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Old 31st January 2011, 03:57 PM   #1
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Default anybody want to help me with the first step towards diy amplifier?

i know that if i want to plug my amplifier into the wall i will need a toroidal transformer.

and using any of the amplifier kits on ebay requires 20-30 volts AC
from what i have gathered.. you hookup the transformer to a power filter and then connect the output of the power filter to the amplifier.

this might be my first attempt at a diy amplifier because the amp i have running my back speakers has an internal crossover to seperate midrange/tweeter from bass frequencies. (the bass goes to a subwoofer because its a 2.1 amplifier)
i am looking to replace the amp with something that will provide full range output to the speakers.
but this isnt why i am posting.

what i want to know:
how do you use a toroidal transformer that outputs AC power and turn it into DC power?
i am guessing that the voltage from the transformer alternates its phase.
and the only way to make it DC is to absorb those phase changes with capacitors.
am i right?

i have long desired wanting to hookup a 1,000 watt rms amplifier in the house that is ment for car audio.
and i dont see this desire as changing because i already have a subwoofer for my car audio install but the entire project has been halted from a lack of money.

i just want to have the knowledge to be able to use AC or DC from a toroidal transformer whenever a project comes to mind.
i'd like to know that i can do it either way and stop limiting myself to amplifiers that require AC input. (which brings me back to car audio amps in the house)
i might continue to purchase AC amp kits.. but there are some car audio amps that have superior specifications.. and i can always build in the house and move the hardware to the car when i can finish my car audio install.

and anyways..
if using a bank of capacitors to turn AC into DC .. how does the power filter on these AC amps work?
do they not have the capacity to completely dull the alternate phase changes, therefore the amp is still receiving AC ?
or does the amplifier change the AC to DC with those capacitors and simply requests AC power?
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Old 31st January 2011, 04:18 PM   #2
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Hi
The electronic device that turns ac voltage to dc voltage is called a rectifier.
You then use capacitors to smooth out the gaps created by rectification.
you can make a rectifier from diodes or you can buy them already constructed for you . they are known as bridge rectifiers.
If you want to make a power supply that works off mains ac you require a transformer.the main ones used in audio circuits tend to be iron core iE transformers or torroidial transformers as you mentioned.
now to power a large car amplifier 1000watts you say! will require a large transformer rated at least 1000va and approx 9 volts ac out when you put this volts into a rectifier to get dc voltage you will then have near as dam it 12v dc. You will also need some rather large electrolytic capacitors because of the large amount of current the amplifier will demand. so large torroid and large capacitors equal a large price.
just a question car speakers can tend to be very low sensitivity compared to speakers used in house what speakers will you use with a 1000 watts.
Just to help clear things up a little how many channels in your car amplifier????

Regards mad Mark
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Old 31st January 2011, 04:19 PM   #3
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Bridge rectifier converts the AC to same polarity but choppy voltage, capacitors then smooth this voltage to DC.

Running high power car amps is generally not a good idea in the home because they need a huge power supply. It is often better and cheaper to buy a cheap or used professional PA amp instead.
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Old 31st January 2011, 04:51 PM   #4
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SO SO WRONG - YOU WILL END UP WITH AN EXPLOSION AT WORST.

1. The transformer converts AC voltage from one voltage to another AC voltage depending on the ratio of the turns on its primary and its secondary.

So a mains transformer will, usually have two primaries each of 115V (depending on country of origin). You are from the US so the two 115V primaries need to wired in PARALLEL to give you a 115V AC primary.

This will usually be specified as 0-115 + 0 - 115 (For example RED - ORANGE and BLACK -BLUE). In this case you would connect RED & BLACK together and connect them to LIVE and connect ORANGE & BLUE together and connect them to NEUTRAL.

PLEASE, PLEASE, if your transformer has ORANGE, RED, BLACK and BLUE wires coming out of it do not just connect them as I have suggested.

Many US transformers will only have a 115V primary with only two wires anyway. Only transformers destined for the European market will have dual primaries.

OK - So we have connected the transformer to the mains and the transformer will now transform the 115V line voltage iaw its specifications.

