530 ohms and driven from an unbuffered OP6x7?
That's why your distortion is what it is- and I bet it's actually a lot higher, given the load and the fact that you have gain at HF due to the tone control action.
You have used a high performance, expensive op amp and gotten a less than satisfactory result.
It is easily fixable though.
That's why your distortion is what it is- and I bet it's actually a lot higher, given the load and the fact that you have gain at HF due to the tone control action.
You have used a high performance, expensive op amp and gotten a less than satisfactory result.
It is easily fixable though.
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Hi,
Burr Brown show the OPA627 driving 600 Ohm without buffer in their datasheet.
The data for Self's pre'in post #1 is specified tone controls defeated (and at low output voltages). You are welcome to post data for Selfs pre with tone controls engaged and the HF control set to maximum.
The gain at HF is limited at 23dB (HF fully up), the load at 20KHz is 530 Ohm. The rest is easily worked out.
That depends how we define satisfactory. Also note my original post suggested adding a buffer. That said, I personally would not consider it necessary but tastes vary.
Also, how about we compare my circuits and Self's apples for apples - both with tone control defeated - at 1V out?
Until you show Data for Self's Pre under the conditions that you use to criticise the design I posted, maybe we better focus on what can be compared? Otherwise, you may find perhaps that Self's design is also not all that horrorshow at 7V out and maximum treble boost...
If indeed it needs fixing, the "fix" is in my original post.
I would still suggest that for real world use in real systems it does not NEED fixing.
Ciao T
Burr Brown show the OPA627 driving 600 Ohm without buffer in their datasheet.
The data for Self's pre'in post #1 is specified tone controls defeated (and at low output voltages). You are welcome to post data for Selfs pre with tone controls engaged and the HF control set to maximum.
The gain at HF is limited at 23dB (HF fully up), the load at 20KHz is 530 Ohm. The rest is easily worked out.
That depends how we define satisfactory. Also note my original post suggested adding a buffer. That said, I personally would not consider it necessary but tastes vary.
Also, how about we compare my circuits and Self's apples for apples - both with tone control defeated - at 1V out?
Until you show Data for Self's Pre under the conditions that you use to criticise the design I posted, maybe we better focus on what can be compared? Otherwise, you may find perhaps that Self's design is also not all that horrorshow at 7V out and maximum treble boost...
If indeed it needs fixing, the "fix" is in my original post.
I would still suggest that for real world use in real systems it does not NEED fixing.
Ciao T
In your anxiety to discredit Self you have become unselfcritical to the extent that you condemn him for a behaviour in which you yourself indulged a few lines previously in the selfsame post. Your position is repugnant. It is clear that you take us all for such fools as not to notice.
I,for one, look forward to your investigations into the subjectivist claims that ripping CDs to a solid-state drive as opposed to a rotating hard disk or that ripping CDs in safe mode as opposed to under Windows booted normally both result in superior-sounding copies.
Then again, if any of you would actually had read the article, you'd know how Douglas took care of that.
jan
He sure does love that old warhorse the 5532. For a 30+ year old part it remains remarkable in terms of measured performance, if not sonic reputation. I used it in my THD Analyzer way back when and got great results, and still use it for instrumentation. They are now dirt cheap.
They do have a very good noise figure of merit in regard to the tradeoff between voltage noise and current noise. It is weighed a bit differently than the 4562. I think TI BB now has an op amp out that is a bit more like a 5532 in that respect, but I cannot remember the number.
Doug also loves bipolar op amps and circuits, while I much prefer JFETs, even if there is a slight noise penalty. The obsession with low noise in a phono preamp is a bit over-done, especially in regard to S/N measured with inputs shorted. That is only one important parameter.
I would have expected to see at least one or two JFET op amps in there if he was using a DC servo.
In any case, it should be a very interesting read, and Doug always does his homework.
Cheers,
Bob
Hi,
As the object of discussion was how well DS's design measures I stuck mostly to measurements. We have another thread where we debate how meaningful these measures are.
I will agree that they are in themselves meaningless and I have repeatedly questioned in this very thread here the value of "low THD". My behaviour is quite consistent on that, I merely pointed out that similar noise levels and distortion can be had from a much more simple and direct circuit than that published by DS.
