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Old 20th November 2011, 04:50 AM   #241
MrSlim is offline MrSlim  Canada
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Quote:
Originally Posted by petegt View Post
@ zog666 that looks like a sweet set up

Must admit during the short tests iv done these amps do sound good!

Running 86v rails

I have changed the components LJM suggested but the resistor next to the voltage regulator on the heat sink (changed from 2k2 to 3k 1 watt) runs very hot still.

maybe change to 2 or 3 watt?
It wouldn't hurt, its always better to err on the side of conservatism
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Old 20th November 2011, 09:55 AM   #242
alkasar is offline alkasar  France
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@zog666, why adding the big caps between smps and amps ?
usually, huge caps are not needed with an smps. Did you try with and without them ?


ps: smps300R main advantage over a350smps, is the regulated output. I prefer to use regulated smps for classD amps, as their psrr is not so great
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Old 20th November 2011, 12:43 PM   #243
zog666 is offline zog666  Australia
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Quote:
Originally Posted by petegt View Post
@ zog666 that looks like a sweet set up

Must admit during the short tests iv done these amps do sound good!
Thanks, and agreed about the sound.. still I've got a few ideas to replace the coupling capacitors, but just listening to the amp as it is for now. The resistors on mine get warm, but not mega hot so far (with just +-60v) , but I'll keep checking them.

Quote:
Originally Posted by alkasar View Post
@zog666, why adding the big caps between smps and amps ?
usually, huge caps are not needed with an smps. Did you try with and without them ?
I added them on advice of Cristi from Connex Electronics after he was asked what I was using the SMPS for. Adding that extra reserve of power makes sense to me. I haven't tried it without them, that would be an interesting and easy thing to try.

I soldered on 63V rated capacitors on the L20D boards.. since the PSU is regulated it should be "locked in" at 60V so I shouldnt have to worry about that 3V margin? - I do have some 80V rated low ESR caps as well in the bag of bits.

And while I'm here.. another pic..
Click the image to open in full size.
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Old 20th November 2011, 02:17 PM   #244
alkasar is offline alkasar  France
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Quote:
Originally Posted by zog666 View Post
I added the caps on advice of Cristi from Connex Electronics after he was asked what I was using the SMPS for. Adding that extra reserve of power makes sense to me. I haven't tried it without them, that would be an interesting and easy thing to try.
interesting. I would love to undestand Cristi rationale. Do you have the link of the discussion if it was not private ?

A single smsp300R is undersized for a 2x200W amp. The power supply at +/-60V can only deliver 3.3A peak. You won't get the full power from the L20D. However, for reasonable listening level, this may not be an issue.
I wonder if Cristi recomended the large caps as a way to compensate for a short power supply ?
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Old 20th November 2011, 08:01 PM   #245
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So folks, I've been looking at options to drive an active system, and it crossed my mind that these would work well for the bass end. But, and this is where you chaps might be able to help, if feasible, it would be nice to use another for the mid and high as well, so how easy would it be to modify these boards to make them back to stereo? I have the IR app note, but can't really tell from the pics I've seen how the LJM board differs. Ta in advance.
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Old 21st November 2011, 02:58 AM   #246
MrSlim is offline MrSlim  Canada
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Originally Posted by pinkmouse View Post
So folks, I've been looking at options to drive an active system, and it crossed my mind that these would work well for the bass end. But, and this is where you chaps might be able to help, if feasible, it would be nice to use another for the mid and high as well, so how easy would it be to modify these boards to make them back to stereo? I have the IR app note, but can't really tell from the pics I've seen how the LJM board differs. Ta in advance.
There is nothing in the design that limits their bandwidth. They are perfectly fine for use as full audio frequency amps, so you could use them for each speaker in your system. The fact that they are so small makes them attractive for multi amp systems, like building blocks almost..

The boards are mono, which means you need to buy a pair for stereo, but that's why they are sold in pairs. LJM just decided to split the IR reference design (which is stereo) into two mono units.
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Old 21st November 2011, 03:01 AM   #247
MrSlim is offline MrSlim  Canada
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ZOG666, love the paint stir stick re-use..
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Old 21st November 2011, 09:20 AM   #248
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Originally Posted by MrSlim View Post
The boards are mono, which means you need to buy a pair for stereo, but that's why they are sold in pairs. LJM just decided to split the IR reference design (which is stereo) into two mono units.
Thanks, I misunderstood the references to this amp earlier on that said it was based on the IR schematic, so assumed it was stereo.
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Old 21st November 2011, 12:06 PM   #249
zog666 is offline zog666  Australia
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Originally Posted by alkasar View Post
interesting. I would love to undestand Cristi rationale. Do you have the link of the discussion if it was not private ?
link not available, but I think it was because the SMPS300R has smaller capacitance than one I was going to use? Cristi sometimes checks this thread so maybe he has some input?

Quote:
Originally Posted by alkasar View Post
A single smsp300R is undersized for a 2x200W amp. The power supply at +/-60V can only deliver 3.3A peak. You won't get the full power from the L20D. However, for reasonable listening level, this may not be an issue.
I wonder if Cristi recomended the large caps as a way to compensate for a short power supply ?
The full power of L20D is overkill for me and I was going to undervolt it anyway with the previous power supply I chose.. I was not expecting to run it at anywhere near full capacity. If I had been more aware of the L15D when I ordered I would have got them, as it would have made the power supply selection easier!
I am considering this particular build an approx 150W per channel amp.

Quote:
Originally Posted by MrSlim View Post
ZOG666, love the paint stir stick re-use..
yes... but does the type of paint affect the sound? .. It shows I just wandered around the garage looking for spare bits of "stuff" when figuring out the capacitor mount.
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Old 21st November 2011, 12:26 PM   #250
alkasar is offline alkasar  France
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Originally Posted by zog666 View Post
I am considering this particular build an approx 150W per channel amp.
well... not really or it depends on the "Watt" you consider
It's a common mistake with smps : you cant' just use the rated W from SMPS to get Wrms for the amp.

150Wrms amp in 8ohms requires 4.33Arms. Which is 6A peak on a sinusoidal. Per channel.
"commercial watts" are different


Quote:
yes... but does the type of paint affect the sound? .. It shows I just wandered around the garage looking for spare bits of "stuff" when figuring out the capacitor mount.
everyone knows that black painted amps sound better than silver ones
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