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Jointdead 28th December 2011 06:34 PM

Building a gc amp, advice required.

I plan on making a budget amp on the gainclone platform, but I have close to null expirence in making the schematics part. I know how to solder and the basics about components, anyways here are the specs that I'd like for the amp:

1. 2x 40w rms at 4 ohm's
2. 1x 150 w rms at 4 ohm's
3. If possible then one volume control for the 150w and one for 2x 40w.

all help, suggestions and links for research would be apreaciated.

ps. For the 150w chanel I plan on using a rocksford fosgate 300w max 10" woofer and for the 2x 40w some midrange speakers which I havent decided on yet, so again any suggestions are welcome.

AndrewT 28th December 2011 09:01 PM

40W into 4r0 and capable of driving a 4ohm speaker is certainly OK and do-able.

150W into 4r0 is not do-able.

If you bridge some chipamps to allow higher voltage drive, then you get double the power into double the impedance.
If 150W into 4r0 is the result after bridging then you need to build a pair of chipamps each rated at 75W into 2r0 AND capable of driving a 2ohm speaker.
That is outside the capability of the 3886 and any of it's lower powered brethren.

If each of the pair of 75W into 2ohm amplifiers were made from sets of paralleled chipamps (see BPA300) then you can deliver more current.

Let's look at current delivery and current capability.

75W into 2r0 is equivalent to 17.4Vk and 8.7Apk.
The maximum current demand of a reactive speaker can be around 3times the demand of an equivalent resistor.
Expect the 2ohm speaker to demand upto 26Apk on fast transients.
Each chipamp is rated at 7Apk at 25degC operating temperature.
I guess you could make a stab at building a 4chip parallel set and then bridge them into an 8chip BPA400 to achieve 150W capable of driving a 4ohm speaker.
That's why I said "not do-able" earlier.

Jointdead 29th December 2011 05:15 AM

I guess I could do 2 different amps then, one for the 2x 40 chanels and one for the 150w chanel, but on what platform should i build the 150w amp?

danielwritesbac 31st December 2011 05:26 PM

What is the DCR, size, and efficiency of the speaker for the 150w amplifier?
Do you have the model number and/or the datasheet for the speaker?

Boscoe 31st December 2011 09:12 PM

STK4050? It does only specify 8 ohm loads and you need to design yourself some pcbs due to the original suggested application oscillated a lot from what I heard. If your interested I get ya the link I would do anyway I'm just on my iPhone.

danielwritesbac 1st January 2012 05:59 PM

Depending on speaker DCR, the datasheet application of TDA7293V in modular "slave" parallel will do it. On most of the 4 ohm speakers, it may do about 130w or so.

suntechnik 1st January 2012 07:55 PM


Originally Posted by Jointdead (
1. 2x 40w rms at 4 ohm's
2. 1x 150 w rms at 4 ohm's

1. 2xLM3886
2. LME49830 (LME49811)

Jointdead 3rd January 2012 07:06 PM

the specs for the woofer, would be
RMS: 150W
MAX: 300W
4 Ohm
85 db

Rockford Fosgate P1S410

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