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Old 5th August 2013, 04:52 AM   #211
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After googling I found that LTspice supports 3 nested steppings. It should then be possible to plot LG for 0*Vin , 0.1*Vin and 1*Vin (and possibly 1.1*Vin at the clipping edge). From then on it's probably copy/paste the LG function and update the run identifiers to match the Vin steps. I'll give this a try this afternoon
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Old 30th August 2013, 03:56 PM   #212
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I think I got my final version done.. I also changed the target output specs to what I originally wanted to build:

500W/4Ohm, 250W/8Ohm

0.000093% THD @ 20KHz, full power, 8Ohm load
68deg phase margin
10.4dB gain margin

This amp, dubbed MF500 should eventually be a perfect upgrade from the old '86 Elector 1KW amp (Crescendo 1). It should have the clarity and finesse of my MF80 project, with the handsome power of a Crescendo! All thanks to fast BJT, MOSFETs and complex compensation. I already can't wait to listen to it

The outputstage PSU consists of 2x 2x55V/850VA for a total AC power of 1.7KW and an array of 8 10.000uF/100V caps, 4 per rail.

A fun detail is that one channel will amplify the inverted version of the signal, while the speaker output polarity has also been swapped to keep a net effect of zero phase. This will significantly improve OPS PSU usage as with each half wave, both the positive and negative supplies will supply current, at an about equal ratio. Both secondaries are loaded on every half wave instead of one secondary taking care of a half wave and the other of the other half wave. So both transformers are used to their full potential, on both the negative and positive half of the signal.

That should be a more than a decent supply to bring a tight, powerfull bass to life regardless of power level, up to the rated power Together with the new topology and used compensation, this should also bring a transparent, well defined sound stage at the rated power with extremely low distortion figures.

I'm soon to start on putting the OPS supply together and put it all on a base plate. Once I get to actually building the prototype, I'll open a new thread with pictures of my progress
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Last edited by MagicBox; 30th August 2013 at 03:59 PM.
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Old 30th August 2013, 04:01 PM   #213
RNMarsh is offline RNMarsh  United States
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Hi,

Your power level is just about right for my use as well. The room size, speaker effeciency, and SPL all say 250W/8 minimum. Will you be offering the DIY community a way to build it... pcb etc?

Thx-RNMarsh
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Old 30th August 2013, 04:19 PM   #214
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Quote:
Originally Posted by RNMarsh View Post
Hi,

Your power level is just about right for my use as well. The room size, speaker effeciency, and SPL all say 250W/8 minimum. Will you be offering the DIY community a way to build it... pcb etc?

Thx-RNMarsh
Hi there,

Yeah through the build log I would gradually add the PCBs as I design them. It's by no-means going to be an easy one to build, though I plan on keeping simple the amp design as a whole. The case is going to be 19"x40cm depth, at least, the build I'm planning. It will have a IPS/VAS supply including transformers per channel too. And I plan to use an 8-pin uC (ATtiny13) for power management, much like astx has done. It's going to be a challenge to me as every new project is. MF80 was just one step.

As for the power, yes it's great to have that an amount of power of dynamic range, especially with music that has been mastered that takes a wide dynamic range in account. At least, that's my opinion

Edit:

As for the uC's and for instance ECX10N/P20 pairs, I could assemble kits of "essential parts" once it's built and tested and distribute those.
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Last edited by MagicBox; 30th August 2013 at 04:34 PM.
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Old 2nd October 2013, 03:46 AM   #215
nacder is offline nacder  Hong Kong
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Hi MagicBox, any progress update?
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Old 7th October 2013, 04:19 PM   #216
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Not yet, times are a bit uncertain for me. I did order two small PCBs for wiring which arrive probably in the next two weeks.

It didn't stop me from improving the simulated design though. I loosened the THD requirements some to have more flexibility for stabilization.

It's now specced 2ppm @ 20KHz/250W/8Ohm with a phasemargin of 65 degrees and a gain margin of 13dB. Still with the evil output inductor though
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Old 7th October 2013, 10:45 PM   #217
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If you lose the inductor, it will be because the amplifier is creating it virtually, in which case it will be a very distorted inductor. The passive output inductor indirectly enables an amplifier to have lower distortion.

What makes it evil anyways? You can locate it away from the board by a twisted pair of wire, in any orientation you want. Even 1nF of capacitance across the inductor shouldn't matter. You could also make a toroidal air-core inductor, which just takes a little time.
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Old 12th February 2014, 03:51 AM   #218
nacder is offline nacder  Hong Kong
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Its been quiet for a while, hope you have some new progress. Any update on the circuit?
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