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Old 28th March 2013, 03:03 PM   #41
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Can you tell me a good program with highlight net?

For the balance, I have lot (hundred of meters) of cables all around the stage and I already have experience with non-balanced stuff, it's very common to take in some noise or hum here or there. I already have the opamp and the staff to read the unbalanced signal, i only need a solution to transform the 35V (more or less) to 15V

The lm7815 isn't good for me because of it's maximum voltage of 35V, I read about the lm317 and lm337, and I am thinking to add two of that, so I can also put some led, some functions like limiter with bicolor led etc.

The other stuff are for my pleasure, but the balance it's necessary for me for the reason that I don't have only my piano and the stage monitor but also many other kind of strange instruments and microphones.
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Old 4th April 2013, 11:40 PM   #42
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Hello everybody, after few days of working, I checked and re-checked the schematic I wrote and with some courage I tried to build the circuit on to the board.

Here are some pics:

First few resistors (and a diode), few marks as reference to the positioning of each component.
Click the image to open in full size.

Bottom:
Click the image to open in full size.

Few other resistors, and other marks.
Click the image to open in full size.

Bottom:
Click the image to open in full size.

Few other steps (bottom)
Click the image to open in full size.

Almost done (transistors and capacitors added)
Click the image to open in full size.

Bottom with thicker tracks:
Click the image to open in full size.

Heatsink:
Click the image to open in full size.

Actually my work is at this point:
Click the image to open in full size.

Still missing: few condenser (not arrived yet to the shop), few hole in the heatsink (the one for the BC547 and for the screw of the two darlingtons), obviously the two main transistors.

What do you think about my job? What about the traks, are them thick enough?

What will be the steps to do to test the amp? I first tested the transformer with barely the diode bridge. Can you please tell me a step by step guide, not to ruin all this work?
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Old 5th April 2013, 12:45 AM   #43
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The cheapest solution is to simply buy an amplifier and speaker cabinet.
You will never make one for less because companies can buy in bulk.

I built my own amplifier so I could fix it myself if it went wrong.
But I bought a set of 800w disco speakers for 90.
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Old 5th April 2013, 12:56 AM   #44
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Quote:
Originally Posted by nigelwright7557 View Post
The cheapest solution is to simply buy an amplifier and speaker cabinet.
You will never make one for less because companies can buy in bulk.

I built my own amplifier so I could fix it myself if it went wrong.
But I bought a set of disco speakers for 90.
Sorry m8, what is it about this thing you said?
Until now I have spent about 80 euros. I already have the cabinet, maybe the cone, twitter, speaker grille etc etc. I don't buy cheap audio gear, like behringer, karma or worse something for "DJs". It's a while that I buy only medium quality gear, and if I buy something that is not good is because I did it, and only to recover a bad (past) purchase

By the way, this is DIY audio don't it? Why you tell me not to Do my self? LOL

I do not need a new stage monitor, I already have 4. This is a project to save a very bad purchase made couple years ago. Do you think I am wrong?
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Old 5th April 2013, 01:18 AM   #45
JMFahey is offline JMFahey  Argentina
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Looks good, hope it works.
And if not, recheck connections, the project is good.
Remember to connect it through a lamp limiter for the first time and until you check all voltages are reasonable.
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Old 5th April 2013, 01:19 AM   #46
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ok, so I need only a 60w (i.e) light bulb?

and how to set the trimmer to the correct value? how can I know if a voltage is reasonable?
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Old 5th April 2013, 01:33 AM   #47
JMFahey is offline JMFahey  Argentina
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Yes, a 60W (filament) bulb is fine.
a) "Reasonable" is basically to have +/-40V or thereabouts rails, less than 100mV Dc at the speaker output and whatever the Project suggests across the ballast resistors , don't have the instructions in front of me now, but it's a few mV meaning, say, 20 to 30 mA bias current.
What we basically want to check is that there is not some **catastrophic** failure caused by a wiring error, doubly possible here because of the homemade board.
Best is to see a bulb blink and darken to dark orange or less, but even if it stays bright, it means we have just saved many $$$ in parts and Million$ in frustration.

Rail voltage will be somewhat lower, maybe +/-30 and even +/-25 , because of the bulb, nothing unexpected.

What we don't want is a constantly bright bulb and, say , +/-5V rails or some other absurd value.

*If* everything looks normal, connect a speaker and listen to some music (1 or 2 W only, we're testing functionality here, not running in Monza or something).

*If* everything's fine, connect straight with no bulb, **recheck** bias voltage and then apply signal and let it loose.
After 5 minutes check with the advanced, NASA approved "Therm-O-Finger" that the heatsink does not think it wants to fry eggs or something.
Repeat every 5 minutes for 1 or at least 1/2 hour.
Enjoy.
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Old 5th April 2013, 01:36 AM   #48
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OK, now I have only to wait for the component missing!
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Old 9th April 2013, 01:50 AM   #49
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at last the component arrived! Today afternoon I went to the shop to buy the last components.

After few hours of drilling, soldering etc I reached this result:
Click the image to open in full size.

Immediately I re-checked the scheme, the pcb and tested for continuity each track. All was good.
I put some silicon paste and a mica sheet between the heatsink and the three transistors, connected my light bulb, tester ready, and powered on the amp.

A bad hum came out from the driver, the bulb was glowing hard. I knew something was wrong. Turned off.

Re-checked all again, There was a transistor turned, so instead of CBE I was connecting as EBC. this is due to its strange positioning (is T6, the one IN the heatsink) upside down that send me in troubles.

I retry again to power up the amp. No changes, same hum from the driver.

Re-checking again I found a big mistake in the pcb, a track that should go to -40V was actually going to +40V. Fixed it the result is this:

turning on
a little flash of the light bulb
the bulb is not even glowing, completely cold.
the amp is working, voltages are fine (about 35V)

now I tried without the bulb, voltage is about 42/43 volts, nothing burned nor there is too much heating.

All seems to be OK


Tomorrow I will do other tests.

Is there any preference in ohms for the driver?
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Old 9th April 2013, 03:28 AM   #50
JMFahey is offline JMFahey  Argentina
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8 ohms would be fine, but if all you have a 4 ohms one, go for it.
Don't drop the bulb limiter yet, use it a little longer until

a) you actually hear 1 or 2 W music into the speaker

2) you have checked biasing.
Follow Velleman's instructions.

3) and even after you connect it straight, no bulb, play some music and touch the heatsink every 5 minutes.
Warm is good.
Hot but bearable is acceptable.
Unbearable is not good.
Sizzling/BBQ temperatures: pass the Tabasco Sauce, please.
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