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Old 5th November 2005, 09:52 PM   #381
tangen is offline tangen  Norway
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Default Parallelling LM3875

I'm enjoying my LM3875 kit I ordered from Peter Daniel (very nice guy to do business with). The resulting amplifier was really astonishing. But, it would have been nice with some more power. Have anyone tried to parallell LM3875? What kind of resistors were used? And how did it sound?

Best regards
Jan Ove Tangen
Norway
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Old 6th November 2005, 05:38 AM   #382
rdf is offline rdf  Canada
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Thank again! Actually, your description suits my needs very well. For me the hardest part of tuning a SET is cleaning up the top end. One of the LM3875 kits sounds like just the ticket for an alternate reference, to go with the other two tube amps and five pairs of speakers cluttering the place that is.
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Old 6th November 2005, 09:19 PM   #383
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Thanks to the courtesy of a forum member, here's the detailed schematic of LM4780 rectifier's board.

C1/C2 as supplied are 10uF Panasonics FC, but you can experiment with different values as well. Recently some people tried 100/50 BG N caps here (with Panasoncs 1500/50 FC on the amps board) and the results were very good. You might also choose to not install those caps at all.


R1/R2 and C3/C4 are snubber components as suggested by Carlosfm. I'm not a fan of snubbers and I'm not using them. The current values can be found here: http://www.diyaudio.com/forums/showt...529#post748529 There are additional holes on the board, where a cap up to 10,000uF can be installed when snubber is used (that cap would be on schematic in place of C1/C2 and the small 10u caps are not being installed then.

R3 is used to limit the current through the LED and for a small Panasonic red LED, I'm using 68K resistor.

I will be soon posting similar schematic showing the amp board.

Thanks Todd
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Old 7th November 2005, 01:43 PM   #384
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OK, here it is, a proper schematic for LM4780 amp board: two options available, bridged configuration is the same as stereo (a balanced signal needs to be supplied to the amps input). The connections diagram also matches the board's layout (nice touch, Todd)

Resistors values are as follows:

R1/R2 = 22K
R3/R5 = 680R
R0/R4 = 22K
R6/R7 = 270R
R8/R9 = .1R
Rm = 10K
Rz = 2.7R
Cz = .1 uF

The (red) jumper for parallel config mounts like that: http://www.diyaudio.com/forums/attac...amp=1115409304

CHG can be used for connecting circuit ground to the chassis. I'm using 10R resistor when doing that. Please also note that currently 270R series resistors are being used (instead of 1K).
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Old 7th November 2005, 04:04 PM   #385
adolphe is offline adolphe  Canada
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Very nice. I just finished soldering in the jumpers for my bridged boards yesterday. I'm waiting on my transformers before wiring up the inputs and outputs. These schematics will make things a lot easier.

Thanks!
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Old 11th November 2005, 12:09 AM   #386
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Default Phone Stage

Hi Peter,

How is the phone stage coming along? And hey will it invert phase? As this would mate well with your DAC.

Cheers,
Anthony
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Old 11th November 2005, 12:43 AM   #387
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It's not gonna happen before NewYear. I'm presently extremally busy with amps building.

The DAC phase can be corrected (to non reversing). You simply need to reverse the connection of two traces from input buffer chip to the receiver. The next board version will have it corrected, I'm also working on optional USB interface.
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Old 11th November 2005, 02:44 AM   #388
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Default Phone and Dac

Hi Peter,

OK about the Phone stage - keep us posted.

RE: A couple questions about the DAC kit.

With the Dac when will the new boards be ready and how much for the Premium?

Cheers,

Anthony
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Old 11th November 2005, 11:06 AM   #389
lohk is offline lohk  Europe
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Thanks for the phase reversal correction hint - it is just that simple, very good!

Will you use the PCM2704 for the forthcoming USB DAC input?


I listen to the DAC everyday with pleasure, and already - as it seems to be always - there are friends lining up for one to be made for them...

all the best
Klaus
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Old 11th November 2005, 03:24 PM   #390
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I'm still not into using computer as a music source ( I have 3 decent transports: ML31.5, ML37 and Technics ZL-1000, all of them modified), but on suggestion from a forum member, I decided to give it a shot. USB interface will be based on PCM2707, but I'm still not into details here yet.

I have left ony 3 of the gold plated all-in-one boards, so I will be ordering new batch pretty soon. There won't be much difference, mostly fine tuning of some traces.
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