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Old 5th October 2004, 07:09 PM   #31
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Really good. I was about to place an order for the LM3875 kits, but I'll be happy to try these new kits. I suppose a 25V transformer (25*1.414 = ~35VDC) would work well with these amps? Recommended VA rating for the transformer (~200VA?)? I suppose that these chips will need a significantly larger heatsink that the 3875s?
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Old 5th October 2004, 07:17 PM   #32
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Quote:
Originally posted by m0tion
I suppose a 25V transformer (25*1.414 = ~35VDC) would work well with these amps? Recommended VA rating for the transformer (~200VA?)?
This should be fine (especially when using one such transformer per channel, but not neccessarily).

Those chips idle on a warm side, but the heatsink does not get hot, like with class A amps. Any reasonable size will be OK.
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Old 5th October 2004, 07:30 PM   #33
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Peter,

How about those Avel-Linberg 2X28.4 V toroids from ApexJr. Are they underpowered for the job at hand ?

I'd really like to build a 5 channel HT amp so using 5 of these would be very interesting for me ($$$).
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Old 5th October 2004, 08:04 PM   #34
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150VA per channel will work for HT, but I'm not sure if 28.4 V AC on secondaries isn't too high. It may produce 40V DC (or even more than that if you mains voltage is on higher side) and this is the max rating for the chip. It may be pushing it a bit too much.

I would rather buy one toroid first, and see what I'm getting after rectification.
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Old 5th October 2004, 09:07 PM   #35
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Jean-Pierre & Peter-

Use the one from Apex.jr and use the LM338 regulator.

I am doing just that for a 5 + 1 amp with 6 torids. All but the sub torid are regulated. Drop the voltage to 30-33 VDC and have a "toite"(please excuse the Austin Powers quote) pwr supply.

As for unregulated, I would do as Peter suggests and try one first.


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Troy
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Old 5th October 2004, 09:21 PM   #36
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Quote:
Originally posted by rabstg
Jean-Pierre & Peter-

Use the one from Apex.jr and use the LM338 regulator.

I am doing just that for a 5 + 1 amp with 6 torids. All but the sub torid are regulated. Drop the voltage to 30-33 VDC and have a "toite"(please excuse the Austin Powers quote) pwr supply.

As for unregulated, I would do as Peter suggests and try one first.


Thanks,

Troy
Would you mind sharing more information with this forum ? I am quite "green" in chip amp and this kind of stuff. The only thing I actually built, well I'm actually still building it (still waiting for some parts to finish the case), is Brian's LM3875 chip amp. I'd really like to see how you implemented the regulator chip.

You might want to start a new thread in order to avoid hijacking this thread.
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Old 5th October 2004, 09:26 PM   #37
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No need to elaborate, digi01 says it all here:

REGULATOR PSU protel layout share

Let me know if you have any problems with the link.

Thanks again,

Troy
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Old 5th October 2004, 09:37 PM   #38
troystg is offline troystg  United States
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Here is the finished PCB.

my regulator pcb


I have mine sitting in the post office right now. They tried to deliver and I was out of town so I need to go pick them up.

Thanks,

Troy
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Old 5th October 2004, 11:03 PM   #39
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Quote:
Originally posted by rabstg
Here is the finished PCB.

my regulator pcb


I have mine sitting in the post office right now. They tried to deliver and I was out of town so I need to go pick them up.

Thanks,

Troy
Thanks for the info. The PCBs have already been ordered. If I use the part values suggested by digi01, will this get the voltage low enough for the LM4780 ?

Also, I just received an email from Steve from ApexJr and he said that he has a good stock of those toroids so if others are interested...
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Old 6th October 2004, 12:31 AM   #40
troystg is offline troystg  United States
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Hey Jean-Pierre-

"If I use the part values suggested by digi01, will this get the voltage low enough for the LM4780 ?"

Yes it will work as designed however I suggest you adjust the regulated voltage to around 30 VDC so the regulator does not have to work too hard.

Thanks,

Troy
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