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Κυριακή, 21 Δεκεμβρίου 2014

simple high-pass filter

My recently made amplifier has too much bass.I needed something to lower it.I wanted something very basic-not complicated- and this what I came up with.A high-pass filter.

Notice at 00:26 how the bass is reduced as I turn the resistor all the way to the right at 20K.When I turn the variable resistor to the left the bass is increased.



This is the simplest form of a high pass filter circuit- a capacitor and a resistor.

Schematic here.



Here is very basic high-pass filter with an opamp.

Προσθήκη λεζάντας
Gain is determined by R2/R1.

This site has an online calculator to help you calculate the values of the capacitor and the resistor.

According to the calculator-in my case- 100nF capacitance combined with 20K resistance gives 79.58 Hz.This is the cut-off frequency. 

Or if you are into math you can calculate the values yourself with this formula.

f_c = \frac{1}{2 \pi \tau} = \frac{1}{2 \pi R C},\,

f is frequency in Hz
pi is 3.14 or 22/7
R is the resistor value
C is capacitor value

arximastoras.blogspot.com
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Σάββατο, 20 Δεκεμβρίου 2014

transformerless power supply for LEDs or don't try this at home.

Transformelesss power supplies are useful lighting LEDs.Before I go any further I would like to point out that this is the most dangerous circuit I've ever made so far.It is definitely not for amateurs.The shock risk is very high because of the design of this circuit.For more info on this read the Danger section of this post.

I've reproduced the circuit  found in this site to power a 10watt LED.





Some of the specs
input power 240 AC/50hz
output 15 volts DC
driving a 10 watt LED that draws 220 milliamps
output current 1.2 amps according to the designer of this circuit

Here are the parts I've used.

two 2uF/250Volts  film capacitors in parallel (the output depends on this cap-more caps in parallel more amps.Higher voltage rating-higher DC output)
10M resistor in parallel with the caps above.This resistor acts as a bleeder.It discharges-it bleeds- the caps after you turn the circuit off.Otherwise they can remain charged for a very long time making them a shock hazzard.
four 6 amp diodes (four amp or more are needed-double the outpout amperage which is 2 amps) as a rectifier bridge.This rectifies -turns the AC to DC.
3700uf/16volts electrolytic capacitor (I should have used higher voltage rating but that's what I had)
one 15volt zener diode to limit DC output.This one filters the ripple on the rectifier bridge output making the DC wave smoother

one 100ohm/10watt resistor in series with one of the mains lead to protect the circuit
one 10ohm/5watt resistor

5Amp fuse-always use a fuse.If something goes wrong- and I wish it won't-some of excessive current will go to the fuse not the circuit or even worse you!!


Danger

Remember this circuit is VERY DANGEROUS.The mains is not isolated from the circuit in any way like it would when using a transformer.Furthermore spark gaps appear because of connections being too close to each other.This happens mainly around the mains input points where power is high.

DON'T build this if you are an amateur and do not know exactly what you are doing.

Did you notice the LED is still on even though the plug is disconnected?That's because of the capacitor still having power stored.

Take a look at the spark gaps created in my circuit because the strips are too close to each other and had solder on them.

Tesla's rule of thumb was working with one hand when dealing with high voltage.

Look at the spark gaps!!



arximastoras.blogspot.com
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Δευτέρα, 15 Δεκεμβρίου 2014

Our youtube channel

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Awesome 20W TDA2003 bridge amplifier!

I've built this simple bridge amp based on the old TDA2003.This amp puts out great sound with low distortion

I've used the schematic found in  this site.


Here is the actual pcb in a STR8 box!



It is better to use spring clips for your speaker cables...

The spring clips eliminated some or the crackling!

instead of these


Problems you may face after building the circuit

crackling noise
When I turned on the amp everything was ok at first but after a while when it heated up a very annoying
crackling noise appeared even at zero volume.The hiss was there even with the audio cable disconnected.This sounded like a heat problem.When it heated up some bad tracks where expanding due to heat causing the crackling.So,I resoldered all tracks and joints and the problem was solved.

loud noises when not audio in cable not connected
That's an easy one.Connect 1.5Kohm resistor or more from audio in (Vin) to ground.See the resistor in the image below?



other things you can do for sound problems  
Additionaly you can add ferrite beads to the AC and DC input and the speaker cables as well.A more complex solution would be to use a low-pass filter circuit between the audio source and the amp.I have yet to build a low-pass filter circuit to try it my self.

Some noises can be eliminated by simply adding a 102 cap between audio Vin and ground.

If you get a buzz from the speakers then it is probably interference from another device.Turn off all other devices and disconnect every external device you can from your computer.I had an external monitor plugged in to the vga-in on the side of my laptop.I found by mistake that this was a major source for the buzz I got on my speaker. The power cable to the laptop gives out noise also.

