This is a bit off topic, but look at the MA-600 schematics, I'm not lying. The low-side amp makes the output stage rails move up and down so half the voltage falls over each half of the amp. Having the emitters grounded makes driving the low-side amp easy. Quite elegant.
http://www.crownaudio.com/pdf/legacy/ma6001200_main_brd.pdf
The drawback is that you need separate supplies for each channel, but I haven't seen any mentions of multiple channels from the OP of the thread so that is moot.
Only needing half the amount of energy storage compared to a non-bridged amp for same bass performance is an inherent property of bridging (or running one channel inverted). It's true for standard bridged amps too, not just this "special" topology.
For bass frequencies where it is needed most, a non-bridged amp uses only one half of the power supply energy storage at a time. By using the whole power supply all the time this waste of power supply energy storage capacity is mitigated.
http://www.crownaudio.com/pdf/legacy/ma6001200_main_brd.pdf
The drawback is that you need separate supplies for each channel, but I haven't seen any mentions of multiple channels from the OP of the thread so that is moot.
Only needing half the amount of energy storage compared to a non-bridged amp for same bass performance is an inherent property of bridging (or running one channel inverted). It's true for standard bridged amps too, not just this "special" topology.
For bass frequencies where it is needed most, a non-bridged amp uses only one half of the power supply energy storage at a time. By using the whole power supply all the time this waste of power supply energy storage capacity is mitigated.
This is Crown's Class H amp circuit, which they at that time claimed to have reinvented (didn't know it had been uninvented though).
Yes! By balancing the speaker output around ½ supply Voltage you can save a bit on the PSU.....
However the Voltage translator stage has app. the same component count as two standard VAS stages, not saving you much there.
Yes! By balancing the speaker output around ½ supply Voltage you can save a bit on the PSU.....
However the Voltage translator stage has app. the same component count as two standard VAS stages, not saving you much there.
Back to the original topic... Especially if you want a ready to go PCB layout, I would suggest simply bridging two Asian-made PCB's, kits or complete modules using LME49810's and you'll get something close to 400 watts (mono) into 8 ohms at vanishingly low distortion. If it's "only" 380 watts that's just a small fraction of a db and you're never going to notice. Given this isn't a commercial design that doesn't have to meet some published (marketing driven) specification, the exact power target shouldn't matter?
Power transformers are usually the single most expensive part of an amp (especially if you ignore the chassis). So I can understand wanting to use what you have. And yes, you'll need more power supply capacitance because of the effective 4 ohm load. But given the low voltages, that won't be very expensive or hard to do. There are lots of Asian power supply boards with 6 or 8 filter caps on them for dirt cheap. Also, the LME49810 has excellent PSRR so it will reject quite a bit of ripple quite nicely.
There are negative aspects to bridged amps, but if you want to use your transformer, they're probably worth it. The biggest issue is the extra parts cost and need for a bigger heatsink. But all combined, especially if using the above modules, the extra cost won't likely exceed a new 500+ VA transformer.
All you need to do is use a simple opamp to invert the drive to one of the modules (ideally using an op-amp with low voltage noise and use low value resistors to have the op-amp noise below the power amp noise--the LM4562 would work great). If you want a circuit for that, just ask.
If you try to do a "grounded bridge" design like the Crown, you're not going to find a ready made PCB and you're going to have to deal with lots of design issues, stability compensation, thermal bias tracking, etc. And the whole thing could go up in smoke. There are many suppliers of LME49810 boards including http://pansonaudio.com (aka panson_hk here on DIYA) and others like http://connexelectronic.com
If you want to save money, you could probably also get by with an LM4702 based design on a single PCB but you would need 2 output pairs per side and most LM4702 boards only use a single pair.
EDIT: In thinking about it, depending on how the amp is going to be used and how well heat sinked it is, you *might* be OK with an LM4702 with single pairs on each channel in which case an off-the-shelf board will work. But I'd be be tempted to use output transistors with a higher current rating and larger SOA than the usual 2SC5200/2SA1943 most of those boards are designed to use. If the amp is for pro use, or may see difficult loads that dip well below 8 ohms, or otherwise will have a hard life, then you want 2 output pairs for each of the bridged amps. One issue with many of the Asian DIY boards is they often lack protection circuitry. With the MOSFET versions, that's usually OK. But with the bipolar designs, it's a bit risky--especially in a bridged design. So 2 pairs (or SOA protection) would be a good idea.
