What part of an amplifier can be killed by a speaker ? - Page 1
Forum section: electronics / projects

author: Hextejas
author_rank: Frequent Contributor
timestamp: February 11, 2018, 05:23:11 pm
content: I did not know how to phrase the subject so I will try and explain here.While I was shopping for some speakers, a few years ago, I liked and bought a pair of KEF C-80s which are 4 ohm.The salesman asked me about my amp and also told me about another customer who had an expensive amp that was blown out by the same speakers because of the increased current draw.So, as I look around for a DIY kit amp, what will I need to do to it, so as to not light it on fire with my 4 ohm speakers ?I have seen some amp kits that have a switch selectable impedance on the rear panel.Some say 4-8 whereas others say 6-8. I think that I would like my amp to be able to handle 4-8 ohm but do not know what the circuit design would look like.Is there any hope for me or should I get new speakers .😂😂Thanks

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 11, 2018, 05:57:17 pm
content: The output MOSFETs need to be able to handle the current, generally not a problem when high current MOSFETs are so cheap nowadays. Easiest way to be sure is to just get a module that specifically says it will work with 4 ohm speakers.

author: Audioguru
author_rank: Super Contributor
timestamp: February 11, 2018, 06:03:18 pm
content: Most modern amplifiers can drive 4 ohm speakers. A speaker impedance switch was used 60 years ago on vacuum tube amplifiers.

author: Hextejas
author_rank: Frequent Contributor
timestamp: February 11, 2018, 06:47:53 pm
content: Quote from: Audioguru on February 11, 2018, 06:03:18 pmLol, Audio, a tube amp is just what I am looking to try and build/buy.

author: fourtytwo42
author_rank: Super Contributor
timestamp: February 11, 2018, 07:09:08 pm
content: Quote from: Hextejas on February 11, 2018, 06:47:53 pmWould have helped if you said that in the first place but most tube amps have an o/p transformer to match the plate impedance to the speaker, if you use 4 ohm speakers on an 8 ohm amp the plate impedance will be half that designed and likely cause significent non-linearity and all kinds of distortion. There was/is a reason for correctly matching speakers.

author: Hextejas
author_rank: Frequent Contributor
timestamp: February 11, 2018, 10:11:23 pm
content: Quote from: fourtytwo42 on February 11, 2018, 07:09:08 pm42, I didn't know that they were related. I thought that any amp could have that issue. Anyway, when you say that with the plate impedance being 8 ohms and the speakers 4 ohms, it will be 1/2 the design. Won't the plate be twice?And is it the design of the o/p xformer that must consider the impedance of the speaker ?For example, if I see a tube amplifier design that gets lots of good reviews and is affordable, what would i have to check or do to it so as not to damage the speakers ?Thanks

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 11, 2018, 10:19:27 pm
content: Aren't a lot of tube output transformers "universal" in that there are multiple taps to allow selection for different designs?I would suggest just using a modern module to drive the speakers and a tube stage in front of it to get the tube sound.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 11, 2018, 11:16:35 pm
content: Quote from: Hextejas on February 11, 2018, 05:23:11 pmpower amp will eventually blow even if designed for 4 ohm speaker...i wonder why they call the term audio phool maybe because they like to turn the gain and volume to maximum to prove the expensiveness of their power amp. And sometime expensive means a christmas blinking lights on the enclosure, on the inside are about the same as averagely priced amp. Anyway for the past week my work is exactly this, learning and repairing car audio power amp 1500-2500w. 6 unit fixed, all class ab, 1 unit left to fix, a 2000w class d amp.. I tend to think output power bjt will tend to blow first, but out of the 6 units, i only replaced 1 blown bjt. the most damage occurence is the smps mosfets, i replaced like 20 of them.. the worst tortured unit got shorted transformer i have to unwind, rewind and insulate the burnt enamel with tapes.. fwiw...

