I have the same behavior on one board. If I remove the Op-Amp, the amplifier starts normally, the lamp goes out, the diodes light up. If I put the op-amp, the lamp lights up.
Power drops to 10V, because the circuit is short-circuited.
Thanks Stef, then maybe because I am using a bulb tester the rails are getting limited. I have to test now without the bulb tester to get the full rails of +/-33vdc. Also yes I use a OPA1641 and shorted the input, so when you say use a 100R where do you want me to put it to test the initial setup. Or should I just remove the shorting of the input signal and test the amp?
I have a poorly wired board. Another board should be arriving soon, hopefully it will run fine. This will be my third try, (the last).
The output transistors are not hot in my amp. Also which version of the amp boards do you use? As I am using the original Tibi designed the longer board with 2 power transistors.
NEVER REMOVE THE OPAMP or R13 will burn.
To switch on the board without opamp for testing purpose, you can solder a 100K resistor on C1. Don't forget to remove it after the test.
Use a 100R. As the opamp is not protected by a LPF at input, you will catch all noise if you do not short input.
Stef.
To switch on the board without opamp for testing purpose, you can solder a 100K resistor on C1. Don't forget to remove it after the test.
Use a 100R. As the opamp is not protected by a LPF at input, you will catch all noise if you do not short input.
Stef.
I am using the original board so its the smd based opamp that I am using so did not remove it from the amp board. But instead I have removed the input signal shorting wire to check the amp again. The behavior is the same like 2.82vdc across the R10/12 and around 152mV across a 0.1R resistor in series with the positive rail but still with the bulb tester.
Yes thats true as with the lamp itself I see around 1.5A being consumed on the amp because of which the bulb is glowing fully. How to go about figuring out the issue on the amp? Did you verify yours or going to build another amp board?
I still haven't figured it out. I ordered another board.
The current consumption is like a short circuit. If you remove the op-amp, the board starts normally.
Sorry to say, but I not understand what you are doing. Provide pictures, montage details etc.
Unfortunately I'm not a wizard to read others mind.
Regards,
Tibi
Sorry Tibi, I thought you looked at my earlier posts when I started testing using a simple bulb tester. To put in perspective the step by step approach here you go:
Amp has all the good quality parts from element14 and rsdelivers distributors. OPA1641 is the smd opamp which I used directly on the amp board.
1. Using a 22vac 300VA trafo and LT4320 CRC psu board but the R is shorted per your suggestion for this kind of class B amp. Gives around +/-33vdc stable.
2. Used a simple bulb tester to run the initial tests of the amp, and now the rails show around +/-10.12vdc
3. On power up with the bulb tester, the bulb initially glows for a flash of a second and then goes off and then immediately comes back blinks for 2-3 seconds and glows fully does not get switched off so I presume the current is being drawn by the amp board.
4. Checked the voltage across R10/12 having 47/1W and its around 2.82v and 3.12v corresponds to around 60mA current flow so I guess the input stage is good.
5. Offset was hovering around 0.5-1.4mV and slowly dropping towards 0
6. But the LEDs were not lit and Stef suggested that i need at least 24vdc or optimal 30vdc on the rails for them to glow. As I am using a bulb tester the current/voltage is being limited, so I am fine with the LEDs for now.
7. Power transistors are not hot but maybe very slightly warm at this stage.
8. Now I used a 0.1R/5w BPR resistor in series with the positive rail on the amp and checked for the voltage across it. This is around 152mV with the input signal being open and being shorted/closed its around 173mV. So the amp is drawing around 1.52A to 1.73A.
Need your suggestions to look for any issues with my above results or is it good to remove the bulb tester and test the amp!
Here are some of the pics for your reference
Thanks
Which BS250 are you using ?
https://www.vishay.com/docs/70209/70209.pdfTake care on DGS
Regards,
tibi
https://www.vishay.com/docs/70209/70209.pdfTake care on DGS
Regards,
tibi