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Old 21st January 2013, 12:33 PM   #11
Qfactor is offline Qfactor  Singapore
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Hey, thanks plenty for the heads up!
One more question, why would a 6v power supply suffice instead of 9v?

Thanks again! Let you know the outcome when I've worked on it!
This kit cost me about 8 bucks! And in stereo too! (Two of each!)
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Old 21st January 2013, 05:47 PM   #12
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Quote:
One more question, why would a 6v power supply suffice instead of 9v?
Much longer and cheaper run time.
You should have plenty of output so the extra voltage isn't needed.
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Old 25th January 2013, 03:18 PM   #13
Qfactor is offline Qfactor  Singapore
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Quote:
Originally Posted by sofaspud View Post
Much longer and cheaper run time.
You should have plenty of output so the extra voltage isn't needed.
Hi, ok will change it to 6v instead then.

One other thing I just noticed upon inspecting the kit.
If you refer to the image I attached in my earlier post again, the schematics show the 10uF capacitor at the input with the positive towards the input. On inspecting the kit PCB, I noticed the "+" is facing the 10k potentiometer, instead! In other words the input connects to the -ve of the 10uF cap (according to the PCB)
Now, which should I follow? Coz this would mean that when I attach the other capacitor-resistor inputs(to mix the 4 inputs together), I would follow the same orientation,ie, input to -ve of the cap lead?
Is that right?
Thank you for all your help!
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Old 25th January 2013, 08:14 PM   #14
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Go by the schematic orientation, but don't install C1. The four inputs replace it and connect directly to the potentiometer.
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Old 26th January 2013, 12:29 AM   #15
Qfactor is offline Qfactor  Singapore
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Quote:
Originally Posted by sofaspud View Post
Go by the schematic orientation, but don't install C1. The four inputs replace it and connect directly to the potentiometer.
Thanks. Yes, I was just using C1 as the starting lead for the 1st input (in series with a resistor, of course)

Alrighty...now to warm up the iron
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Old 11th May 2013, 01:52 PM   #16
Qfactor is offline Qfactor  Singapore
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Hi, in January, you gave some tips on how to modify an amp schematic to a mixer/headphone amp combo.
I finally managed to get this up and running successfully!!

However, I was wondering if I could get your advice again on the fact that the trim pot of 10k came up rather sensitive when I set the volume. From a minimum setting, I only needed to turn up less than a quarter turn before it became too loud!
What's the easiest way to decrease the volume sensitivity so that I can set the trim pot to around midway for a "comfortable" level?

Thanks!

Quote:
Originally Posted by sofaspud View Post
Go by the schematic orientation, but don't install C1. The four inputs replace it and connect directly to the potentiometer.

Last edited by Qfactor; 11th May 2013 at 02:00 PM.
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Old 23rd May 2013, 04:08 PM   #17
Qfactor is offline Qfactor  Singapore
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Bump
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Old 24th May 2013, 01:11 AM   #18
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Quote:
Originally Posted by Qfactor View Post
What's the easiest way to decrease the volume sensitivity so that I can set the trim pot to around midway for a "comfortable" level?
Thanks!
Sorry for the delay. Either I just missed your message or it didn't show up in my subscribed thread list.
Probably the easiest would be to put a series resistor on the input, just ahead of the 10k pot. I'd start with about 4.7kΩ and adjust that value up or down as necessary.
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Old 25th May 2013, 05:38 PM   #19
Qfactor is offline Qfactor  Singapore
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Cool! And thanks for taking the time to reply! Was begin to wonder if you just happened to browse this thread that time only!

On another similar note, I "suddenly" got this urge to make things go even smaller(!!) so, was wondering if I used the same capacitor values for the input and output that were suggested (10uF for each input and 1000uF for the output) with this (attached) BC109-based amp, would it work?
Thanks!
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File Type: jpg image.jpg (191.9 KB, 54 views)

Last edited by Qfactor; 25th May 2013 at 05:44 PM.
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Old 25th May 2013, 06:04 PM   #20
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The capacitors form a high-pass filter with the accompanying resistances. Fc = 1/2*pi*R*C
Assuming a high input impedance at the chip itself, the signal sees only the potentiometer resistance (approximately). 10μF at the input is fine with the 10k-15k potentiometer/series resistor value; it would also work as the coupling cap between mixer and distribution amp, if such coupling is required.
At the distribution output, it is a different situation. There, the circuit is feeding the relatively low-impedance headphones. The lower impedance demands a higher value capacitor to maintain the low frequency crossover point.
For 32Ω headphones, I wouldn't go lower than 470μF, which puts Fc at about 11Hz.
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