Let us assume that you have a 115V (Primary) - 24V (Secondary) transformer.

The secondary will produce approximately 24V AC, I say approximately because the transformer will behave differently depending on how much current (amps) you are sucking out of it. More about current later.

If you were to connect an Electrolytic capacitor across the transformer secondary. At best you would cause both the transformerand the capacitor to get VERY VERY hot and eventually something would fail, or at worst the whole experiment would explode.

2. You have to turn the AC into DC.

This is the job of a diode or a number of diodes. As you are a total newbie, let's keep it simple. You will need a BRIDGE RECTIFIER.

This needs to be rated AT LEAST THREE TIMES THE AC VOLTAGE so 100V would be a good choice, and at LEAST TWICE THE AC CURRENT.

As we are only experimenting a 100V 5A Bridge Rectifier will prove my point.

The Bridge Rectifier will have four connections, marked ~ / ~ / + / -. It's simple to see that the ~ and the other ~ are the AC connections. The + and the - are the DC output after the diodes have done their magic.

3. Now we have RAW DC.

This WILL NOT BE 24V DC. With 24V AC you will get approximately 24 x 1.414 - 1.4V = 32V DV.

4. Now come the capacitors.

The job of the capacitors is to act almost like a short life battery. The DC voltage still is in pulses, like a camels back, one after the other. What we need to do is store some of the energy that is being provided during the high part of the pulse so that we can iron out the cleavage between the lumps.

Think of them like a battery. As the lump gets bigger its charges up the battery, when the lump gets smaller the battery discharges to fill in the gap.

I'm trying to keep this to REAL BASICs here guys so don't condemn my Noddy explanation.

4. OK - what about current.

The transformer is quite happy transforming 115V AC into (in my example 24V AC). We now have to consider how much current (amperes) we need to drive the amplifier. Whereas VDC = VAC * 1.414. IDC = IAC * 0.7071. If you need 10A DC you will need a transformer that can provide 15A AC.

This is what is meant by the VA rating of the transformer. Within reason you simpy multiply I AC * V AC and add a factor of about 10%. 24 x 15 x 1.1 = 400VA.

5. Back to reality.

You would like to build a PSU to power a 1000W RMS Car amplifier.

If it is a true 1000W RMS (which is unlikely). then we ought to be considering building a 2000W Power Supply.

Most Car Audio is specified to run at about 15V.

So we are looking at 2000 / 15 = 133A.

1. Your Transformer would need to be a minimum of 2000VA at (15 / 1.41)V = 10V

The transformer and the diodes are completely unrealistic. These amplifiers are designed to operate with one or more HUGE car batteries supplying them.

Last edited by Andy5112405; 31st January 2011 at 05:10 PM.
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Old 31st January 2011, 04:59 PM   #5
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i have a jl audio 12w7 that has never really had a chance to perform.
i bought an amp for it.. but the amp had lots of ground noise.
i hooked it up in the house to listen for ground noise and it was still there.
after that, i had lots of bills and couldnt afford a new amp.
this was like 4 or 5 years ago.

i wanted to use the 12w7 to give a hefty boost in the frequency range of 10hz - 20hz only.
i already have two 12 inch woofers and thought it would be cute to hookup an amp in the house until i have all the pieces for the car audio install.
i still need woofers/mids/tweeters/crossovers and four channel amplifier.
i had some amps for the mains.. but i sold them since i didnt have the money for the subwoofer amp.

i mean..
i would look at the prices to run the amp at full power, and it was consideraly cheaper to run the amp at 75% or 50% .. i would take that route.
i really dont plan on using the 12w7 as a permanent subwoofer in the house.. but that may change in the future.

finding a DJ amp that can power the 12w7 was looked into.. but i didnt see anything mentioning being stable at 3 ohms

i am still thinking about selling the sub and purchasing something with an impedance that is easier to match with an amplifier.
then i would probably get two of them so i have lots of sound pressure.
but i havent had a chance to hear what the 12w7 can do.. and i would like to know what i have before deciding on selling it.

