Just completed all connections and fired the rig.
Right Channel:
Shunt outputs are
+24V (I can adjust it with the trimmer)
-35.7V (I can NOT adjust it)
Input offset -2.5mV to -1.9mV oscilating (When I switch off, this offset starts rising until it reaches 30mV and than goes down)
Output offset Wild oscilation between +12 and -10V
On switch on, opamp leds light imediately... after a while the negative shunt leds light up and 5 seconds latter finally the positive shunt leds light
Left channel:
Shunt outputs are
+21.4V (I can not adjust it and the leds are very dim)
-24V (I can adjust this value with the trimmer)
Input offset: 9.6V steady
Output offset: 12.75V steady
Leds on the opamp flicker.
This is going to be harder than I was hopin for
on the shunts:
the LEDs on the shunts should come on at about the same time, roughly 3-5 seconds after turn-on. if they don't, maybe one of them is reversed (i had 6 mounted the wrong way in one board... so much for late night building).
the LEDs for the opamp are brigghter in my build, i use OPA134 which consumes more current than what flows in the shunt leds, so it should be brighter.
at that point you should be abe to measure around 3v from gate to source of the power mosfet, and 1.25v across the big resistor(the two testpads right next to the resistors, in the middle of the shunt). check the polarity of the bipolars in the shunts, and also the elcaps.
can you post a scope shot of the voltage at the RIAA? (check the connector for external riaa). timing 50ms per division, that should show low frequency oscillations, the main reason why the LEDs for the servo should flicker. in my build, the oscillations were building up in voltage so that the output would saturate at the positive rail, jump sharply to negative and work its way back up.
All,
Friday my ‘away mission’ ended, and yesterday I took the day of.
Betelgeusian New Year is great, but I can not get used to traveling those distances.
Ricardo, let’s see if we can resolve your PSU problems.
This looks like a failure in the string of LED’s (as hesener noted) (reversal or breakdown of one of the LED’s). If all the LED’s are inserted correctly and the regulator does not operate (e.g. has a high output voltage) then you should be able to regulate the current in the LED’s (and thus the brightness of them) with the potentiometer (be sure to start with the potentiometer at its maximum resistance). When you are unable to change the amount of light that you get from the LED’s then for sure one is broken or reversed. Use a 9 Volt battery and a 10 KOhm resistor to check the LED’s for functioning and polarity a voltmeter parallel to the LED under test should indicate about 1.9 Volt.
If Vdg of the Mosfet is very low then the transistor is suspect (but the LED’s should light up). If, on the other hand, Vdg is very high (let’s say more than 4 Volt) this would indicate that the Mosfet is suspect (again the LED’s should light up).
The fact that the regulator seems to oscillate at a low frequency puzzles me a bit, most probably it is the Vbe (parallel) resistor in combination with the capacitor that is in parallel with the LED’s that sets this frequentie. This indicates that the transistor and Mosfet are operating and that the problem should be found in the string of LED’s (as above).
Finally you can test the pre-voltage-regulator and the CCS by shorting the power supply with a 10 Ohm resistor. The CCS is set for 150 mA, and thus you should measure 15 Volt across the 100 Ohm resistor. The voltage across the input and output of the LM317 should be the 6.2V – Vbe = 5.6V, this would indicate that the pre-voltage-regulator functions correctly (and the CCS also).
This makes the CCS and the pre-voltage-regulator suspect. First check the input voltage of the pre-voltage-regulator (it should be 35 Volt like for the other channel I guess). Then check the voltage across the input and output of the LM317 this should be (as above 5.6 Volts, if this is more than the zener is suspect. The zener can be checked with the 9 Volt battery and a 10 KOhm resistor, check the zener voltage with a multi-meter (I think (I did not test this in circuit)).
You may short CE of the pre-voltage-regulator, then the CCS should work normally (but it is way more noisy) and the shunt regulator should function. Again the functioning of the CCS can be checked using a 10 Ohm resistor.
Do not dispare we are here and we will help you.
Regards,
Frans.
Friday my ‘away mission’ ended, and yesterday I took the day of
. Betelgeusian New Year is great, but I can not get used to traveling those distances.
Just completed all connections and fired the rig.
Right Channel:
Shunt outputs are
+24V (I can adjust it with the trimmer)
-35.7V (I can NOT adjust it)
Input offset -2.5mV to -1.9mV oscilating (When I switch off, this offset starts rising until it reaches 30mV and than goes down)
Output offset Wild oscilation between +12 and -10V
On switch on, opamp leds light imediately... after a while the negative shunt leds light up and 5 seconds latter finally the positive shunt leds light
Left channel:
Shunt outputs are
+21.4V (I can not adjust it and the leds are very dim)
-24V (I can adjust this value with the trimmer)
Input offset: 9.6V steady
Output offset: 12.75V steady
Leds on the opamp flicker.
This is going to be harder than I was hopin for
Ricardo, let’s see if we can resolve your PSU problems.
