Hi group.
A friend just gave me one hell of a heavy power amp. It is a C.A.S Optimum II. I do believe it is a Canadian made amp.
Rear of casing says it is capable of 1200wrms in 8 ohm bridged. It is in fact a double mono block amp. Very heavy and big. It uses several MJ15025/24 outputs.
It needs care, few outputs and capacitors.
And my question:
The power supply seems unusual. The transfo dont have a center tap at its output. The ground is taken from the mid tap of 2 bank of capacitors (see my attached short schematic).
Also, all the T03 outputs dont have any mica isolators. I tought at first it was wrong since a lot of peoples played in it before me. But after i realised the power supply, it makes me wonder what is its design.
If you have any idea, let me know, id like to fix it !!
thanks
A friend just gave me one hell of a heavy power amp. It is a C.A.S Optimum II. I do believe it is a Canadian made amp.
Rear of casing says it is capable of 1200wrms in 8 ohm bridged. It is in fact a double mono block amp. Very heavy and big. It uses several MJ15025/24 outputs.
It needs care, few outputs and capacitors.
And my question:
The power supply seems unusual. The transfo dont have a center tap at its output. The ground is taken from the mid tap of 2 bank of capacitors (see my attached short schematic).
Also, all the T03 outputs dont have any mica isolators. I tought at first it was wrong since a lot of peoples played in it before me. But after i realised the power supply, it makes me wonder what is its design.
If you have any idea, let me know, id like to fix it !!
thanks
Attachments
Hi Pat Allen,
That amp must be then a copy of QSC amp...
As it has got the following...
Grounded Collector amplifier ....no mica insulators between Devices and Heatsink
AC coupled output as the Transformer has no center Tap..
Follow this link to QSC schematic..for help..
http://www.qscaudio.com/support/library/schems/Discontinued/USA Series/USA400.pdf
regards,
K a n w a r
That amp must be then a copy of QSC amp...
As it has got the following...
Grounded Collector amplifier ....no mica insulators between Devices and Heatsink
AC coupled output as the Transformer has no center Tap..
Follow this link to QSC schematic..for help..
http://www.qscaudio.com/support/library/schems/Discontinued/USA Series/USA400.pdf
regards,
K a n w a r
wow, super interesting !!
the schematics look a lot like what i have...
in the lot he gave me there is 2 Proximity model 500 and a Nikko Alpha 220, all dead, with missing outputs or main caps, but all fixeable with patience.
Any of these amps worth the time to fix them ? (inlcuding the QSC clone ) ?
thanks.
the schematics look a lot like what i have...
in the lot he gave me there is 2 Proximity model 500 and a Nikko Alpha 220, all dead, with missing outputs or main caps, but all fixeable with patience.
Any of these amps worth the time to fix them ? (inlcuding the QSC clone ) ?
thanks.
pat allen said:
QSC Clone could be an intersting project as it could serve your friend with much more reliability....That design is the main key for the Success of QSC amps....
Ok, thanks.
One question remains...i do believe the transistor needs to be "matched " ?
all the base of the transistors are common, there is 6 npn/pnp per channel.
thanks for any other inputs.
btw, i will do a complete reverse of this amp.
One question remains...i do believe the transistor needs to be "matched " ?
all the base of the transistors are common, there is 6 npn/pnp per channel.
thanks for any other inputs.
btw, i will do a complete reverse of this amp.
Hi Pat,
The Nikko Alpha 220 should be rebuilt as something else. I have two and they don't sound great. The original outputs would be expensive to source. Main caps may have leaked. Alpha 440 and 450 are famous for doing exactly that. Someone here on teh forum built a leach clone in a 220 I think. The reports were that they turned out well. PCB layouts for your chassis too.
-Chris
What I am going to say is very important. Those Proximity amps are fire hazards. Don't even think about repairing them! They were made in Quebec. Count those as chassis for future projects.
The Nikko Alpha 220 should be rebuilt as something else. I have two and they don't sound great. The original outputs would be expensive to source. Main caps may have leaked. Alpha 440 and 450 are famous for doing exactly that. Someone here on teh forum built a leach clone in a 220 I think. The reports were that they turned out well. PCB layouts for your chassis too.
-Chris
anatech said:
Thanks for the advices for the Proximity amps, yes they were made in Quebec, well, in Montreal to be precise, which is 1 hour away from me. Those 2 amps were used in a disco mobile long time ago and they did the job well then, and yes, it looks like they turned into huge mess, nothing is good in them but the chassis, heat sinks and transfo. The guy who gave them to me is the original owner, he told me he used them for at least 10 years before they literaly melted
That is back into the 80's 
I am defenitively rebuilding the QSC clone because it is far more simpler, and later the Nikko.
Thanks again.
Hi Pat,
I saw many in the 80's. Each took the speakers with them. The 250's seemed to be popular here. Flames? Yeah!
-Chris
I saw many in the 80's. Each took the speakers with them. The 250's seemed to be popular here. Flames? Yeah!
-Chris
And, to finish...
I made one channel of the C.A.S work, since none of its outputs are dead.
Sounds fair, no bad noises or bad smell. I will put it to test with resistive load to see if it can handle something.
We will see. I will downgrade it a bit, with the transfo of the Prox 500.
My plans are to use this amp in bridged mode with an Alpine dual voice coil 12 inch subwoofer (rated at 1000 wrms/3000peak), and a huge transmission line (know about El Pipo ?)
Thats gona be cool i think.
I made one channel of the C.A.S work, since none of its outputs are dead.
Sounds fair, no bad noises or bad smell. I will put it to test with resistive load to see if it can handle something.
We will see. I will downgrade it a bit, with the transfo of the Prox 500.
My plans are to use this amp in bridged mode with an Alpine dual voice coil 12 inch subwoofer (rated at 1000 wrms/3000peak), and a huge transmission line (know about El Pipo ?)
Thats gona be cool i think.
I remember an amp I fixed for a disco 250 W/ch, but I can't remember the model. The output terminals were shorted because of poor external wiring and not even rudamentary protection. Components (metal film resistors) were "puddled" on the board. 5 shops wouldn't touch it. It wasn't difficult to fix except for finding some parts. I added some rudamentary protection and thump supression.
But, I hated working on some low quality Fisher amplifiers.
One Pioneer receiver kept coming back to this one shop for repairs until they gave it to me to fix for them. I added two varistors across the power supply caps so that the absolute maximum supply voltage of some of the amplifier IC's was never exceeded. It never came back again.
But, I hated working on some low quality Fisher amplifiers.
One Pioneer receiver kept coming back to this one shop for repairs until they gave it to me to fix for them. I added two varistors across the power supply caps so that the absolute maximum supply voltage of some of the amplifier IC's was never exceeded. It never came back again.
Hi Pat,
Those Proximities bring back a few nightmares! I kept one for it's chassis but lost it. Don't ask.
The little Nikko is a nifty little amp. I might try to fix it. As I said, they didn't sound great, but they looked neat.
-Chris
Those Proximities bring back a few nightmares! I kept one for it's chassis but lost it. Don't ask.
The little Nikko is a nifty little amp. I might try to fix it. As I said, they didn't sound great, but they looked neat.
-Chris
I have enough stuff to bring back to life the Prox 250 for free, i will try and if it works, i will see if i can add some active protections or any others improvement. But for now, i am focussed on the C.A.S for my El Pipo project 😀
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