| Eddie Wolve |
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).. |
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| Leolabs |
| Possibly a BTL configuration. |
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| Workhorse |
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 |
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| zeonrider |
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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| 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. |
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| Workhorse |
| 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:
http://www.diyaudio.com/forums/show...&threadid=68415
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 |
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| Eddie Wolve |
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. |
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| skygtr |
Eddie Wolve
the amp power supply used +-94V.
see : |
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| skygtr |
the amp power supply used +94V.
see : |
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| Eddie Wolve |
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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| sakis |
watch it my friend i have the exact same amp with simular problems and when i had to repare it i just end up with a full box of fake transistors ......
be very very carefull where you buy them from
sakis |
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| Eddie Wolve |
Thanks Sakis.
I actually wondered if I had genuine transistors in the amp in the first place!!!, which may have been why it blew the first time. I have a reputable supplier in Australia so hopefully I won't get ripped off. I guess I will soon find out. I'll certainly make another post if I have problems..
Cheers.
Ed. |
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| The Saint |
Hi Eddie
these type of manufactures often lie about they specs .
there is no way this amplifier would handle 2 ohms.
If it wasn't class G or Class H
With +-94 volt rails 3 pairs of output devices would be lucky to
handle 4 Ohms.
I think you are correct in assuming that it is not class G or H.
I have a bunch of 2SC5200 and 2SA1943 Bipolars.
and they are the real deal.
Contact me via my web site if you want a price.
once again you may have damaged drivers as well. |
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| Eddie Wolve |
Thanks Anthony.
I have already ordered the opt's through Wes Components ( I have a trade account there..) But you can probably read between the lines...that is, My Amcron finally gave up the ghost and when I went to use my brand new spare Which I have carried arround for the last 7 months (ie the GemSound 4505), that died as well....! Oh well that will learn me.
As it turns out the NoSound err sorry GemSound 4505 has quite beefy driver transisters, they are Toshiba 2SC5198 and 2SA1941, (with a 140v and 10amp rating) and seem to have tested OK in circuit. See how we go.
Ed. |
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| sakis |
my amp i thing was also constructed with fakes so thats way they met the creator so fast .....from looks and only the looked cheapy made to me also ......
also in my lab exist a chinese made amp called limit full of these kind of transistors also gone with the wind ...
onother called agusta chinese italian factory with exact same problems
i have been unable to get A1943 and C 5200 that are guarrantied in a resonable prise so i am really tempted to put inside legend 8 boards from bora
will see about that at this point seems that i have made somethings wrong while constructing them so i ma still looking at it |
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| Eddie Wolve |
| Good luck with your search...Sakis. Maybe you could try Anthony, (previous post on this thread) for your 5200's and 1943's....By the way, what price are you paying for these over in Greece...? |
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| sakis |
well a was asked to pay 4.10 euros each and these people claimed that semiconductor was made by HARRIS meaning that its supposed to be a fairly relable and good semiconductor.....and also minimum order 200pcs and delivery after 2 months !!!!!! expensive i think !!!
other provider asked about 3.90 for toshiba but there was a hell of a lot of fake noise arround them .....
funny also story somebody gave me 3.50 euros for the one trs and 5.10 for the other of same brand ...fairchild i think ....and thought how the fu** this can be possible for complementary trs ????
any way greek market can often be strange about things like that ....
still working on boras legend 4 and legend 8 that looks so nice and simple BUT NOT MANAGED TO GET IT RIGHT YET ,......LOL !!!!!
but i am working on it ..... with passion !!!!!
given the opertunity i dlike one more time to thank bora for his very much help so far and this wonderfull community and all this nice people existing here THANKS PEOPLE !!!!!! |
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| skygtr |
| gemsound powerAMP SCH, |
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| Eddie Wolve |
Thanks SkyGTR.
It's a little different, but it is certainly a great help. |
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| Eddie Wolve |
OK....Just an update..
Put in new (and additional) output transistors as the photo shows. And replaced all the mica washers for silicon rubber ones.
As it turned out apart from a diode which also blew that's all that went pop..
Put it on a load test and she seems to be working OK...But haven't (and wont) put her on 2 ohm loads....
It does run very warm however...
Anyway see what happens.
Ed |
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| Nordic |
| I recently built the DX amp useing fake 5200 and 1943s... no problems yet... |
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| dj_krypt |
Anyone around the Newcastle area able to take a look at my 4505. I had been using for around 2 months as my main amp with out any issues. It pretty much got daily usage. So i packed it up because i got a new setup.
Unpacked it Saturday night at a gig. Wired it up flicked the switch and POP. Brief blue spark was seen in the front of the unit and both fuses were blown. I unplugged everything from the amp and switched out the fuses with new ones which also blew.
