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Post by Hexspa on Jul 5, 2020 7:03:48 GMT
I remember Ethan saying that different speaker resistances didn't sound different. But lately I've been reading about impedance - something I never studied - and several issues pop up.
The first being that impedance-matched systems drop level when loaded in parallel. I hope I'm saying that right. With modern voltage matching, this is less of a problem yet impedance concerns appear to still remain. On p.165 of TAE, Ethan goes into potential impedance-caused distortions when, for example, feeding a 150ohm mic into a 150ohm input - as unlikely as that seems to be.
Really what I'm asking is that, in the case of a Marshall amplifier, wouldn't load impedance matter? I don't see what their output impedance is - the heads just say 'load' which I take to mean 'nominal load'. I was 19 when we did the informal comparison but we agreed - totally not inebriated - that 4, 8, and 16ohm loads with the same cabinet sounded different.
Can anyone elaborate on practical impedance?
And am I right in thinking that the high impedance creates a sort of 'reserve' of electrons at the input which regulates the current whereas a low resistance basically is like trying to punch air?
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Post by rock on Jul 5, 2020 16:17:16 GMT
There are an answers to all your questions. You learn all this, probably gradually, when you study electronics. As you go along, your questions change as you begin to understand more. I never knew it all and have forgotten much of the details of what I ever learned. It's easy to review what I need/want to know these days with the internet but it easier if you know the questions to ask.
Impedance is not in the first chapter. It really helps is you have a grasp of DC circuits and Ohms law. Passive components; resistors, capacitors, inductors. Then you get to AC electronics and impedance. If you really want a solid understanding. Check out tutorials rather than trying to think of it with mental constructs and analogies. I'm not trying to be condescending but I don't think it'll be too difficult for you to systematically work though beginning exercises.
As usual, maybe someone else has a better answer. In the meantime, I'll mull over your questions an see what I can come up with for you.
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Post by rock on Jul 5, 2020 18:55:12 GMT
Really what I'm asking is that, in the case of a Marshall amplifier, wouldn't load impedance matter? I don't see what their output impedance is - the heads just say 'load' which I take to mean 'nominal load'. I was 19 when we did the informal comparison but we agreed - totally not inebriated - that 4, 8, and 16ohm loads with the same cabinet sounded different. Let's start with this one. So tube amps all need output transformers because tubes run at high voltage (300 to 500VDC more or less) and low current. Speakers, on the other hand, are looking for lower voltages and higher current and that's what the transformer does. The output transformer has different taps to accommodate different speaker impedances. You're supposed to switch the tap to the correct speaker impedance but if you experiment you see there are differences in the sound. At low levels, there's little risk but with it cranked up, you may have issues. Just for clarity: Your speaker cabinet IS the load. The load does not come from the amp. My Marshall 50 watt Plexi (reissue) has a selector switch with 4, 8,&16 Ohms but that selects the transformer tap to match it TO the load (speaker). If you don't have your speaker cab connected, you don't have a load on your amp (I'm sure you know that's a bad thing!) Here's a better explanation: www.thegearpage.net/board/index.php?threads/can-someone-explain-safe-amp-to-speaker-mismatching-to-me.1726490/I hope this helps |
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Post by Hexspa on Jul 6, 2020 10:57:17 GMT
Ya, I should probably read that book in order. I get that the speaker is the load and that impedance is made up from resistors, capacitors, etc. Ok, better keep studying. Thanks.
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Post by rock on Jul 6, 2020 13:26:57 GMT
About loudspeaker AC impedance VS DC resistance. Both can be measured but DC resistance is very easy with any regular ohm meter but measuring impedance is trickier. In the first link, you'll see you can measure the DC resistance with Method 1 which is simply reading the DC resistance of the voice coil. This is NOT the impedance. (but it's relative and since Speakers are fairly standardized, you can easily use DC resistance measurement to estimate the rated Impedance. Method 2 explains how to actually measure Impedance but the point I want to make is that speaker impedance is complex and is a different value at every frequency and you can plot a graph very much like an SLP graph. I'm not suggesting that you try to measure the Z (now), just note what is involved. www.wikihow.com/Measure-Speaker-ImpedanceHere's a link, I googled AC impedance VS DC resistance and here's one article. There are others. www.physlink.com/education/askexperts/ae517.cfm |
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Post by Hexspa on Jul 7, 2020 9:20:06 GMT
One day I'll have to get into this, rock. Not today though  I'll be sure to revisit this because I'm at the stage where even my own questions overwhelm me. Cheers. |
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Post by rock on Jul 7, 2020 13:43:19 GMT
Yeah, I get it, most of us have bigger fish to fry. When it really comes down to it, all we really need to know about speakers is if they are, flat enough, loud enough, clean enough and go low and high enough. It may be fun to know the other stuff if you have the time but unless you're designing speakers, it might not be that useful.
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Post by Hexspa on Jul 8, 2020 9:21:41 GMT
Not only speakers. One of my bucket list projects is to assemble some kind of audio kit - a preamp or compressor. That's not going to happen with the kind of knowledge I have today. You ever do something like that? A Seventh Circle or CAPI?
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Post by rock on Jul 8, 2020 14:53:58 GMT
Yeah, I've built kits before and designed some custom circuits too. Making your own PCBs is doable (not exactly easy) with software and photo sensitized boards etc. but for very simple circuits, you can draw traces with resist pen directly on the copper and etch the exposed copper away to make your PCB, drill holes and you're done. I added some features to my 1947 Hammond CV (like a B3) like spring reverb and tube based Hammond percussion. I built new circuits from scratch but I did not "invent" anything new, I just redesigned old ideas to my liking.
Depending on what you have done before, it's usually recommended to start with something simple. I'm not familiar with Seventh Circle or CAPI but I just looked at them and it's looks like very nice stuff. If it comes with good instructions, you should be fine. One little hitch is if you do make a mistake and it fails to work, troubleshooting may be necessary to get it going. That's true for any DIY project, even putting up window shade (I just did that yesterday but that was pretty easy ha ha).
My kid was on a guitar pedal building kick a year or so ago and started building them from pcbs from Mad Bean and Aion and sourcing parts from Tayda etc. He has no formal electronics training so I helped him a little but he was on his own for the most part. Reading schematics and identifying parts is helpful. Often a good visual check will uncover problems so it's the first thing on the "TS Flowchart".
It may sound mundane, but reading/memorizing the resistor color code is very useful. One way to practice is to buy a bulk assortment of resistors and sort them into parts bins. After a while you'll pick out a 10k from a 4.7k or a 1M at a glance.
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Post by Hexspa on Jul 9, 2020 17:39:48 GMT
Awesome. Maybe I'll start with something like a guitar pedal. I still have to fix my humbucker install so I'll have to see what's next. Thanks.
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I'll be sure to revisit this because I'm at the stage where even my own questions overwhelm me.