# Quick question- Voltage increase when rectified

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#### spitso

##### Member
Hi

Just a quick question. When you rectify AC to DC does the voltage increase? If so is there away in calculating this?

Im finding circuits on how to make a 100w audio amplifier and this was written so i was just curious. Does anyone have any good audio amplifier circuits, perferably around 100w and also 2-chanel (left and right)

cheers

#### stevez

##### Active Member
AC voltage usually varies in sinusoidal fashion from zero to a maximum then down to zero to a maximum negative value then back to zero - repeating from there. The value of AC voltage is usually expressed as RMS - Root Mean Square - you can look up the rest from there.

Usually a rectifier circuit also contains a filter capacitor that charges while the diode or diodes conduct. That capacitor will charge to the peak voltage of the AC waveform minus losses for the rectifier if there is little or no load applied. The measured peak value may appear to be more than the AC voltage however if the AC voltage were expressed as peak initially rather than RMS you'd see a slight drop.

Have a look a simple power supply circuits - many of the explanations include graphics to help visualize what I've stated.

#### tcmtech

##### Banned
Hears a 170 watt IC with full specs and circuit diagrams.
Go nuts!

Multiply your AC volts by 1.414 that will give you your peak DC voltage.

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#### chemelec

##### Well-Known Member
Hears a 170 watt IC with full specs and circuit diagrams.
Go nuts!

Multiply your AC volts by 1.414 that will give you your peak DC voltage.
And for Output Current, multiply by .707
But Also Consider Starting with EXTRA Current to allow for Losses in Filter Caps.

#### audioguru

##### Well-Known Member
Here is a 170 watt IC with full specs and circuit diagrams.
The LM4652 is obsolete. National stopped making it when too many of them failed.
Its power was 170 Whats at a horrible-sounding 10% distortion.
It was actually only 70 Watts into 8 ohms and 125 watts into 4 ohms at clipping.

ESP Projects Pages - DIY Audio and Electronics has many pretty good power amplifiers. There are many other audio projects there.

#### tcmtech

##### Banned
I never said it was a good one! He just asked for a schematic. He never specified that he wanted a good one or one that was in current production! What do you expect for free!

#### spitso

##### Member
as the maltese say

Cheers for the help. Please feel FREE to refer any other good/powerful audio amplifier circuits.

#### tcmtech

##### Banned
I my younger days I spent countless hours looking over amplifier schematics. Its how I learned all the electronics symbols and how circuits worked in real life applications.

Once I figured out how the amplifiers worked it became easy for me to boost them for much higher running power both by raising the supply rail voltages and building up the output stages and current handling components.
Drop the output ohms capacity to under .5 ohms. WOW does that give you some punch! your speakers reactance is not always 4 ohms, most amplifiers have a current limiting sytem to keep them stable durring the low ohms points in a speakers power draw.
hense the 8-4-2 ohm ratings.
(this can beat up a cheap speaker rather fast though)

I ran Profile brand amplilfiers. I liked them because they had good sound, simple rugged circuits and could easily be boosted to run at double their factory ratings! Bugged the crap out of the guys with the big name stuff to get walked all over by a middle class brand powered system.
And yes they would over heat and shut down rather fast! The other guys just did not need to know that part!

Learn your electronics! Electronics nerd pays well!

And sinse you were so nice about everything heres 3 amp IC spec sheets, Plus that 170 w is not obsolete! Digikey caries it for around $15 and these other 3 are in there catalog as well for around$15 each.
have fun!

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#### audioguru

that 170 w is not obsolete! Digikey caries it for around $15 1) Google says it is obsolete. 2) National doesn't make it anymore. 3) Digikey doesn't have any today and will not have it in the future. #### Attachments • 41.1 KB Views: 90 #### spitso ##### Member Thank-you for your continous help I'm thinking i might go with tcmtech's 120w (mono) 60w(stereo). I would like to use this as stereo and i believe the attached image is the schematic i should use? Aswell does anyone know the percentage distortion with stereo use. What would be the best voltage you think? Also is this a strong chip, not going to be damaged easily because its quite an expensive ic +$20

thank-you

just quickly went over circuit again...their doesnt seem to be volume control??? how could one be added in without destroying the ic?

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#### tcmtech

##### Banned
Weird, The 170w IC is still in the last catalog. oh well. it must just be a printing error. my mistake them. I did not look for it online.
Just read the rest of the data sheet it tells you everything. you just have to look for it.

#### audioguru

##### Well-Known Member
I'm thinking i might go with tcmtech's 120w (mono) 60w(stereo).
I would like to use this as stereo and i believe the attached image is the schematic i should use?
Aswell does anyone know the percentage distortion with stereo use. What would be the best voltage you think?
Look at the datasheet for all the details. Figure 5 has additional parts to protect it from oscillation.

just quickly went over circuit again...their doesnt seem to be volume control??? how could one be added in without destroying the ic?
Use a 10k log volume control at the input. The datasheet shows it.

#### tcmtech

##### Banned
He is one more I have a schematic for. (my tech info archive is is over 14 gig)
This one is still available at digikey, I checked this time! its about \$13

It should meet all of your design specs needs from small to 300+ watts per channel.

Go nuts! And create alot of smoke while your learning!

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