buzz. i'm gonna have 0.6A bias pr fet. and wondering if the best way is to use external sinks or main sinks for the diodes. the main sinks will run pretty hot i guess. 125+W pr side on 2x 10.080" profiles, 6" long.
on the other hand. with external sinks. how will the transaction be, when you WANT the diodes to conduct. i'm way out of the 1A ranch. maybe connect the diode sink with the main sinks with 2 L profiles?
i can not crank up the bias with rail voltage of +/-50V😀😀
on the other hand. with external sinks. how will the transaction be, when you WANT the diodes to conduct. i'm way out of the 1A ranch. maybe connect the diode sink with the main sinks with 2 L profiles?
i can not crank up the bias with rail voltage of +/-50V😀😀
I sent the payment on the 7th of Dec, the day I posted here that I finally ordered. It's in the board fab and Fed- Ex's hands now. I promise to get them in the store ASAP when they arrive.
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What would be a suitable alternative for the 2SA1837 and 2SC4793.They don't seem to be available from Farnell or RS and the only supplier I've found are asking close to a fiver each.
Andrew I did'nt check those two.I tend to deal mainly with Farnell.
Buzz you are a gent thank you.
Buzz you are a gent thank you.
Sanity check time for me....
V3, 4 pairs per channel, biased to 3,0 amps per polarity, 50 volt rails. That gives 0,75 watts/FET, or 0,35 Volts. Total bias current is 6 amps.
Now total dissipation is 8 * 50 * 0.75 = 300 watts. That can easily be spread over 4 regular sized F5 heatsinks at 75 watts per heat sink -- each heatsink carries one pair of FETS.
Efficiency is around 33% at full class A power. Does that sound about right?
As for Transformer VA, clearly 300 VA is needed just to run the bias. Now, add the load requirements. P=150 rms = 300 peak.
So, P=IV , V = 50 says I = 6 amps peak. That is another 300 VA to power class A operation. (That checks with doubling the bias current to come out of class A).
So far, the transformer has to be 600 VA *bare minimum*.
What do you spec for Class A/B overhead? Do you limit the VA to provide 50% of the steady state operating current of the output transistors?
Also, how do the diodes impact the heatsink size?
V3, 4 pairs per channel, biased to 3,0 amps per polarity, 50 volt rails. That gives 0,75 watts/FET, or 0,35 Volts. Total bias current is 6 amps.
Now total dissipation is 8 * 50 * 0.75 = 300 watts. That can easily be spread over 4 regular sized F5 heatsinks at 75 watts per heat sink -- each heatsink carries one pair of FETS.
Efficiency is around 33% at full class A power. Does that sound about right?
As for Transformer VA, clearly 300 VA is needed just to run the bias. Now, add the load requirements. P=150 rms = 300 peak.
So, P=IV , V = 50 says I = 6 amps peak. That is another 300 VA to power class A operation. (That checks with doubling the bias current to come out of class A).
So far, the transformer has to be 600 VA *bare minimum*.
What do you spec for Class A/B overhead? Do you limit the VA to provide 50% of the steady state operating current of the output transistors?
Also, how do the diodes impact the heatsink size?
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Gentlemen,
I am helping a forum member with his F5T -- I will save you the details and ask;
Would there be any problem building a v3 with ~ 42v rails and only 2 pair of output transistors?
Thank you,
-Jim
I am helping a forum member with his F5T -- I will save you the details and ask;
Would there be any problem building a v3 with ~ 42v rails and only 2 pair of output transistors?
Thank you,
-Jim
there is no point making current hungry load oriented solution , without full current capability
catch is - what's limiting factor , responsible to just two pairs choice ?
catch is - what's limiting factor , responsible to just two pairs choice ?
The reason for the high voltage rails is due to a mistake when ordering the transformer. So am trying to see if there is a good solution to using the parts on hand.
Or maybe put a Zen-style regulator in the PSU, referenced to 32v, There is at least a 4v insertion loss, I think... so would have to burn up 6-7v at ?200w?... That would take too many transistors. Nevermind.
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If each Fet can handle 12 amps full load, then derating to 60% for longevity gives you a max of 7.2 amps/FET. That's and additional 1.2 amps x 4 fets *the other 4 are off*. Which is 4.8 amps or an extra 240 VA.
70% is 8.4 amps/FET => 2.4 * 4 = 9.6 amps or an extra 480 VA. That is a 1080 VA transformer.
Derating to 80 % gives your 9.6 amps/FET, or an extra 4 x 3.6 = 14.4 amps or 720 VA for a total of 1320 VA.
Looking at this backwards, if you have a 1500 va transformer, you've got 900 VA above 150 watt class A. 900 / 4 = 225 VA /FET = 4.5 amps. Which means that each FET can push 10.5 amps steady state, which only derates to 10.5/12 = 87.5 percent.
I'm not so sure this is a good idea. It is looking like a 1KVA transformer is about the max you want to supply to this sort of monoblock.
70% is 8.4 amps/FET => 2.4 * 4 = 9.6 amps or an extra 480 VA. That is a 1080 VA transformer.
Derating to 80 % gives your 9.6 amps/FET, or an extra 4 x 3.6 = 14.4 amps or 720 VA for a total of 1320 VA.
Looking at this backwards, if you have a 1500 va transformer, you've got 900 VA above 150 watt class A. 900 / 4 = 225 VA /FET = 4.5 amps. Which means that each FET can push 10.5 amps steady state, which only derates to 10.5/12 = 87.5 percent.
I'm not so sure this is a good idea. It is looking like a 1KVA transformer is about the max you want to supply to this sort of monoblock.
If i had that high a rail voltage, I would b looking at more fets, not less. I would be shooting for fet temp in 35-40C max before heatsink, just my 2C. You never know with all these crazy DIY folks😀
I'm struggling with this. Counting is hard....
If each Fet can handle 12 amps full load, then derating to 60% for longevity gives you a max of 7.2 amps/FET.
600 VA is used for 150 watts class A into 8R0. That's 6 amps of pure class A power. That is 1.5 amps over each FET, for a total of 2.25 amps/FET
You've got 5 amps/fet left to go, or 20a amps total. That makes for 1600 KVA total transformer size.
Is that about right?
If each Fet can handle 12 amps full load, then derating to 60% for longevity gives you a max of 7.2 amps/FET.
600 VA is used for 150 watts class A into 8R0. That's 6 amps of pure class A power. That is 1.5 amps over each FET, for a total of 2.25 amps/FET
You've got 5 amps/fet left to go, or 20a amps total. That makes for 1600 KVA total transformer size.
Is that about right?