I recently received a very interesting email from Walt Kester, my friend and former co-worker at Analog Devices Inc. (ADI). In it he was announcing the online availability of about 30 ADI books. I am paraphrasing his note as follows:
This link will take you to a PDF file that allows you to download material out of any or all these books:
The PDF file has active links to the table of contents and the actual files for all the books published over the 50 year history of ADI, including a collection of op amp articles by Ray Stata from the 1960s.
Thanks for assembling such a powerful collection, Walt! I’m sure many readers will find this most useful.
Looking for a low noise reference circuit for an audio regulator, at 2.5V? But you’ve found bandgap circuits too noisy? Read on!
Consider the simple circuit to the right, which I call the GLED431. Just 3 low cost parts, all easy to get. It acts like an extremely low noise 2.5V zener. On my setup, noise measures around 2nV/√Hz, so if you take out the measuring system noise, the actual noise is likely below 1nV/√Hz. Really quite good. We’ll have more on this later on, in 2016.
While the GLED431 performance is very high for noise, you will need to apply about 5mA (or more) to make it work. Yes indeed, this current threshold is much higher than that of the TL431. But, it also has around 1/100 the noise! Caveat(1): The voltage won’t be as tight as typical bandgap ICs, nor as low for temperature drift. Those are conscious tradeoffs.
Here are some Vout measurements on a sample set of 5 LTL-4231Ns, in the lab prototype shown, after 1 minute warmup:
Not too shabby! In the schematic, the leftmost R values are just as shown from lab tests, as trimmed for the 2.500V target Vout. Obviously, just use a single 150Ω RN60D unit for this R. Note that the forward voltage of the LTL-4231N green LED (LiteOn) and the Vbe of the ZTX951 (Diodes Inc.) conveniently add, producing the desired Vout of 2.5V. Caveat(2): These two parts should not be changed if you expect to get close to 2.500V!
In use, if you are building say, a 5V regulator, select a series resistor so that 5mA is supplied to the GLED431 cell (499Ω). With this, also be sure to select a very low noise op amp, and reduce all the surrounding resistances, so as to minimize their noise contributions. Finally, be careful to minimize capacitive loading.
I am now releasing this simple version, as a Christmas present to the readers. Stay tuned for more, have fun with the GLED431, and have a great holiday!
We are pleased to note that Gary Galo has recently made a very large Guest Contribution to this website. This is in the form of a series of his notable preamp modification articles, that appeared in AudioXpress. The articles are listed below in the sequence they appeared. Click the individual link for a given article. A ZIPfile with all the articles is available as well, at the end.
The four (+) part series on modifications to the Adcom GFP565 preamp:
After fighting various forms of SPAM comments for way too long, we’ve decided to try a new system for comments from users. It is effective now, and will enable a comment sent via email, on any aspect of this website.
Simply use MakeWebComment at WaltJung.org as your target email, after changing the ” at ” appropriately (no spaces, subbing an uppercase 2). That’s it. Write on!
Due to several requests, the ‘Classic Articles’ page from the old WaltJung.org has been restored, and now includes various updates. To access, see the Classic Articles Page to the right, or just click on the name here.
This will allow easier access to quite a few older articles such as those related to SID/TIM, and more recently, quite a number on composite audio stages. Enjoy!
It is with great pleasure that I am today announcing a new feature page at Waltsblog, one devoted to Ebook editions of my old books by Howard W. Sams and other publishers. Some of these books go back as far as 1974, long before today’s world of digital versions and instant accessibility to their technical content.
I have had requests for many years about making these older books available, and it has been a struggle to get to this point. Nevertheless, this point is here now, and I am tickled with the first results. I think you will be also.
This new page can be found at Walt Jung Ebooks, accessible on the right. Simply follow the instructions there, noting those books which are available. As always, feedback is welcome. You can of course make a request for another book; this will be helpful.
In Grayson King’s ‘Valkyrie’ Preamp Guest Contribution post, a related piece was mentioned. This one is Klaus Noll’s Showcase: A Headphone Amplifier, which appeared in AudioXpress in May of 2003. We are pleased to add this work by Klaus as another Guest Contribution.
Klaus Noll’s article is similar to Grayson’s in that it describes a line-stage type preamp with a wideband composite amplifier using the AD744/AD811 pair, but optimized for headphone use. It also differs with regard to the power supply regulators used, which are similar to the Improved Regulators from Audio Electronics of 2000.
In response to my query on posting his article here as a Guest Contribution, Klaus said:
“Thank you very much for your flattering letter which arrived today a little belated. Of course you can put the article on your website, after all it is your intellectual property which I used to build what I think must be one of the five best headphone amplifiers in the world. Thank you again and kind regards.”
Well thanks to you Klaus, first for building such a fine preamp/headphone amp, and for sharing the details via AudioXpress. And of course, for offering it now, as a Guest Contribution here.
Both Grayson and Klaus have created worthy DIY audio projects, with full PCB patterns and part details, and it is great to be able to reprise them here.