Author Topic: The problem with really big power amps...  (Read 7853 times)

Offline kalith

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Re: The problem with really big power amps...
« Reply #15 on: October 25, 2017, 08:54:39 PM »
I have to say i have been hoping that the Amp Whisperer would get a bee in his bonnet for something larger and more "MEATY". I have even been saving on the side so that i wouldn't be left flat footed again but don't tell him that   :tongue:
My thoughts is why not look at doubling the specs of the SM150 to someting like 300W @ 8Ohm | 600W @ 4Ohm and 900W @ 2Ohm ?
From what i have seen on the power amplifier side of things those ratings should still probably be in the top 10% of BIG power amps and pretty much beyond the conventional norm of usable power unless you got one of those speakers from back to the future(https://www.youtube.com/watch?v=aP_Z3s8Zas0)

Needles to say i will be watching this one with much anticipation.
If there could be a request it would be for some funky VU meters. Just the nostalgia talking from Dad's 80's Sony Amp but they do look cool  :notworthy:

Offline handsome

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Re: The problem with really big power amps...
« Reply #16 on: October 27, 2017, 09:28:28 AM »
700W/8 implies sine waves and we don't listen to those. a 700W/8 capability should be sustainable if you just listen to music through the the device - inrush, rectifier and protection issues aside - you will never require 700W continuous (you would need a 7000W amplifier just to enjoy 10dBs of dynamic range!) but you will benefit from the headroom that results. For more practical high power though Class G (tiered power supplies) is the usual solution.

Offline JimGore

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Re: The problem with really big power amps...
« Reply #17 on: October 31, 2017, 07:40:31 AM »
These fancy classes are all good, but somehow leaves me feeling a bit blaaaah when it comes to listening to actual music.  Sure, from a tree hugging, oil saving, green-peace point of view it's the way to go...

My brain is somehow stuck in the 70s - I drive a 6.0 liter push rod V8 (daily driver) and my motorcycle is a Harley.  What's all this class D and class G stuff anyway? Sounds like modern technology & people trying to get clever  :giggle:

I will do the old school thing again - class in the first 2 letters of the alphabet.  Yes, it will generate heat, and yes it will be heavy, and yes it will probably cause trouble, but how fun is life without those things anyway?

In the interim I have managed to source some seriously hefty industrial heatsinks (from Italy) which are used for heavy current industrial power diode, thyristor and rectifier modules.  I like the shape too.  I have ordered samples and paid for it, so hopefully those will be coming through shortly.

As for the bridge rectifiers, I once again looked towards the heavy industrial suppliers and have managed to source some beautiful 1600V / 72 Amp single phase rectifiers with screw terminals from Europe, so I reckon a pair of those will do the trick.  I have 4 on order.

Transformer wise I am most likely going to scale down slightly, at least for the first version, down to a pair of 1.5kVA per channel, so 3kVA in total.  Much easier to work with, and physically smaller so that always helps.  Once I have things working I can always build a set with much bigger transformers and see what effect it has on the sound.

Finally, for the chassis I have decided to go for a more industrial look (this thing is kind of a welding machine anyway), and will build the entire thing out of 10mm aluminium plate, all CNC machined and bolted together in such a way as to show off the thickness of the plate.

The chassis will need to be rather large in order to fit everything in, as well as to ensure we have enough heat sinking capability.  I went to buy the plate this past Friday, and must say that it's even bigger than I was thinking, so I may need to rethink just how large I am realistically able to make this thing.  Anyway, what's nice about the 10mm plate is that the entire chassis will become part of the heatsink "system".  10mm plate is thick enough to effectively transfer the heat all over, so there are some gains to be had on that front.

So my new plan is to build a set of enclosures completely and then see what, where and how I can manage to fit everything in.  I am pretty good on CAD, but somehow it's a bit easier to be creative when I have the parts in front of me.

I will go through the trouble of having the transformers in their own "enclosure" inside the chasssis (also 10mm plate) and keep all the mains voltage things inside that so it can help shield some of the magnetic flux.  Not that aluminium is all that effective really, but it's easy to work with and will at least help a bit.



Why?  Because I can and I love it  :rubhands:

Kind regards,
Ian.

Offline Samayanaya

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Re: The problem with really big power amps...
« Reply #18 on: October 31, 2017, 11:39:33 AM »


Awesome stuff! Can't wait to see the design  :2thumbs:

Offline pwatts

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Re: The problem with really big power amps...
« Reply #19 on: October 31, 2017, 04:34:49 PM »
Magnetic fields diminish by distance cubed. So physical separation regardless of material very quickly brings improvement if stray flux is an issue.

Offline CAD

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Re: The problem with really big power amps...
« Reply #20 on: October 31, 2017, 07:21:54 PM »
I know nothing about building amps and most of what is discussed is Greek to me.
Interesting reading however and really looking forward to seeing this monster take shape.

Thanks for sharing this journey with us Ian.Keep the posts and pics coming  :2thumbs:

Quote
Why?  Because I can and I love it  :rubhands:

Quote of the year  :clap:
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Light travels faster than sound. This is why some people appear bright until you hear them speak.

