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.
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.
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In The Audio Amateur issue 2 of 1981, two Dynaco ST150 amp modification articles appeared. One was titled ‘The ST-150-BJ-1 A Boak-Jung Modification of the Dynaco Stereo 150 Amplifier’, and it was authored by Pat Amer. This article was on the general ST150 modification process, and it included both circuit upgrades and a set of power regulation mods. The specific power mods were developed by Jim Boak, who also wrote a related article, titled ‘Power Modifications for the ST-150-BJ-1‘. This second article is definitely Dyna ST150 oriented, but Jim also wrote a more general version, within The Audio Amateur issue 1 of 1980, titled ‘A Family of Power Amplifier Regulated Power Supplies‘.
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).
Back in Audio Amateur issue 1 of 1980 David M. White Jr. published a very worthwhile system tool project, titled A Dynamic Range and Clipping Indicator. With a full instruction set including PCB layout, parts list, and a detailed schematic, this design uses an LED array for display of dynamic signal peaks.
Dave recently upgraded the original hardware, as part of a complete system restoration. He has retired to a new home, and is now busy on the listening room and upgrading his home-built electrostatic arrays along with the associated complex crossover and drivers. As for the Clipping Indicator, he has indicated that all parts are still available, but today’s modern LEDs should provide longer lifetimes than did the old parts. Thanks for sharing a useful design with us once again, Dave!
Recently, we had an occasion to review some very old Audio Amateur articles, dating all the way back to issue 4 of 1975. Among them was Morrey’s Super Oscillator, by Walter T. Morrey. This article was a landmark piece in a couple of regards. It provided a comprehensive update for the Heath IG-18 sine wave oscillator, a popular test bench instrument of the period. In it Walt Morrey lays out numerous IG-18 improvements, going far beyond the typical DIY “tweaks”. The replacement op amp topology used for the IG-18 is just as sound today as it was in 1975 (setting device availability as a side-issue). In fact, some of the cascoding features used within individual stages were not only superior then, but also remain so today.
It would be interesting to see someone develop this op amp circuit into a discrete part modern realization, using some of today’s improved complementary SMD active parts. Thanks to Walt Morrey for sharing this classic with us!
(originally posted Feb 2013)