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.
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.
Over the next few days, we will be changing the Blog pages and the hosting service for WaltJung.org. While we are sure things will work out in the end, there may be some temporary interruptions to email, and possibly some web pages. Please bear with us, and thanks!
As of PM of July 18th, we are now running under a new installation of WordPress, with all new web hosting. Fingers crossed!
Further update, July 24th: We did have some hickups with web hosting, which is now resolved.
Not only do the articles describe a useful mod path for the Dyna ST150, but they are still generally applicable within almost any power amp, especially the power mods. Many thanks to Pat and Jim for their help in making these articles available.
We are happy to be able to make these three articles once more available, under the category of Guest Contributions. And, it is also a pleasure to renew contact with both Pat and Jim, after 30-plus years!
We are very pleased to be able to have available here in PDF format Mike Sulzer’s classic articles from The Audio Amateur, issues 2/1980 and 1/1981. These two articles are: A High Quality Power Supply Regulator for Operational Amplifier Preamplifiers (published in TAA issue 2/80), and Regulators Revisited (published in TAA issue 1/81). A ZIPfile package of these two articles is available, for fastest downloads.
These two articles are unquestionably classic mileposts among DIY audiophiles, and essentially started the serious development of quality regulation as an integral part of higher performance audio schemes.
Our sincere thanks go to Guest Contribution author Mike Sulzer for responding to the initial request from Waltsblog reader Nikolaos Baxevanakis, and making these articles available. So, enjoy the articles Nikolaos!
Of course, we hope that many other readers (and re-readers) may also do so.
Chris Paul asked a question on an old NE570/571 gain control application, causing some digging on my part to resurrect the 1977 Ham Radio article. The results are posted as the most recent By Request entry (right).
Audio editor and publisher Edward T. Dell Jr. passed on last week, not long after celebrating his 90th birthday with his family and friends, including many from his local parish, All Saints’ Church, in Peterborough, NH. His funeral will take place at 11AM on Saturday, March 9, at All Saints Church.
Ed was born February 12, 1923, and died February 25, 2013. He was very well known among audiophiles, having published thousands of their articles in his various audio-related publications — The Audio Amateur (TAA), AudioXpress, Audio Electronics, Speaker Builder, and Glass Audio. These audio publications began back in 1970 with TAA, in Swarthmore, PA. Later on Ed moved his Audio Amateur, Inc. operations to Peterborough, NH. He was recognized by the Greater Peterborough Chamber of Commerce in 2010 as one of their “Legends of Business: Publishing Pioneers”.
Over the past 40 years, I was fortunate to write many articles for Ed’s various magazines, beginning in TAA issue 2/1973. That was the start of a long and fruitful relationship. Ed Dell was a pleasure to work with on those articles. Today, this is a satisfying thing to me, knowing that many of them are here as web versions, hopefully useful for some time yet.
It is difficult to write a concise summary of a person’s work spanning more than four decades, and capture the essence in a couple of sentences. Shortly after learning of Ed’s passing, I exchanged some emails with fellow author Jan Didden, on the influence of Ed’s work. I said this to Jan: “Ed Dell certainly did leave large footprints along the path towards better audio, especially our DIY audio, where he was really the one who did the most. He was simply a great enabler for folks like you and me.”
Well, I think that’s a true statement centered on Ed’s greatest contribution; he enabled and encouraged many people to tell stories of their audio designs, especially with home built equipment. Yes, he was also a great editor, and one learned lots of useful insights on audio technical writing working with him. But the combination of a skillful editor sharing your own objective of making better audio working on your articles was, to me at least, a most invaluable thing. I’m sure that many other authors feel the same way. Ed’s love of audio was the same as mine, and this was perceived mutually!
In 2011 Ed Dell sold his publishing assets to the Elektor group, which today publishes audioXpress. They recently published an online memorial, Edward T. Dell, Jr.: In Memoriam.
Jan Didden interviewed Ed Dell for the pages of audioXpress in October of 2011, and has kindly made this available on the web. Jan has also started an “Ed Dell memorial” thread on DIYAudio, which can be found here. Understandably, one can find many comments there underscoring the value of Ed Dell’s audio efforts. Waltsblog readers can also leave comments here as well, should they wish (just register first). I especially want to encourage any of Ed’s many authors over the years to do so.
Our audiophile editor/publisher friend Ed Dell deserves honor for all the good work he did for so many years. He’ll be missed here, as well I’m sure in many other places populated by audio nuts. He has left truly a great tangible legacy within all those audiophile magazines, for forty-plus years. So, I’d advise you to hang onto them!
Condolences to Ed’s family on their loss. And, thanks to son Chad Dell, who helped with several details of this memorial.