300V/us power amplifier - Page 1
Forum section: electronics / projects

author: chris_leyson
author_rank: Super Contributor
timestamp: November 03, 2016, 07:47:43 pm
content: Found this article by Giovanni Stochino, Electronics and Wireless World April '97,http://www.keith-snook.info/wireless-world-magazine/Wireless-World-1997/300V%20us%20power.pdf. Looks interesting, around 1MHz bandwith before the Zobel network, anybody ever built one of these ?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 03, 2016, 11:40:06 pm
content: I've built some peppy amps before. I forget if I have any pictures or circuits handy, though.This is a small (TO-92) scale example:Using the standard approach (diff amp, volt-amp stage, follower), over 10MHz is not terrifically hard.Win Hill (of AoE fame) had posted about a wideband amplifier some time ago, but I can't seem to find the reference (or he pulled the Dropbox link). Feels like Google is trying to bury newsgroups as hard as they can...The standard approach is limited by phase shift across the stages. You can't build an amplifier any faster than the fastest follower you can find, and you can't drive the follower any faster than its input impedance allows (mainly, its capacitance, which loads the VAS, which therefore has to draw as much bias current to get the job done). Voltage swing (dV/dt, without sacrificing much saturation voltage range) is pretty easily solved by using cascodes, at least.To go higher, you must build an amplifier that can have more than 180 degrees of phase shift across it. This only makes sense with small feedback loops around individual stages, which means, your amplifier ends up looking more like an increasing chain of RF amplifiers.You can still use the traditional diff-VAS-follower structure, but the global feedback loop must be slowed way down (it becomes a DC servo only), and the gain and distortion of each individual stage must be tamed. So, the diff amp gets generous emitter degeneration resistors (and maybe cascodes or complements), the VAS is split into a chain of several stages, of increasing power capability, and the follower might be reworked to have some voltage gain itself as well.Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 03, 2016, 11:44:48 pm
content: Aha, I found it in my downloads. The title is AMP-70A-2. Here's a thread on dA,http://www.diyaudio.com/forums/solid-state/287023-winfields-100w-dc-10mhz-1000v-us-amplifier.htmlbut that's not really very helpful. You may have to e-mail him hill@rowland.harvard.edu to get a reproduction of the circuit.Tim

author: 2N3055
author_rank: Super Contributor
timestamp: November 04, 2016, 12:36:36 am
content: Quote from: T3sl4co1l on November 03, 2016, 11:44:48 pmThere is link to a dropbox with details...https://www.dropbox.com/sh/dno89om1uezxs8a/AACoJsLyNazSQZvE9_cTcH4Ja?dl=0

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 04, 2016, 01:07:22 am
content: Quote from: chris_leyson on November 03, 2016, 07:47:43 pmThe IRF640 and IRF9640 used in this amplifier may have been 'improved' by IR (later Vishay). The 'improvements' include die shrinks. They preserved the switching performance, RDSon and Qg, but wrecked the SOA. They were under the belief that 'nobody' uses MOSFETs in the linear region!! If you can find older MOSFETs they will probably work better than newer ones.Giovanni Stochino was (is?) a highly regarded amplifier designer, so the engineering is sound (if you excuse the pun).Link:https://linearaudio.net/authors/340Are you interested in this design for HiFi or for use a general purpose laboratory amplifier?Regards,Jay_Diddy_B