Hi All - I've just finished assembling a phono stage pre-amp project based on Rod Elliot's P06 phono stage, P05C power supply, and P99 subsonic filter. I was testing the completed modules yesterday using the instructions given by Rod's website and found that the P99 subsonic filter seems to have issues.
I have used LM4562 op-amps in the P06 module and OPA2134 in the sub-sonic filter. P05C and P06 appears to be functioning correctly.
Testing routine was to connect the module using 100R 1-watt safety resistors in series with the +ve/-ve supply, then measure the voltage at the output pins of the op-amps (pins 1 and 7). With power applied, apparently the DC at the output pins should read no more than a few mV - perhaps even 0mV - for both op-amps. I am using a multi-meter for testing, and using the P05C power supply which is running off a 15-0-15 toroidal transformer, regulated to 15v output (reads at a steady +14.97v / -15.11V)
For the P99 subsonic filter, I am getting very different readings between different pins on each op amp. Some pins are 10s of mV, others are over 100mV. I have checked the following:
I am wondering if one or both of the op-amps is faulty, or if there are other things I should be checking to try and rule out issues? My testing kit is a UNI-T UT-89XD multi-meter. Any suggestions and recommendations would be very well received.
Edited by moderation to remove reported image
I have used LM4562 op-amps in the P06 module and OPA2134 in the sub-sonic filter. P05C and P06 appears to be functioning correctly.
Testing routine was to connect the module using 100R 1-watt safety resistors in series with the +ve/-ve supply, then measure the voltage at the output pins of the op-amps (pins 1 and 7). With power applied, apparently the DC at the output pins should read no more than a few mV - perhaps even 0mV - for both op-amps. I am using a multi-meter for testing, and using the P05C power supply which is running off a 15-0-15 toroidal transformer, regulated to 15v output (reads at a steady +14.97v / -15.11V)
For the P99 subsonic filter, I am getting very different readings between different pins on each op amp. Some pins are 10s of mV, others are over 100mV. I have checked the following:
- All electros are correctly oriented.
- All resistors values are correct.
- Continuity tested the supply rails to the op-amps, seems fine.
- Check all solder joints for bridging / dry joints etc, again, seems ok.
- When assembling I checked all component values with the meter and picked components that were closely equal values, so all components were checked with the meter prior to assembly.
- I have visually inspected the board and I cannot see any breaks to the traces or visible damage.
I am wondering if one or both of the op-amps is faulty, or if there are other things I should be checking to try and rule out issues? My testing kit is a UNI-T UT-89XD multi-meter. Any suggestions and recommendations would be very well received.
Edited by moderation to remove reported image
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FYI I built mine a couple of weeks ago using TL072 opamps and the DC was 1 - 5mV on the output pins 1 & 7 of both opamps. The measured distortion and noise using the TL072's is less than phono amp circuit I'm using it with.
Are you testing the circuit with the inputs shorted?
Otherwise, noise will be picked up and amplified.
Between the two opamps are three capacitors - two electrolytic & one ceramic.
It is hard to be certain from the photo but to me it looks like one of the electrolytic may be dry jointed.
Maybe just reflow the joints on all three.
It is hard to be certain from the photo but to me it looks like one of the electrolytic may be dry jointed.
Maybe just reflow the joints on all three.
Yep, the recommended opamps include the ones used (also NE5532, TL072, LM4532). The were purchased from a small outfit here in the UK who I have used previously and generally been satisfied with. I suppose there is always the outside chance that they are counterfeits though...
Great, good to know yours is working as intended. I have full faith in the design, and Rod's guide is super comprehensive.
Nope, I did not short the inputs. I'll certainly give this a try, hopefully I'll get some time tomorrow evening to test again.
Thanks all for the suggestions. I'll report back
Hi All - small baby and full time job means I only had time to fiddle about with the phono pre-amp this weekend.. I have tried the various recommendations.
I tested again with shorted inputs, sadly no improvement (in fact the pin-1 voltage on the 2nd opamp was over 1.0v!).
I checked the solders again, they all look ok but I carefully reflowed any that didn't look quite as good as they could - again, no improvement...
I plan to de-solder and replace the opamps.
Thanks again for the suggestions. I also plugged the phono stage into a test amp and speaker, it is working but there is a rather loud 50hz hum too. I'll post separately about this issue.
I tested again with shorted inputs, sadly no improvement (in fact the pin-1 voltage on the 2nd opamp was over 1.0v!).
I checked the solders again, they all look ok but I carefully reflowed any that didn't look quite as good as they could - again, no improvement...
I plan to de-solder and replace the opamps.
Thanks again for the suggestions. I also plugged the phono stage into a test amp and speaker, it is working but there is a rather loud 50hz hum too. I'll post separately about this issue.
See attached
1 looks like a dry joint
2 all these joints also look suspect
If you are using silver based solder get hold of some lead tin it tins the joint more readily . You will probably have to remove the solder from all of these joints especially ( 1 ) and clean the legs/pins before the solder will properly take .
Image removed by moderation.
1 looks like a dry joint
2 all these joints also look suspect
If you are using silver based solder get hold of some lead tin it tins the joint more readily . You will probably have to remove the solder from all of these joints especially ( 1 ) and clean the legs/pins before the solder will properly take .
Image removed by moderation.
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