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Old 1st September 2008, 11:50 AM   #1
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Default How to determine if class G/H?

Hi,

I was curious about an amplifier that I had in my possssion and decided to pop the hood.

What am I looking for to see if something is class G, H or other?

I'll try to attach some pictures...
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Old 1st September 2008, 12:10 PM   #2
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Even better I found circuit diagrams...

http://www.altronics.com.au/download...2004-07-05.PDF
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Old 1st September 2008, 12:54 PM   #3
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It's probably a Class A/B amplifier.
The schematic shows a fixed + and - voltage of 63 volts.
In Class G or H, the supply voltage would not be fixed.
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Old 1st September 2008, 01:00 PM   #4
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Class H usually has at least 2 sets of Power supply rails. Your schematic shows +/-63V rails. Class H would typically have rails also at twice that voltage +/- 126V with a step system between the rails that would swing the amp up to the higher rail on strong signal demands that would otherwise exceed the lower rail voltage.

QSC's schematics are one example of this. there available online to look at.

Class G i don't know much about???
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Old 1st September 2008, 01:18 PM   #5
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Hi guys,

I'm not an amp building fella, more of a speaker building chump, so I wasn't sure. Thanks for the clarification.

Is there anything else interesting that you can tell from the schematic? Any potential for mods to improve performance?

It's rated at 400W x 2 into 8 ohms, 600 into 4 ohms.

I will try and post some pictures tonight.

It's designed as a PA amp so have cooling fans.

many thanks,
Thanh.
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Old 1st September 2008, 01:34 PM   #6
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Frequency response looks good (I Googled the Model) 10Hz-50KHz -1.5dB.
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Old 1st September 2008, 03:44 PM   #7
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Internals-

Click the image to open in full size.
Toroidal transformers- 5.5" diameter, 2.5" high. CD inserted for scale.

Click the image to open in full size.
Fan forced heatsinks, 5 pairs of transistors per channel.

Click the image to open in full size.
6,800uF 100V capacitors, 6 in total.


I'm starting to doubt the 400W per channel rating.
Surely you would need bigger transformers than that?

regards,
Thanh.
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Old 2nd September 2008, 07:46 AM   #8
djk is offline djk
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400W/8R?

Maybe 200W continuous. The rail votage is 63V, 200W/8R requires 56.6V peak.

I might buy 400W=200W/8Rx2 and 600W=300W/4Rx2.
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Old 2nd September 2008, 09:52 AM   #9
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Thanks. Maybe I should have retitled this thread
Debunking Unknown Brand Amplifiers with Ambiguous Specifications.

:-)

Thanks for the enlightment. This is a DIY audio website after all, and I'm trying to learn. Is there a quick and dirty way to calculate power output given a rail voltage of +/- X Volts?

This is not my own amp, so I'm not afraid of hearing honest feedback.

I've been using it to power my woofer system, and it was beyond reproach.

For full range use however, I don't have a verdict yet.

regards,
Thanh.
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Old 2nd September 2008, 05:43 PM   #10
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After carefully reviewing the specs, the rated ouput was-

"TA 1KHz THD 0.1%"

After reading
http://www.rocketroberts.com/techart/powerart_a.htm

I suspect that rating is peak power.

So this amp is good for around 200W continuous into 8 ohms, which seems more realistic given that the toroids at probably around 500-600VA each...

Now to install some silent fans...

Can anything be done about the switching out the NE5532 opamps?

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