Here is the live amp used with an 80Watt speaker! Each of three drivers is 8ohms.



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Σάββατο, 6 Δεκεμβρίου 2014

Κύκλωμα για να ανάψετε λάμπες LED εκτός δικτύου με λιγότερη κατανάλωση απ'το δίκτυο.


Εδώ αναπαρήγαγα το κύκλωμα της 'λυχνίας του λύγγα' (lynx joule lamp) και κατάφερα να ανάψω δύο  λάμπες LED -3 βατ η κάθε μία ,6 βάτ συνολικά.

Είχα πολλές δυσκολίες στην κατασκευή αυτού του κυκλώματος - το μαγνητικό σύρμα είναι πολύ ακριβό στην Ελλάδα (αν ξέρει κάποιος που μπορεί να βρεθεί φτηνό ας το πει) και έπρεπε να χρησιμοποιήσω κομμάτια διαφορετικής διαμέτρου που τα ένωσα μεταξύ τους.Παρ'όλα αυτά δούλεψε.Δεν κατάφερα όμως να ανάψω λάμπα CFL για την οποία χρειάζεται διαφορετικός μετασχηματιστής και κύκλωμα.Η CFL απαιτεί πολύ περισσότερη ενέργεια και βολτ.

Παρατηρήστε ότι ένα από τα ποδαράκια του LED πηγαίνει στο συλλέκτη (collector) και όχι στον πομπό (emitter).Έτσι το τρανζίστορ 2N3055 μπορεί να αντέξει περισσότερο σε ένα πλήγμα , αν για παράδειγμα, συνδέστε μια μεγαλύτερη απ'ότι πρέπει μπαταρία .

Εδώ είναι οι προδιαγραφές του κυκλώματός μου .
χάρτινο ρολλό κουζίνας περίπου τριών εκατοστών διαμέτρου
Περίπου 700-800 στροφές το δευτερεύον καλώδιο με διάμετερο 3,5 χιλιοστά περίπου
160 στροφές το πρωτεύον με καλώδιο λάμπας.Με λιγότερες στροφές οι λαμπτήρες δεν ξεκινούν.
ένα  τρανζίστορ ισχύος 2N3055 με ψύκτρα
δίοδος από τον πομπό στη βάση (base-emmiter)
έναν πυκνωτή 100nF σε σειρά με το καλώδιο της βάσης.
Η δίοδος υποτίθεται ότι προστατεύει το τρανζίστορ , αλλά παρατήρησα ότι μειώνεται λίγο επίσης  και η κατανάλωση των αμπέρ.

Ο πυκνωτής 100nF μειώνει την κατανάλωση αμπερ λίγο περισσότερο.




Τί κερδίζω σε κατανάλωση απ'αυτό το σύστημα.

Οι δύο λάμπες μαζί σ'αυτό το κύκλωμα τραβούν 3 βατ συνολικά ,ας είναι δύο ενώ στο δίκτυο η κατανάλωση είναι διπλή τρία συν τρία έξι βάτ.Μισή κατανάλωση δηλαδή!

arximastoras.blogspot.com
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Another lynx joule lamp replica

I've replicated the Lynx joule lamp circuit and managed to light two 3 watt LED lamps -6 watts total.

I've had many difficulties building this circuit-magnet wire is very expensive here and I had to use several pieces of different gauge and joined them together.Nevertheless the aircore did work.I couldn't get a cfl or a bigger LED lamp to light though.

Notice that one of the LED leads goes to the collector not the emitter.This way the 2N3055 transistor can take more amps and not blow if you for example connect a bigger battery.

Here are my specs.
about 1'' diameter paperoll
About 700-800 turns secondary.Not sure how many exactly.Most part of  the coil is 27 gauge.
160 primary (with less turns the lamps would not start).I've used lamp wire here.
one 2n3055 power transistor with heatsink
a diode from emitter to base
a 100nF cap in series with the collector wire.
The diode is supposed to protect the transistor but I noticed that the amp draw decreases a bit also.
The 100nf decreases the amp draw a little bit more.


arximastoras.blogspot.com
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Παρασκευή, 28 Νοεμβρίου 2014

Tesla coil Tuner


I've built this small by very useful circuit to help me tune my first Tesla coil.It was designed by Terry Fritz.You can find the schematic here.

I've used one 102 tantalum capacitor here (1nF) because my coil is rather small.For bigger coils use twice the capacitance (two 102s in parallel).You may use even less capacitance.The LEDs should have multiple bright points when tuning the secondary.

Notice that when I connect the two probes together with an aligator clip both LEDs light up.That's a sign that the circuit works.

Parts I've used
NE555 IC
two 10uF electrolytic capacitors
two LEDS green and red
two 470ohm resistors
one 102 tantalum capacitor
5K potentiometer (POT)
9Volt battery
switch

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