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Old 25th February 2020, 09:04 AM   #2421
Bonsai is offline Bonsai  Europe
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Quote:
Originally Posted by thimios View Post
Salas DCG3!
A set of full range speakers too.
Fane 12-250TC.
Mine SX still under construction....
Very nice Thimios!

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Old 25th February 2020, 09:35 AM   #2422
thimios is offline thimios  Greece
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Quote:
Originally Posted by Masaksi View Post
Where i can find pcb for that salas DCG3 pre amp?
Quote:
Originally Posted by Bonsai View Post
Very nice Thimios!

Thanks bonsai, i had to repair my friend's laser machine for this lettering procedure.
Difficult work, many hours, many days, a lot of troubles.....
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File Type: jpg IMG_20200127_095542.jpg (666.7 KB, 401 views)

Last edited by thimios; 25th February 2020 at 09:38 AM.
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Old 30th March 2020, 06:33 PM   #2423
Joel Wesseling is offline Joel Wesseling  Canada
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Hi, I'm returning to my NX-AMP build after several years away from it. Hoping to get a little help here.

Previously, I was in the final start-up stage, but had some issues getting it stabilized. Last Communication I had with Bonsai, it was suggested that I purchase new output transistors because I had got them from ebay and they could be Counterfeit.

1) Can you suggest a reliable source for the matched output Transistors?
2) Is there anything else that I should be aware of, changes etc?

Late 2017 is when I stopped the work..
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Old 30th March 2020, 07:46 PM   #2424
Bonsai is offline Bonsai  Europe
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Joel, no need to match the output transistors. The best source for these devices is either Mouser or Digikey. Another alternative is RS Components.

Be very wary of buying semiconductors off eBay- always use a reputable distributor.
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Old 1st April 2020, 10:51 PM   #2425
Joel Wesseling is offline Joel Wesseling  Canada
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Thanks, Bonsai!

I Ordered them from Mouser. I sure hope I can get it working
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Old 2nd April 2020, 06:37 AM   #2426
Bonsai is offline Bonsai  Europe
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Old 1st May 2020, 10:24 PM   #2427
Joel Wesseling is offline Joel Wesseling  Canada
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Back on the Ovation NX. Installed new output transistors. I tried to adjust current across +ve and I'm getting slow drift while adjusting R6 and cant get it to stabilize. It's not as bad as I had before but looks like the same issue, about 5 minutes to drift 30ma. R20 is 220 ohms and I believe I changed it from 33 ohms previously. The installed Q20 is BC560C and I believe it is equivalent to BC557C.

I'll continue to search for the issues. Any suggestion will be appreciated
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Old 1st May 2020, 10:59 PM   #2428
Bonsai is offline Bonsai  Europe
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Joe,
The bias current will take about 10 minutes to settle.

1. Adjust it to minimum
2. Drive the amp at circa 1/3 power for 20 minutes
3. Adjust the bias current to the specified value

This completes bias set-up

The amp will usually power up at about 1/2 to 2/3 of the value set above and then take a few minutes to reach the set value. It will drift around by 5-10% over a 1-2 minute window under normal operating conditions - depends on power level, ambient temperature and thermal conditions (eg exposure to air currents etc) in tne amolifier housing.
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Old 4th May 2020, 06:33 PM   #2429
dennismiller55 is offline dennismiller55  United States
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Default My NX Build

I have populated the PS+Protection and both amplifier boards.

The PS+Protection board passes the test Andrew outlined in his instructions. I am using the transformer Andrew recommended from Tiger Toroids. This is giving me +/- 52V rails.


Amplifier Testing and Setup (page 41)

Step 9: On each of the amplifier boards I have adjusted Iq for 300mA after board has stabilized for 20 minutes. Note: After 20 minutes my heatsink temperature was around 35c.

Step 12: The outputs emitters should read 42mV +/-5mV. I am OK here. They seem a little low at 38mV on Q2/Q4 and 40mV on Q1/Q5. But they are with the 5mV tolerance.

Step 16 (offset): I can adjust the offset to 0V. However, the readings slowing drift up and down. Sometimes up to +10mV or down to -10mV. Back and forth. These readings seem very sensitive to temperature. I can blow on the amp card and see a increase in the speed of the drifting offset voltage.
  • Is this normal?
  • Can I assume that once the amplifiers are housed in an enclosure that the offset will be more stable?


After the boards were completed I noticed that Andrew soldered his boards touching or sitting directly on top of the heatsink devices. I left room between the amp boards and the heatsink devices. Was there some thermal considers for Andrews approach?

Here is a picture of my board/heastsink. Am I OK here? Or should I move the board to sit on top of the heatsink devices?
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Last edited by dennismiller55; 4th May 2020 at 06:48 PM.
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Old 4th May 2020, 07:03 PM   #2430
Bonsai is offline Bonsai  Europe
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Dennis,

Your attachment to the heat sink looks ok!

The drift you see is due to thermal gradients across the input devices. It may be a bit lower if you had just seated the PCB directly onto the output devices as I did, but it’s a non issue.

Once your amp is boxed up and loosed to settle thermally, the drift window will decrease.

Make sure your source output is AC coupled.

Your bias current is set correctly, you are good to go! Remember the output emitter degenerate resistors are 5% tolerance and you then also have the Vbe spread in the output devices so there will be some variation in the emitter resistor voltage drops.

Last edited by Bonsai; 4th May 2020 at 07:06 PM.
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