A5 behaves strangely

[kirc]

Again me

Give me a hint!
I was replace R40-R42 and R64-R66 from 1ohm to 0.8ohm and bias is higher. Bias is now more then 3A. Can I do fine twaking with R19 ? Is this a correct way ?

many thanks,
Leon

 

[wuffwaff]

Hi,

this is the right way

William

 

[Stabist]

Wuffwaff - now one Q from my side ...
this problem that Leon situated with - is it only the consequence of "built in" charachteristics of transistors - or is it also consequence of the fact that PSU voltage is for 2V lower than in original design??

 

[wuffwaff]

Stabist,

2V power supply voltage has very little influence. The current through R19 will change a bit because of the different voltage but this will be very small.

William

 

[kirc]

Now I replace ZTX450 with BC550C, but there is still no more than 1.6A of bias per rail.

I will put additional resistors in parallel with R40-R42 and R64-R66 to have about 0.85ohm. This will give more bias - and then I'll trim it with R19.

Let's go to work

 

[kirc]

Now I have about 2.1A bias per rail. Yupie
Thanks for help - for now

Leon

 

[kirc]

Now I was tested a new configuration and power on 8ohm is about 52W, but there is only about 25W power on 4ohm load.

I was replace a R21 with trimer pot, but I can only lower power on 4ohm, no matter if I increase or deincrease R21. What can it be wrong now ???

please help ?

This is sinewave output on 8 ohm load. Good for me, but just a half of that power on 4 ohm load

 

[wuffwaff]

Hi Kirc,

2.1A with 50% ac-current-gain should give around 50 watts 8 ohm (voltage limited) and 35 watts 4 ohm (current limited). (4.2A peak current)

25 watts 4 ohms means only 3.5A paek current or 1-2.1/3.5 = 40% ac-current-gain

To get 90 watts 4 ohms (if you want that) you must raise peak current to 6.7A. With 2.1A bias this means around 68% ac-current gain. .

To get this you must lower R21 until 68% of the ac current flow through the upper source resistors and 32% through the lower source resistors (at 10 watt 8 ohms for example)
Try something like 390 ohms for R21.

William

 

[rchua77]

Hi,

I have the same problem with the positive sine wave being squared off when i pass a sine input signal through my Aleph5.

I'm not too sure if I understood the solution correctly, decrease the 1 Ohm source resistors of the output MOSFETs?

Is there other methods of solving this problem?

Regards