+ - 42v SUB amp

[-_nando-_]

Hi people !

I won a 200VA Transformer from a friend, and it's 30+30v. As everybody knows, after retification (two 5,000uF 50v, I won too) it gives 42+42v.

I need make an amp to drive a 4Ohms subwoofer, and the sub is 12 inch, 125W RMS, and I want to use that transformer !

I found this amp, and I want to know what you think about it, if it seems to be good...

Please, ignore 1W resistor at the output... I'll use 5 or 10W.

An externally hosted image should be here but it was not working when we last tested it.

And if anyone have a good schematic, please put here !


Thanks !!!!

 

[AndrewT]

Hi,
how did you get that schematic through the 100k limit?

The first opamp should be an inverting topology to give a summing node for the R+L channels.

The power amp looks OK for low voltage rails but I would change the transistors to more modern types and increase the current capacity (doubled output stage) for 4ohm sub use.
I am not sure about the bootstrap? on the input though.
Try Baxandal mod to the quasi output stage.

 

[Tekko]

That schemo is a guitar amplifier, not usable for a subwoofer.

 

[-_nando-_]

That schemo is a guitar amplifier, not usable for a subwoofer.

Yes, that's true, but using two pairs of MJ15003, with 5W resistors, and cutting the mixer stage of, it should be usable for sub. I'll use with an active crossover

Or I'm wrong and this amp is not suitable for sub use anyway?


edit: Does anyone have a better schematic?


Thanks !!

 

[Tekko]

I don´t think it has sufficently good low freq response. Amps designed for just guitar is designed to only work around from lowest 100Hz to acouple of kHz as highest.

Possibly it starts rolling off already at around 100hz which makes it useless for sub.

Look for a bass amp schemo, a bass guitar prolly goes as low as 20hz as lowest which makes it more suited without too mutch modding.

Also a guitar amp also has some distortion as default even in clean mode which will be noticed easily if ran as sub amp.

 

[-_nando-_]

Understood...

This schematic looked so nice... Well uahauha...



I can't find schematics that works with this voltage... Aways more or less than...

This amp must be cheap, I'm spending my money with other project.

Maybe this is a good option:

http://www.ampslab.com/c200_1.htm

But working with 42+42v... The components of this c200 are cheap !

The SUB is 4Ohms 125W RMS... I think c200 with that transformer will work fine...


But, I still looking for other amps to this project.

Let me explain, this project consists:

One LM4780 (60W x2) driving four speakers:

http://www.bravox.com.br/produtos/caixaacustica_mini35.asp

Will be two speakers for each channel, they're 4 Ohms, so 8Ohms for each channel. As you can see in the site, the speaker is 20W RMS, so 60W on 8Ohms will be more than enought. I'll use HIGH PASS.

And onde solid state (or not, depending of what I'm gonna find) amp to one 125W 12" subwoofer, using lowpass.

It will be instaled in a room that my girlfriend teach people how to dance And it will not be played too loud... I think it's a great project, don't you think?


Oh ! I need a good crossover project too !


Thanks a lot !

 

[AndrewT]

Hi Nando,
did you say two 4ohm speakers in series to give 8ohm?

You can run a dual voice coil speaker with the two coils in series but it is a bad idea to run two speakers in series. Slight imbalance due to production tolerances mean the speakers do not equally share the drive signal. They interact with each other and you completely upset the Q of each.

It is much better to run two smaller 4ohm capable amps dedicated to each driver.

 

[AndrewT]

Hi Nando,
most amps can be run from a variety of supply voltages.

You just have to scale some of the component values to ensure the correct operating currents.

The big danger is when you increase the supply voltage above the safe level that the designer has given you.