Post by AudioHTIT on Aug 15, 2023 15:02:06 GMT -5
I've had VOMs for as long as I can remember, some decent, some cheap, usually good enough to do the simple things I ask of them. Then some time back I wanted to see numbers instead of looking at scales and the like, and got a DVM. It looks fancy with Fluke like yellow, but it's a cheap Harbor Freight Cen-Tech, and though NASA won't be calling to do any testing on the Artemis, it's also done what I've needed.
This summer I've been tinkering with guitar amps and one of the things I find myself doing is measuring base level background noise. I can do this two ways; the easiest is to put my wonder meter across the extension speaker output (or the speaker terminals themselves), leaving the controls all the way down, I generally get readings between 4 and 20 mV (20 usually means there's something wrong). I'm also assuming the output impedance of most power amps is low enough, and even my cheap meter's resistance is high enough, that it doesn't affect this kind of measurement.
The other way is to use my UMIK-1 and iPad AudioTools to measure the SPL at a given distance (I use 1' to overpower background noise), and always use my 50+ year old, home built JBL D120F cabinets for consistent sensitivity. SPL is more trouble, but it gives me a real world number that I can evaluate in the context of an amp that's not built for HiFi, also that an amp that might be good for a gig or stage, could be noisy for the studio.
Sometimes I try to see how I can affect the noise by rolling tubes through the amp, and occasionally I can get down around 2mV -- I suspect my meter isn't all that accurate at that point. I should mention I've also used a similar technique measuring phono cables on my turntable. Doing a little Googling I found there are NanoVoltMeters (NVMs?) that get very low, but the first few that came up were in the multi-K-buck range so I dismissed them. So my question is, does anyone know of a reasonably priced DVM that would accurately measure 1mV, or maybe even tenths of an mV? (I see many talk about their maximums, but few their minimums ... what's up with that?)
Edit: I realize I’ve used the word ‘accurately’ and that it is one of the specs you pay for, so I’ve left it somewhat open.
This summer I've been tinkering with guitar amps and one of the things I find myself doing is measuring base level background noise. I can do this two ways; the easiest is to put my wonder meter across the extension speaker output (or the speaker terminals themselves), leaving the controls all the way down, I generally get readings between 4 and 20 mV (20 usually means there's something wrong). I'm also assuming the output impedance of most power amps is low enough, and even my cheap meter's resistance is high enough, that it doesn't affect this kind of measurement.
The other way is to use my UMIK-1 and iPad AudioTools to measure the SPL at a given distance (I use 1' to overpower background noise), and always use my 50+ year old, home built JBL D120F cabinets for consistent sensitivity. SPL is more trouble, but it gives me a real world number that I can evaluate in the context of an amp that's not built for HiFi, also that an amp that might be good for a gig or stage, could be noisy for the studio.
Sometimes I try to see how I can affect the noise by rolling tubes through the amp, and occasionally I can get down around 2mV -- I suspect my meter isn't all that accurate at that point. I should mention I've also used a similar technique measuring phono cables on my turntable. Doing a little Googling I found there are NanoVoltMeters (NVMs?) that get very low, but the first few that came up were in the multi-K-buck range so I dismissed them. So my question is, does anyone know of a reasonably priced DVM that would accurately measure 1mV, or maybe even tenths of an mV? (I see many talk about their maximums, but few their minimums ... what's up with that?)
Edit: I realize I’ve used the word ‘accurately’ and that it is one of the specs you pay for, so I’ve left it somewhat open.
