Hi Jcat,
your 50+50Vac transformer will give just over +-70Vdc at the amp Vrails.
This potentially will give a peak ouput voltage of about 60V into your load.
A 4ohm speaker will draw a peak current of about 15Apk at this voltage as the PSU starts to sag. But with your 2kVA transformer it should not sag too much.
You are asking a lot of 2pair of 2922 transistors. You also need to consider that the minimum impedance of your 4ohm speaker may be 3ohms and if you put a sustained bass note through the speaker at above half ouput power the peak currents are even higher and the power dissipation in the BJTs is enormous (big heatsinks are needed if you use this power continuously)
Just either side of the minimum impedance (in a vented enclosure)is very high reactance where the Vce of the output transistor can nearly equal the Vrail while passing peak current. Then your transistors will get excessively hot very quickly.
For a 15Apk output capability I recommend +-30mF to +-40mF smoothing capacity.
Finally, if you go to 2ohm capability then both the BJT power dissipation ability and the smoothing capacitance need to be doubled.
your 50+50Vac transformer will give just over +-70Vdc at the amp Vrails.
This potentially will give a peak ouput voltage of about 60V into your load.
A 4ohm speaker will draw a peak current of about 15Apk at this voltage as the PSU starts to sag. But with your 2kVA transformer it should not sag too much.
You are asking a lot of 2pair of 2922 transistors. You also need to consider that the minimum impedance of your 4ohm speaker may be 3ohms and if you put a sustained bass note through the speaker at above half ouput power the peak currents are even higher and the power dissipation in the BJTs is enormous (big heatsinks are needed if you use this power continuously)
Just either side of the minimum impedance (in a vented enclosure)is very high reactance where the Vce of the output transistor can nearly equal the Vrail while passing peak current. Then your transistors will get excessively hot very quickly.
For a 15Apk output capability I recommend +-30mF to +-40mF smoothing capacity.
Finally, if you go to 2ohm capability then both the BJT power dissipation ability and the smoothing capacitance need to be doubled.
Hi Jcat,
just ran some numbers through Bensen's spreadsheet for you.
2pair 2922 at Tc=35degC (very cool) can take an 8ohm load to 45degree phase angle and just be on the limit for continuous operation using the DC SOAR. However 4ohm can only go to 24degree phase angle and any power above about half of maximum used continuously risks damaging the output stage due to excursions outside the SOAR. this all requires that you keep all four BJTs at no higher than Tc<=35degC.
A 2ohm resistive test load at Tc=25degC takes the BJTs right onto the DC SOAR. If one were to run slightly hotter due to imbalances you are likely to blow during full power testing.
I have seen a recommnedation to check for instability by loading the amp with a resistive load = half nominal load. your output is unlikely to survive this.
3pair would turn it into an effective 6ohm to 8ohm amp.
4pair would suit 4ohm 45degree phase Tc<45degC loading.
An awfull lot of pairs for 2ohm loading.
just ran some numbers through Bensen's spreadsheet for you.
2pair 2922 at Tc=35degC (very cool) can take an 8ohm load to 45degree phase angle and just be on the limit for continuous operation using the DC SOAR. However 4ohm can only go to 24degree phase angle and any power above about half of maximum used continuously risks damaging the output stage due to excursions outside the SOAR. this all requires that you keep all four BJTs at no higher than Tc<=35degC.
A 2ohm resistive test load at Tc=25degC takes the BJTs right onto the DC SOAR. If one were to run slightly hotter due to imbalances you are likely to blow during full power testing.
I have seen a recommnedation to check for instability by loading the amp with a resistive load = half nominal load. your output is unlikely to survive this.
3pair would turn it into an effective 6ohm to 8ohm amp.
4pair would suit 4ohm 45degree phase Tc<45degC loading.
An awfull lot of pairs for 2ohm loading.
Thankz sir andrew. I gain some knowledge from you. I'll just stop its load until 4 ohms only. coz it cost a lot if i have to use a big transformer, heatsink at they same time the transistor.
I'll try to assemle the leach power amp. Is that a better one? How much i can load with it, sir? how about the power supply unit? Thanks again...
I'll try to assemle the leach power amp. Is that a better one? How much i can load with it, sir? how about the power supply unit? Thanks again...
Sir Tony,
Regarding with my transformer, i'll just check it later on when i go to our province. i ddnt remember of the the center leg and thickness of it. What i remember is that i ordered it in our electronic market here and it is 15A with 50-0-50Vac.
I just want to have a Power Amp that can be as loud as a one unit of power amp being used by a disco mobile.
Thanks sir..........
Regarding with my transformer, i'll just check it later on when i go to our province. i ddnt remember of the the center leg and thickness of it. What i remember is that i ordered it in our electronic market here and it is 15A with 50-0-50Vac.
I just want to have a Power Amp that can be as loud as a one unit of power amp being used by a disco mobile.
Thanks sir..........
jcatiwalaan said:
ok, just to give you and idea, the amps i made in the early 80's had a transformer with 2inch center leg stacked to 3inches, measured 6inW x 5 inchesH x 3inchesD this is for the core alone. this will give you an idea of how yours stack up. my traffos had a 110volt center tapped, biffiliar wound secondaries.
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