Due to generosity of the one and only Nelson Pass at previous Burning Amp festivals, I now own 5 very large, very heavy (about 50lbs) toroidal transformers. So I need something to do with them...
Backing up: over the past little while, I've been developing some active speakers, using whatever amps I had on hand. They will soon be threeway, and I was looking at building more gainclones, but then realized that the only way I could easily using the transformers I got from Nelson was to use one of the LME chips. So here we are.
Its pretty straightforward, straight out of the National App sheets:
Here is the pdf for the power amp. Pretty nice, pretty easy. Gonna use the board layouts in the pdf, and get matched IRFP FETs from tech-diy.com
Here is the pdf for the power supply.
One of the nice things about this module is its scalability and bias flexibility. The bass drivers will be powered by one module, capable of 335W into 4 ohms, using only four mosfets, while the mid driver will be scaled down, using only two. The tweeter will also be scaled down, but will be biased much higher than the other sections - National put a nice little graph of the distortion at different bias levels - check out Fig. 8 in the power amp pdf. Not shabby.
My only questions so far mostly regard the power supply.
The toroid I plan on using is labeled 40-30-0-30-40 Vac, 15A, for a total of 1200VA. I plan on using the 40Vac taps, resulting in +/-54Vdc rectified, with about 11amps available. Now, my first question - is this transformer large enough? Might seem like a dumb question, but it will be powering all six modules. I estimate that I'll have at least 700W of actual amp power available, which should be plenty.
The next question is the capacitance - I plan on building a single power supply for all six modules. National uses 80000uF for a single channel of amplification! If I did this for six channels, it would cost about $600! That's not going to happen. Would someone please suggest a reasonable amount of capacitance? I happen to have four 25,000uF caps, rated at 75Vdc, and would like to use them. Am I pushing the voltage rating to close to the rails? Any thoughts would be appreciated, as I'd like to place my parts order as soon as possible.
The last thing is just a sanity check: I plan on using two 1' sections of heatsink from this guy. Rated at .375C/W, I will attach three modules per 1', along with two silent fans per section. That should keep the temp down fine, I hope. National recommends a .6C/W heatsink per module.
Anyway, I'm really excited about this! I think it is going to be a nice amp!
Backing up: over the past little while, I've been developing some active speakers, using whatever amps I had on hand. They will soon be threeway, and I was looking at building more gainclones, but then realized that the only way I could easily using the transformers I got from Nelson was to use one of the LME chips. So here we are.
Its pretty straightforward, straight out of the National App sheets:
Here is the pdf for the power amp. Pretty nice, pretty easy. Gonna use the board layouts in the pdf, and get matched IRFP FETs from tech-diy.com
Here is the pdf for the power supply.
One of the nice things about this module is its scalability and bias flexibility. The bass drivers will be powered by one module, capable of 335W into 4 ohms, using only four mosfets, while the mid driver will be scaled down, using only two. The tweeter will also be scaled down, but will be biased much higher than the other sections - National put a nice little graph of the distortion at different bias levels - check out Fig. 8 in the power amp pdf. Not shabby.
My only questions so far mostly regard the power supply.
The toroid I plan on using is labeled 40-30-0-30-40 Vac, 15A, for a total of 1200VA. I plan on using the 40Vac taps, resulting in +/-54Vdc rectified, with about 11amps available. Now, my first question - is this transformer large enough? Might seem like a dumb question, but it will be powering all six modules. I estimate that I'll have at least 700W of actual amp power available, which should be plenty.
The next question is the capacitance - I plan on building a single power supply for all six modules. National uses 80000uF for a single channel of amplification! If I did this for six channels, it would cost about $600! That's not going to happen. Would someone please suggest a reasonable amount of capacitance? I happen to have four 25,000uF caps, rated at 75Vdc, and would like to use them. Am I pushing the voltage rating to close to the rails? Any thoughts would be appreciated, as I'd like to place my parts order as soon as possible.
The last thing is just a sanity check: I plan on using two 1' sections of heatsink from this guy. Rated at .375C/W, I will attach three modules per 1', along with two silent fans per section. That should keep the temp down fine, I hope. National recommends a .6C/W heatsink per module.
Anyway, I'm really excited about this! I think it is going to be a nice amp!
Hi,
I'm building a similar project starting here. My amp modules are all the same, ~150 watts/8ohms. I'll be using a 40-0-40 750VA transformer so I envy your 1200VA!.
I'm using 2 power supply with this single transformer, one for each "channel" (bass, mid, high) The total capacitance I'm using is 5 x 4700uf or 23500uF total per rail, so I think you will easily make do with 25K. 75VDC rated caps are plenty good for 56VDC rails.
I used his heatsinks for a couple of other projects include one of those sections for a 1000 watt sub amp. I think that 2 of those will be ok.
Good luck with your project!
I'm building a similar project starting here. My amp modules are all the same, ~150 watts/8ohms. I'll be using a 40-0-40 750VA transformer so I envy your 1200VA!.
I'm using 2 power supply with this single transformer, one for each "channel" (bass, mid, high) The total capacitance I'm using is 5 x 4700uf or 23500uF total per rail, so I think you will easily make do with 25K. 75VDC rated caps are plenty good for 56VDC rails.
