On 07/01/2021 18:11, pinnerite wrote:
On Wed, 6 Jan 2021 20:37:27 +0000
Fredxx wrote:
On 06/01/2021 20:16, pinnerite wrote:
Ten years ago I bult a low-noise pre-amp based on a 1970's article in Elektor magazine.
It used a TBA231 dual op-amp IC.
It didn't work but I did not have time to test all the copper runs etc before I wa over-whelmed with 'work'.
This week I took it out and started fault-finding.There was one open connection, poorly soldered. I then checked the power links throughout the board and they were fine.
Next i connected in a little waveform generator to the input and one of those timy LCD screened chinese oscilloscopes to the output. Nothing.
So with no shortcircuits, I concluded that the capacitors were OK whch only leaves the IC.
I do not have another TBA231 or equyivalent but have no idea how to test the chip.
I am a bit out of date with electronics since my heydays
So any suggestions will be welcome.
I suggest you measure all the voltages on each pin and come back here
for analysis.
For Info the datasheet:
http://www.bg-electronics.de/datenbl...ise/TBA231.pdf
Although the example test circuit doesn't include the use of Output Lag.
This circuit does:
https://www.vinylengine.com/turntabl...719d&mode=view
Thank you. That focussed the one or two brain cells that I have left.
The DC voltages on the chip with both no external connections (audio oscillator and oscilloscope) were virtually the same:
Pins Voltage Pins Voltage
1 14.3 14 23.6
2 22.5 13 0.43
3 21.0 12 22.9
4 21.1 11 21.0
5 0 10 21.0
6 0 9 0.9-1.6
7 0 8 0.9
Thanks too for the links. I downloaded the spec sheet.
I've only just noticed your reply.
One thing is of note. For rails of +/-15V the common mode input range is
+/-10V min to +/-11V typ.
Since all input pins are either the same as -V pin or within ~1V, that
suggests you're operating the device out of spec. Some old op-amps would
exhibit strange behaviour in these conditions which could explain the
behaviour on the 'b' side.
This op-amp looks designed for split power rails and not 0V and 24V. Can
you check your power supply side and check if this was meant to be +/-12
with a ground; where the inputs (and output) are ground referenced?
If this power setup is intended then you need an op-amp that includes
ground in the common mode input range. Is there any way of posting your
circuit on some sharing website?