Power supply Capacitors

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#41
lopan said:
vdi nenna

The caps will not drawl much more voltage (there may be a peak voltage...I'm not 100%, most likely!)

Just for clearity sake one does not draw voltage as it is a potential -- one does draws current and this is what can destroy the bridge
Click to expand...


A friend is supposed to be sending me a copy of the schematic. Hopefully we will know more, once it arrives. I've tried lookng for the bridge but with this design I haven't been able to locate it. I'm hoping the schematic will clear that up.

Blessings, Terry
 
#42
The soundcraftsmen amps use what is called a PCR or Phase Controlled Regulator Power supply.

The Regulator works light a cheap light dimmer!

it uses SCR's to switch the ac wave off and on during the ramp up and ramp down portion to regulate the voltage at +/-70Vdc

Im not explaining this well....let me try again...


The transformer with no load is around 90V or so i think.

Under light load, the PCR switches off the wave early in the cycle. It monitors the voltage rise on the upswing of the sine and when it reaches 70V it shuts the SCR off and uses the capacitor to hold the voltage up until the next sine comes along.

Under heavy load, the PCR switches off the wave later in the cycle, or even allows a complete wave cycle to maintain +/-70vdc under load.

So the caps are critical! and 11,000uf is barly large enough (IMHO) for a design that is 200+wpc. I doubled that in my modified 800's and added bypass caps.


It is a very interesting regulator design. Cheap, Efficient, very little power gets dissapated as heat. and as far as i can tell, has little negative effect on audio.

Im sure that there has to be some switching noise involved, wouldnt there be???

as far as i know. no other company ever used this design!

I have the schematics for these amps. i could post the Power supply schematic here if anyone wants to take a look and comment.

I have been fascinated with these amps for many years now. Fun, cheap, little ******s that sound pretty darn good.


Zero 😎
 
#46
I'd like to see the schematics

Hi Zero,

I really would like to see the schematics if you would be kind enough to post them or email them to me.

still4given@yahoo.com

I recently received caps for the Hafler amps I have been fixing. Just to test, I install two of them in the Soundcractsmen amp. I played very nicely. the caps were running about 67VDC each. What a fine sounding amp. Better than my Haflers to my ears.

Only problem is that these caps are too tall for the Soundcraftsmen. It needs 2" X 3.625". The ones in the Hafler are 4 1/8"

Zero, When you increased the uf did you do anything to the bridge? I found some 18000uf caps that will fit but I was concerned with overloading the bridge.

Thanks, Terry
 
#47
Well the "Bridge" you speak of, is not a bridge rectifier in the traditional sense. the bridge is made up of 4x 10 amp 400V SCR's

10 amp SCR's i have found to be plenty, but you can upgrade them to 12 amp or higher if you can find them in the same TO-220 style case. (im using some BIG 60 Amp industrial monsters in a test unit).

A bigger improvement is to upgrade the heatsinks on the SCR's. Stock is a round washer or rectangular piece of metal. I found some nice aluminum heatinks that allowed them to run a bit cooler. Be care full as there isnt much room in there and the +/- terminals and trasnformer connections are right there!!!

Also watch out for those solder lugs! the solder pads likes to crack! I removed them from my board and soldered the wires directly to the boards on the bottom side. this allowed more room on the top side.

I will have to hook up my scanner again, once i do i will scan the schematics and send them to you!


Zero 😎
 
#48
Zero Cool said:
Well the "Bridge" you speak of, is not a bridge rectifier in the traditional sense. the bridge is made up of 4x 10 amp 400V SCR's

10 amp SCR's i have found to be plenty, but you can upgrade them to 12 amp or higher if you can find them in the same TO-220 style case. (im using some BIG 60 Amp industrial monsters in a test unit).

A bigger improvement is to upgrade the heatsinks on the SCR's. Stock is a round washer or rectangular piece of metal. I found some nice aluminum heatinks that allowed them to run a bit cooler. Be care full as there isnt much room in there and the +/- terminals and trasnformer connections are right there!!!

Also watch out for those solder lugs! the solder pads likes to crack! I removed them from my board and soldered the wires directly to the boards on the bottom side. this allowed more room on the top side.

I will have to hook up my scanner again, once i do i will scan the schematics and send them to you!


Zero 😎
Click to expand...


Hey, that's a good idea, moving those underneath. I'll have to look at that. May I ask what size the bypass caps were that you added when you increased the size of the caps? Did you just bridge them across the filter cap lugs?

Also, you could fax the schematics to me if that would be easier.

310 865-9934

Blessings, Terry
 
#50
P.S. i put them across the tops of the screw terms on the top of the boards, but i added bypass caps tot he SCR's on the bottom of the boards...kinda fugly...but it works...


I will dig the scanner out as i would really like to get a thread going and some comments on the PCR design!!!


Zero
 
#56
I own a pair of Soundcraftsmen PCR800 power amps.

Recently the amp used for the right channel has been slowly losing gain and depth of bass. When shut down and with a signal still running the amplifier drops out much faster than the other amp. Also there are a pair of LEDs that light up when the power is shut down and glow untill the caps drain. The lights now go off immediately.


I don't know if the problem is from dieing power supply caps, or bypass caps, or???

Any ideas?


Thanks,

Bob
 
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