This looks like a failure in the string of LED’s (as hesener noted) (reversal or breakdown of one of the LED’s). If all the LED’s are inserted correctly and the regulator does not operate (e.g. has a high output voltage) then you should be able to regulate the current in the LED’s (and thus the brightness of them) with the potentiometer (be sure to start with the potentiometer at its maximum resistance). When you are unable to change the amount of light that you get from the LED’s then for sure one is broken or reversed. Use a 9 Volt battery and a 10 KOhm resistor to check the LED’s for functioning and polarity a voltmeter parallel to the LED under test should indicate about 1.9 Volt.
If Vdg of the Mosfet is very low then the transistor is suspect (but the LED’s should light up). If, on the other hand, Vdg is very high (let’s say more than 4 Volt) this would indicate that the Mosfet is suspect (again the LED’s should light up).
The fact that the regulator seems to oscillate at a low frequency puzzles me a bit, most probably it is the Vbe (parallel) resistor in combination with the capacitor that is in parallel with the LED’s that sets this frequentie. This indicates that the transistor and Mosfet are operating and that the problem should be found in the string of LED’s (as above).
Finally you can test the pre-voltage-regulator and the CCS by shorting the power supply with a 10 Ohm resistor. The CCS is set for 150 mA, and thus you should measure 15 Volt across the 100 Ohm resistor. The voltage across the input and output of the LM317 should be the 6.2V – Vbe = 5.6V, this would indicate that the pre-voltage-regulator functions correctly (and the CCS also).
This makes the CCS and the pre-voltage-regulator suspect. First check the input voltage of the pre-voltage-regulator (it should be 35 Volt like for the other channel I guess). Then check the voltage across the input and output of the LM317 this should be (as above 5.6 Volts, if this is more than the zener is suspect. The zener can be checked with the 9 Volt battery and a 10 KOhm resistor, check the zener voltage with a multi-meter (I think (I did not test this in circuit)).
You may short CE of the pre-voltage-regulator, then the CCS should work normally (but it is way more noisy) and the shunt regulator should function. Again the functioning of the CCS can be checked using a 10 Ohm resistor.
This is going to be harder than I was hopin for
Do not dispare
we are here and we will help you.Regards,
Frans.
Thank you Frans. I will surely get it right.
But to eliminate possibilities, I disabled the shunts and powered the boards with a bench psu... now one of the channels works allright but the other one has a steady +14v output offset... can Q15 be the cause of this issue ?
I want to eliminate this offset before I start working on the shunts again.
But to eliminate possibilities, I disabled the shunts and powered the boards with a bench psu... now one of the channels works allright but the other one has a steady +14v output offset... can Q15 be the cause of this issue ?
I want to eliminate this offset before I start working on the shunts again.
Are there any specific requirements for ideal LED Vdrop in this application?
For any North Americans waiting on the sidelines to build the Paradise, Mouser has the Fairchild versions of BC327-40 and BC337-40 at the best price (~$9 for 250pcs). DigiKey is MUCH more expensive and only has OnSemi in stock.
For RIAA: WIMA FKP2 or Panasonic PPS SMT, or try both?
For any North Americans waiting on the sidelines to build the Paradise, Mouser has the Fairchild versions of BC327-40 and BC337-40 at the best price (~$9 for 250pcs). DigiKey is MUCH more expensive and only has OnSemi in stock.
For RIAA: WIMA FKP2 or Panasonic PPS SMT, or try both?
Yes, Mouser has much better prices on discrete semiconductors.
FKP2 and SMD PPS are both fine. The problem with the PPS is that the usually do not come in better then 5% tolerance so you have to match them to 1% if you do not want more deviation than +- 0.1dB.
Frans, yes, thats right. good idea.
FKP2 and SMD PPS are both fine. The problem with the PPS is that the usually do not come in better then 5% tolerance so you have to match them to 1% if you do not want more deviation than +- 0.1dB.
Frans, yes, thats right. good idea.
pps 6800pf 50v 1206 2%
Seem to be of non-magnetic construction as the endcaps are brass
smd-film-capacitors
Seem to be of non-magnetic construction as the endcaps are brass
smd-film-capacitors
Just replaced Q15 by a new 327
Left channel has 0 input offset but output is still 14v
PS: I edited this message because the readings were wrong
Now this is quite a good idea.
Latter I will be working on the shunts.
Last edited:
2,5 mV is quite normal and in the specs of the Opamp. It does no harm at all.
What servo opamp are you using ?
When you want to bring it down to guarantied less then 0,1mV you have to use OPA827 or OPA627. You can also select the servo opamps. Some are better then others of the same bread.
What was wrong with Q15 ?
What servo opamp are you using ?
When you want to bring it down to guarantied less then 0,1mV you have to use OPA827 or OPA627. You can also select the servo opamps. Some are better then others of the same bread.
What was wrong with Q15 ?
