Even thats big Dave, why didnt you go 100va or 200va like inko suggested as that's all you need for a 100w amplifier and yours is only 25w?
Would you use less then what you have now?
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It was not criticism or attack. I just expressed my opinion.
I completely understand your passion for DIY.
Today I received a package with PCBs.
Actually you did criticise and sort of attack and your opinion wasn't constructive. You didn't ask the right questions about the build and only made assumptions
Your built boards and design I couldve ripped into, but this is DIY audio, each to there own and to discover there own way. About time you got some proper pcbs, I'd like to see where it leads you.
Go big on the power supply
Nice build Vishalk. Very tidy. I'll study that later for tricks and inspiration when I get around to a Class A amp.
Oversized power transformers make sense to me.\
50W/8 Ohms = 28.3 V peak / 3,53 Amperes peak
100W/4 Ohms = 28.3 V peak / 7,07 Amperes peak
200W/2 Ohms = 28.3 V peak / 14,14 Amperes peak
400W/1 Ohm = 28.3 V peak / 28.28 Amperes peak
800W/0.5 Ohm = 28.3 V peak / 56.57 Amperes peak
A 200VA transformer with say 25-0-25 secondaries is only going to provide around 2.6A continuous which allows 50w continuous into 8 ohm @ 2.5A.
100w into 8ohm continuous requires more like 3.5A at higher voltage.
Say 35-0-35 secondaries: 70v x 3.5 = 245VA, derate by 0.65 for rectification into a capacitive load you need 376VA to put a real 100W into 8 ohms.
Start driving 6 or 4 ohms speakers and we can see from above that the current requirements are going up quickly.
This is why the old Krell KSA50 required 2 men to lift despite being 'only 50w'. It was designed to put power into any load.
Oversized power transformers make sense to me.\
50W/8 Ohms = 28.3 V peak / 3,53 Amperes peak
100W/4 Ohms = 28.3 V peak / 7,07 Amperes peak
200W/2 Ohms = 28.3 V peak / 14,14 Amperes peak
400W/1 Ohm = 28.3 V peak / 28.28 Amperes peak
800W/0.5 Ohm = 28.3 V peak / 56.57 Amperes peak
A 200VA transformer with say 25-0-25 secondaries is only going to provide around 2.6A continuous which allows 50w continuous into 8 ohm @ 2.5A.
100w into 8ohm continuous requires more like 3.5A at higher voltage.
Say 35-0-35 secondaries: 70v x 3.5 = 245VA, derate by 0.65 for rectification into a capacitive load you need 376VA to put a real 100W into 8 ohms.
Start driving 6 or 4 ohms speakers and we can see from above that the current requirements are going up quickly.
This is why the old Krell KSA50 required 2 men to lift despite being 'only 50w'. It was designed to put power into any load.
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Hi all,
Regarding Vishalk's build and trannies. This circuit is Class A and dissipates about 80W per channel, 160 total. Rule of thumb per Linsley Hood is to derate trannie ac specs to about 65% for dc. Thus 225va would be the minimum warranted.
Next this is continuous draw. To prevent stressing the trannie to the max and it getting to hot, a margin would be prudent. Hence 300VA would be reccomendable for a stereo build as a minimum (take in to account ac line fluctuations etc).
500 VA per channel is overkill but does not hurt. The trannies will be less stressed reducing fields etc. Furthermore, the psu has some series resistance following the diodes. This somewhat reduces peak currents. This in combination with overspecced diodes will reduce stress in the diodes keeping the signal cleaner with less ringing and sidebands and emf. (not to fond of the psu cap bypasses in that aspect)
Psu capacity is large but not uncommon for a circuit like this. Hiraga specced more...
Just my 2 cents but let's take this back to the build thread. This Thread is for the nice pic's so i can get jealous.
Joris
edit: inko already replied
edit2: @vishalk, nice, you've understood why i send that tekst.
Regarding Vishalk's build and trannies. This circuit is Class A and dissipates about 80W per channel, 160 total. Rule of thumb per Linsley Hood is to derate trannie ac specs to about 65% for dc. Thus 225va would be the minimum warranted.
Next this is continuous draw. To prevent stressing the trannie to the max and it getting to hot, a margin would be prudent. Hence 300VA would be reccomendable for a stereo build as a minimum (take in to account ac line fluctuations etc).
500 VA per channel is overkill but does not hurt. The trannies will be less stressed reducing fields etc. Furthermore, the psu has some series resistance following the diodes. This somewhat reduces peak currents. This in combination with overspecced diodes will reduce stress in the diodes keeping the signal cleaner with less ringing and sidebands and emf. (not to fond of the psu cap bypasses in that aspect)
Psu capacity is large but not uncommon for a circuit like this. Hiraga specced more...
Just my 2 cents but let's take this back to the build thread. This Thread is for the nice pic's so i can get jealous.
Joris
edit: inko already replied
edit2: @vishalk, nice, you've understood why i send that tekst.
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All right vishalk
At first I thought it was an AB class amplifier.
I later realized it was class A, but I enjoyed teasing you
it's all good hence why I said ask the right questions before you judge. I knew you were teasing, just playing along 
I bought 10 225VA toroids for dirt cheap (but got shipped 16). It had the right voltages, and was sitting there. The amp sounds really good.
If i had to pay real prices i might go down to 160VA, and had/habe trafos of lesser VA that i had considered using (something like 2 x 60VA IIRC), but that small only because they were on hand and cost next to nothing.
dave
Here a recent post with a very similar amplifier (except 4 channel), with 200VA per pair of amplifiers.
Chip Amp Photo Gallery
Same 18v DC rails (optimumcurrent delievery for low impedances as opposed to maximum power into 8Ω).
dave
from your "half-kW" capable amplifier? Liquid cooling? Tons of copper? I see no space for normal heatsink.goldtune tsa
full may design full symetrical darlington vas
,super protect and super softstart , advanced grounding for zero hum.
video YouTube
full may design full symetrical darlington vas
,super protect and super softstart , advanced grounding for zero hum.
video YouTube
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