QUASI Amplifier for Beginners

[AndrewT]

A Quasi Output Stage uses either all NPNs or all PNPs.
If you want to use complementary transistors, then choose a different amplifier.

 

[44250]

any help pls give me a schematic of 550B used the complementary c5200/a1943 for the output stage? Thanks

read first few pages of this thread

 

[yehan]

Help,,,, b550' when i put the power 50 0 50, 15 ampere, the mje 350,340 becomes hot even with out load. And resistor 2pcs, 22k 1/2 watts become hot also. What is the problem thanks...

 

[djk]

Is that a 50-0-50 AC at the transformer, or ±50VDC at the filter caps?

22K?

There are three. The only one that should get hot at idle is the one powering the constant current source. Depending on your rail voltage it may need to be rated at 2W~3W. The feedback resistor, if 1/2W, may get hot during test, it should be OK for music.

The MJE 340/350 run class A, hot all the time. Depending on the rail voltage they may need a small heatsink, they may be dissipating as much as 0.75W, you don't want them over about 85°C

 

[yehan]

Thanks djk. How about, when i put the vdc 100 0 100, 15 ampere the circuits not damage? And how much the power? The output trans 10 pair..thanks
I try 5200 2 pair 35vpk sounds good..

 

[yehan]

Is that a 50-0-50 AC at the transformer, or ±50VDC at the filter caps?

22K?

There are three. The only one that should get hot at idle is the one powering the constant current source. Depending on your rail voltage it may need to be rated at 2W~3W. The feedback resistor, if 1/2W, may get hot during test, it should be OK for music.

The MJE 340/350 run class A, hot all the time. Depending on the rail voltage they may need a small heatsink, they may be dissipating as much as 0.75W, you don't want them over about 85°C

50vdc. Thanks

 

[djk]

±50 VDC will have the 22K for the constant current source running with about 0.45W, I would use a 2W resistor. ±65V is 0.77W, I would use a 3W resistor. Most of these size resistors de-rate to zero at 150°C, so running at 1/4th rated power inside a 55°C chassis will mean the resistor is about hot enough to boil water.

Above the design limit of ±65V you will need to change to higher voltage parts for the BC546 and MJE15030/31 and calculate your resistors for the increased power.

I used to buy the blank $6 Pass A40 boards (for the 40W class A design) and change every part on them to run at ±95V with six pair of MJ15024/24 for outputs and 2SA1302/2SC3281 for drivers. It would deliver between 600W/4Ω~800W/4Ω depending on the transformer VA.

 

[yehan]

±50 VDC will have the 22K for the constant current source running with about 0.45W, I would use a 2W resistor. ±65V is 0.77W, I would use a 3W resistor.

Above the design limit of ±65V you will need to change to higher voltage parts for the BC546 and MJE15030/31 and calculate your resistors for the increased power.

I used to buy the blank $6 Pass A40 boards (for the 40W class A design) and change every part on them to run at ±95V with six pair of MJ15024/24 for outputs and 2SA1302/2SC3281 for drivers. It would deliver between 600W/4Ω~800W/4Ω depending on the transformer VA.

I used mje5032,5033' then mje350'mje350, then the bc546 i change to 2sa970 what resistor i change to handle 100vdcpk. Thanks..
Iwant to get 1000 watts in one channel ten pair 2sc5200 output.

 

[yehan]

Mr djk what is the calculation to change higher voltage. I want 100vdcpk. To get higher wattage output. Instead bc546 i change 2n5551, the 2sa970 the pin not the same...help me to apply 100 volts dc supply.

 

[yehan]

help at negative rail fuse always burn when high volume i used 50volts dc 15 ampere

 

[nigelwright7557]

Are you getting oscillation on the lower output transistor ?
I found I had to slow down the lower output driver transistor wit h220pf from C to B.

 

[yehan]

What lower trans? You mean output transistors? Help me for this problem i used 5200, and 1943 complementary.i make short the resistor 100 ohms from mje15031 to the negative rail.

 

[apexaudio]

Hello Mr. Mile,

What's the value of those caps and diodes?

Regards,

DUS = 1N4148
Use this pcb as start point and AX11 schematic with MJ15003/15004 in output... and you will have nice smal PA amp with overcurrent protect (BC546, BC556, 1k, 470R...)

 

[ariyanto]

DUS = 1N4148
Use this pcb as start point and AX11 schematic with MJ15003/15004 in output... and you will have nice smal PA amp with overcurrent protect (BC546, BC556, 1k, 470R...)

good work mr mile?

 

[yehan]

how much watts of this quasi amp. and how much the maximum voltage +-DC and ampere of transformer thanks?

 

[yehan]

to get 550 watts @ 4 ohms what is the maximum power and current of transformer

 

[AndrewT]

Pmax = Vac * Iac = Vac^2 / Rload = Iac^2 * Rload.
Using the middle version we have Pmax = Vac^2/Rload.
Rearrange that to find the output voltage for your 550W target.

 

[AndrewT]

For good economy, reasonable size and good music performance, you can use a transformer rated from 550VA to 1100VA. You choose to suit your budget and the space available.

 

[desertstorm]

QUASI amplifier..

Any body can hepl me where to find PCB layout of apex 550W ORIGINAL version? thank you so much in advance..

 

[wiljj78]

Any body can hepl me where to find PCB layout of apex 550W ORIGINAL version? thank you so much in advance..

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