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Old 28th April 2012, 06:13 PM   #11
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very very important : the cable you use from pcb to transistors you need to split it having a flat cable including B C E connections is a very bad thing to do...twisting is even worst .

You need to at least remove the base cable from the pack
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Old 10th May 2012, 08:02 AM   #12
Aniket is offline Aniket  India
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Thanks friends.
I did some changes. Increased the +ve FB resistor to 3.3K from 2.2K.
Increased 3.3K resistor to 5.6K keeping the zener in place. The amp stays cool at idle, but the output trans. get a bit hot while playing music. Sound is really good with crisp treble and clear vocals. Bass is good too.
@Stormrider- KSA3503 are really hard to find, i looked out for MJ15003/4 but they turned out to be fake ON semi's.
@AndrewT- Input trans. are BC556B, please advice if BD139/40 are not good Vas devices. Mention any substitutes.

Regards,
Aniket
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Old 10th May 2012, 10:50 AM   #13
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Look up Greg's data for devices. He has a table of suggested VAS devices with a few oddballs thrown in for comparison.
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Old 10th May 2012, 11:02 AM   #14
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Add a second pair of output transistors before attemting >50 watts output into 4 ohms. "

A Crown D150 only uses one pair and can drive 140W/4Ω, the D150AII was rated at 155W/4Ω.

http://www.crownaudio.com/pdf/legacy...spec-sheet.pdf

The original DC300 would do 340W/4Ω at clip with two pair of 2N3773.
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Old 10th May 2012, 02:51 PM   #15
Aniket is offline Aniket  India
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Please send me Greg's link
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Old 10th May 2012, 03:10 PM   #16
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What is the rail voltages of that crown amp ? Looking at the 2N3773 datasheet, at 50V Vce, you can pull about 3A through a single 2N3773, so up to 50V rails seem to be safe with a 4 ohm load.
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Old 15th May 2012, 05:07 AM   #17
Aniket is offline Aniket  India
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Should i add more output trans. ??
will this increase performance/ power?? by how much?
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Old 15th May 2012, 07:25 AM   #18
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"What is the rail voltages of that crown amp ?"

If I remember correctly, about 50V.

"Should i add more output trans. ??
will this increase performance/ power?? by how much? "

If you like.

If you have a good heatsink and adequate thermal grease and good insulators it is probably OK with one pair.

A second pair would just allow it to handle low impedance loads better, it would probably not put out any more power.
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Old 15th May 2012, 08:10 AM   #19
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Moar OP devices does lower THD alittle though, atleast in ltspice it does.
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Old 15th May 2012, 05:04 PM   #20
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Hello Aniket

A suitable vas transistor sould have a minimum ft of 125 mhz and a cob lower than 10 pf.

Your cdom capacitor of 220 pf are quite much too high value, you should reduce it to 47 pf and also put a 10 pf capacitor between vas collector pin and the base of the second input transistor like in the image I include, this 10 pf capacitor are a phase lead capacitor.

Bye

Gaetan
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