Aleph Jzm Kit Build Support

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#42
Very close to completing my build Transformer is a Toroidy TS 300VA 240V sec 2X18V What will be the Rs value on the snubber PCB ? one in the Quasimodo results is listed as 230 volts not sure if 10 extra volts will make a difference. that was 12R.

Thanks
 
#43
^ Hi Alan - This really belongs in the Quasimodo thread, but it may be helpful to others. So, as long as we don't veer too far OT, we can leave this ONE answer here. If others feel compelled to chime in, we'll move it to a more appropriate thread.

The snubber resistor value (Rs) for a typical arrangement (you didn't mention what schematic you're using, but don't worry about it).... is INDEPENDENT of the actual mains supply voltage. However, it absolutely depends on the arrangement of the primary winding(s). This can be confusing because often people may refer to a dual primary arranged in parallel as "115V" and a dual primary arranged in series as "230V" or some other.

tl;dr - If that transformer has a single primary configuration and the person providing the value used the same transformer model number; rock on and use 12R.

For some additional information, those that are interested can read Mark's exceptional document in the first post of the Quasimodo thread.

https://www.diyaudio.com/community/...rmer-snubber-using-quasimodo-test-jig.243100/

One section of particular interest is copied below.

Note that the transformer referenced is from Figure 9 on Page 8 and is a DUAL primary configuration.

1725625333744.png


1725625286508.png
 
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#44
Building the Aleph Jzm using the power supply from R. Thatcher.

I have finished building this power supply and have a problem.
The power supply seems to be working properly, both rails measured +-26.3V and +-26.4V without load. The problem is both the LEDs did not come on. I checked the voltage at the connections of the LEDs and they read also 26V, which I think is too high...I was using 25K, 1/4W resistors at R15 and R16. I thought maybe both resistors are open (not likely) and replaced them with 35K resistors and the result it the same. I checked the voltage before and after the resistors and they read 26Vdc as if the resistors are not there.

I am not sure if I missed something.

Thanks
 
#45
Hi - What you've described is interesting. I understand what you've done, but using 35k would probably be fairly dim. When you describe taking the voltage measurement "before and after" the resistor, please tell us exactly how you placed your probes (red and black) and the polarity of the voltage readings for each measurement.

Try this first. Take your DMM set to diode mode and place the probes directly onto the LED leads. The way the LEDs sit proudly above the PCBs, you should be able place the probes on the legs directly. If the LEDs do not light with the first orientation, reverse the probes. If they do no light in the second orientation, the LEDs are likely dead. If they light up, please tell us which probe orientation made them light up for each LED. Red probe to "center" of board or to "edge" of board.

That should help narrow things.
 
#47
I placed the black probe on the chassis ground connector and the red probe on one side of the resistor, then I placed the red probe on the other side of the resistor, the difference is around 1 volt.

I have now removed the LEDS and they both light up when I placed the red probe on the long side of the terminal..I have now reversed them and they are ok now. Both lighted up.

I was following the LEDs connections on the amp board, the short lead from the LED going to the positive side, but it seem the long lead should be on the positive side of the connection for the power supply.

Lucky I didn't blow anything.

Thanks for all the help.
 
#49
I've never installed a LED backward before.

Wait...no...that's not right.

I somehow manage to install them wrong about 50% of the time and I know that's something I do 50% of the time and yet it still happens 50% of the time. It's paradoxical. It's almost as if I just guess and say, ahh 50/50 chance and solder away. :rofl:

Glad it was a simple fix.
 
#55
Reporting back, it has been a long time until I got 5 pairs of IRFP 150N. Does it matter that the original does not have the " N" it is from a different manufacturer. Please look at the beginning of this thread for what happened.
Being under the assumption that insufficient heatsink capability led to the demise of the FETs I simply went ahead and soldered the new ones in. Since I hadn't adjusted the Pot's from their middle position I assumed it a good starting point, power on...and immediately the "+" side's blue LED went out, pulled the power and measured both FETs had continuity (which they should not). So maybe there is something wrong with the way I put the board together. I checked all transistors T1-T4 for orientation and location, then all resistors. The other board is running well, hot at 70 degree Celcius, 460mV across R28 and R29, OV offset and good sound. So I do have one specimen to compare it to. I did find all values as per schematic, except R8 at 5K instead of 10K. Unsoldered R8 measured it at 10K, soldered back, now it measured 10K (that makes no sense, but I just report and maybe you have an explanation for it). On the working board, it measures 10K. Yes...measurements are in a network, but for the most part it worked and I still had the working one for comparision.
So I checked without FETs...hardly any current and both blue LEDs working ...checked all soldering points for possible shorts...nothing. So what's next? A new pair of IRFP150Ns? And the same happened again. So what's next? I could unsoldered the working FETs from the working board and put another new pair in the (working) board. If it shorts right away, there is something with the FETs I got (but I think that is not going to happen), but if it doesn't then there must be something wrong on the not working board (next items would be to desolder the transistors and measure across them). Suggestions for the search are very much welcome.
Cheers
Brxl
ale.jpg
 
#56
brxl said:
Does it matter that the original does not have the " N"
Click to expand...

irrelevant

brxl said:
The other board is running well, hot at 70 degree Celcius,
Click to expand...


what exactly is at 70C?

remind us - do you have mosfets mounted at (any sort of) heatsink, and did you check that they are surely isolated/not shorted to hsink?
if possible, show us, proudly, copper side of pcb, so we can judge (and sentence!) your soldering work ....... :devily:
 
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#57
Hello,
thanks for checking this thread and answering so quickly. I measured the working board at 70C at the TO247 housing. Yes, big heat sinks now and no continuity from heatsink to any of the pins of the FETs.
One thought that keeps coming back to me...originally both blue LEDs had come up and the "+" side's went after a little while. Now it happens immediately (and takes out both FETs). Is there a possibility that such an event would have destroyed the driving transistors and now they just open the FETs fully? I did simple checks on the BC546 and 556 as diodes, works out (continuity in one direction and same values for both boards). Could I do the same for the JFETs?

'

Ok, here it goes
und.jpg

I made an intentional extra connection on the R6 toward R8, after the desoldering had lifted a bit of the copper trace.
 
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