I understand that to those who worship him as god this is heresy, too bad.
It would behove DS well to progress from simplistic "minimum THD" to "lowest distortion audibility" which involves looking at the spectrum of a given THD as diagnostic and applying weighting. In many caes if you look at his investigations the lower THD comes at the cost of less favourable audibility of distortion. Howver as he has not done so for the better part of 3 decades to my knowledge I will not hold my breath.
So, any volunteers for THD(20KHz) of DS's preamp with the treble control all the way up and 7V output signal?
This is not to place undue emphasis on this measurement, but rather because the fact that the circuit I suggested has around 0.05% THD under those conditions, without actually showing how much better the circuit from DS actually is.
Ciao T
As the object of discussion was how well DS's design measures I stuck mostly to measurements. We have another thread where we debate how meaningful these measures are.
I will agree that they are in themselves meaningless and I have repeatedly questioned in this very thread here the value of "low THD". My behaviour is quite consistent on that, I merely pointed out that similar noise levels and distortion can be had from a much more simple and direct circuit than that published by DS.
I understand that to those who worship him as god this is heresy, too bad.
It would behove DS well to progress from simplistic "minimum THD" to "lowest distortion audibility" which involves looking at the spectrum of a given THD as diagnostic and applying weighting. In many caes if you look at his investigations the lower THD comes at the cost of less favourable audibility of distortion. Howver as he has not done so for the better part of 3 decades to my knowledge I will not hold my breath.
So, any volunteers for THD(20KHz) of DS's preamp with the treble control all the way up and 7V output signal?
This is not to place undue emphasis on this measurement, but rather because the fact that the circuit I suggested has around 0.05% THD under those conditions, without actually showing how much better the circuit from DS actually is.
Ciao T
At 20KHZ and 8V rms it will do 10ppm THD with the circuit a few pages ago
using a 5532.
The OPA627 has no valuable spice model , at least the ones at my disposal,
and does not produce realistic figures since in the sames conditions
it yield zero HD , wich is a joke , since many use this very model
to make spice sims that will indeed produce great but completely
false results.
You should be aware that it s in inverting mode and in such a configuration,
dont expect a OPA627 to beat the ancestor.
This graph was posted by there by Gerhard :
Attachments
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Sure, inverted the NE works great. Fet Opamps have usally problems with transfer linearty because input impedance is not linear. The OP!627 is even a good example because the input Fets are cascoded. The OPA134 is much worse athough you can find it in very high prices equipment ( f.a. in older Rowland ) because of the "sound".
Hi,
There are some of us who understand what his regimen is and don't need
teaching to suck eggs about the finer points of distortion "audibility" or
circuit design / philosophy/ layout in general.
I don't agree with him in some respects but have still learned a lot from
his stuff, and I think that is the position of many here. He isn't a god, and
has never pretended to be, but you do know where he tries to stand.
People are allowed to think differently, but its just tedious you get the
same old very tired arguments in any thread about D. Self's stuff.
rgds, sreten.
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From your numerous post here one might get the impression you believe
you know everything in every field, so probably you want to be the audio
god instead of him... ;-)
Then again, if any of you would actually had read the article, you'd know how Douglas took care of that.
jan
Just be clear, I was referring to the OPA6x7 devices. The input 'part' of this opamp is outstanding, but you need to be careful about what kind of load you drive. But, easily fixed so that you end up with the best of both worlds. But, it burns a whole in ones pocket that's for sure.
As a reminder I pointed out years ago that this general op-amp topology has a dramatic, at times, increase in noise beyond audio frequencies. It may not matter but it is a hidden problem.
Hi,
But that is not the circuit D Self uses and this circuit alone is not useful for a complete preamp (it needs a buffer before it) while mine is.
So, anyone for D Self's circuit at 7V RMS output and the treble control fully up?
Ciao T
But that is not the circuit D Self uses and this circuit alone is not useful for a complete preamp (it needs a buffer before it) while mine is.
So, anyone for D Self's circuit at 7V RMS output and the treble control fully up?
Ciao T