The leakage current for a capacitor is rated by the units voltage rating not the applied voltage. (To make things worse at low voltage for long periods the leakage current will go up!)
So if you have more than one microamp of current leakage at 10K you will have 10 millivolts of change in the DC level if the wiper lifts. Even at a gain of only 30 db without the 100K that pop would be at -8 db!
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D V V . I think the boosted op amp idea is great . Alas my notes on my circuit are lost although so much like what you did to be not worth showing ( No 3 ) . This version would drive a 4 ohms speaker . The results were what one would get working from theroy alone . All the better rules applied I should say ( decoupling , gain etc ) . This was a class A design running approximately 1 A . It used simple diode and resistor bias ( vbe was tried for bias also ) .
Notice how both op amps are loosely speaking generics of 741 . Notice also how 5534 is unhappy . Better op amps were tried with startling differences . The 5534 problems are easy to cure with comp cap . However.....
The LF 351 N was kept as control during tests . It was much better than expected . TLO71 measured almost the same , it sounded different and to me less good .
The test also shows how the 5534 marginally had a higher output . I reran these tests and can say they are representative . Note all op amps had a surplus of current to drive the output stage .
The amp works well with no output stage feedback to the op amp . This is shown with feedback .
I was going to design a discreet op amp after this and never got far . A blameless TDA2050 if you like .
These are just my workshop notes .
Over the years, I have come to regard boosting op amps not as an idea per se, but rather as a method of completing them. This was imply because despite the 50 mA and upwards of what the sepcs sheets say, I found that in real life, NOT ONE failed to sound better and more relaxed, not to even mention the bass cntrol and gravitas, with boosting than without.
Inititally, that Data Sheet is just a blank piece of paper which cannot complain no matter what you write. I find that all too often, it reflects the designers' good wishes rather than reality.
But I was sold on the idea the first time I made a two stage phono RIAA project, published by an engineer working for Burr-Brown Germany, one Holger Hermann, and published in a German magazie called "Funk" I think. Both op amps were used in pure linear mode, and the EQ network was put between them (original schematic attached).
When I added current boosters, that board REALLY took of. To date, that remains one of the best ever ophono stages I have ever heard.
Granted that lytics can have terrible soakage and forming issues, at equilibrium decent ones are pretty much settled down, with the current piecewise-linearly dependent on applied voltage. At low-enough voltages the I-V curve really does pass through the origin. So what is the worst-case d.c. offset between the emitters of Q1 and Q2? That will determine the current through the capacitor, and piling on the terms to determine the offset, I agree with Scott that you just can't conjure all that many millivolts, nor all that big a transient if VR1 even goes from a short to an open. For the more likely failure of wiper lifting, but track continuity preserved, the effect is even smaller.
I think of the conjectures so far, the notion that R14 sets a minimum gain and trims variations in VR1 out (which means the schematic should have an asterisk beside the value), and possibly that it has an effect on the effective VR1 taper, are the most plausible.
Someone from a very large telecom firm insists that the dark current in a photodiode is in the dark at 0V, i.e. the thermodymanically impossibe result. Same is true of a capacitor at equilibrium.
British designs
D V V you always seem puzzled at British design . I call it make do and mend like we suffered in war time . Just when we were getting complicated along comes Bob Stuart to settle us back in our comfort zone .
Allegedly Bob gave a talk in the early 1970's ( late 60's even ) that was called approximately " Distortion in Audio Amplifiers Due To Loss of Information " . I don't find it by Googling . The story is endless and will stop there as far as the personalities are concerned . . Tone controls are obvious victims of Bob . Remember the word " Information " is a near Holy word in Cambridge . I did ask Bob about this and he seemed to agree about the talk having happened . He said worst for him he couldn't be the one to do it first because he was tied up in other things . I met Bob through a friend of his . His 101 105 was wonderful . Loss of Information was passing from stage to stage . Photo copies of the one before it so to speak . I am neutral on this let me tell you . However it has the ring of common sense to it .
Even the blameless amp is minimalist .
Now , you were at Cambridge I think and must have known Bob ? How is it you didn't follow the British way ?
