50w @ 8r / 100w @ 4r / 200w @ 2r

[sajti]

I agree, with peranders.

If You desing Your amplifier to give 200W/2ohms, there should be no problem with 50W/8ohms. When I planned my amplifier, I want to make strong amplifier for 240W/2ohms, and less than 1% of distrotion. Of course it will provide 60W/8ohms with very low distortion, and in pure class "A", because of the high bias.

Sajti

 

[costiss]

lets go from the beginning.. so psu
(i lowered the power requirement a bit, as i ll probably not need it)
32Wrms @8R = 2Arms= 2.83 Apeak @ 22.64Vpeak dc plus a 4-6 V drop in the output.. 2 x 28Vdc @ 3A /ch = 2x20V 120VA transformer/ch + 2 x 6800u/ch for 8R
double those figures for 4R ->240VA/ch + 2 x 15000u/ch
same for 2R ->480VA/ch + 2 x 26000u/ch
these are for an amp:
32W @ 8R
64W @ 4R
128W @ 2R
....So... could pleaaaase aaanybody help me now?..... its not really an easy job to design an amp up from the beginning...
requirements are relatively medium, but for the 11.32 A peak rating for the 2R load... deep in thoughts... maybe: 3 pairs of irf540/9540 (seen those in 50W amps @ 8R, so 3 pairs could handle the current... @ 3.711 A peak per device), with the drains on the output (so that the swing can go up closer to the rails)..dont recall who they call this topology... common something i think..
any comments are appreciated... feel free to be rude if sth is toooo b**************y...

 

[millwood]

so your Vcc is about 28v. and peak current on a 2ohm load takes place when the irf is fully conductive. or (28-6)/2=11amp. Both n and p channel irfs will hanle that no problem.

the maximum power dissipation on the mosfet takes place at about half the rail voltage (or 14v) when the output current is about 7amp. power dissipation on the mosfet is about 7amp*14v=100w, less than the rated 150w for those devices.

so one output device per side will work but i usually use a safety factor of two -> a pair each side.

 

[moamps]

Hi,

Once again I will suggest amplifier published in Elektor 10/90 with these characteristics:

Continuous power (THD 0.1%):60W/8E, 110W/4E, 170W/2E
music power1kHz, 20ms on, 80ms off) 200W/2E
THD: from 0.0006% on 50W/8E on 100Hz to 0.06% on150W/2E on 10kHz
IMD:0,05% by 1W/4E
SR: greater then 30V/uS
Peak current: 15A
Output impedance: 0,04 by 10 kHz
PS (monoblock): transformer 2x25V/225VA, elcos 4x10000uF
input devices: SSM 2210,2220
output devices: 3x BD911/912

I was building this amp before ca 5 years. Was very good and stable.

Regards

 

[costiss]

i dont recall of this amp elektor published...i shall have a look there, too... now for the irf idea, i have a preliminary schematic...think im going with three pairs, need the intermediate driver stage . input on the toshiba k389/j109 double jfets. aaaa and the thermal stabilization circuit.... heres what ive got till now..

 

[sajti]

Hi,

I try to use some very cheap switching MOSFETs as output stage. Not good idea The IRF540/9540, or 540N/9540N pairs are not really suitable for audio output. There are very big difference between the N, and P channel devices, even if You apply closed loop output stage, with local feedback.
Lateral MOSFETs are better, but not easy to get them in my country, and the price...
My favourites are the good quality BJTs. For low impedance, and high power You have to use triple darlingtons for the output stage.
My amplifier planned to give 240W into 2ohms. This is 30V, and 15A peak. 4 pairs of MJL21193/94 result some B=60-90 with this current. This means 160-250mA current for the driver MJE15030/31 with this current I can get B=150. The predrivers are BC639/640 with B=100, output current 1-2mA.
Of course this stage is much more complicated than 4-6 pairs of 540/9540, but it sounds much-much better!

Sajti