I used his heatsinks for a couple of other projects include one of those sections for a 1000 watt sub amp. I think that 2 of those will be ok.
Good luck with your project!
What's the maximum mains supply voltage?
What will be the maximum open circuit voltage from your transformer if the supply is at maximum?
You will probably find that 40Vac can be used with 63Vdc capacitors for all worst conditions through your 1200VA toroid.
My 230:40Vac 1000VA transformer produce 58Vdc at the amplifier and with 4% regulation and +6% (254Vac) on the mains comes to just under 63Vdc in worst case conditions (PSU fuses blown with 254Vac on the transformer).
What will be the maximum open circuit voltage from your transformer if the supply is at maximum?
You will probably find that 40Vac can be used with 63Vdc capacitors for all worst conditions through your 1200VA toroid.
My 230:40Vac 1000VA transformer produce 58Vdc at the amplifier and with 4% regulation and +6% (254Vac) on the mains comes to just under 63Vdc in worst case conditions (PSU fuses blown with 254Vac on the transformer).
Not the Europeans. On the British continentAndrewT said:
people are just as much buying and using an increasing amount of electric and electronic devices demanding ever more power, while at the same time protesting against any new power plants for varying reasons. On that conditions energy suppliers cannot keep up the old standards, so they embraced the opportunity to turn to the less strict IEC standards. Rumour has it that the actual tolerances (115 or 230 V +10 %/-15%) are going to be widened further, because some countries have difficulties to even stick within those limits.I stand by my statement.pacificblue said:
Not the Europeans. On the British continent
Harmonisation of the 220/240Vac is the only reason the UK had to lower the previous 226Vac limit to 216Vac.
Our systems are properly designed, properly built and well run, even after privatisation.
rather than a simple "yes/no", I gave him "how to".
Hopefully he now knows "how to" in future.
Your simple "yes/no" means he and others keep coming back with the same question because it doesn't help them learn.
Hopefully he now knows "how to" in future.
Your simple "yes/no" means he and others keep coming back with the same question because it doesn't help them learn.
even for a low regulation transformer my "normal" supply voltage gives a PSU voltage with quiescent current set to 210mA above your maximum. A "how to" gets around this conflicting information.
Lowering the allowed limits does not oblige the energy suppliers in the UK to lower their standards. And if you say your systems are still fine, what harm has been done?AndrewT said:
The reason for harmonisation rather lies in international industrial interests than in European force. You still pay in £ instead of €, and still drive on the wrong side of the street, both of which does not give me the impression that Europeans can force a lot upon you.
And the reason, why the tolerances are so high can rather be found in the US of A, with their very different infrastructure than in Europe.
Lets do a little off the cuff power dissipation estimation...
from the an-1850 pdf:
PD(AMP)MAX = VCC^2/(2pi^2RL)
where Vcc is the sum of the + and - rails (guessing 108V for my case) and RL is the resistance of the load, lets assume 8ohms. The modules have four devices total, and the above equation gives 74W total power dissipation, each device sees about 18.5W.
My woofer will be about 4 ohms, which gives total power dissipation of 148W and 37W per device. Not bad if you derate the devices to 90W max for SOA.
There are a few things I don't understand. Is this calculation for a signal swinging to the rails? Isn't power dissipation higher with the signal at about half the rail voltage?
Lets calculate total quiescent power dissipation. The woofer will be biased at about 100mA - would this give 10.8W loss with no signal? The tweeter I plan on biasing up to 1A, so I guess the power dissipation will be 108W total. How's that sound?
So for the tweeter module working into 8 ohms, does the 108W of quiescent power loss add to the 74W of max power loss, meaning each device will possibly be seeing 45.5W power loss at maximum?
The other thing I don't understand is how changing the number of devices changes the power dissipation - it seems like fewer devices would lead to less power available and therefore less power dissipation, but the above equation doesn't factor it in. Seems like the power dissipation per device would actually be higher. I was hoping that using fewer devices on the tweeter module would help compensate for biasing it higher, but it looks like it will just make them blow faster..
from the an-1850 pdf:
PD(AMP)MAX = VCC^2/(2pi^2RL)
where Vcc is the sum of the + and - rails (guessing 108V for my case) and RL is the resistance of the load, lets assume 8ohms. The modules have four devices total, and the above equation gives 74W total power dissipation, each device sees about 18.5W.
My woofer will be about 4 ohms, which gives total power dissipation of 148W and 37W per device. Not bad if you derate the devices to 90W max for SOA.
There are a few things I don't understand. Is this calculation for a signal swinging to the rails? Isn't power dissipation higher with the signal at about half the rail voltage?
Lets calculate total quiescent power dissipation. The woofer will be biased at about 100mA - would this give 10.8W loss with no signal? The tweeter I plan on biasing up to 1A, so I guess the power dissipation will be 108W total. How's that sound?
So for the tweeter module working into 8 ohms, does the 108W of quiescent power loss add to the 74W of max power loss, meaning each device will possibly be seeing 45.5W power loss at maximum?
The other thing I don't understand is how changing the number of devices changes the power dissipation - it seems like fewer devices would lead to less power available and therefore less power dissipation, but the above equation doesn't factor it in. Seems like the power dissipation per device would actually be higher. I was hoping that using fewer devices on the tweeter module would help compensate for biasing it higher, but it looks like it will just make them blow faster..
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