What Class Is This Amplifier? - Page 1
Forum section: electronics / beginners

author: ed_reardon
author_rank: Regular Contributor
timestamp: June 03, 2017, 10:53:24 am
content: Hi all,Been scratching my head over this one, see the other thread about the '100V line amp'.https://www.eevblog.com/forum/chat/'100v'-audio-amplifier-any-experts/The heatsink has four big BJT's, ah thinks Ed, I don't know a lot about amps, but this isn't a high quality amplifier, it'll be complementary pair of BJT's per channel, something class-B related.No, it has four NPNs- TIP35C's from ST to be explicit.I'm an idiot, and I don't know a lot about amps, but I can't get my head around how this works?!Any suggestions? I can't make it fit with any amplifier class I can find.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 03, 2017, 11:28:09 am
content: Link back to the other thread. It's not ovbious what you are talking about. Just by the fact that it's 4 NPN's doesn't really say much. Could be some kind of class A.

author: MagicSmoker
author_rank: Super Contributor
timestamp: June 03, 2017, 11:57:09 am
content: If the output stage is all one polarity of transistor then it is likely a "totem-pole" Class AB type.

author: Audioguru
author_rank: Super Contributor
timestamp: June 03, 2017, 02:02:15 pm
content: Why is there no schematic of this amplifier posted here??

author: KJDS
author_rank: Super Contributor
timestamp: June 03, 2017, 02:31:38 pm
content: Quote from: Audioguru on June 03, 2017, 02:02:15 pmThat would make it easy to answer the question.

author: madires
author_rank: Super Contributor
timestamp: June 03, 2017, 02:48:37 pm
content: Example for single rail:http://www.electroschematics.com/269/audio-power-amplifier-60w-with-2n3055/And for split rail:https://www.electronica-pt.com/circuitos/en/audio-amplifiers/200-220w-amplifier-circuit

author: mikerj
author_rank: Super Contributor
timestamp: June 03, 2017, 04:48:59 pm
content: You can make a Class B or AB output stage from transistors of one type, have a search for "Quasi-complementary output stage".

author: Benta
author_rank: Super Contributor
timestamp: June 03, 2017, 04:57:44 pm
content: Quote from: mikerj on June 03, 2017, 04:48:59 pmBasically, you can make any class of amp from A to D if you like.It was normal in the 60s and 70s designs to to use only NPNs in the output stage, simply because availability of PNP silicon power devices was poor, and they were expensive.

author: ed_reardon
author_rank: Regular Contributor
timestamp: June 03, 2017, 05:24:56 pm
content: Quote from: madires on June 03, 2017, 02:48:37 pmThe split rail schematic superimposes quite nicely over what I have in front of me on the bench. Whichever that may be.Sorry for not proving a schematic, I do not have one for this obscure amplifier, but yes I know it's a rather vague question. I was being too literal in my interpretation of the classes, amplifiers aren't something I deal with often so please forgive me.The amplifier is 2000's vintage, late 2006 by the QC stickers.Cheers all.

author: Circlotron
author_rank: Super Contributor
timestamp: June 04, 2017, 12:14:44 am
content: By the late 70's quasi complementary output stages were obsolete. The magazines of the day were full of complementary symmetry designs. Look up ETI480 for example.