My Nightingale PTS01 preamp phono stage has gone south. I have lost most of the gain and the highs. My first response was to check the tubes, as I had just replaced the three new Sovtek 6922/6DJ8 (too noisy!!) with NOS Telefunken PCC88/7DJ8 (very, very, quiet). I pulled the tubes and tested (all perfect), rolled in the circuit (no change), so started to look further. What I found is that the phono stage, which I had believed was a tube stage, is in fact an AD797 Op Amp. I then went to the scope to test for noise and gain with various input / output variable, signal generator, etc. via the phono and line inputs, and concluded the problem is with the phono AD797 op amp phono stage. I have now spent this morning considering what may have occurred here, and have a theory on which I solicit your comments. The AD797 literature includes an "ESD Caution" describing the potential for "permanent damage...for devices subjected to high energy electrostatic discharges." Is it possible that the momentary loss of ground from my TD124, or the ground wire connection resting on the carpet (this happened), would be enough to short out the AD797??
The AD797 is a single opamp . I assume you have a dip package.
Check the supply voltages at Pin 7 (+ voltage) and Pin4 ( - voltage ). The chip can take only +/- 15 volts and so they should not be higher or very much lower ( maybe +12 volts and - 12 volts).
If the voltages are OK , the chips MIGHT be defective . Depends on what follows in the cicruit.
If I were you I would remove the chip VERY carefully using a desolder wick and possibly a solder sucker and install a machined 8 pin DIP socket . Then I would check the supply pins for supply voltage ( Pin 7 + supply a pin 4 - supply).
You can always plug in a cheap TLO71 or NE5534 and see if it works.
In any case BEFORE removing anything better confirm that all supply voltages are normal ! With both channels gone it must be something common to those channels.
Cheers.
Check the supply voltages at Pin 7 (+ voltage) and Pin4 ( - voltage ). The chip can take only +/- 15 volts and so they should not be higher or very much lower ( maybe +12 volts and - 12 volts).
If the voltages are OK , the chips MIGHT be defective . Depends on what follows in the cicruit.
If I were you I would remove the chip VERY carefully using a desolder wick and possibly a solder sucker and install a machined 8 pin DIP socket . Then I would check the supply pins for supply voltage ( Pin 7 + supply a pin 4 - supply).
You can always plug in a cheap TLO71 or NE5534 and see if it works.
In any case BEFORE removing anything better confirm that all supply voltages are normal ! With both channels gone it must be something common to those channels.
Cheers.
Thanks for the quick reply. The AD797 is in a socket and could be easily removed. The voltage at the socket are -10v (pin 4) and +10v (pin7). I will pull the device and test out of circuit, then try one of the plug in replacements to test while locating a replacement AD797. What are your thoughts on the possible reasons for failure of the in-situe original AD797 ?
eleakist said:
This theory borders with sci-fi. The 797 is a bipolar device and as such not particularly sensitive to static.
The fact that both channels have vanished is quite suspicious as you need both opamps to die simultaneously. Not that it can't happen. Could it be the PS?
Edit:
It seems to be a mono preamp. Then it's quite possible the 797 is dead.
AD797 and electrostatic discharge
Call it sci-fi if you wish. When such a caution is published by the maufacturer (Analog Devices - ESD Caution - page 5), I call it science. Yes, you are correct, this is a mono preamp. I have concluded that the issue is not the p/s as all supplied voltages, being at 10v, are within specifications of 5v to 15 v.
Call it sci-fi if you wish. When such a caution is published by the maufacturer (Analog Devices - ESD Caution - page 5), I call it science. Yes, you are correct, this is a mono preamp. I have concluded that the issue is not the p/s as all supplied voltages, being at 10v, are within specifications of 5v to 15 v.
Re: AD797 and electrostatic discharge
And i was beginning to wonder what science was
Of course static damage is real. What i meant was that a disconnected ground connection (i assume you are talking of the tonearm ground wire) or cable passing over carpet is extremely unlikely to cause static damage.
I have yet to see a bipolar opamp killed by static, moreover one which is already soldered in circuit.
If the 797 is indeed dead it may have died for no apparent reason at all.
eleakist said:
And i was beginning to wonder what science was
Of course static damage is real. What i meant was that a disconnected ground connection (i assume you are talking of the tonearm ground wire) or cable passing over carpet is extremely unlikely to cause static damage.
I have yet to see a bipolar opamp killed by static, moreover one which is already soldered in circuit.
If the 797 is indeed dead it may have died for no apparent reason at all.
Solution - AD797 Op Amp - Nightingale PTS01
Well the problem is solved. I now know the what and where, but not the how, why, or who. I pulled the op amp today and replaced with a TL071 as suggested for testing. No change so traced the phono input / output and ground circuit. I discovered that all paths led to ground - apparently someone has tried to fix this issue before and reversed the two phono AD797 board pre output wires going to the tube stage. Tried a line source at the tube and all was well. Issue seemed be on the phono board that included the AD797. Desoldered the board (small and very delicate) and began to trace the path from phono input thru output. Found that the first resistor 95k was shorted and someone had damage a 10pf cap while attempting a repair (leg was broken at cap so was intermittent). Replaced both (only had a 100k resistor), remounting the original AD797 as worked well and is better quality than TL071, - shazzam, the gain is back and phono sounds great. Thanks to all who contributed their analysis and ideas. A sounding board such as this is alway beneficial as I diagnose these sort of quirky issues.
Regards,
Barry
Well the problem is solved. I now know the what and where, but not the how, why, or who. I pulled the op amp today and replaced with a TL071 as suggested for testing. No change so traced the phono input / output and ground circuit. I discovered that all paths led to ground - apparently someone has tried to fix this issue before and reversed the two phono AD797 board pre output wires going to the tube stage. Tried a line source at the tube and all was well. Issue seemed be on the phono board that included the AD797. Desoldered the board (small and very delicate) and began to trace the path from phono input thru output. Found that the first resistor 95k was shorted and someone had damage a 10pf cap while attempting a repair (leg was broken at cap so was intermittent). Replaced both (only had a 100k resistor), remounting the original AD797 as worked well and is better quality than TL071, - shazzam, the gain is back and phono sounds great. Thanks to all who contributed their analysis and ideas. A sounding board such as this is alway beneficial as I diagnose these sort of quirky issues.
Regards,
Barry
"...........AD797 as worked well and is better quality than TL071...."
That is no surprise I guess . Since your chips are on a socket , you can try different single opamp chips and see the difference in your set up. Happy hunting.............if you want to experiment !
It could turn out to be quite interesting.
Cheers.
That is no surprise I guess . Since your chips are on a socket , you can try different single opamp chips and see the difference in your set up. Happy hunting.............if you want to experiment !
It could turn out to be quite interesting.
Cheers.
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