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Category: Articles
OPEX-1: A Discrete OPAMP for Audio
This design showcases a discrete opamp for audio applications. It features very low noise, low distortion and a class A output stage that will deliver 1ppm distortion into a 600 Ohm load at 12 V peak. OPEX-1-Discrete-Opamp
Solid State Relay with PCB Layout
A complete relay that is smaller than a Tyco RT series EMR Simple_solid_state_relay_Updated . This design uses a small double sided PCB and some SMD components. Here are the Gerber files SSLR. The recomended mosfets for this design are the PSMN4R3-100PS[1] for supply rails of up to +-50 V absolute maximum, and for supply rails of up…
Augmented Feedback Error Correction (AFEC)
AFEC is a simple technique that augments the feedback of an amplifier to dramatically improve the Large Signal Non-linearity (LSN) distortion performance by up to 20 dB across the audio band. Additionally, AFEC acts to remove any DC offsets and also improve PSRR significantly. Augmenting the feedback in a manner similar to that described in…
Output Coupling Inductors
Inductors on the output of an amplifer are used to isolate the amplifer from capacitive loads at HF and ensure stability. There has been quite some debate on DIYaudio.com as to whether they are audible, necessary, or just the result of designers being overly cautious. Some very well known designers in the field have decided against using…
Oscillation Sniffer
No ‘scope? This simple circuit can help you quickly see if you have any oscillation problems on your opamp or amplifer circuit. Note, its NOT designed to be connected to high impedance nodes. Oscillation Sniffer by Bonsai
H.S. Black: Feedback
Feedback, or its application by humans as control theory, despite the protestations of audio designers that eschew its use, is an entirely natural phenomena. Every time you reach out to pick up an object, get up and walk around, or write something on a piece of paper, feedback data from multiple body sensors are being…
Measuring TIM
This paper by Leinonen, Otala and Curl investigates the measurement of TIM, a hot topic in the 1970’s and early ’80’s after its potential to cause sonic degradation by the incorrect application of feedback around high loop gain solid state amplifiers. Now days (2017), there is a very complete and thoroughly in-depth understanding of TIM…
A Concise Overview of TIM by Bob Cordell
This set of articles was written in the early 1980’s by Bob Cordell, a few years after Matti Otala identified TIM (Transient Inter-Modulation) as the probable cause of sonic imperfections in high feedback solid state amplifiers in the 1970’s. Otala’s paper sent shock waves through the amplifier design community but sadly it ended up ‘subjectivizing’…
The Monolithic Op-Amp: A Tutorial Study
This was an invited paper at the ISSCC in 1974 by James Solomon, who at the time worked for National Semiconductor (acquired in 2011 by TI). Those were heady days in semiconductors, with major process and circuit design breakthroughs taking place at breakneck speed. The general purpose microprocessors’ pivotal role in powering the Apple II…
Marshall Leach Opamp Tutorial
Marshall Leach (RIP) was a Professor of Electrical Engineering at Georgia Tech University best known for his Leach Amplifier which he used as a practical vehicle for teaching his students the finer details of analog design, feedback, thermal compensation and power electronics. Hundreds of Leach Amplifiers were built over the years by his students,…