So yeh if someone can recommend someone around the Newcastle area that would be great. |
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| Eddie Wolve |
Sorry DJ I can't help you out there mate... I don't know how much your knowledge is when it comes to amplifiers etc... But when you do get it fixed, I STRONGLY encourage you to have the serviceman insall another pair of Output transisters... It is a bit more work, but these amps are designed on absolute limits of the component ratings (probably not even sufficient) and a bit more load sharing of the OPT's will add to the reliability... Notice I did call this amp 'Nosound' NOT Gem sound in an earlier thread...
Goodluck....
Ed. |
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| wg_ski |
| quote: | Originally posted by Eddie Wolve
OK....Just an update..
Put in new (and additional) output transistors as the photo shows. And replaced all the mica washers for silicon rubber ones.
As it turned out apart from a diode which also blew that's all that went pop..
Put it on a load test and she seems to be working OK...But haven't (and wont) put her on 2 ohm loads....
It does run very warm however...
Anyway see what happens.
Ed |
Just make sure you put in the emitter and base stopper resistors for the extra OPT pairs, or the extra expense will be for nothing.
An older QSC of similar rating (400/ch, 8 ohms) with the same supply rails uses 8 pairs of MJ15024/5 outputs. Those will almost never blow outputs, even when running 2 ohms, but the associated heat produced will cause them to cut out in the middle of gigs and have electrolytic cap failures.
The amp lasting only 20 seconds with only 5 pairs is par for the course. |
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| wg_ski |
| quote: | Originally posted by Nordic
I recently built the DX amp useing fake 5200 and 1943s... no problems yet... |
Wouldn't expect it to. With only +/-38 volt supplies you could use 2N3055's and it would hold up. Distortion might be a little higher than with the better transistors, but the SQ of "blameless" amps tends to be more a function of the front end and proper layout techniques. |
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| dj_krypt |
| Hi Eddie, I've got a mate looking at my amp whose a bit of guru when it come to these things. What do u think of the idea of putting higher rated OPTs rather than the extra ones? Exactly whats involved in adding the extra pair? Also what kind did u replace yours with? And how's it testing up? |
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| Eddie Wolve |
Hi DJ.
There are probably plenty of others in this forum more qualified than me on that topic, but I also considered replacing the OPT's with higher rated ones, but at the end of the day, there are not many 'off the shelf' OPT's here in Oz that are actually more rugged than the 5200's and 1943's, and reasonably priced. At the end of the day, the original circuit was designed for these OPT's (ie power supply voltage, protection circuitry etc).. Plus it saved me having to replace 24 pairs of OPT's...
All I did was replace those horrible mica washers, cleaned the heatsink up, (got rid of all the burrs etc -), added the extra components to the Power Amp main PCB (ie Emitter and Base resistors) and added the extra OPT's. I also slightly increased the quiescent current to account for the extra OPT's... (I had the 2nd channel to determine what the bias current was and just increased the fixed channel to suit).
So far it has run OK, on 4 ohm loads, but I haven't pushed it that hard (ie clip leds just flashing sometimes) and it has not missed a beat (So far....) It does get very warm however...But I would NEVER run it in Bridge mode...
ALSO, check the main supply fuses.... Mine had 2 x 15Amp fuses...out of the box, so was probably ment for 110V supplies.. I changed them to 7 amp and they have not blown yet...
Good luck and let me know how you went... |
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| dj_krypt |
| Thanks heaps for all your help Eddie. Just wondering where you sourced your 2SC5200's from and how much you paid? |
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| Eddie Wolve |
Hi DJ..
I have a trade account with Wes Components, but they have a retail store here :
http://www.wagner.net.au/
As far as I know, they stock the real Toshiba OPT's, not cheap copies.... The trade list price is $6.45 each, so you might pay a bit more...
Regards,,
Ed |
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| dj_krypt |
| A diode also blew. Does it matter what type i use to replace it? I know it has to be heavy duty. Just wondering if there is a difference. |
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| Eddie Wolve |
That's a really hard question to answer without knowing what diode it actually is..!
If you read my earlier posts in this thread, you will find I had one go pop too, that was just a standard rectifier type diode... a 1N4007 from memory.... It has a rating of 1 amp.. I would not change this, as it turns out, it acts as a type of protection when it goes 'pop' (ie shorts out causing fuses to blow) from memory...
If you 'up-rate' the diode it may cause other (more expensive) components 'down circuit' to blow if you have a similar fault occur in the future..
Read the markings on the diode, if that's what it is, I would replace with the same one... If you want to up-rate it, go for a 1N5408 (3 amp) one..
Regards,
Ed. |
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