Low Power Amp

Don't try the Edwin Amp for the sub because it is not strong in that area. Moreover the output is capacitor coupled - although it is a fairly good amp for highs or as a full-range. Remember that it is an (outdated) design of the 1970s but still useful.

Try that TDA1514A. It is a 40w8E/50w4E chip. Drive capability is extremely good. If you are able to get hold of a circuit design by Maplin using this IC, you will be able to achieve a damping factor of 1000 and also bridge the amp for 100w8E.

You won't regret this choice for a very good but low cost sub amp.

P.S. I have some of the circuits that keep cropping up in these pages. I only have Electronics Workbench v.5 for drawing schematics. Can I send these schematic files as attachments for the benefit of those who do not have access to these circuit diagrams. Could someone please enlighten me in this regard. Thanks.
Dear samual
I know edwin is old design. It has output capacitor. But it can removed by +/- dual power supply. I was looking at it from the point of simplicity. Regarding TDA 1514 pulling full 50W from the ic will be OK? Otherwise i think i can go for LM 3886. Which will be better choice now. Either going for Edwin with capacitor removed or LM 3886. Regarding schematics circuit maker is better tool. I use it. Just let me know if u want to know more about it.
a single LM3886 will not be able to meet your requirements unless you can alter the power supply voltage depending on the output load......... hence why i suggested using 2 LM3875 .... they carry a slightly lesser rating 56W not 68W and also have no mute function so they cost less. I like this approach because it is still quite cheap and is very versatile ... and the mute function is usually handled by the preamp anyway, you generally dont need it on the amp chip.

I'll post that schematic tonight as promised.
Here is the schematic it is by no means perfect and the gain may need adjusting for your needs ... more on that later when I post the completed schematic.

LF411ACN run off +/-15V and the LM3875 +/-28V this will give you the power required. I will post a revised version of this soon with volume control and mute function added.


  • lm3875.gif
    19.9 KB · Views: 847
I am currently designing the pcb for my project which is not identical but i can make a couple of changes to it to suit your needs ... I will then post it here. I have not made this as of yet but i will keep the pcb design close to that of the one available @ http://sound.westhost.com just with the added components to hopefully minimise problems ... I will post the completed schematic within a week and a PCB layout next month along with my findings....

The other ic is an opamp LF411ACN made by National to be exact.

You could use the TL072 but this is 2 opamps in the one package which I dont like because of the crosstalk. You could use TL071 which is a single opamp like the LF411ACN but some of the specs are not quite as nice. If you choose to use these parts you may need to alter any pcb patterns I supply to compensate for different pin positions ... also if you use LF411ACN get the ones made by National as they have slightly better specs then the competitors versions.
you are correct. the 2nd and 3rd opamps form inverting servos ... integrators to be precise. also yes the resistor ratios are dependant on the gain of the amp... in the final schematic that i will post in about a week the gain will be adjusted properly for this purpose (@ the moment the amp requires 721mVrms to achieve rated output ... this may or may not change.)

Rated output will be 40W into 6ohms or 60W into 4ohms

I will post complete specs for the amp with the schematic.
Here you go Palesha...

This is very close to finished....

LM3875 use +/-28V
LF411ACN use +/-15V

S1 and S2 form the phase switch and are actually 1 x DPDT switch. When they are in the down position as shown, the output is in phase with the input ... When in the up position the output is 180degree out of phase with the input. If you want a continuously variable phase control i can change it accordingly but there are downsides that come with the added flexability.

S3 and S4 form the mute switch and are actually 1 x DPDT switch.

The circuit sums the stereo input channels then controls phase then volume then mute in that order when moving from left to right.

721mV rms is required @ the +ve terminal of U4 to drive the amp to full power.

Continuous rated power is 30W into 8ohms, 40Winto 6ohms, 60Winto 4ohms.

If you want you could replace the opamps with higher quality ones so long as they are fet input, unity gain stable and have a slew rate of around 15V/us or greater you shouldnt have any problems .... given this is a subwoofer amp it isnt necessary.


  • lm3875.zip
    34.4 KB · Views: 82