the amp that i had was two channel and offered the ability to play at 2 ohms bridged.
i think the coil was bad and the amp was running off of capacitors alone.. because there was severe oscillation when i turned the gain up.
that might have been good to pressurize the cabin with the oscillation.. but the rest of the output wasnt loud enough.
the extreme moving in and out mixed with playing the requested frequencies resulted in a rather dull output.
so dull that i dont think the subtle details would have made it through the rear seat.

besides, having the subwoofer amp connected caused the other amp to have interference.
i trashed the project and have been wanting to use the subwoofer ever since.
but i wont dare put it in my car without having an amp and speakers for the doors/rear deck.

you said aim for 9 volts.. does that mean rectifiers always add to the voltage?
i understand that if the phase of the AC signal is changing.. a rectifier would force one half of the wave to be the same phase.
which is going from ^v^v^v to ^^^^
and that is why there are still dips in the signal.. which is why the power filter is needed.

thanks a bunch.
you really hit the nail on the head and solved my question.

anyways..
i have felt what AC voltage from the wall feels like.
and those shocking lighters feel different.

am i right when saying AC from the wall looks like ^v^v^v^v^
and the voltage from one of those shocking lighters is ^^^^^^
?
because the lighter felt like it wasnt changing phase.. so i thought i would ask.
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Old 31st January 2011, 05:47 PM   #6
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Location: wigan
Quote:
Originally Posted by richie00boy View Post
Bridge rectifier converts the AC to same polarity but choppy voltage, capacitors then smooth this voltage to DC.

Running high power car amps is generally not a good idea in the home because they need a huge power supply. It is often better and cheaper to buy a cheap or used professional PA amp instead.
I second that
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Old 31st January 2011, 06:02 PM   #7
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Join Date: Dec 2010
Location: wigan
hi again
no one as hit the nail on the head yet. please dont try to make a psu yet.
have a look around in the psu thread and learn a little about them first.
i would wait untill you get your car. That way you have no reason to mess with mains power at the moment. if you want to learn have a good look around this forum then when you get stuck come back and ask.
Be Carefull Regards madMark
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Old 31st January 2011, 06:06 PM   #8
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Quote:
Originally Posted by Andy5112405 View Post
SO SO WRONG - YOU WILL END UP WITH AN EXPLOSION AT WORST.

1. The transformer converts AC voltage from one voltage to another AC voltage depending on the ratio of the turns on its primary and its secondary.

So a mains transformer will, usually have two primaries each of 115V (depending on country of origin). You are from the US so the two 115V primaries need to wired in PARALLEL to give you a 115V AC primary.

This will usually be specified as 0-115 + 0 - 115 (For example RED - ORANGE and BLACK -BLUE). In this case you would connect RED & BLACK together and connect them to LIVE and connect ORANGE & BLUE together and connect them to NEUTRAL.

PLEASE, PLEASE, if your transformer has ORANGE, RED, BLACK and BLUE wires coming out of it do not just connect them as I have suggested.

Many US transformers will only have a 115V primary with only two wires anyway. Only transformers destined for the European market will have dual primaries.

OK - So we have connected the transformer to the mains and the transformer will now transform the 115V line voltage iaw its specifications.

Let us assume that you have a 115V (Primary) - 24V (Secondary) transformer.

The secondary will produce approximately 24V AC, I say approximately because the transformer will behave differently depending on how much current (amps) you are sucking out of it. More about current later.

If you were to connect an Electrolytic capacitor across the transformer secondary. At best you would cause both the transformerand the capacitor to get VERY VERY hot and eventually something would fail, or at worst the whole experiment would explode.

2. You have to turn the AC into DC.

This is the job of a diode or a number of diodes. As you are a total newbie, let's keep it simple. You will need a BRIDGE RECTIFIER.

This needs to be rated AT LEAST THREE TIMES THE AC VOLTAGE so 100V would be a good choice, and at LEAST TWICE THE AC CURRENT.

As we are only experimenting a 100V 5A Bridge Rectifier will prove my point.

The Bridge Rectifier will have four connections, marked ~ / ~ / + / -. It's simple to see that the ~ and the other ~ are the AC connections. The + and the - are the DC output after the diodes have done their magic.