The Brits don't do minimalist design because they can't do complicate ( I can't but that is different ) . They do it because it's a passion . Also they are very business minded .
Rotel would be my example of us doing it right .Cheap and good enough for any music lover . Crazy how good it can be when asked to be . Some top end amps are not as good as it to my ears . That's my view and it wont be changing . I am not saying those amps in a narrow field of use don't have merit . I am saying get them off of their territory and they don't impress .
If asking I can not imagine your amp being one of them . It's just too carefully thought out .
You know if someone re-chipped a Rotel and new PSU who knows how good it could be ? Is a Naim so different to that ?
Anyway that is it .
D V V you always seem puzzled at British design . I call it make do and mend like we suffered in war time . Just when we were getting complicated along comes Bob Stuart to settle us back in our comfort zone .
Allegedly Bob gave a talk in the early 1970's ( late 60's even ) that was called approximately " Distortion in Audio Amplifiers Due To Loss of Information " . I don't find it by Googling . The story is endless and will stop there as far as the personalities are concerned . . Tone controls are obvious victims of Bob . Remember the word " Information " is a near Holy word in Cambridge . I did ask Bob about this and he seemed to agree about the talk having happened . He said worst for him he couldn't be the one to do it first because he was tied up in other things . I met Bob through a friend of his . His 101 105 was wonderful . Loss of Information was passing from stage to stage . Photo copies of the one before it so to speak . I am neutral on this let me tell you . However it has the ring of common sense to it .
Even the blameless amp is minimalist .
Now , you were at Cambridge I think and must have known Bob ? How is it you didn't follow the British way ?
The Brits don't do minimalist design because they can't do complicate ( I can't but that is different ) . They do it because it's a passion . Also they are very business minded .
Rotel would be my example of us doing it right .Cheap and good enough for any music lover . Crazy how good it can be when asked to be . Some top end amps are not as good as it to my ears . That's my view and it wont be changing . I am not saying those amps in a narrow field of use don't have merit . I am saying get them off of their territory and they don't impress .
If asking I can not imagine your amp being one of them . It's just too carefully thought out .
You know if someone re-chipped a Rotel and new PSU who knows how good it could be ? Is a Naim so different to that ?
Anyway that is it .
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No wonder you would, but bear in mind the target audience for this. It's supposed to be an easy to make model for the DIY community, and their 627, 637 and similar op amps were always damn expensive, at least in Europe.
And consequently, EXTREMELY hard to find.
If memory serves, OP 37 has some still high quality features, even today, after so many years, such as:
Noise - 4.5 nV/sq.rt Hz maxium at 1 kHz
Offset - 100 uV maximum
Drift - 0.4 uV/deg. C
CMRR - 100 dB minimum
Speed - 11 V/uS minimum
in addition to which it is widely available, and at a fair price.
I would have been happier with about double that Slew Rate, but even so, I still keep a solid stock of them et home.
Ultimately, if it's not your choice, AD 829 seems like a fair candidate to replace it. Not to even mention LT 11115.
Nigel, I was NOT in Camebridge, I was at the foot of the Quantock Hills in Somerset - one side the Quantock forest, other side green pastures in pure British Racing Green (if there's a greener green than that, I haven't seen it), and Bristol channel on the thrid side. Lord Taunton knew where to build his home, until 1962 that was a National Health board hospital for lung diseases, so you can imagine the purity of the air. On a clear night, I could see Wales.
My school, Quantock School, moved there from Bristol in 1962. In a triangular position with Taunton on one side, and Bridgewater (biggest Clarke's shoes factory in the UK at the time). Strictly countryside.
In terms of education, the school was under the auspices of Cambridge, we did their O and A levels. And we got their brainwashing regarding quality of examinations.
As I'm sure others did from Oxford.
My greatest stroke of luck regarding ye olde England was to get there before the Old World England went down the drain, like most such places the world around. I did get a whiff of the old type of family businesses, where you were no stranger, but a regular, and what you usually bought would be waiting ready and packed when you arrived even without asking.
