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Old 15th April 2011, 12:24 AM   #1
rsdio is offline rsdio  United States
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Default Sons of Zen: The Modular Power Amplifier

Hi folks,

I have been reading many of Papa's articles and I have some questions from a particular angle. If my area of interest has already been discussed, then please reply with links to existing articles so I can catch up.

My impression so far is that the Zen amps are low power, but that they can be combined in parallel to increase power. I think that I read that the Pass X1000 has 80 FET circuits, and I presume they would be in parallel.

Here's my idea / question: Has anyone considered making a modular backplane board with high-current card-edge connectors so that multiple individual Zen power circuits could be added in parallel to build a more powerful amplifier in a scalable fashion?

I'm thinking that there would be a need for a minimum of 7 pins. That's 3 pins from the power supply for the positive and negative rails as well as ground, plus 2 each for balanced audio input and balanced speaker outputs. As you might be able to glean, I am in favor of the balanced power designs that I have been reading about. Given the current requirements, doubling up on pins might be smart, so that would be a 14-pin connector. I don't know what the standard card-edge connector sizes are, but they might be larger than a mere 14 pins, so excess pins could be used to increase capacity on the power supply and speaker outputs to handle more current.

My idea is that this would not only allow increasing the power of an amplifier without building a whole new project from the ground up, but when individual FET circuits burn out, they could be more easily replaced in a modular fashion. Not only replaced, but individual boards could be tested in a smaller circuit to measure their health before they are added to the backplane.

The obvious challenges are whether such connections would ruin the audio, and also whether they could even handle the current. It might be possible since some of the Zen designs only draw 2 A to 4 A for a single circuit, and each added power module would have its own private connection. I sure have the impression that those old-school 1970's card edge connectors have a lot of current capacity. Another obvious factor is that the power supply would need to be capable of driving a full backplane, even if it starts out with only one power module, otherwise it would defeat the purpose if the power supply had to be replaced to add another power module; then again, maybe a modular power supply would be a handy feature.

I was also hoping (or dreaming) that it would be possible to put some sort of fault LED on each Zen power board that would show failure. Then, if your amplifier suddenly loses power, you could glance at the indicators to see which modular board is fried. At the moment, I have no idea how that might be accomplished. Clip detection would probably be much easier than complete failure detection, unless there's a trick that I'm missing. I suppose that once I start building FET amplifiers, I'll probably get a sense of the common modes of failure. In any case, removable modules would make testing and replacement easier, even without individual fault indicators.

One related but minor question is whether each FET gain circuit would need its own current source. I happen to prefer the constant current source designs to the high-wattage power resistor variations. My assumption is that each parallel circuit would need its own constant current source, and that the power supply would obviously need to be capable of providing the additional current.

So, what do folks think of these ideas? Has this been discussed before? How feasible does it seem? How many modules should I plan for?

Brian Willoughby
Sound Consulting

P.S. I was originally brought to diyAudio when someone pointed me to Nelson Pass and his Zen amplifier designs. Since then I've mostly been hanging out in the digital audio DIY section with discussions of DAC topics like current-to-voltage followers and I2S interconnects. But I have been very interested in building one of the Zen variations to sit between my DAC and speakers, and have been reading the articles mostly in chronological order based upon their original publication dates. I have not built any power amplifier yet, but I have some plans for the ultimate digital audio listening signal chain!
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Old 15th April 2011, 01:40 AM   #2
Bigun is online now Bigun  Canada
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Interesting concept - stock up on boards for extra power !


Connectors can be tricky with high currents - long term reliability - so would have to be carefully engineered with good quality parts.
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Old 15th April 2011, 01:46 AM   #3
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Say you parallel 2 zen amps the distortion will go down some but the power
will be about the same. For more power you would need more supply voltage
not just more output devices.
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Old 15th April 2011, 04:01 AM   #4
rsdio is offline rsdio  United States
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Quote:
Originally Posted by woody View Post
Say you parallel 2 zen amps the distortion will go down some but the power
will be about the same. For more power you would need more supply voltage
not just more output devices.
Ah, thanks for the hint. I guess I need to keep reading the many Zen variations. I do recall reading that a pair could be paralleled for more power, but maybe that doesn't work for more than two?

I really got the impression that the current would need to be doubled, but not the voltage. As I said, I still have a few articles to read, and I have a feeling that I'm still going to pull ideas from more than one Zen circuit rather than literally follow just one of them exactly.