Power transformers are usually the single most expensive part of an amp (especially if you ignore the chassis). So I can understand wanting to use what you have. And yes, you'll need more power supply capacitance because of the effective 4 ohm load. But given the low voltages, that won't be very expensive or hard to do. There are lots of Asian power supply boards with 6 or 8 filter caps on them for dirt cheap. Also, the LME49810 has excellent PSRR so it will reject quite a bit of ripple quite nicely.
There are negative aspects to bridged amps, but if you want to use your transformer, they're probably worth it. The biggest issue is the extra parts cost and need for a bigger heatsink. But all combined, especially if using the above modules, the extra cost won't likely exceed a new 500+ VA transformer.
All you need to do is use a simple opamp to invert the drive to one of the modules (ideally using an op-amp with low voltage noise and use low value resistors to have the op-amp noise below the power amp noise--the LM4562 would work great). If you want a circuit for that, just ask.
If you try to do a "grounded bridge" design like the Crown, you're not going to find a ready made PCB and you're going to have to deal with lots of design issues, stability compensation, thermal bias tracking, etc. And the whole thing could go up in smoke. There are many suppliers of LME49810 boards including http://pansonaudio.com (aka panson_hk here on DIYA) and others like http://connexelectronic.com
If you want to save money, you could probably also get by with an LM4702 based design on a single PCB but you would need 2 output pairs per side and most LM4702 boards only use a single pair.
EDIT: In thinking about it, depending on how the amp is going to be used and how well heat sinked it is, you *might* be OK with an LM4702 with single pairs on each channel in which case an off-the-shelf board will work. But I'd be be tempted to use output transistors with a higher current rating and larger SOA than the usual 2SC5200/2SA1943 most of those boards are designed to use. If the amp is for pro use, or may see difficult loads that dip well below 8 ohms, or otherwise will have a hard life, then you want 2 output pairs for each of the bridged amps. One issue with many of the Asian DIY boards is they often lack protection circuitry. With the MOSFET versions, that's usually OK. But with the bipolar designs, it's a bit risky--especially in a bridged design. So 2 pairs (or SOA protection) would be a good idea.
On the original topic, I agree with RocketScientist, Steve Dunlap et. al. The transformer may be the single most expensive part so using one you have will save you money if it is suitable. It is suitable in this case, for a bridged amp. The 400W should be possible to meet unless the amplifiers used have unusually high rail loss.
I second the idea of using standard amplifiers and bridging them; the Crown circuit is just something I brought up when someone said you MUST build two complete amplifiers, which is, demonstrably, not true.
Absolute current, voltage and capacitance values don't say anything in themselves. The other two needs to be known too to be able to draw conclusions.
I second the idea of using standard amplifiers and bridging them; the Crown circuit is just something I brought up when someone said you MUST build two complete amplifiers, which is, demonstrably, not true.
Of course it's 0.25. And how much is 0.25 times 4, which was the question? One.pacificblue said:
Having a center tap or not does not matter. Don't you know what happens to the capacitance of seriesed capacitors? It's the same energy storage either way. For example, a half bridge amp has one 100V 10mF capacitor per rail. The corresponding bridge amp would have one 40mF 50V per rail. That's equivalent to one 20mF 100V capacitor across the rails, ie. the two original caps in parallell.pacificblue said:
200€+ over here if I already have a suitable 80V 2000VA transformer, without centertap, which I wouldn't be able to use otherwise.pacificblue said:
The current waveform is different in the both cases, that's the whole point. It's the different peak-to-average ratio of the different waveforms that makes the difference in power supply utilization at low load current frequency. The peak-to-average ratio of PSU current is double in a half-bridge amplifier compared to a full-bridge.pacificblue said:
If it isn't obvious why you can't use average current in ripple calculations, when the frequency of the load current is low, I can't help you. Please look at the stupidly exaggerated example again.pacificblue said:
Please show some respect for the difference between peak values, instantaneous values, average values and RMS values. They are totally different quantities. Moreover, you can't just add and subtract RMS and peak values if waveforms are different. Also, please don't try to repeal the first law of thermodynamics. That the current draw (measured in some arbitrary way) is double in the bridge amp is irrelevant as the voltage (measured in a corresponding way) is halved. It's the difference in peak-to-average ratio of the current that gives you the advantage in a bridged amp.pacificblue said:
Absolute current, voltage and capacitance values don't say anything in themselves. The other two needs to be known too to be able to draw conclusions.
