Classic 150 watts for Modification

[AN214Q]

Dear DIY fanatics,

New here, I've got this schematics from school days in the early 90's. Its been long time using this amp at home and planning to upgrade same schematic and power for outdoor use up to 2 ohms.
Original supply was +- 50v . Want to make it +- 75 volts.

DIY experts are invited to join, comment and revise this circuit.


regards...

 

[audiomachines]

the ouput stage could definitely benefit from an upgrade MJ15016/15, MJ15003/4. Wow a 2N3055/ MJ2955 on an 88VDC supply?, those must be originals OP's lucky you.

 

[latala]

this is an old maplin circuit sounds ok but the output transistors are over run as far as the voltage is concerned you can use mj15024/5 with good results
trev

 

[jaycee]

You cannot simply just boost the supply with a few tweaks. Look for an amp circuit which is designed for this.

 

[sreten]

Hi,

There is no point upping the rail voltages if 2 ohms drive is intended.

The circuit has no SOA protection, so it will work into 2 ohms,
for how long probably depends on how heavily its used.

rgds, sreten.

 

[AndrewT]

A 2stage EF is unlikely to perform well into 2ohm speaker loading.

I would not even recommend it for 4ohm speaker loading.

Start afresh with a design suitable for +-80Vdc into 2ohm loading. You are targeting ~120Apk. That is ambitious.

 

[AN214Q]

can we put SOA protection to this circuit? How would it look like, do you think it works?

regards.

 

[AN214Q]

Hi,

I have revised here old circuit, DIY experts are welcome to advice.

Regards

 

[jaycee]

It won't work. The BD139/140 will not withstand the voltage. You will need more than 2 pairs of output transistors to run 500W RMS into 4 ohms - at least 6 pairs of TO-3 devices to be safe.

 

[AndrewT]

Yes, with the BDs there, the rails should be <=+-40Vdc and this would give a maximum power output of ~70W into 8r0.

That would be just right for a single output pair.

 

[AN214Q]

Hi Jaycee, Andrew,

Thank you for the advice, I've change bd's to D669A & B649. would it be works now?

regards.

 

[AndrewT]

Wrong devices for VAS.
649/669 are good drivers.

You need very low Cob, high fT, eg. a1360/c3423

You don't need a high Vce device for q4. A 25Vce would be high enough.

 

[AN214Q]

Sir Andrew,

Thank you for advice.

Can you please edit and modify this circuit, put better parts because i want to test this circuit ...

Regards...

 

[Bong Conde]

@AN214Q sir if you like try this simple design.this can work up to -/+70vdc rail voltage.just add one more pair output transistor.this can handle 4ohms speaker,with a good heatsink & force cooling

An externally hosted image should be here but it was not working when we last tested it.

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