TDA7294 Power Amp, 120Wrms

[Pevlu]

This is my first post!!
Thank you all in diyaudio, many times you've solved my questions. Now it's my time to post mine here.

So I'm trying to make a modular preamp and power amp, the preamp cranked up outputs 1.1V peak (0dbu), and I want to make this signal to go 120Wrms (8 Ohms) using some power amp IC (I've chosen the TDA7294 cause I kinda know its datasheet but if you like another one better, tell me!)

I've made my research and I think that making a brigde setup +/-24Vcc, 40 linear gain, 29dB ,I should be able to get to this level. But what if I use the FX return? Then I could go much higher and then I risk blowing up my speakers.

Can anyone give me some advice? Thank you all in advance

ps. Cabinet I plan on using: Harley Benton G212 Vintage Vertical – Thomann Espana

 

[PRR]

...........I could go much higher and then I risk blowing up my speakers.....

You are in control.

If it is TOO LOUD, turn it down.

If the speakers will not get loud without burning, get louder speakers.

 

[rayma]

I'm trying to make a modular preamp and power amp, the preamp cranked up outputs
1.1V peak (0dbu), and I want to make this signal to go 120Wrms. I think that making a
brigde setup +/-24Vcc, 20 linear gain.

You will need about 6dB more gain to reach full output for 8 ohms, and the preamp would be the best place.

 

[Pevlu]

If it is TOO LOUD, turn it down.

Yeah, but I want to design the circuit to be as safe as possible, I don't really want to dial a pot and check voltages while I'm playing.

 

[Pevlu]

You will need about 6dB more gain to reach full output for 8 ohms, and the preamp would be the best place.

I don't quite understand this, my power amp gain is 26dB so a 1.1Vpk square wave outputs 120Wrms at my speakers.

 

[Pevlu]

I think I've found a solution?!

Supplying this bridged amp with +/- 22V limits the maximum output at 120W at a 8Ohm load as specified in the datasheet, and using the 80-120W range I can get a range of harmonic distortions. If you go further than 120W the amp just clips (I think?)

 

[NanoFarad]

You can go upto +/-25vDC or maybe little more with large heatsink and 8ohm load. +/-25v is recommended by manufacturer. For gain 27dB is a sweet spot.

 

[Joseph K]

I don't quite understand this, my power amp gain is 26dB so a 1.1Vpk square wave outputs 120Wrms at my speakers.

Hm. No. There is no such thing and calculation, like 1,1Vpeak square wave..

One calculates in rms.. 1,1Vrms*26dB gain = 1,1Vrms *20 = 22Vrms. On 8ohm that is 60,5W...

 

[nigelwright7557]

Dont forget bridging means using higher impedance speakers.
If single amp runs into 4 ohms, then bridged it must be into 8 ohms.

Limiting power supply voltage should protect your speakers.

I ran a 225WRMS amp into 200WRMS speakers on a mobile disco for years and they survived.

 

[Pevlu]

Hm. No. There is no such thing and calculation, like 1,1Vpeak square wave..

One calculates in rms.. 1,1Vrms*26dB gain = 1,1Vrms *20 = 22Vrms. On 8ohm that is 60,5W...

Yeah, i kinda messed up the gain value. By 20 linear I mean each IC, so its 29 dB in total so it outputs 120W maxed

 

[chermann]

Hi pevlu

22Vrms means about 31Vpeak Voltage and if you calculate a drop of your supply of about 3-4Volt--> means you need about 35V at your amp boards.
as far i remember... like the LM3886 the limit for 4R using is +/- 29V.
chris

 

[Pevlu]

I get it, but since I'm using a bridged setup, I should be able to get the 120W with such low voltage. But what you say about the voltage supply drop is something I didn't even thought about, so yeah now I see a stronger reason to follow this.

You can go upto +/-25vDC or maybe little more with large heatsink and 8ohm load. +/-25v is recommended by manufacturer.

 

[MAAC0]

Limiting power supply voltage should protect your speakers.

No, it doesn't !! Amp will clip earlier if pushed hard and clipping is what destroys speakers. Tweeters are the first ones to go. An heavy clipping amp for long time blows a speaker with more rated power.

The best protection is incorporating monitoring.
A Clip indicator or a VU tells You what levels You can go up. Even Your trained ears can do it. A DC fault circuit is also handy for catastrophic failures.

 

[Pevlu]

No, it doesn't !! Amp will clip earlier if pushed hard and clipping is what destroys speakers. Tweeters are the first ones to go. An heavy clipping amp for long time blows a speaker with more rated power.

The best protection is incorporating monitoring.
A Clip indicator or a VU tells You what levels You can go up. Even Your trained ears can do it. A DC fault circuit is also handy for catastrophic failures.

I think of making a guitar amp so clipping should be an usual thing to deal with

 

[chermann]

Pevlu
be carefully with accepting distortion at a tweeter! a guitar amp should sound not always clipping

 

[nigelwright7557]

If you are playing against the limits of an amp you can come across problems.
If one track is 0db the next might be a little more and overload the amp/speakers and distort.
Its better to have a more powerful amp and speakers and run it at 50-75%