How many pairs?

[kasiss]

I'm building an amp with 4 pairs of transistors (2sc5200, 2sa1943)
I'm litle confused wit SOA of them

What power supply voltage cold they handle for 8ohm and voltage for 2ohm load? (at max output power)

I red, that forfor that number of devices on load it is ~ +/- 55V (Is it true?)

pls help ....

 

[AndrewT]

Hi,
just ran some numbers on 4pair 1943 @Tc=40degC

they can run to 185W into 4ohms at a phase angle of 60degrees. and be on the DC SOAR limit.

They can also push about 285W into 2 ohm at the same 60degree phase angle but this time they exceed the DC SOAR and are half way towards the 100mS limit.

A good indication of their suitability is what they can achieve into half load impedance. Into 1ohm 450W at 45degree phase angle but this time two thirds towards the 100mS SOAR limit.

the 2ohm and 1ohms loads were @+-43Vrails the 4ohm was +-45Vrails.

With +-55Vrails 145W 8ohms just outside the DC SOAR,
270W 4ohms well outside the 100mS SOAR.
470W 2ohm 22degree phase @DC and 40degree phase @ 100mS.

I usually design for DC SOAR with VI limiting, but other say I am too pessimistic and recommend 100mS.
You choose how reliable you need it to be.

BTW. into low loads and driven hard, big sinks will struggle to keep the Tc at or below 40DegC.

 

[matajumotors]

With +-55Vrails 145W 8ohms just outside the DC SOAR,
270W 4ohms well outside the 100mS SOAR.

Pls tel me how can i see or calculate it?

is the +-55Vrails 145W 8ohms for 4 pairs?

If i wold like to feed it with +/-60V ? What "safe power" i cold get?

 

[AndrewT]

Hi,

numbers on 4pair 1943 @Tc=40degC

this says so.

 

[csl113]

i think that the suply voltage should vary with the topology...

i mean that you can't put 4 pairs at the same voltage if one is in class A, one in class AB, B and H , there is a different voltage for each...

for exemple i wanted to see how high could i run a amp that had only one pair of 2sc5200/2sa1943.....at +/- 60V at a 8 ohm speaker load i couldn't blow it, but at +/- 68V it finaly distorid itself...

amp's with 4 pairs i run them at +/- 80V, and they run smoothly with 4 ohm loads ,and +/- 90V max in 8 ohm

a amp that had 3 pairs at +/- 80V runs 8-10h/day at near maximum for more then 10 years in a club and it never faild so far... (inside a 8 ohm subwoofer)

p.s. none of the above amp's had any VI limiters, only termic protection

 

[AndrewT]

Hi,

amp's with 4 pairs i run them at +/- 80V, and they run smoothly with 4 ohm loads ,and +/- 90V max in 8 ohm

I told you that others say I am pessimistic.

 

[jacco vermeulen]

i think that the suply voltage should vary with the topology...

Yeah, opinions may vary.

Here's a picture of one with 6 Sanken output devices, the 150 watt versions, 2SA1215/2SC2921.
This one is 50 watts class A and 200 watts/8 Ohms in class AB.
You can imagine the size of the powersupply yourself. SK56 heatsinks(300mm long), 0.36 C/W. These blocks do not require a suitcase of spare fuses.