Hi
I have what is a very simple question (well not for me), but its in area I would rather not make a mistake!
I have almost finished assembling my F5 and I would like to make sure the mains switch, fuse holder and spade connectors used for attaching the mains to the panel mount fuse holder, and the 35A bridge rectifiers are up to the job.
What current rating would you recommend with a 500VA transformer on a 250V mains supply? I am currently using two CL60s wired in series with mains live and a 1.25T fuse.
Thanks
I have what is a very simple question (well not for me), but its in area I would rather not make a mistake!
I have almost finished assembling my F5 and I would like to make sure the mains switch, fuse holder and spade connectors used for attaching the mains to the panel mount fuse holder, and the 35A bridge rectifiers are up to the job.
What current rating would you recommend with a 500VA transformer on a 250V mains supply? I am currently using two CL60s wired in series with mains live and a 1.25T fuse.
Thanks
I think the 1.25A fuse is an admirable target to set for your safety.
But without sufficient resistance in the primary transformer secondary I fear it may rupture too often. Two CL60s may not be enough cold resistance.
Try 1.6A or 2A.
2.5A is too big, passing a longterm 600W and ~1200W for many seconds, maybe even tens of seconds.
In every case use a T rated fuse (= anti-surge = time delayed)
But without sufficient resistance in the primary transformer secondary I fear it may rupture too often. Two CL60s may not be enough cold resistance.
Try 1.6A or 2A.
2.5A is too big, passing a longterm 600W and ~1200W for many seconds, maybe even tens of seconds.
In every case use a T rated fuse (= anti-surge = time delayed)
Hi Andrew
I took on-board your previous advice with regards to using 3xCL60s if using a 1.25T fuse. I have a spare CL60 and intend to fit this if the fuse blows too often
Do you have any tips regarding current rating for the ancillaries?
Thanks
Hello
I plan to build a F5 amp soon.
But I dont have experience with psu's with such high current (except for tube filaments).
My first psud simulation for the available torroid tranny, 20-0-20VAC (centre tapped single winding) 300VA gives me this result:
My questions:
- Isn't 300mV ripple much too high?
- What is adequate ripple for an F5 (or PSRR)?
- What is a realistic resistance value for the caps in psud?
Thanks for hints
Franz
P.S.
Of course, I know I must build a positive and negative rail. I will do this by connecting the centre tap to gnd. Thats why I simply simulate 40VAC.
I plan to build a F5 amp soon.
But I dont have experience with psu's with such high current (except for tube filaments).
My first psud simulation for the available torroid tranny, 20-0-20VAC (centre tapped single winding) 300VA gives me this result:
An externally hosted image should be here but it was not working when we last tested it.
My questions:
- Isn't 300mV ripple much too high?
- What is adequate ripple for an F5 (or PSRR)?
- What is a realistic resistance value for the caps in psud?
Thanks for hints
Franz
P.S.
Of course, I know I must build a positive and negative rail. I will do this by connecting the centre tap to gnd. Thats why I simply simulate 40VAC.
6A of continuous load is too high.
A single F5 is biased to 1.3A. That is the continuous load that the F5 puts on the PSU.
A two channel would be biased to a total of 2.6A but would be quite difficult to keep cool.
NB.
computers only give you the right answers if you ask the right questions.
A single F5 is biased to 1.3A. That is the continuous load that the F5 puts on the PSU.
A two channel would be biased to a total of 2.6A but would be quite difficult to keep cool.
NB.
computers only give you the right answers if you ask the right questions.
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Hi Franz
I will be using a pair of Conrad MF35-151.5 heatsinks attached to a single case.
I listened to a pair of F5 mono-blocks yesterday with much smaller heatsinks, and was really surprised how cool they were. I could have rested my hand on the sinks all day!
65W of dissipation per F5 channel (1.3A * +-25Vdc)
Assume a sink of 0.2C/W and Ta=25degC.
Delta Tsink-ambient ~13Cdegrees.
But 0.2C/W rating is for DeltaT=70 or 75degC.
Apply correction factor of ~1.3 Actual Tsink = 25 + 1.3*{13} = 42degC
Delta Tc-sink ~65/2 * 0.5C/W ~ 16Cdegrees.
Actual Tc = 42+16 = 58degC.
De-rate FET for Tc gives Pdmax = 110W for a 150W @ 25degC device
Delta Tjunction-case ~0.83 * 32.5 = 27Cdegrees.
Tj ~ 58 + 27 = 85degC.
Finding room for two 0.2C/W sinks gives a big heavy chassis.
Do the calculations for two 0.3C/W sinks in a common chassis.
Assume a sink of 0.2C/W and Ta=25degC.
Delta Tsink-ambient ~13Cdegrees.
But 0.2C/W rating is for DeltaT=70 or 75degC.
Apply correction factor of ~1.3 Actual Tsink = 25 + 1.3*{13} = 42degC
Delta Tc-sink ~65/2 * 0.5C/W ~ 16Cdegrees.
Actual Tc = 42+16 = 58degC.
De-rate FET for Tc gives Pdmax = 110W for a 150W @ 25degC device
Delta Tjunction-case ~0.83 * 32.5 = 27Cdegrees.
Tj ~ 58 + 27 = 85degC.
Finding room for two 0.2C/W sinks gives a big heavy chassis.
Do the calculations for two 0.3C/W sinks in a common chassis.
Many of us have no idea what that Conrad is... could you instead state dimensions?
If there is one thing that a properly biased F5 is not, is cool running.
With a very massive heatsink they do only get moderately warm... but since many folks are reading along and maybe trying to build it seems like a good idea to make clear what results are gotten with what things...
A report of cool running makes one think of underbiased...
thanks,
_-_-
Why not suffice to take the noise level in the F5 manual as granted : 60 microvolts ?
Calculate ripple for full output of a class AB amp : much higher than 300mV.
Conrad MF35-151.5 : 350mm length (~13-3/4") , 151.5mm height ( ~6")
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Many of us have no idea what that Conrad is... could you instead state dimensions?
If there is one thing that a properly biased F5 is not, is cool running.
With a very massive heatsink they do only get moderately warm... but since many folks are reading along and maybe trying to build it seems like a good idea to make clear what results are gotten with what things...
A report of cool running makes one think of underbiased...
thanks,
_-_-
Hi Bear
I haven't powered up my amp and wont until fitting some heatpads (I'll get in there first!
)
I'll have a word with the owner of the F5 and ask him if its biased to the recommended spec. His heatsink profile was smaller than the attached picture.
Here is my F5, built March of 2009, with Conrad MF35-151.5 heatsinks.
I could hold my hand on it for much more than five seconds.
I'm currently running two F5 boards in parallel per sink. Now that is quite hot.
But it does sound better. More current for the current hungry SEAS Thors (4Ohm).
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