F5 power amplifier

[rebos123]

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.

[udailey]

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/Dk...name=BC2313-ND
Cheap and cool looking.

Uriah

[AndrewT]

it's one CL60 for each parallel 110/120Vac primary.
When on 220/240Vac put the same two CL60 in series.

Like I said
one CL60 for 110/120Vac
two CL60 for 220/240Vac.

[Babowana]

Originally posted by AndrewT
it's one CL60 for each parallel 110/120Vac primary.
When on 220/240Vac put the same two CL60 in series.

Like I said
one CL60 for 110/120Vac
two CL60 for 220/240Vac.

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 . . .

[udailey]

Andrew,
Why would you double up on the CL60's if voltage was 230 or 240?
Uriah

[Renron]

Originally posted by Babowana



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 . . .

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

[AndrewT]

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.

[udailey]

Thanks Andrew. Makes sense now. Since the are in series they resistance is doubled and less current can pass. If they were in parallel we would allow double the current.
Uriah

[AndrewT]

Originally posted by Renron



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

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.

[Renron]

Thanks AndrewT,

Your explanation of the 220Vac double pole switch makes perfect sense. I should have learned by now, not to doubt you.

Ron