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Chip Amps Amplifiers based on integrated circuits

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Old 24th December 2016, 11:11 AM   #11
delange is offline delange  Belgium
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Quote:
Originally Posted by Peterphuket View Post
But I have a question concerning the power supply. on connector K7 you'll need 2 times 40V AC, from where you'll apply that?
The SMPS500R has an aux output. In my case (dual 55 volts PS), there is a dual 16 volts aux output. I'll use the +16 volts to power the LED of the 4N25.
To do that, I don't use R20, D3, D4 and C14 on the Q-Watt PCB. R19 will be 1k5 ohms and D3 will be replaced by a wire. I then connect the 16 volts of the aux output to K7 (first and second position; third position is unused).
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Old 24th December 2016, 11:17 AM   #12
delange is offline delange  Belgium
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Originally Posted by popchops View Post
Hi guys.

I cannot believe the main heatsinks (300x120x40mm in my case) will ever get to 75 deg C. At 0.5 deg/W that's about 90W waste heat!

I like the idea of Speakon connectors but I also need some way to connect my high-impedance active sub to both left and right channels. At present on my old Rotel amp, I have wound these 4 wires (left signal+ground, right signal+ground) around the speaker binding posts on the amp. The sub side of this cable has a 4-way Speakon interface.

If I switch to Speakons out of my new amp then I need another (third) speaker output (4-way) for the sub. Has anybody done this? Am I barking up the wrong tree?
You could use 4 way Speakons on your Q-Watt amplifier. This way, each Speakon can have left and right (+ and - 1 for left channel; + and - 2 for right channel).

You will need to make your own speaker cables:
* "left" speaker speakon: use + and - 1 for main speakers. Use + and - 2 for right channel sub.
* "right" speaker speakon: use + and - 2 for main speaker. Use + and - 1 for left channel sub.
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Old 24th December 2016, 11:18 AM   #13
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40V AC is intented to come direct from a transformer before rectification to 55V.
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Old 24th December 2016, 02:19 PM   #14
delange is offline delange  Belgium
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Quote:
Originally Posted by popchops View Post
40V AC is intented to come direct from a transformer before rectification to 55V.
The purpose is to switch off the speaker relais immediately after power has been switched off. By using the aux output of the SMPS I do the same.
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Old 25th December 2016, 12:50 AM   #15
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Quote:
Originally Posted by popchops View Post
Hi guys.

I cannot believe the main heatsinks (300x120x40mm in my case) will ever get to 75 deg C. At 0.5 deg/W that's about 90W waste heat!

I like the idea of Speakon connectors but I also need some way to connect my high-impedance active sub to both left and right channels. At present on my old Rotel amp, I have wound these 4 wires (left signal+ground, right signal+ground) around the speaker binding posts on the amp. The sub side of this cable has a 4-way Speakon interface.

If I switch to Speakons out of my new amp then I need another (third) speaker output (4-way) for the sub. Has anybody done this? Am I barking up the wrong tree?
@Popchops,
It depending where you lives, like me in the far east with an average temperature between 30 and 40 degrees Celsius, it is not so special.
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Old 25th December 2016, 11:07 AM   #16
delange is offline delange  Belgium
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Join Date: Jan 2012
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Question: did anyone use a multi-turn potmeter for P1?
I find it a bit hard to accurately set the idle current with the supplied potmeter. Due to this I'm think about replacing P1 with a multi-turn variant. I'm curious about other people's experiences with this.
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Old 25th December 2016, 11:09 AM   #17
AndrewT is offline AndrewT  Scotland
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Most would use a 10turn or 15turn ot 25turn Variable resistor to adjust settings that are sensitive.
Setting the output bias voltage is a sensitive procedure and using a 3/4 turn VR is not easy.
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Old 29th December 2016, 09:32 PM   #18
calpe is offline calpe  Gibraltar
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Hiya,
I too have been following the project on Elektor Labs.
I'm interested to have some views/feedback on cases to fit two Q-Watt boards and two SMPS's inside one case.

Apart from that having ordered the recommended heatsinks, i assume they have to be mounted so that the 'fins' point out, rather than lay the heatsink flat with the 'fins' pointing downwards?

I've included a Spares list that should help constructors (sorry its pdf).

Cheers
Attached Files
File Type: pdf Spares list 31-08-2016.pdf (126.0 KB, 48 views)
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Old 30th December 2016, 08:29 AM   #19
AndrewT is offline AndrewT  Scotland
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To be fully effective the gaps between the fins must pass cooling air.
This requires that the fins be vertical so that the partially warmed air in contact with the fins can rise up through the gaps. The gaps act like chimneys.
It was probably shown to you in science classes at early school.
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Old 30th December 2016, 08:59 AM   #20
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there is no overcurrent, or short circuit protection, and no clip protection.
trusting all that available power to a single pair of output transistors seems optimistic to me. why not add a few more power transistors in paralell ?
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