John Curl's Blowtorch preamplifier part II - Page 3498 - diyAudio
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Old 13th February 2013, 07:47 AM   #34971
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Quote:
Originally Posted by Esperado View Post
I wonder why they don't exist in a standard OPA case ?
If you're talking about the xDSL line drivers in SO8, there's AD8017

Limited to 12V supply though, otherwise top notch part and super-cheap on Taobao
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Old 13th February 2013, 02:00 PM   #34972
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Quote:
Originally Posted by DF96 View Post
Could someone remind me of the mean free path for electrons in, say, normal electrical copper?
3 times 10e-6 cm.

jn
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Old 13th February 2013, 03:00 PM   #34973
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Quote:
Originally Posted by jneutron View Post
3 times 10e-6 cm.
Sounds about like my mean free path out in our garage.

se
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Old 13th February 2013, 03:04 PM   #34974
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Quote:
Originally Posted by qusp View Post
yep i'm just pretty familiar with this crossover (TPA6120 vs THS6012) and already knew of the designs done by jcx and threads over at head-fi. the TPA isnt the only part, there is a few of the old natsemi DSL parts make nice headphone amps, the loads are pretty similar if you think about it. like the TPA they are often current feedback.

ps. dont be so tense Richard
Yes I endorse jcx's efforts. The one we did used one of the drivers intended for the consumer premisis end and was only USB powered. IIRC the CMoy headamp from the headwise forum with the AD8397 is close (+5 with 2.5V common mode level). You should be able to get 8V p-p even at 32 Ohms
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Last edited by scott wurcer; 13th February 2013 at 03:17 PM.
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Old 13th February 2013, 03:07 PM   #34975
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Quote:
Originally Posted by Esperado View Post
I wonder why they don't exist in a standard OPA case ?
No major manu uses through hole technology anymore.
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Old 13th February 2013, 03:25 PM   #34976
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I do like the TPA6120/THS6012 but having started using it I really haven't surveyed the alternatives since - its too easy having the "audio speced" datasheet

and I haven't put up any project schematics - advanced multiloop version I've built was too complex, doesn't like hot plugging TRS headphone jack/plug shorting the multilooped outputs - initiates a large signal oscillation - the chips survive but have to power cycle the amp to quench it

eventually I may revisit conditional stability "nonlinear compensation" (anti-windup clamp diodes are a start)

for a safer diy project amp I'd 1st just back off on the order of the multi-loop compensation - CFA can be used as unity gain buffers with a feedback R

Last edited by jcx; 13th February 2013 at 03:27 PM.
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Old 13th February 2013, 03:28 PM   #34977
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Quote:
Originally Posted by scott wurcer View Post
No major manu uses through hole technology anymore.
Video killed the radio stars
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Old 13th February 2013, 03:33 PM   #34978
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Well, where we? Some here think that 5V/us op amps are better than OK, then somebody else insists on 1000V/us op amps are much better. A ratio of perhaps 200/1.
What is really necessary when it comes to slew rate? Of course, the answer is partially: IT DEPENDS. Well, what does it depend on? First, AMPLITUDE. All else being equal, the necessity of driving more volts to do its job, makes the POWER AMP a prime candidate for high slew rate. In fact, modern power amps are up to 28.2 times more prone to slew rate limiting, than the driving preamp, because that is their fixed gain. The preamp, being behind the power amp will always work 28.2 times lower voltage level with a JC-1, for example, or many other power amps. Of course, some amps only have a gain of 10 or so, therefore the preamp is then somewhat more prone to needing somewhat more slew rate, and this is WHY we set the slew rate limits at 5V/us for preamps and 50V/us per 100W, or 100V/us for 400W power amps.
The next factor that is VERY IMPORTANT in setting slew rate limits is the WORKING BANDWIDTH of the audio system.
Some people seem to love limited bandwidth and perhaps they seek it out, so their slew rate needs are minor, yet others, are wide bandwidth enthusiasts, and they want an effective bandwidth of over 100KHz, even 1 MHz, if possible. It would seem that such wide bandwidth would attract RF, and interference to pass on with the audio signal, and the only way that these added signals do not create IM with the audio signal or each other, is to have extremely high slew rates, more than any audio signal, itself could possibly need. So, 1000V/us might well be useful. Also, advanced techniques that create this very high slew rate, invariably increases the gain bandwidth, potentially reducing PIM, and any other dV/dT related distortion. So now, we have a reason for very high slew rate.
Why do I use medium slew rate speeds today, rather than the very high slew rates like amps I designed in the past, is subject to another discussion.
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Old 13th February 2013, 03:47 PM   #34979
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It may well be that surface mount is taking over the world. So what? There was a time when discrete semiconductors took over from tubes, back in the middle '60's and people traded in their Marantz and Mac tube gear for solid state. And what did they get for it? It will be the same for surface mount. MANY pitfalls in surface mount, marginal parts, etc.
I personally will probably design with discrete components with IC's added in, when useful or necessary, for the rest of my lifetime, but you all go right ahead!
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Old 13th February 2013, 04:31 PM   #34980
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There are numerous advantages to the newer leadless SMD packages (as well as SMD in general). The device packages with the thermal pads on the bottom allow us to get the heat away from the actual chip more efficiently as long as you lay the board out correctly, as well as reduced package parasitics.
Quote:
It will be the same for surface mount. MANY pitfalls in surface mount, marginal parts, etc.
Sorry John I have to disagree with you BIG time on this, most of todays electronics are much more reliable than they use to be, and with the number of electronic devices built each day (6 billion discrete components placed a day) and failure rates very low, this view is just wrong. There are numerous advantages to surface mount, not just the ones above, high speed digital would not be able to achieve the speeds it is without SMD packages and the lack of parasitics, analogue can be laid out with the smallest loop areas you can imagine... And surface mount is not new, I have been laying out boards for surface mount devices since the late 80's (88-89ish), 24 years approx, that is quite a long time. It has revolutionised electronics and even though some die hards may think it is inferior you are wrong. With some of todays op-amp packages I can get 2 8 pin op amps and discrete circuitry in the same area as the origional 8 pin SOIC (1.27mm between pins).
So no SMD is very benefitial to design and is not inferior, at the end of the day you are likely to have the same die in a standard DIP package as you are a new DFN package, the difference bing the old package has long leeds and a lead frame (parasitics) and is harder to get the heat away from the chip...
As I said its not new technology, there is no it will be the same for SMD, its been here for years.
And if you want high slew rates you need to minimise parasitic inductance for one, something SMD devices can do.
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