Last edited by rsdio; 15th April 2011 at 04:04 AM.
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Old 15th April 2011, 06:28 AM   #5
Bigun is online now Bigun  Canada
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It depends on load impedance, you can double the power from an 8 Ohm load to a 4 Ohm load by doubling the current - no change in voltage.
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Old 15th April 2011, 08:16 AM   #6
rsdio is offline rsdio  United States
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Originally Posted by Bigun View Post
It depends on load impedance, you can double the power from an 8 Ohm load to a 4 Ohm load by doubling the current - no change in voltage.
Ah, THAT's what I remember reading. Makes sense now.

I will need this, since my LINN speakers are only 4 Ω in passive mode.

Beyond that, I guess I'll need to pay attention to power boosting techniques as I finish reading the Zen articles. I've made it from 1977 to 2002, so there are only a few articles left (and then tens of thousands of diyAudio postings).
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Old 15th April 2011, 02:16 PM   #7
qusp is offline qusp  Australia
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Bigun, it depends on more than that, in some situations when you bridge an amp into the same load, the apparent impedance of the speaker load is halved, but so is the class A power into that lower impedance.

but you arent talking about bridging it each time, so the load impedance would remain the same wouldnt it? each module is already a balanced module and you would simply be adding to the current drive by adding another one in parallel; though really you should perhaps also be changing the source resistors for better current sharing each time.

if your current source has enough drive its not a given that you would have to add another one with each set of output devices.

check the amphenol TW series hybrid dsub connectors, these have far more than enough current capability @ 20A, though they arent cheap. one thing you would have to watch is that the inductance of the connector and modules does not send the amp into oscillations , as you really should keep trace length to a minimum.

its an interesting idea, these designs are apparently simple, but because of the nature of the system each addition changes the behavior of the rest of the amp and certain resistor values should be changed, which kinda defeats the purpose a bit.

Last edited by qusp; 15th April 2011 at 02:19 PM.
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Old 15th April 2011, 07:50 PM   #8
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What I think he is asking is if a board can be designed that one could add extra output transistor modules to boost the output. The answer is yes but the power supply will have to be boosted also.
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Old 15th April 2011, 08:23 PM   #9
rsdio is offline rsdio  United States
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... I'm also realizing that heat sinks would pose a challenge. It would be difficult to share a large heat sink with a variable number of modules. Each card could have its own heat sink, but then spacing between modules becomes an issue. Maybe a Cray computer arrangement with a cylinder of connectors in the center and modules that fan out radially for more heat sink area further away from the connectors.

I think I should start by building my favorite: a Son of Zen with SuperSymmetry, and see how that goes before I try some crazy modular design.

@qusp: Thanks for the connector suggestion. I will look into those parts.
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Old 3rd December 2011, 07:58 PM   #10
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Quote:
Originally Posted by rsdio View Post
Hi folks,

I have been reading many of Papa's articles and I have some questions from a particular angle. If my area of interest has already been discussed, then please reply with links to existing articles so I can catch up.

My impression so far is that the Zen amps are low power, but that they can be combined in parallel to increase power. I think that I read that the Pass X1000 has 80 FET circuits, and I presume they would be in parallel.
Here's my idea / question: Has anyone considered making a modular backplane board with high-current card-edge connectors so that multiple individual Zen power circuits could be added in parallel to build a more powerful amplifier in a scalable fashion?
So, what do folks think of these ideas? Has this been discussed before? How feasible does it seem? How many modules should I plan for?
Brian Willoughby
Sound Consulting
P.S. I was originally brought to diyAudio when someone pointed me to Nelson Pass and his Zen amplifier designs. Since then I've mostly been hanging out in the digital audio DIY section with discussions of DAC topics like current-to-voltage followers and I2S interconnects. But I have been very interested in building one of the Zen variations to sit between my DAC and speakers, and have been reading the articles mostly in chronological order based upon their original publication dates. I have not built any power amplifier yet, but I have some plans for the ultimate digital audio listening signal chain!


Very interesting idea. But connectors for modular concept is from my view a bad solution. Electrocompaniet's Ampliwire 100 uses such a concept - the power module is pluggable on the rectifier/capacitor PCB and often in this area all pins and PCB itself is scorched/damaged. Pics I have upload anywhere here on diyaudio. I would prefer a soldered version.
Basicly my approach mentioned by post 787 about
bipolar (bjt) transistor families for audio power output stages
could be a solution, because there are a lot of MOSFETs in various SMD outlines in the meantime available.
In opposite to the approach about
Beast with a Thousand JFETs
this solution needs only 10-100 MOSFET in parallel mode operation, dependent of the wanted output power resp. current.

Last edited by tiefbassuebertr; 3rd December 2011 at 08:15 PM.
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