My new amplifier

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Paco

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Joined 2003
audiohum.com
#1
Hi all,

I finished my new amp and preamp a couple of weeks ago. It’s a 250W single ended mosfet design (not my design). It took me more than two months to finish the amp, since I started sourcing the parts, thinking about how to build the housing and asking the designer how to implement it until I finally had music from it! I’m very happy with the results!

I wanted a high power amplifier that was able to move my 3 way loudspeakers, and a partner top quality preamplifier. I decided to use monophonic high quality PSUs in both the power amplifier and the preamplifier. RCA are WBT NextGen AG and the binding posts are made of gold platted pure copper.

Each channel PSU consist in a 1000VA 50+50V toroidal transformer, 6 Mundorf Mlytic-HC 47000uF caps and one rectifier bridge made with 12 IR HFA15TB60 HEXFREDs in a custom made PCB (I had to triplicate the diodes because with such large capacitors banks –about 0.3F per channel- and due to their very low impedance, even double could explode). You can here some photos.
Regards,
Paco


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.


An externally hosted image should be here but it was not working when we last tested it.
 
#3
Fireplace

Well, in fact the fireplace here in Cordoba useless during most of the year. Right now we have about 15ºC and during the day we will reach 25ºC. With those temperatures the heatsinks of my amp are enought to keep the house warm, they reach about 50ºC after 3-4 hours of work 🙂
 
#8
What Upupa means is that you cannot just parallel diodes and hope that they will share the current equally. Diodes are individuals and their characteristics will differ. That means that one diode may take almost all the current, and you gained nothing from using three diodes instead of one. Maybe it could work if you match the diodes very closely, but I don't know if that would be safe either. Perhaps one could use small resistors in series with each diode, but I have never seen that solution. Perhaps Upupa has some magic trick?
 
#14
Christer said:
But you will have the same problem for the initial surge current, that it may not be shared between the diodes. On the other hand, a single diode can often handle a very large surge current. Check the data sheets.
Click to expand...

Some amount of current sharing is going to happen anyways during highest peaks, but sharing is not equal. I remember seeing(somewhere?) -20% derating for two parallei diodes, ie 2x10A in parallei would result 16A max rated diode.
 
#16
Yes, it's working perfectly. The designer (David White) warned me not to use only single diodes in the rectifier with such big capacitance on the PSU, even more bearing in mind their low impedance (the caps are rated with a ESR of 5 mOhm at 100Hz) . I went the safe way and I built the rectifier bridge for three units in parallel.
Regards,
Paco
 
#17
mzzj said:


Some amount of current sharing is going to happen anyways during highest peaks, but sharing is not equal. I remember seeing(somewhere?) -20% derating for two parallei diodes, ie 2x10A in parallei would result 16A max rated diode.
Click to expand...

Be careful with such rules of thumb, since it depends on the diodes. The reason you may get some reasonable current sharing is that the diodes already have a series resistance. However, that is a resistance that is unavoidable rather than intentional, so the manufacturers try to minimize it. If we don't take this resistance into account, then two diodes of the same type need only differ 20 mV in forward voltage drop to differ a factor two in current.
 
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