by Guy Torio
On Monday, October 23rd, John Hardy of the John Hardy Company gave a presentation on the considerations in audio circuit design. This first meeting of the year was a joint meeting with the Columbia College AES student section. The meeting and proceeding Pizza social were held at Columbia College.
John began his presentation with an informal discussion of component quality and spent a good deal of time talking about the merits of using quality capacitors. Components with higher than average temperature ratings (105 degrees Celsius) typically last much longer (based on experience John gained from re-capping several consoles). John went on to discuss how ceramic capacitors have received some bad press because reviewers were not aware of the different grades of ceramics and their radically different performance attributes. John only recommends the COG type of ceramic capacitors for serious audio design, since their capacitance and dissipation factor is virtually constant with temperature, frequency, DC voltage, and AC voltage variations. Known for his high quality microphone pre-amps, John discussed the challenges of packaging power supplies with strong radiated magnetic fields close to electronics while trying to achieve a noise floor of just 129 dBV. John is a strong advocator of input transformers for audio electronics due to their superior common-mode rejection ratio and spoke about how publications not recommending transformers for audio where plagued with bad measurement techniques and erroneous results. He did admit that if you are going to use transformers for audio work they should be of the highest quality. John then went on to show a slide presentation of various electronic design projects he has worked on during his career including a multi-track tape machine record and playback electronics, custom sound reinforcement console designs for dB sound, and production iterations of the 990 discrete Op Amp. During the presentation he discussed various aspects of design including minimizing the number of components, designing for expandability, grounding schemes, manufacturing issues, and packaging.
The Chicago section would also like to extend its appreciation to Mr. Hardy for taking the time to share his work with us at last month's meeting. Special thanks to the members of the AES Columbia Section for making the facility arrangements and providing a relaxed atmosphere for our first meeting of the year.
