Benjolin Osc problem

oscilloclast · Joined: Sep 29, 2005 Posts: 49 Location: VA

Rob,

The output of Osc 2 is a downward sloping ramp (it should be a triangle) and a very weak pulse (it should be stronger like the pulse out on Osc 1). Any suggestions on where the problem may be? All of my IC's have sockets and I have replacements for all of them (if I need to switch them).

Thanks,
David

State Machine · Posted: Fri Dec 04, 2009 2:15 pm Post subject:

As is the case most of the time, bad IC's are usually not the casue of a problem but more a wrong value component surrounding them. Try the simple thing and check the components in each oscillator one for one as they are identical circuits .. for example ..... R12 and R5, R6 and R13 ... ect ....

Also, check for "bent under" pins on IC2, 6, and 3 ....

After you check that these components are correct .... then check for solder bridges around these components to make sure they are ONLY connected to where there supposed to be. ... if thats good .. then ......

on U3 pins 5 and 2 .. with power OFF, check that they are connected together and to ground. This is the reference to the output amplifier that creates the pulse , P2 ....

Lets try these things first ....

Bill

oscilloclast · Joined: Sep 29, 2005 Posts: 49 Location: VA

Bill,

Thanks for the tips. I actually replaced all of the chips (I used sockets when I built it) but the problem turned out to be some switched resistors. The output waves are correct now but I'm getting +/- 5v on bth triangles and +/- 10v on both pulse (so I need to look into this descrepency).

Thanks,
David

State Machine · Posted: Sat Dec 05, 2009 5:33 pm Post subject:

Good news ... Very Happy

BTW, the pulse will be larger in amplitude than the triangle waves so there is nothing wrong. The TRI waveforms feed an approximately 9 dB amplifier stage so that is OK ...

The pulse output is feed back via the 100K resistor (R3/R10) into the OTA to reverse the current into the integrator ...

With a split 9V supply (+9V/-9V), you would not get any more then 18V P-P ideally but the TL074 does not go to the rail so it;s something less. I say this because you mentioned that you had +10/-10 and that equates to 20V P-P, unless I misunderstood what you said??

Bill

oscilloclast · Joined: Sep 29, 2005 Posts: 49 Location: VA

Yep your right, I should have said +/- 8v.

Thanks,
David