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Chip Amps Amplifiers based on integrated circuits

Build an active stage monitor - STK4048V
Build an active stage monitor - STK4048V
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Old 20th February 2013, 12:49 PM   #1
gianmarco is offline gianmarco
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Default Build an active stage monitor - STK4048V

Hello everybody, I am a new user of this forum, I have been reading for long time and now I decided to register and write some questions to you all.

Long time ago I bought a small "laney" stage monitor that had turned out to be a fake one, not a laney at all, nor the amplifier nor the cone.

After few days of usage the amplifier broke, I don't know very well the reason.
I opened it and saw that was a stk4048V amplifier.


Today arrived my new STK4048V chip from U.K. and I started to wonder if, using some pieces from the old broken pcb, I could make a not-lasting-only-two-days amplifier.

I have the transformer (very heavy) I have the new chips and I can test all the components of the old PCB. Maybe I need to change the cone, but I do not know how because I do not have another amplifier.


And here come your help, if someone wants to spend few minutes or few hours to help me I need to:

- Know if the old scheme is a valid and working one or, in case, change it.
- Know if there is something I can do to improve the scheme.
- Know how to properly test if the old components are good or burned.
- Know how to test the old cone
- If the cone is gone (and maybe the cone was not compatible with the amplifier) know how to choose a new cone.

I have a very beautiful wood case, like a real stage monitor, with the grille, space for a tweeter and a woofer etc.


If someone knows the stk4048V and wants to help me, please answer to this message. In a few days (because I have two university exams) I will post the circuit scheme.

I do have:
- low tension solder station
- digital multimeter

I do not have:
- oscilloscope
- spectrumscope

Have a nice day, Gianmarco
p.s. sorry if I made any mistake with the language, I am Italian.
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Old 20th February 2013, 04:19 PM   #2
Mooly is offline Mooly  United Kingdom
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Build an active stage monitor - STK4048V
If the unit is "fake" then I think the first think to confirm is that the power supply voltages to the STK are correct and not to high.

I would recommend using a "bulb tester" for initially powering and testing so as to avaoid damage to the new IC's.
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Old 20th February 2013, 04:22 PM   #3
gianmarco is offline gianmarco
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Can you please explain what a "bulb tester" is? just putting a light blub (220V ?) in the out of the IC?

Tomorrow I will work to write the circuit, then I will post what the actual values of voltage are.
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Old 20th February 2013, 04:26 PM   #4
Mooly is offline Mooly  United Kingdom
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Its just a mains filament 100watt bulb placed in series with the mains supply to limit current in the event of a fault.

You'll find many references to it on the forums.
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Old 20th February 2013, 04:28 PM   #5
gianmarco is offline gianmarco
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I have already a 2A fuse in series with the main supply, isn't that enough?
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Old 20th February 2013, 06:12 PM   #6
Mooly is offline Mooly  United Kingdom
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The bulb works on a different principle. When the filament is cold it has a low resistance. Measure one and see If the current drawn by the amp is low, the filament stays at a relatively low resistance and drops only a little voltage.The bulb isn't lit. If there is a fault and excess current is drawn the resistance rises rapidly, the bulb lights and the current is reduced saving damage.
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Old 20th February 2013, 06:48 PM   #7
gianmarco is offline gianmarco
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cool!
I have the old IC, do you think is better to use that one instead of the new one? I don't now if is the IC or something else that is causing problems.
Perhaps I'm not sure that the cone is working, and if it is, I am worried I could burn it.
Do the bulbs save the speaker also?
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Old 20th February 2013, 06:59 PM   #8
Mooly is offline Mooly  United Kingdom
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The bulb would probably give you time to save the speaker but you should have confirmed that there is no DC present before even thinking about connecting the speaker.

You need to be methodical. Check the supplies and, assuming it runs off "split" or dual rails (as most amps do) you then check that the speaker output is at zero volts DC.

The old IC may or may not be faulty. Only careful voltage tests will tell.
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Old 20th February 2013, 07:03 PM   #9
gianmarco is offline gianmarco
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ok tomorrow I will re-connect the old IC, put the light bulb in series to the main supply, test if is there any DC voltage. If the DC is zero then I put the speaker and take some voltage in the circuit.

Is there any method with the multimeter to check if the speaker is dead or not?
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Old 20th February 2013, 07:07 PM   #10
Mooly is offline Mooly  United Kingdom
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You can measure the resistance on your meter. It will be around 4 to 10 ohms. Also connecting a 1.5 volt battery across the speaker will cause the cone to move in or out depending on polarity. Assuming its a large speaker then the cone should move freely and easily. Any rubbing or "scratchiness" indicates a problem.
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