Gemsound PA-4505 Amp

Eddie Wolve · 8th August 2006, 03:26 PM

Hi all.

Just thought I would post this thread, showing a few internal pics of the Gemsound PA-4505 amp (400 watts -8 ohm / channel). - According to their data anyway...!

I haven't had a good chance to put it through its paces yet, but the power supply seems to be a bit better than the old EXA series.. But I do wonder how you can get "400 Watts" at 8 ohms with less than 63v rails (see photos of power supply caps)..

Leolabs · 9th August 2006, 01:09 AM

Possibly a BTL configuration.

Workhorse · 9th August 2006, 02:08 AM

Hi Eddie,

Its a Class-G amp....2 Transistor pair for upper +-Tier and 3 Transistor for Lower +-Tier..and the Capacitors must be in series Configuration....63+63V assumingly...

regards,
K a n w a r

zeonrider · 9th August 2006, 10:27 AM

Workhose is totaly right.Those 3+3 big tr. is probably BJT, & 2+2 smoller Fet( IRFP 250 ). This is similar construkcion like PHONIC Amps, like PIII 3000/ 2000/1000/600. For example I , have all fabric srvice manual for PHONIC.
Ciao.

Eddie Wolve · 9th August 2006, 01:42 PM

I've always thought that series caps in power supplies was a no- no...Maybe a Gemsound innovation (to save money)...

Has any one got any schematic theory links on class 'G' amps.??

Here's a quote on class G from one of my books from G. Randy Slone "Class G is a novel idea.......in light of the requirement to supply quad power supply rails......".

So I think you nailed it Kanwar... The 63v caps would form part of the quad power supply..

Ed.

Workhorse · 10th August 2006, 03:34 AM

Quote:

Originally posted by Eddie Wolve
I've always thought that series caps in power supplies was a no- no...Maybe a Gemsound innovation (to save money)...

Has any one got any schematic theory links on class 'G' amps.??

Here's a quote on class G from one of my books from G. Randy Slone "Class G is a novel idea.......in light of the requirement to supply quad power supply rails......".

So I think you nailed it Kanwar... The 63v caps would form part of the quad power supply..

Ed.

Hi Eddie,

Here is a link to my Class-H Thread:

The Class - H Amplifier

Class-G uses Multiple Supply rails and also uses Series connected Devices to decrease the heat dissipation and boost the efficiency...

regards,
K a n w a r

Eddie Wolve · 4th March 2007, 02:33 AM

Well.....here is an update of this amp....To cut a long story short, I bought this amp as a back-up, so I never really used it until recently....The amp is rated in it's specs as bridgable at 4 ohm loads..So I ran 2 Selenium WPU1505's subs and the amp lasted about 20 seconds and the power fuse blew, then kept blowing.. The amp was still under warranty, but would cost me heaps just to get it back for service. Anyway, I pulled it apart and found that 3 of the output transistors had blown. THIS AMP IS NOT A CLASS G. As the photo in my first thread shows, there seams to be upper and lower tier OPT's, but the gaps on the heat sink are just for extra OPT's (probably for the higher spec'd model) The OPT's (which are 5200's and 1943's).

Anyway, I have ordered new 5200's and 1943's (plus extra's for the gaps in the heatsink) to make it more reliable and hopefully handle the lower loads better.

By the way, after pulling the power supply out, the supply caps are infact in SERIES.

There you go..DO NOT OPERATE THIS AMP AT 4 OHM LOADS IN BRIDGE MODE...BETTER STILL DON'T BUY THIS AMP.

skygtr · 4th March 2007, 03:41 PM

Eddie Wolve
the amp power supply used +-94V.
see :

skygtr · 4th March 2007, 03:42 PM

the amp power supply used +94V.
see :

Eddie Wolve · 5th March 2007, 07:05 AM

Yep. Thanks SKYGTR..That looks like the power supply..

You wouldn't have the schematic for the rest of the amp so that I may use it when the amp blows up again....

Cheers.

Ed.

9th August 2006, 10:27 AM	#4
zeonrider diyAudio Member Join Date: Mar 2004 Location: Belgrade RS	W is right Workhose is totaly right.Those 3+3 big tr. is probably BJT, & 2+2 smoller Fet( IRFP 250 ). This is similar construkcion like PHONIC Amps, like PIII 3000/ 2000/1000/600. For example I , have all fabric srvice manual for PHONIC. Ciao.

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9th August 2006, 01:09 AM	#2
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Possibly a BTL configuration.

9th August 2006, 02:08 AM	#3
Workhorse diyAudio Member Join Date: Dec 2004	Hi Eddie, Its a Class-G amp....2 Transistor pair for upper +-Tier and 3 Transistor for Lower +-Tier..and the Capacitors must be in series Configuration....63+63V assumingly... regards, K a n w a r

9th August 2006, 01:42 PM	#5
Eddie Wolve diyAudio Member Join Date: Dec 2005 Location: South Hedland	I've always thought that series caps in power supplies was a no- no...Maybe a Gemsound innovation (to save money)... Has any one got any schematic theory links on class 'G' amps.?? Here's a quote on class G from one of my books from G. Randy Slone "Class G is a novel idea.......in light of the requirement to supply quad power supply rails......". So I think you nailed it Kanwar... The 63v caps would form part of the quad power supply.. Ed.

4th March 2007, 02:33 AM	#7
Eddie Wolve diyAudio Member Join Date: Dec 2005 Location: South Hedland	Well.....here is an update of this amp....To cut a long story short, I bought this amp as a back-up, so I never really used it until recently....The amp is rated in it's specs as bridgable at 4 ohm loads..So I ran 2 Selenium WPU1505's subs and the amp lasted about 20 seconds and the power fuse blew, then kept blowing.. The amp was still under warranty, but would cost me heaps just to get it back for service. Anyway, I pulled it apart and found that 3 of the output transistors had blown. THIS AMP IS NOT A CLASS G. As the photo in my first thread shows, there seams to be upper and lower tier OPT's, but the gaps on the heat sink are just for extra OPT's (probably for the higher spec'd model) The OPT's (which are 5200's and 1943's). Anyway, I have ordered new 5200's and 1943's (plus extra's for the gaps in the heatsink) to make it more reliable and hopefully handle the lower loads better. By the way, after pulling the power supply out, the supply caps are infact in SERIES. There you go..DO NOT OPERATE THIS AMP AT 4 OHM LOADS IN BRIDGE MODE...BETTER STILL DON'T BUY THIS AMP.

5th March 2007, 07:05 AM	#10
Eddie Wolve diyAudio Member Join Date: Dec 2005 Location: South Hedland	Yep. Thanks SKYGTR..That looks like the power supply.. You wouldn't have the schematic for the rest of the amp so that I may use it when the amp blows up again.... Cheers. Ed.

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