac supply and the two primaries in parallel (or in the PASS diagram one CL60 to each 110/120Vac primary) has to pass the surge/start up current from ~160Vpk to two parallel primaries.

a 300VA 220/240Vac transformer will require a maximum of 1.3Aac when working at full rating. Note the maximum current is halved compared to the 110/120Vac transformer.
A CL60 + CL60 in series with the 220/240Vac supply and the series pair of primaries will pass approximately half the surge/start up current from 320Vpk to two series primaries. This double CL60 achieves a similar reduction in start up current compared to the 110/120Vac.

If one tries to use the 220/240Vac mains with a single CL60 then the doubled 320Vpk will try pass double the start up current through the combined CL60 resistance + primary resistance of the de-energised transformer.
 
#4,649
Renron said:



BABO,

AndrewT is right, he said "it's one CL60 for each parallel 110/120Vac primaryl"

Key words are " each parallel 120/120Vac"

AndrewT:

Papa disagrees with you on how many are needed for a 220Vac application. See below.

Ron
Click to expand...
A dpdt switch changes over the 110/120Vac connections to the 220/240Vac connections and maintains the use of the two thermistors.
I hope when PASS showed the 240Vac version that some license was used to omit the second thermistor from the switched over diagram.
If two thermistors are there to absorb the start up energy of the 110V transformer then two thermistors will absorb a similar amount of energy in starting up the 240V transformer.
 
#4,653
Power Supply 240V

Wow, that was interesting. 😀

Back to my power supply:
I'm still not sure if that will be good to use
with two transformers with 225VA each.
Does this matter how big those transformers are?

I mean 300VA is not the same as 450VA.
That is the reason why i asked about calculation.


I can not post pictures at this moment.
But i would like to put in this new schematic.
The schematics i posted are not ok, sorry for that.
500 Downloads :yikes:

Thanks to Andrew and all the other good guys around,
and of course to the Oracle.🙂
This forum is very impressive.
 
#4,655
Sisyphism said:


I mean 300VA is not the same as 450VA.
That is the reason why i asked about calculation.
Click to expand...


The sizes of the transformers are just scale of their sizes, and the bigger the better in handling the amount of current.

Meanwhile, the actual current on the primary side is depending on the actual current on the secondary side (load current) and the turns ratio of the coils, independent of the transformer size. If you are going to apply the similar bias current and the similar total filter capacitance as the original F5, one CL60 is enough on the primary side when you are going to use 220-240VAC main. But, when you are going to use 110-120VAC main, you want to use two CL60s because the primary current will double up, compared with in case of 220-240VAC main.

You do not believe in the primary currents mentioned as above . . . ? Go to the drawing in post#4646 and see the fuse sizes--1.25A for the 240VAC main and 2.5A for the 120VAC main.

Happy diy!

😎
 
#4,656
Sisyphism said:
really
Click to expand...

Hope you realise that the constant power draw of an F3 channel is 100W, and the F5 does 60W.

A General Electric CL60 thermistor handles 4.5W dissipation.
The thermistors in the F3 power supply are loaded with about half an amp of current.
If you calculate the Ro value at that current with the X-Y trick, it follows that the thermistors are running at 20% maximum continuous rating, as Babowanabanana and moi would say.
The Oracle has been loading his semis and passive parts at 25% or less since way back to the Threshold days.

Your 15 Ohm Siemens B57237S series thermistors are loaded with a constant draw of something like 0.267 amp in your schematic.
If you calculate the corresponding resistance value of the thermistor with the k-n numbers at that current, roughly the same as the X-Y numbers of the CL60, you'll end up with a dissipation of some 0.6W each.
The B57237S handles 3W constant dissipation, so they run at 20% MCR as well.
 
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