author: Hextejas
author_rank: Frequent Contributor
timestamp: February 11, 2018, 11:21:56 pm
content: Quote from: NiHaoMike on February 11, 2018, 10:19:27 pmIs there a name for such a critter ? A hybrid of some kind ?Thanks

author: james_s
author_rank: Super Contributor
timestamp: February 12, 2018, 12:57:21 am
content: I seem to recall it was the output stage generally responsible for the "tube sound" of a power amp, and the input stage on mixing/recording devices. I don't see much point in a tube amp with solid state outputs, unless you just really want some glowing tubes.

author: Audioguru
author_rank: Super Contributor
timestamp: February 12, 2018, 01:45:39 am
content: Toob amplifiers produce even harmonics distortion and compression distortion that some people like. The output transformer cut high audio frequencies making the sound "mellow" that some people like instead of turning down the treble tone control knob.Toob amplifier outputs matched the speaker impedance that allowed the speaker to resonate and make a "boomy" sound that some people like.Modern solid amplifiers produce none of the above distortion, their output impedance is 0.04 ohms or less so that they damp the resonances of speakers and produce sounds that sound real, not canned.

author: Hextejas
author_rank: Frequent Contributor
timestamp: February 12, 2018, 03:14:32 am
content: I do like the look of them and what I wanted to do was to put one next to my integrated amp, a Nad, and with everything else being the same, listen to the differences, and see which I like best.I am also a newbie+ at building these types of devices so there is an element of personal satisfaction in being able to say that I built it.

author: KhronX
author_rank: Frequent Contributor
timestamp: February 12, 2018, 01:56:36 pm
content: http://sound.whsites.net/valves/myths.html

author: Hextejas
author_rank: Frequent Contributor
timestamp: February 12, 2018, 03:22:11 pm
content: Quote from: KhronX on February 12, 2018, 01:56:36 pm

author: KhronX
author_rank: Frequent Contributor
timestamp: February 12, 2018, 03:23:42 pm
content: Sorry, that was meant mostly as a response toAudioguruMy bad for not expressly pointing that out...

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 12, 2018, 03:34:43 pm
content: Back 60 years ago it was common for a firebottle amplifier to have an output transformer that had separate taps for 4, 8, and 16Since that is an antique technology today, it is not as easy to find such transformers. But they are still available (although maybe not instantly "off-the-shelf"). For example this Edcor CXPP10-10K has 4and 8output taps. But they only make them "on-demand".https://www.edcorusa.com/cxpp10-10k

author: KhronX
author_rank: Frequent Contributor
timestamp: February 12, 2018, 03:37:51 pm
content: Replacements for guitar amplifier output transformers are still made (Hammond comes to mind, but i'm sure there are others), although i have considerable doubts they're anything near "hi-fi" or "full-range".Quote from: Richard Crowley on February 12, 2018, 03:34:43 pm

author: fourtytwo42
author_rank: Super Contributor
timestamp: February 12, 2018, 08:39:32 pm
content: Quote from: Hextejas on February 11, 2018, 10:11:23 pmPlate or anode impedance is usually several Kohms so the output transformer is a step down ratio. The speaker impedance is reflected at the plate multiplied by the transformer ratio, most output valves are designed to operate over a fairly narrow range of impedances hence the taps on the output transformer for different speaker impedances. Serious mismatch can eventually lead to anode over dissipation and early failure of the valve but a more immediate effect is a complete change in the sound qaulity.It is unlikely you will damage your speakers unless the amplifier is very powerful relative to there rateing, simply look for an amplifier with selectable output impedances one of which matches your speakers.

author: james_s
author_rank: Super Contributor
timestamp: February 12, 2018, 08:41:32 pm
content: I don't know whether tube amps sound any better than solid state, but they certainly are cool. With something as subjective as music it's hard to define "better" anyway, no matter how perfectly accurate the equipment is at reproducing the sound there are still countless variables in the path between the performers and your ears that mean it will never sound quite the same anyway.

author: fourtytwo42
author_rank: Super Contributor
timestamp: February 12, 2018, 08:43:03 pm
content: Quote from: NiHaoMike on February 11, 2018, 10:19:27 pmMost musicians would disagree with you, a lot of harmonics and soft distortion is created in the output stage/output transformer combination and furthermore the highish source impedance also causes drivers to behave quiet differently so there are many contributers to "valve sound" beyond a simple bottle