capacitor posts split heredarkwind j,
I do not know why you explicitly need 400 watts. But, with that transformer you could get the information off the web and make a really nice Leach Low TIM amplifier. Unless you have extreme speaker requirements that particular amp design will handle most jobs quite successfully.
I believe Dr. Leach still sells the original pcb's for this amp. The last time I checked they were 25.00 for a stereo set. Without some pretty good skills and experience a 400 watt item could cause you more headaches than you every need.
Take the advice of some of the previous members and build a smaller, simpler version of something first. Jan has some nice designs on his website and he is always around to assist.
Remember higher watts means 80 to 100 volt caps in the power supply which translates. MONEY. Have fun.
Tad
I do not know why you explicitly need 400 watts. But, with that transformer you could get the information off the web and make a really nice Leach Low TIM amplifier. Unless you have extreme speaker requirements that particular amp design will handle most jobs quite successfully.
I believe Dr. Leach still sells the original pcb's for this amp. The last time I checked they were 25.00 for a stereo set. Without some pretty good skills and experience a 400 watt item could cause you more headaches than you every need.
Take the advice of some of the previous members and build a smaller, simpler version of something first. Jan has some nice designs on his website and he is always around to assist.
Remember higher watts means 80 to 100 volt caps in the power supply which translates. MONEY. Have fun.
Tad
darkwind_j said:
Generally it's a bad idea to run bridged amps into anything less than an 8 ohm load. If your speakers are 8 ohms, they'll be 4 ohms in parallel, and each of the bridged amps will see a 2 ohm load.
With your supply voltage, a 2 ohm load means peak currents (especially considering the impedance will likely dip below 2 ohms at some frequencies) of over 25 amps.
A 2 ohm load means way more dissipation and losses. So you'll need much larger heatsinks. And to meet the Safe Operating Area requirements at high temps for the output transistors you would need at least 3 pairs of outputs transistors for each half of the bridge and 4 or more pairs would be better.
And even if the output stages are big enough, 2 ohm loads are challenging in other ways like Vcesat losses, Re losses, Vbe drop, power supply ripple, ground currents, wiring losses, power supply losses, etc.
So you might want to consider a new power transformer after all? Even if you can manage to build a bridged amp that will survive driving a 4 ohm load, it will be a big challenge to get it to perform well.
If this is for pro use, I'd just buy a cheap high power pro amp. You can get lots of power for around $200 - $300 US that will probably outperform any bridged amp you can build and might even cost less in the end. All those output transistors, big heatsinks, etc. won't be cheap.
Another thought is to buy a cheap dead power amp that has a power supply closer to what you need and either repair/modify it or build your DIY amp using its transformer, chassis, heatsinks, etc.
Tony said:
I don't agree with that. A 400 watt mono amp needs about 600 VA for worst-case continuous operation with a sine wave. A quality 625 VA toroid weighs about 11 pounds (5 KG) not 30 pounds. Even a stereo 400w/ch amp would only need 22 pounds for continuous operation. And most don't size the transformer for continuous sine wave operation as it can be much smaller when playing music rather than sine waves.
Further proof of this can be found in high power pro amps with conventional (not switch-mode) power supplies. The Crown XLS 402 for example produces 900 real watts bridged and the entire amplifier with steel chassis, heatsinks, power supply caps, fan, circuit boards, etc. weighs only 26 pounds. These amps are designed to be run to clipping for hours on end.
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