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:
Part one, from the 11/03 issue of AudioXpress.
Part two, from the 12/03 issue of AudioXpress.
Part three, from the 01/04 issue of AudioXpress.
Part four, from the 02/04 issue of AudioXpress.
A follow up, from the 12/04 issue of AudioXpress.
Miscellaneous letters and corrections.
Another preamp article, on Gary’s design of a music library preamp, for the Crane School of Music, SUNY Potsdam.
A zipped file with all seven articles (~12megs).
It is a real pleasure to be able to make this landmark series of preamp articles available to the readers of this website.
Our thanks to Gary for making all of this possible, and for executing some superb examples of true DIY craftsmanship!
We are happy to announce a new article on higher performance audio regulators, one that has been too long in gestation. Nevertheless it is finally here, and is now available via the References & Regulators page, just see the latest entry (scroll down, to May/June of 2015).
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!
In response to some requests, the Walt Jung Books page has been restored with some updates. Click on the above link, or see page link to the right.
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.
Since I’ve been running this website, I have had numerous emails about past articles. These have increased of late, which is a good thing. One of the more interesting developments have been the “By Request” and the “Guest Contributions” categories. Here’s an excerpt of a recent email one from Vladislav Polur, which falls into both. I have made some minor edits, for clarity:
“I am sending you a link about a review of a preamplifier made based on your article about using video op amps in audio. I could not find the author of the preamplifier. The reason I am interested in this design is because I had a chance to listen to an amplifier based just on signal op amps, within my friend’s system. It was a great experience; it sounded better than any amplifier I had a chance to hear before, tube or solid state.”
I think Vladislav may have given me a bit too much credit for the entire preamp realization, even it was/is in part based on my work appearing within Gary Galo’s POOGE-5 article. That box insert did in fact use video op amps, and it was titled High Performance Audio Stages Using Transimpedance Amplifiers. That preliminary piece sets the stage for the highlight item of this post, as follows below.
The item that matches up best with Vladislav’s listening experience and his cited link was Grayson King’s preamp project. This work was from the 1994 series of The Audio Amateur, and was entitled Valkyrie: A Line-Stage Preamplifier. The preamp was Grayson’s senior project while at Clarkson University in pursuit of his EE degree. It was developed under the tutelage of Gary Galo, and it did indeed make not just a fun university project, but also a great example of a worthy project for others. Grayson did do a fine job with his preamp! After graduation he took a job with Analog Devices in Boston, working in the same department as I did then, applications engineering.
It is a pleasure to help Grayson’s preamp to find some new friends here, and I want thank him for helping to make it all available once more, as a “Guest Contribution”.
A final note for those pursuing line stage performance. Another such preamp was described in Klaus Noll’s Showcase: A Headphone Amp, in AudioXpress, May 2003.
I recently received an email from a reader, Anton, residing in Moscow, Russia. He had built a version of the Improved Positive/Negative Regulators from Audio Electronics, Issue 4, 2000. While his circuit was functional, he was concerned by the fact that when he applied a 360mA load, the output voltage dropped, an apparent loss of regulation. This sounded to me like the regulator didn’t have enough drive under load, so I suggested some things to check:
Is the D7 LED ON, under all conditions? If it goes out, it means the pass transistor is starved for current, and the output then falls. If you have a pass transistor with a Beta of 100, a 360mA load means the current source must provide 3.6mA. But note that this is close to what it can do with R19 (Fig. 1) at 249Ω. You may need to drop this resistor down some, if you really need 360mA of output. Note: there was a discussion on this very topic, on page 11 of the original article, under the topic “Change of Current Source Resistor” (i.e, R19). The upshot here is that the older R19 value of 100Ω provided for more current, so I suggested that Anton lower this resistor value, to see if it fixed the voltage dropping under heavy load. He later reported back changing R19 to 160Ω (just for test), and it worked correctly with the 360mA load.
I was glad that he got it working OK, and pointed out should drop that R19 value down some (if he does in fact need 360mA). I left that for him to determine. If you need much less current, then leave the value as it is.
The moral of the story is that the circuit is robust, but it does have fixed limits. So, if you find the output dropping unexpectedly, check the load current carefully, both on board and external.
Thanks for the report, Anton!
This was a great article and I actually built a test circuit based on Figure 16a in part 2 of the article. However, I wanted to use the source for a mosfet in a headphone amp circuit. The circuit is designed to operate the mosfet at 150 mA. I used a more robust transistor in place of the pn2222a. It worked just fine and I was able to dial in 150 mA of current. However, I don’t have the test equipment to measure performance. I’m curious if anyone has tried to get more current out of this circuit and what type of performance resulted.