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Old 20th May 2007, 02:56 PM   #1501
Nordic is offline Nordic  South Africa
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Got a little further....
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Old 20th May 2007, 04:45 PM   #1502
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Default Perfect Nordic...interesting that i am painting an enclosure with the same colour you

are using.

Was a mix...the colour i have made mixing materials...it has a corrugated, not flat, not shining finishment.

I like it, your enclosure...it is perfect.

My paint is not finished.... two coatings more will be needed and them a varnish will be used (not a brigth varnish)

regards,

Carlos
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Old 20th May 2007, 05:40 PM   #1503
Nordic is offline Nordic  South Africa
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Wanna heavy Pedro ?

It is soooooooooo heavy lol.... thanks for the kind words... yes it is not flat blue, it is a blue green hammertone... that spray that looks like metal beaten with a hammer...
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Old 20th May 2007, 06:29 PM   #1504
kvholio is offline kvholio  Netherlands
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Looking good, Nordic.
Lovely vintage look, reminds me of old guitar-amps and tube-gear.
The hammertone you're referring to, is it like this (this is the grey variety) ? We call it hamerslag overhere.
Gives a very nice rugged look

Click the image to open in full size.

Keeping my fingers crossed for your wisdom-tooth

Best regards,

Klaas
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Old 20th May 2007, 07:17 PM   #1505
Nordic is offline Nordic  South Africa
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yes, like that,
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Old 20th May 2007, 07:44 PM   #1506
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Default Mine Dx case had the painting material prepared by myself


Old style...alike Leonardo Da Vinci.... mixing oils and colours....had that white material we use to cover holes into the wall.... oils, colours and brush heating the surface.

It is nice to make.

Under, you can see the waterproof gray paint.... two more layers and a non brigth varnish will be used.

I will produce details in black...and some knobs will be placed...it will result fine.

regards,

Carlos
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Old 20th May 2007, 07:48 PM   #1507
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Default The colour is alike the forum blue colour...sundown is creating some redish

colour that is not natural.

here is the detail.... the surface was heated by a brush while not completelly dried...to produce that type of surface.

This paint resulted "rock solid".... old style man!

regards,

Carlos
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Old 20th May 2007, 07:53 PM   #1508
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Default Here a more real colour.


Very different to an amplifier...hehe

regards,

Carlos
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Old 21st May 2007, 01:05 PM   #1509
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Default The home page is beeing updated related Dx amplifier adjustments


Because VBE multiplier turn standard, some adjustments will need revision.

The bias trimpot must be adjusted to 700 ohms .

The offset trimpot must be adjusted to 7400 ohms.

Multiturn trimpot will be very helpfull.

The instructions will produce 80 to 110 miliamperes of stand by bias current...idle current....but you may find a better operation point to your transistors tweaking this current to lower values...listening to low level music and searching for quality.

Nordic and Klaas found that 80 to 110 miliamperes is a little bit big compared with their adjustments.

Of course the standard adjustment will work...but if you want to tune it to the best possible performance...use your ears and make small adjustments....and do that will very small volume, also keep those 10 ohms resistances in series with the supplies, because of safety reasons, during your low volume adjustments.

Finally.... after "fine tuning"...remove the resistances.

The amplifier cannot distort when playing very low volume music.

regards,

Carlos
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Old 21st May 2007, 01:11 PM   #1510
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Default The adjustment section, into the home page, will be updated following this text.


Adjusting the bias, and trimming DC offset

Follow the steps below to adjust bias and trim the DC offset.
Note: The test points A, B, C, D and E are shown on schematic and PCB layout.

Step

1 ........... Ensure the power is off and filter capacitors are fully discharged.

2............ Install a 10 ohms (5 watt or higher) protective resistor in series with each of the supply rails—see diagram below.

3 ........... Install a wire or low ohm resistor to short the input.

4 ........... Ensure there is no load on the output (i.e. no speakers connected).

5............
Set your multimeter to the resistance range.

6 ............ Set the bias trimpot (VR2) to 770 ohms PCB – Top View).

7 ............ Set the offset trimpot (VR1) to 7400 ohms (between test points D and E—see PCB – Top View).


8 ............ Set your multimeter to the 2V DC range.

9 ........... Install two multimeters connected across each of the protective resistors—see diagram below.

We are measuring the voltage that develops across the protective resistors when a current flows. Because of the zener diode, Z1, the bias current in the positive rail will be just a bit higher, about 10 milliamps, than the negative rail.

10.......... Turn the power on.

11.......... Adjust the bias (VR2) to between 800 and 1,100 millivolts (0,8 and 1,1 volts) on each rail.

Remember the positive rail will read slightly higher (about 100 millivolts) than the negative rail.

12 .......... Set your multimeter to the 200mV DC range.

13 ......... Install a DC voltmeter between the speaker output and star ground—see diagram below.

14.......... Adjust DC offset (VR1).

Initially try for a DC offset of less than 3 millivolts.
The maximum allowable is 20 millivolts.

15 ......... Return and check the bias, adjust it again.

16 ......... Re-adjust your DC offset to a voltage lower than 3 millivolts.

The voltage there must be stable, not fluctuating.

17 ......... Once more check your bias and adjust if needed.

18 ......... Return to check the offset for the last time. It should be under 3 millivolts.

19 Remove the 10 ohm protective resistors.

20 ......... Repeat the setup for the second amp.

21.......... Connect your audio source and speakers.

22 .......... Now enjoy the romantic sound

regards,

Carlos
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