Offline El Sid

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Re: The problem with really big power amps...
« Reply #21 on: October 31, 2017, 07:58:53 PM »
...have managed to source some beautiful 1600V / 72 Amp single phase rectifiers....

72A!!!  :ROFLMAO:

Love it!

Offline JimGore

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Re: The problem with really big power amps...
« Reply #22 on: November 06, 2017, 05:40:40 PM »
This is one of the current gain stage boards (click for a larger image):



It is one of 2 which will make up a single channel of amplification.  There are 16 pairs of output transistors (32 total) which combined will have a theoretical power delivery capability of 4.8kW.  That's just theory though - we won't be able to keep that cool, nor can the PCB take anywhere near that so the more realistic power delivery capability will be in the region of 33%, which still comes in at a healthy 1.6kW

The traces that matter have all been calculated and oversized - some of them are up to 31mm wide because of a long run.  The power rails for example are 15mm wide (there are 2 sets), and I feed them from the middle of the track, so in effect the length is halved which is how I can get away with them being "only" 15mm wide.  Obviously this will be double thick copper, but even then you need to pay attention to how that current will get onto and off the PCB traces, so care is needed in the design and layout.

On-board we have DC detection on the output as well as one of my SSR implementations - this one capable of making and breaking up to around 150 Amp at 100V, so effectively it is a 15kW relay that works really, really fast as has no moving parts which can arc and weld themselves.  Should be more than capable of handling the power this amplifier will be pushing around.  These extra bits are controlled via an off-board MCU (microcontroller) which will sense any DC and allow the SSR to connect the speaker to the amplifier or not.

Thoughts?

Kind regards,
Ian.

Offline Ampdog

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Re: The problem with really big power amps...
« Reply #23 on: November 06, 2017, 05:50:18 PM »
Most imteresting, Jim!

....and still trying to get the frown off my forehead!  As you say, you are doing it because you can - excellent reason, that.

Perhaps just an example to get matters in perspective: At the open air concert of the three tenors at the Union Buildings some time ago, 12KW of total output power was used. This was not from a single amplifier though; several output lines ran from several amplifiers to multiple loudspeakers.
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline DeonC

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Re: The problem with really big power amps...
« Reply #24 on: November 06, 2017, 09:33:02 PM »
...At the open air concert of the three tenors at the Union Buildings...

OT, but that is something I would have LOVED to attend.
Life is not measured by the breaths you take, but by the moments that take your breath away.

Offline Den123

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Re: The problem with really big power amps...
« Reply #25 on: November 06, 2017, 10:54:36 PM »
Aaah. Jim. A 6L V8!!! My daily drive too.
Love it.

Offline JANNAS

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Re: The problem with really big power amps...
« Reply #26 on: November 07, 2017, 06:54:12 AM »
Ian, I suppose vertical fets will do the job on the O/P devices ? :)

Offline JimGore

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Re: The problem with really big power amps...
« Reply #27 on: November 07, 2017, 07:56:58 AM »
I find that I really enjoy designing electronic circuits for some unknowable reason. It definitely is fun building them too but the research and design part is what really gets me excited  ;D

The PCB shown above will,be mounted to 2 heatsinks sitting side by side such that each row of transistor pairs will be mounted to its own heatsink. That's why the arrangement looks a bit strange compared to other designs. There will be a seperate PCB for the small signal stage (meaning the light current stages) which will mount stacked on top of the cure the gain stage board. The two boards will be connected using a short length of 16 core ribbon cable so it can be unplugged easily.

I also quite like flexible designs that can be scaled up or down for power, and this allows me to do just that. If in future I want to build something with half or double the power it can be achieved reasonably easily by simply changing a few thing.

Ian, I suppose vertical fets will do the job on the O/P devices ? :)

FETs can most definitely be used, though this version is most likely going to be is an all BJT design. I somehow prefer the sound of a transistor to a FET, though with good design I believe that both can sound similar enough to be nearly identical.

How are you enjoying your amp? Still doing good work?

Kind regards,
Ian.

Offline JANNAS

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Re: The problem with really big power amps...
« Reply #28 on: November 07, 2017, 12:16:48 PM »
Thanks Ian, the Slewmaster is still doing its job well. Had been driving AR66bx 4ohm speakers until recently. Now have 8 ohm jobbies in there, no complaints with heat with ether of them and very happy. Have just completed a hybrid build with Nfet and MJL Bjt in the output stage for my daughter. It has a lot of 2nd harmonics and is extremely easy to listen to. But for now  I am finished building 55kg amps !! I will be following your builds ! ;) :thumbs
ps.  You don't perhaps have a few pairs of 2SC4793/2SA1837 available that I can source from you ? :rubhands:

Regards
Jan

Offline Samayanaya

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Re: The problem with really big power amps...
« Reply #29 on: November 07, 2017, 09:33:47 PM »
That design looks serious! What software do you use for the layout?

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