I don't mind telling you that some of the aspects of being there impressed the hell out of me, and still do to this day. I was legally a foreign resident, yet in 1969, I received my notice to come and vote for the local authorities - this distinction between national elections, which I could not do (very naturally), and local elections, which shaped my local life without influencing that of the country, which I could do, is all on its own reason enough to respect the country's social system until my dying day. I'm not saying it was all perfect even then, but I am saying this shows a mature country, with clearly defined distinctions, and proud of it. As it should be.
And that was 1967-1970 period, a time when things were happening, and Britain was THE place to be in Europe, bar none.
But I got my university BSC from the Univesity of Belgrade.
My school, Quantock School, moved there from Bristol in 1962. In a triangular position with Taunton on one side, and Bridgewater (biggest Clarke's shoes factory in the UK at the time). Strictly countryside.
In terms of education, the school was under the auspices of Cambridge, we did their O and A levels. And we got their brainwashing regarding quality of examinations.
As I'm sure others did from Oxford.My greatest stroke of luck regarding ye olde England was to get there before the Old World England went down the drain, like most such places the world around. I did get a whiff of the old type of family businesses, where you were no stranger, but a regular, and what you usually bought would be waiting ready and packed when you arrived even without asking.
I don't mind telling you that some of the aspects of being there impressed the hell out of me, and still do to this day. I was legally a foreign resident, yet in 1969, I received my notice to come and vote for the local authorities - this distinction between national elections, which I could not do (very naturally), and local elections, which shaped my local life without influencing that of the country, which I could do, is all on its own reason enough to respect the country's social system until my dying day. I'm not saying it was all perfect even then, but I am saying this shows a mature country, with clearly defined distinctions, and proud of it. As it should be.
And that was 1967-1970 period, a time when things were happening, and Britain was THE place to be in Europe, bar none.
But I got my university BSC from the Univesity of Belgrade.
Yeah that's pretty crazy. The responsivity of silicon at ~10um is mighty low
With telcom I suppose he may be thinking of some slightly-smaller-bandgap materials, for fiber comm apps, but we're still talking quite dead for staring at room-temperature blackbodies.I made a photosensor-based-motion-detection audio delivery system once, and I operated the photodiode essentially open-circuit, with a CMOS opamp as the preamp. It had the happy feature of being roughly self-logging, so adapted to different ambients. But it worked so well that it required some very opaque packaging indeed not to go off when you didn't want it to.
Completely agreed. It's an unusually beautiful place, by any standards.
The Bazelgette drain is nice . First use of Portland cement . London sewer .
Yes I know . Dunster is nice . I went to the steam railway there about 8 months ago . Bristol has very nice people I find .
On audio topics . Is there a high current output op amp which is cheap and makes 5534 seem it should retire ?
Yes I know . Dunster is nice . I went to the steam railway there about 8 months ago . Bristol has very nice people I find .
On audio topics . Is there a high current output op amp which is cheap and makes 5534 seem it should retire ?
Cinema
Gangster No 1 was a rubbish film . I supplied the Dansette record player for that ( a favour ) .
If , Oh lucky Man . Ipcress file . The list is endless .
I have been researching film sound . I am getting nowhere . What were amps like in 1930 . I know about guitar amps . Not them . PX25 ?
A friend and me were thinking if we could process film optical strip with modern techniques . We reckon the playback was not as good as the recording . There could be a big harvest of new music there .
Gangster No 1 was a rubbish film . I supplied the Dansette record player for that ( a favour ) .
If , Oh lucky Man . Ipcress file . The list is endless .
I have been researching film sound . I am getting nowhere . What were amps like in 1930 . I know about guitar amps . Not them . PX25 ?
A friend and me were thinking if we could process film optical strip with modern techniques . We reckon the playback was not as good as the recording . There could be a big harvest of new music there .
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Modest-power tube amps and horns. Check out the history of Western Electric, among others. My refs are buried in storage or I could be more specific.
One problem with all film optical audio tracks, even relatively recent ones: they wear out in a hurry. That's one of the reasons DTS is a continuing success, supplying audio that merely has to be synchronized to the film. And the "flywheel effect" of their servo system is significant, so some fairly large dropouts can be readily accomodated.
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