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Old 1st April 2012, 04:05 AM   #1
AN214Q is offline AN214Q  Philippines
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Default Classic 150 watts for Modification

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...
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Old 1st April 2012, 05:26 AM   #2
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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.
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Old 1st April 2012, 08:14 AM   #3
latala is offline latala  United Kingdom
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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
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Old 1st April 2012, 09:18 AM   #4
jaycee is offline jaycee  United Kingdom
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You cannot simply just boost the supply with a few tweaks. Look for an amp circuit which is designed for this.
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Old 1st April 2012, 10:05 AM   #5
sreten is offline sreten  United Kingdom
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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.
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Old 1st April 2012, 11:16 AM   #6
AndrewT is offline AndrewT  Scotland
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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.
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Old 1st April 2012, 01:20 PM   #7
AN214Q is offline AN214Q  Philippines
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can we put SOA protection to this circuit? How would it look like, do you think it works?

regards.
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Old 4th April 2012, 12:17 PM   #8
AN214Q is offline AN214Q  Philippines
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Hi,

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

Regards
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Old 4th April 2012, 01:18 PM   #9
jaycee is offline jaycee  United Kingdom
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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.
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Old 4th April 2012, 01:38 PM   #10
AndrewT is offline AndrewT  Scotland
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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.
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