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Mod/upgrade NAD C 541i
Mod/upgrade NAD C 541i
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Old 2nd March 2009, 04:37 PM   #131
klitgt is offline klitgt  Denmark
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Originally posted by kelly
What is the purpose of R375(R376) and R379(R380) in the NAD 542?

If the muting transistors are removed, can these resistors be removed?

Why are there two muting transistors per channel?

As far as I know the resistors are included to make the output more tolerant to capacitance in different signal cables.

Probably it is best to keep these resistors even if you remove the transistors.

I do not know the purpose of the two-transistor construction.
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Old 6th March 2009, 03:31 PM   #132
kelly is offline kelly  United States
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Thank you.
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Old 6th March 2009, 03:35 PM   #133
Pars is offline Pars  United States
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Originally posted by kelly
What is the purpose of R375(R376) and R379(R380) in the NAD 542?

If the muting transistors are removed, can these resistors be removed?

Why are there two muting transistors per channel?
I haven't looked at this particular schematic, and am assuming these are fairly low value (100 ohms or so?), but I thought these were there to prevent the output devices from seeing a dead short when muted?
I also don't know for sure why they always seem to use a pair of transistors, unless a single transistor still provides its Vbe drop to the output and using them in pairs gives more complete muting?
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Old 7th March 2009, 11:25 AM   #134
kelly is offline kelly  United States
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The resistors are 75 ohms. Having one makes sense to keep the opamp from seeing a dead short, although it is internally short circuit protected. I would not see that the input to the next stage would care if it sees a dead short. I always short unused inputs with no problems so far .

I did read something about using more than one transistor to get the required muting level and also about using the resistors to stabilize the outputs to capacitive loads, but I do not fully understand either, hence my question.

Thanks for the input.
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Old 27th June 2009, 12:29 PM   #135
Crimson_Dawn is offline Crimson_Dawn  Italy
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I know that is an old topic...
But i'm starting doing some mods on my Nad C520.
I changed the OP chips, the in and out cap of the amp stage, and i would like to change the 1N4001 diodes.I would like to use schottky diodes, i found 11DQ10 which should do the job quite well, i read in the topic also byw200 and SB300 could do the job...
Can also the 1N5819 work?
Because i can hardly find the other types of diodes...Any good substitute?
thanks a lot for your help,

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Old 29th June 2009, 03:39 PM   #136
Oystein is offline Oystein  Netherlands
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Dear fellow tweakers,

Reading all the positive results with all your tweaks I wanted to share my own experience.
Although this tread is based on the NAD54x series I have an older NAD 524(i). The NAD 524i is an improved version by the Dutch distributor bought in 1998 for 1300 HFL = approx 600 EUR. What they did is using a standard 524 - costing 1000 HFL - and replace the Op-Amps for better types ( the "bastards" removed the text on top so you do not know what they have used ) and they also replaced the parallel coupling caps from 0,22 uF to WIMA 2,2 uF MKT. The main coupling caps are 100 uF Elna but no specific type.
The standard RCA plugs were also replaced by gold-plated heavy duty models.

Since I have much better speakers I realised there would be much room for improvement in the CD / Amp area.
The NAD distributor will supply a copy of any service manual for 15 EUR each so I ordered for the CD player and Amplifier (NAD 317) which really helps if you need to tweak.

Earlier this year I already installed an Euro connector to be able to use better mains cables instead of the standard pre-mounted wire + plug.

Starting with the cd player I decided to install a Tentlabs XO2.2 clock. Because I overlooked the installation guid on the Tentlabs site I started to search on the internet and I happened to find the site of the Autralian brand Burson Audio.
In the weeks before I also had read lots about Op-Amps which were also on my to-do list and so I found the Burson discrete Op-Amp so I realised the potential here.
I ordered a set and last week I installed the XO2.2 clock, discrete Op-Amps and replaced the Elna's for the Silmic II types. I was really amazed about the result.

A friend replaced his Marantz SA11-S1 for a Spectral cd-player some months ago and then I had the opportunity to try his Marantz for a weekend but the difference was not that big to my ears.
Now that I upgraded my NAD I could notice the difference immediately but unfortunately I can not borrow the Marantz anymore to do a new comparison. But I am sure it will blow the Marantz away... which is an expensive cd-player !!

I am also planning to replace the rectifier diodes (Skottky) and power supply capacitors. The 5Vdc that feeds the analog section of the PCM1716 DAC chip is from an 7805 whicch itself is supplied by the 12Vdc (LM317/337) for the analog section. I will replace this 7805 by a LM317 too becuase of the lower noice.
And the muting transistor in the output will go too.

The clock and Opp-Amps are responsible for maybe 80% of the upgrade but the other tweaks are inexpensive so I will continue although the results won't be as shocking as last weekend ;-)

When completely finished next week I will make some pictures for those interested.
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Old 27th July 2010, 09:52 AM   #137
ray_stinger is offline ray_stinger  Singapore
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Hi people, I've recently acquired the NAD C542 player and would like to see what I can do to upgrade/modify the player. Can someone with the service manual send a copy to my gmail address with user ID "friendster" (remove the quote and add [at]gmail.com). Thanks.
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Old 15th August 2013, 12:43 PM   #138
Oystein is offline Oystein  Netherlands
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Maybe a bit late ... I didn't even remeber I posted here but as described above I would post some pictures ;-)

Click the image to open in full size.
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Old 30th August 2014, 12:15 PM   #139
ebogga is offline ebogga  Finland
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Default Mod 541i

Sorry to bring back an old topic...

Was about to trash my old 541i since it had a broken laser + cd pulley belt. But then found this thread and thought I might as well bring it back to life.

After fixing the player have done the following mods:

removed muting caps
soldered sockets for opamps and changed them to 627AU
changed main caps to panasonic ones as per suggestions in this thread

Next I'll do the fixes correcting the reading problems. But I'd really like to try the 541i -> 542 convert and remove the output caps. There was one post here describing the process but being a total newbie at this I can't make out exactly what to do. Here's the quote from user clocknad:

It lool like it is a very simple convert from C541i to 542, by moving stuff around - the 4k7 resistors from mute transistors move up to pin 5 and 6 of the first opamp, adding a 10K between Gnd and after C376, short pin 6 (with 4k7 between) to Agnd, connect pin 5 with DAC out after C376(4k7 in between)

add another resistor 270k parallel with R360 to drop it down to 15k2. remove those coupling cap after the opamp output. NO trace cut needed, and that is the difference between 541i and 542 in the analog section.
Could someone please open the process up for me in detail? I'd really appreciate the help!

Really liking all the improvements in sound so far! Thanks to all the contributors in this thread!
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