John Curl's Blowtorch preamplifier part II

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#90,781
Hello guys can somebody answer my question : im trying to mode my parasound hca-3500 i have no experience but want to do it
im looking to replace c8,c16 diode bridge for fairchild hyperfast diode
question is the bridge has 4 contacts 😛lus , minus and 2 of them goes to fuses , but fairchild has 2 contacts and some of them 3 . can somebody help me to solve this puzzle and tell me which i have to buy and how to plant it on the board
thank you
 
#90,782
Hello guys can somebody answer my question : im trying to mode my parasound hca-3500 i have no experience but want to do it
im looking to replace c8,c16 diode bridge for fairchild hyperfast diode
question is the bridge has 4 contacts 😛lus , minus and 2 of them goes to fuses , but fairchild has 2 contacts and some of them 3 . can somebody help me to solve this puzzle and tell me which i have to buy and how to plant it on the board
thank you
 
#90,783
The bridge has internally 4 diodes. Check the schematic of a bridge.

If you want to replace it with diodes, you need either 4 separate diodes (with 2 pins) or you can use two dual-diodes (with 3 pins), these are internally 2 diodes, sort of half bridge.

Be careful if you want to use dual diodes that the polarity (direction) of the diodes is correct; some are pointing towards the middle pin, some away from the middle pin.

Are you familiar with how a diode works?

Jan
 
#90,785
Hi djovanny,
I'm not trying to upset you, but why are you attempting to perform a task you don't understand with parts that you don't understand? This seems to me like a recipe for disaster.

I'll respectfully suggest that you allow an audio service technician do the work for you. It's cheaper in the long run, and it will be done properly.

-Chris
 
#90,788
This time I have to reluctantly agree with Jan that changing out the diodes is a difficult task to keep track of. I actually have to do it, once again for a Vendetta Research power supply upgrade, tomorrow, and my tech and I have to sort out the diodes and their directions to replace the diode bridges. It is a hassle, even for me.
While I do believe that faster diodes are better, there are more important changes than this for the 3500 to improve it. The primary feedback resistor, for example.
 
#90,789
john curl said:
This time I have to reluctantly agree with Jan that changing out the diodes is a difficult task to keep track of. I actually have to do it, once again for a Vendetta Research power supply upgrade, tomorrow, and my tech and I have to sort out the diodes and their directions to replace the diode bridges. It is a hassle, even for me.
While I do believe that faster diodes are better, there are more important changes than this for the 3500 to improve it. The primary feedback resistor, for example.
Click to expand...

John I will make a note that on this day in this year you actually did agree with me 😎

Seriously, maybe you can do that mod on the OP's 3500. Don't know your rates but why not?

Jan
 
#90,791
Thank you guys for your help , Jhon , replacing r 44 was first task on the Phil's list of upgrades and i just finished it , result was so significant that i deside to continue and replacing diods is a second on the list , i will pass on this since its above my head and will do the rest of upgrades which i will be able to handle, but this amp is a master peace i mate it with aerial 8b and adcom gfp 750 and they sound amaising for the price
 
#90,793
kamis said:
Changing diode bridge with dicrete diodes is a trivial task for average DIY builders compared to some SMD soldering. Point to point wiring with short diode leads is the best method.
Click to expand...
I'm not so sure about that. If the Vendetta Research preamp uses a 1 amp bridge in the RB-15 package {figure attached}, that's an awfully tiny patch of real estate in which to fit four DO41 axial lead devices. Study the mechanical drawing: the lead-to-lead spacing is less than (1/4) inch! And remember that you need to connect four diodes with a total of eight leads, to the four pins of the bridge. If the vertical clearance in the enclosure happens to be small, forget about it.
 

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#90,800
Hi Mike -- Sorry for not responding to your PM sooner. I've made many modifications to my HCA-3500s and changing those diode bridges was the hardest. The bridge is an MB354 or similar and soldered to the bottom of the power supply circuit board, and bolted to the chassis for heat sinking. I would not take the approach in the picture which just puts a capacitor across each diode of the original bridge rectifier. A simpler approach than replacing those diode bridges would be to put a RC snubber across each leg of the bridge. A snubber would typically consist of a resistor and cap in series, usually 5-10 ohms and 0.01 to 0.1 uF.

As for that cap, 200VDC rating or above is fine. It replaces all those metallized polypropylene caps after the voltage regulator for the front end of the circuit. You could get away with using high-quality polypropylene and foil caps of the same value.

There's about 100 parts that get cut out of the HCA-3500 and another 80 or so that get replaced. I did not change the circuit or transistors except for the the DC servo.
 
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