Using a 50v single supply (and trying to split it) with LM3886

[AndrewT]

Hi,
what values of capacitor and resistor gave you half an ohm at 20Hz?

Do you need half an ohm?
I doubt it.
If you are driving 300ohm headphones you definitely don't need half an ohm.
Is 20Hz a good choice?

 

[Rainwulf]

This thread has lost track of itself.

I think the OP has left for greener pastures.

As far as i know, its not possible to run an LM3866 on a virtual earth system using resistors due to the earth being too high an impedance. If you were to use that virtual earth as the termination point for your speaker, its AC impedance will be very low, which is fine for the speaker, but the voltage will jump around, making it useless for a virtual earth.


Sounds ok to me?

 

[405man]

If you look here http://www.quad405.com/ at the Quad 606 schematic the supply is activly split from a single supply.

Stuart

 

[bobodioulasso]

.Hi
Here is my reasoning

At first glance, this seems to be nothing but a split PSU, however, any circuit can be seen from differents points of view.
Mine, here is:

In a single supply power amp, you can move the output cap after the the speaker (i.e. between speaker and ground). Does It changes anything? I do not think so, as the two devices are serial connected. Here is the crucial point.

If you say the junction speaker/cap is sagging, I answer no, because here is applied an audio signal vith an average of 0v. The losses at lower frequencies are not worse than in the normal configuration.

Here we are half way of this circuit.

Now, add a second cap as described. This will not hurt as long as we add two resistors to avoid the dc drift because the caps are not perfectly equals and as long as the average audio signal is oVolt.
We even double the output cap, doing this and lower its impedance .

Please, tell me where i am wrong.

regards

 

[bobodioulasso]

i suddenly realise that the misanderstanding comes certainely from fact i describe a single supplied power amp vith these two caps, not a double supplied one.

 

[mudihan]

To the OP: Is it at all possible to separate the left and right channel ground on the headphones?

It does not seem possible at this stage, unless I redo the whole thing. The circuit board jointed the ground.

This thread has lost track of itself.

I think the OP has left for greener pastures.

I am just reading admirably in the background . Though I have to say that I am pretty set with just getting a new transformer. I do think however that the discussions here are quite educational and may provide great use for someone else.

 

[bobodioulasso]

If you look here http://www.quad405.com/ at the Quad 606 schematic the supply is activly split from a single supply. Stuart

Thank you Stuart. Quad 909 too. We cannot see for Quad 707 but i guess it is the same.

 

[bobodioulasso]

IMHO, in this Quad PSU the two transistors maintain the drift more firmly in case of too big a difference between the two smoothing caps (qetting old, drying) making the amp more reliable. With caps in good condition these can be short circuited. Here we are to my circuit, with these 2k2 i suggested.
Amazing!