John Curl's Blowtorch preamplifier part II - Page 3711 - diyAudio
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Old 23rd March 2013, 01:14 AM   #37101
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Coco Bollo is really related to poison oak and it is the same type of reaction. I found that out the hard way also and always wear gloves and long sleeves now when I work with it. Bonding it to itself to make larger pieces is a real pain and dowels or biscuits are the preferred method of assembly. I use West Systems epoxy to bond it together, it works with oily woods such as teak.
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Old 23rd March 2013, 01:17 AM   #37102
gpapag is offline gpapag  Greece
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Quote:
Originally Posted by simon7000 View Post
Thank you Ed for explaining this number.

My tests there had to do with 78xx too.
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For these regulators, keep the Vin to Vout a minimum of 5V.
For PSU capacitance, see some good work from gootee (this post and on) Power Supply Resevoir Size

George
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Old 23rd March 2013, 04:49 PM   #37103
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Quote:
Originally Posted by gpapag View Post
Thank you Ed for explaining this number.

My tests there had to do with 78xx too.


For these regulators, keep the Vin to Vout a minimum of 5V.
For PSU capacitance, see some good work from gootee (this post and on) Power Supply Resevoir Size

George
George,

You are welcome. The reference you gave on capacitor rating is an interesting method. It is not the way I do it. It is important to allow for line voltage extremes, a few hundred milli-ohms of AC line resistance, power transformer equivalent resistance, diode droop and ripple.

Ripple is more of a linear slope due to the almost constant current draw. Do C dv/dt = I works well for the discharge drop. The charging time gets more interesting due to the rise in transformer output voltage as the capacitor charges.

But is a nice example of good math.

ES
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Old 24th March 2013, 01:09 AM   #37104
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Forgot about this my mother's quilt of the AD712.
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Old 24th March 2013, 01:11 AM   #37105
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And then there's Bob Widlar's general opinion.
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Old 24th March 2013, 01:47 AM   #37106
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And then there's Bob Widlar's general opinion.
Ah, yes: "Binary? Any idiot can count up to one!"

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Old 24th March 2013, 03:12 AM   #37107
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Bob Widlar didn't think much of using IC's for audio preamps, either. '-)
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Old 24th March 2013, 06:27 AM   #37108
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Default Op-Amp Problems ?....

Hello John.
We all know that the typical recording process typically involves passing audio signal through many amplifier stages until the signal is encoded onto a storage medium, generally tape, vinyl or digital.

In the typical playback process, the recovered signal is processed through several low level amplifier stages before being presented to power amplifiers and then reproduced by acoustic transducers of one sort or another.

The recording and storage processing can involve tube, discrete or op-amp stages, ditto playback signal can be passed through tube, discrete or op-amp stages, each low level amplifier type having individual characteristics.

What do you perceive as the 'problems' with op-amp stages ?....is it high levels of global feedback, thermal/mutual coupling of ic circuit elements, internal excess noise generation....or what ?.

Objective information would be good, and your subjective opinion is equally valuable please.

Thanks, Dan.
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Old 24th March 2013, 07:40 AM   #37109
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There are dozens of potential problems with IC's. All we can do is minimize them the best that we can. For example, the JC-3 phono stage (made with IC's) is a bargain, BUT it is not as good as my discrete phono designs. I would not expect it to be.
When I asked Bob Widlar about using IC's for audio back in 1974, at an ISSCC Conference, he directly stated that IC's (up to that time) were NOT the best that could be done for audio circuits. He knew the tradeoffs, probably better than most IC designers at the time.
Of course, IC's have improved, BUT they still have the same residual problems that Bob Widlar knew about intimately.
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Old 24th March 2013, 09:56 AM   #37110
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so nothing specific then?... just a few unnamed yet consistent and persistent issues that havent been solved in 40 years?
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