3. Now we have RAW DC.

This WILL NOT BE 24V DC. With 24V AC you will get approximately 24 x 1.414 - 1.4V = 32V DV.

4. Now come the capacitors.

The job of the capacitors is to act almost like a short life battery. The DC voltage still is in pulses, like a camels back, one after the other. What we need to do is store some of the energy that is being provided during the high part of the pulse so that we can iron out the cleavage between the lumps.

Think of them like a battery. As the lump gets bigger its charges up the battery, when the lump gets smaller the battery discharges to fill in the gap.

I'm trying to keep this to REAL BASICs here guys so don't condemn my Noddy explanation.

4. OK - what about current.

The transformer is quite happy transforming 115V AC into (in my example 24V AC). We now have to consider how much current (amperes) we need to drive the amplifier. Whereas VDC = VAC * 1.414. IDC = IAC * 0.7071. If you need 10A DC you will need a transformer that can provide 15A AC.

This is what is meant by the VA rating of the transformer. Within reason you simpy multiply I AC * V AC and add a factor of about 10%. 24 x 15 x 1.1 = 400VA.

5. Back to reality.

You would like to build a PSU to power a 1000W RMS Car amplifier.

If it is a true 1000W RMS (which is unlikely). then we ought to be considering building a 2000W Power Supply.

Most Car Audio is specified to run at about 15V.

So we are looking at 2000 / 15 = 133A.

1. Your Transformer would need to be a minimum of 2000VA at (15 / 1.41)V = 10V

The transformer and the diodes are completely unrealistic. These amplifiers are designed to operate with one or more HUGE car batteries supplying them.
i see you are trying to teach me some tips to get it right the first time.
the first thing i want to address..
if 24v into the rectifier equals 32v .. how do i setup a capacitor bank that will fill in the gaps but not increase the voltage?

the second thing i want to address:
what are these numbers ' 1.414 - 1.4V '
and how often can i use them?

third thing i want to address:
1.414. IDC = IAC * 0.7071
what is IDC and IAC (input DC and input AC ?)

fourth thing i want to address:
I AC * V AC
what is 'I AC' and 'V AC' ?

i dont know how to define these abbreviations to make sense of your effort.
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Old 31st January 2011, 06:17 PM   #9
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Quote:
Originally Posted by madtecchy View Post
hi again
no one as hit the nail on the head yet. please dont try to make a psu yet.
have a look around in the psu thread and learn a little about them first.
i would wait untill you get your car. That way you have no reason to mess with mains power at the moment. if you want to learn have a good look around this forum then when you get stuck come back and ask.
Be Carefull Regards madMark
i got the principle.. and building a power supply is complex, so of course i have already ran into other questions.

then there is talk about inefficiency and also unexpected additions to the voltage.
i think the unexpected additions to the voltage are what is really going to help when i decide to purchase an amplifier kit off ebay.
i dont want the voltage to go over the specified range.
no sense in building something only to connect a couple wires and have it break.

i suppose while i am learning, i should eventually find out why 1,000 watts takes a huge transformer for a car audio amp.. but a home audio amp can run 1,000 watts.
i am already starting to think about bypassing the transformer on the amplifier and feeding it the proper voltage.
and i understand that the parts inside might be low voltage but high current.
whereas the home amplifiers might have parts that are high voltage which makes it easier to find a reasonable transformer.

i have searched the forums on a few different accounts.
people are talking about having very high voltages on the 'rails'
and that has given me a path to investigate.
something along the lines of feeding the transistors the voltage they need from an alternative power source and bypassing the amplifiers original power input entirely.

anyways.. i am not numb to possible problems.
there are questions i have asked in the post above this one.
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Old 31st January 2011, 06:19 PM   #10
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VAC against VDC.

In its simplest terms think of sand dunes.

V (Voltage) AC (Alternating Current)

Is like the bumps in the desert.

What we are after is what is left when everything has been flattened - ie DC (Direct Current).

If AC is specified as the height of the dunes. DC is the height of the flat plain that is left after the bulldozers have been through.

Mathematically VDC = VAC x 1.4142.

The current is the same but oppositely, so IDC = IAC x 1/1.4142.
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