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Old 5th November 2005, 06:00 PM   #371
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As long as DC voltage does not exceed 40V (per rail), that transformer should be fine.
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Old 5th November 2005, 06:19 PM   #372
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I'm running the LM4780s on 42V rails at the moment, as I stole the 27-0-27 traffo I was using to test another project. They still work, but do get very warm. If you want to repeat this, you will need BIG heatsinks, or fan cooling, and I'm not going to give any guarantees as to long term reliability. It doesn't help the sound either, higher rails seem to close in the dynamics a little.
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Old 5th November 2005, 06:20 PM   #373
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Quote:
Originally posted by Peter Daniel
If you go to my site and enter the LM4780 page: http://www.audiosector.com/lm4780.shtml you will see a link to "Applications Notes": http://www.diyaudio.com/forums/showt...556#post636556 This is where I explained different configurations possible with that board. The board is the step up from the previous design, and offers more options, including bridged/parallel/stereo configurations and snubbers (idea originated by CarlosFm).


I know, I've read it all a few times through. Lots of very helpful photos, but I'm not sure I'd agreed it was explained very well. The schematic on your site covers the amp circuit nicely, but there isn't a schematic or parts list for the power supply board. C1, C2, C3, C4? ... they aren't listed or explained. When you talk about snubbers and bypass caps, it's not obvious to me which you are referring to.

Quote:
Regarding 10u caps, it is recommended to try them in a circuit and decide if they bring improvement or not. Recently, when going with 1500u caps, I'm using 10u cap on negative rail only
http://www.diyaudio.com/forums/showt...436#post584436
So, would the 10u cap placement be labelled as C2 on the rectifier board?

Thanks,
..Todd
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Old 5th November 2005, 06:32 PM   #374
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Hi rdf,


the 4706 GainCard uses a dual 23,5V transformer.
The LM3875 kit is first choice for you.

Carsten
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Old 5th November 2005, 06:47 PM   #375
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Quote:
Originally posted by motherone
Peter's boards are similar to BrianGT's (they developed the original versions together, I think. I believe the 10uF Panasonic are used in the same position that the 4.7uF Black Gate N's are used on the rectifier board. Check the brianGT assembly guide here for more info.

Motherone: I missed your message first time through. Good info. Thanks! That clears up a lot of confusion.

..TAJ
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Old 5th November 2005, 07:06 PM   #376
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Thanks all. The somewhat high voltage was my concern, from memory the datasheets appear to indicate something in the 18 VAC range as the best compromise between power output and avoiding being 'Spiked' by lowish loads. I don't need much power, just a good match. Thanks again.
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Old 5th November 2005, 07:25 PM   #377
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Default Re: 4780 board

Quote:
Originally posted by taj
Question: I've just been reading through this thread from the beginning, but I cannot find any reference to the four 10uF/50v caps that were packaged with the diodes. They're not listed on the schematic on your site, which doesn't really cover the rectifier board.

I'm a little confused about how the board(s) should be populated for the parallel configuration. Particularly regarding those caps. Can you point me towards the necessary information?
Here's the simplified schematic of rectifier's board. C1/C2 are optional and I suggest experimenting with using them (they may improve sound or they might degrade it, depending on your taste and system). Supplied value is 10uF.

For any configuration of amp board, placement of those caps (10u) is not critical and amp will work equally well with those caps or without them. By installing them, you can manipulate amp's sonic signature, and here choice should be yours.

The different configurations of amp board were extensively described in the links I posted previously, but if you have any additional questions, don't hesitate to ask.

With regards to snubber components, those parts are not supplied with a kit, and are optional. The best is to ask CarlosFm for current values, as he changes them quite frequently. At the time the board was developed R1/R2 was 1R and C3/C4 0.1uF. The other resistor (if you find his schematic) has to be soldered directly to cap's pins.

Personally, I don't recommend using the snubber.
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Old 5th November 2005, 07:27 PM   #378
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Quote:
Originally posted by rdf
Thanks all. The somewhat high voltage was my concern, from memory the datasheets appear to indicate something in the 18 VAC range as the best compromise between power output and avoiding being 'Spiked' by lowish loads. I don't need much power, just a good match. Thanks again.
Actually, non inverting configuration seem to sound better with higher voltage. I'm using at least 34V DC per rail, but I'm cdeliberating now switching to even higher voltage.

I was doing some tests with amp connected through the variac, and by increasing the voltage sound was improving as well. Running the amp from 24V batteries produces rather sleepy sonic signature
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Old 5th November 2005, 07:51 PM   #379
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Thanks Peter. Are you using the LM3875 for these tests?
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Old 5th November 2005, 08:05 PM   #380
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Yes, LM3875.

So far people commented that LM3875 has better top end and midrange, when comparing to LM3886 (or LM4780). The other two chips show more "body" and might provide better drive, but for sheer transparency and delicacy of the sound, LM3875 would be still a preferred choice. However, in some systems it may sound a bit thin or even analytical. It's best to build the system around such amp and not trying to fit the amp into existing system
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