I may give them a try then. I have plenty of the 3281/1302 though. I still have those huge NS boards that I bought the bad Sankens for. I may give the 21193/93 a try with those. My problem with those is their size. Need a huge case to accommodate them. Looks like I am going to have to buy some more large heatsinks.
Having to reorder parts is a regular thing with Valery's designs. Every one seems to have some obscure resistance value.😀 On the plus side they are small and cheap, so storing them is easy.
Hi Jeff,
Do you have a working model of this OPS? I'm going over it because it didn't work. Do you have a schematic with the correct values for the VBE multiplier? The schematic I have shows D3 in circuit and NJW3281/1302 for the outputs. I have to assume that if D3 is bypassed then the other resistor values must change as well.
thanks, Terry
Do you have a working model of this OPS? I'm going over it because it didn't work. Do you have a schematic with the correct values for the VBE multiplier? The schematic I have shows D3 in circuit and NJW3281/1302 for the outputs. I have to assume that if D3 is bypassed then the other resistor values must change as well.
thanks, Terry
I've got some boards assembled, but have never installed output devices yet. All the values in the schematic are what Valery simulated to work. We added the LED into the schematic after for future use wit hexfets. What is the board doing?
I fighting everything right now. What is the testing procedure for stand alone OPS? I have tried each of the IPS I have built and they all act different. The X4 and the VFA both cause the light bulb to light and let only about 5V rails. The CFA doesn't bias the circuit at all. I'm presently trying my best to go over each transistor again and making sure I have no sold joints or bridges. I did this twice before but hopefully I missed something. I tried hooking up the IPS's stand alone by shorting all of the pins for the PD+, NFB and PD-. The X4 shows good vb-e for each of the TO-126 transisors but I haven't tried measuring the tiny ones yet. I need to familiarize myself with the layout so I am not trying to touch the legs with a probe.
Yes
Yes
Terry, the approach is right - it makes sense to test the IPS boardsxstandalone first, to make sure they work as expected - no offset, VAS current is 5.5 - 7.5 mA, they amplify the signal.
The six pins that connect to the main board are PD+, NFB and ND-, the center two pins being NFB. Jumper a 100R resistor from both outside pins to the center. VAS current can be measured on the 100R resistors and DC offset can be measured between NFB and ground.
Terry,
When I built up VHEX+ I had problems with one of the amps not working. It took some debugging but it turned out to be a cold solder joint on one of the large SMT resistors. You might try taking an iron tip to reflow all joints on SMTs.
When I built up VHEX+ I had problems with one of the amps not working. It took some debugging but it turned out to be a cold solder joint on one of the large SMT resistors. You might try taking an iron tip to reflow all joints on SMTs.
Mines not acting right either. The input is fine standalone. The output board is fine with no input, but current goes high with the input plugged in. I can't dig any deeper tonight though.
I've still got current flow in the output stage with R34 out of circuit. It appears Q12 isn't shutting the drivers off.
Looks like something's wrong. With Q12 fully open, bias will go below 1V, keeping the whole OPS "off" at idle.
I've dropped the value of R33 to 4k3 to try to increase current through Q12 with no effect. The bulb limiter is actually flickering like the current flow is pulsing. I'm going to get the scope out and see what's going on.
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