What Oscilloscope specs for audio work, diagnosis and repair?
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From: K Fodder on 3 Apr 2010 20:53 To All Thanks for your help. Looks like I might be able to pickup up a tektronic 465 (100mhz) cheaply so does that sound ok or was there a newer 100mhz tektronic model more realible or easier to service? If not I'll go for it. I'll investigate the digital option down the track. Thanks for the other advicr given so far, I've noted it all down. -- --------------------------------- --- -- - Posted with NewsLeecher v3.9 Final Web @ http://www.newsleecher.com/?usenet ------------------- ----- ---- -- -
From: Phil Allison on 3 Apr 2010 21:54 "Bennett Price Top Poster" > Distortion has to be pretty awful to see it on a scope ** Absolute bullshit. > and if you see > it (on a dual trace scope comparing input to output) how will you quantify > it, ** By how it looks on the screen - fool. Peak clipping looks like peak clipping. Crossover distortion looks like crossover distortion. Square wave testing reveals response anomalies, instability and slew limiting instantly. ..... Phil
From: Phil Allison on 3 Apr 2010 22:03 "Jeff Liebermann" "Phil Allison" > >>** DO NOT BUY A DIGITAL SCOPE !!!!!!!!!!!!! > > Why? > >>Almost any ANALOGUE scope with bandwidth of 5 MHz or more is OK - DC >>coupled or not. >> >>Digital scopes absolutely SUCK for audio work. > > Why duz it suck? ** There is no way to prove the point to fools like YOU by posting messages on a newsgroup. Buy anyone familiar with the use of analogue scopes for audio test and repair work will find using a DSO to be mighty irritating and tedious - at best. The displayed traces on a DSO are often very misleading and hence useless for many test procedures that analogue scopes do just perfectly. ..... Phil
From: Jeff Liebermann on 3 Apr 2010 23:34 On Sun, 4 Apr 2010 12:03:59 +1000, "Phil Allison" <phil_a(a)tpg.com.au> wrote: >"Jeff Liebermann" > "Phil Allison" >>>** DO NOT BUY A DIGITAL SCOPE !!!!!!!!!!!!! >> Why? >> >>>Almost any ANALOGUE scope with bandwidth of 5 MHz or more is OK - DC >>>coupled or not. >>> >>>Digital scopes absolutely SUCK for audio work. >> >> Why duz it suck? >** There is no way to prove the point to fools like YOU by posting >messages on a newsgroup. Got it. You can't explain why a digital scope is not usable for analog work. Perhaps I can help jog your memory. See below. Have you ever actually used a digital scope? A sound card based scope? You really should try it some time. I think you'll be pleasantly surprised. Drivel: iPod Touch based sound analysis instruments: <http://www.faberacoustical.com/products/iphone/signalscope/> I'm really tempted. >Buy anyone familiar with the use of analogue scopes for audio test and >repair work will find using a DSO to be mighty irritating and tedious - at >best. Long ago, in my mis-spent youth, I worked in a repair shop that did mostly audio. Not audiophile, but production line warranty repair for various manufacturers of various audio related equipment. The lead tech never used a scope. He would just listen to whatever was coming out of the speakers, scribble down what stage or device was blown, and move on to the next machine. My job was to do the unsoldering and replacement. His batting average was about 80% correct. I couldn't even come close to that level of accuracy, especially without a scope. One day, I saw him try to use a scope, and fail. He didn't know how. 40+ years later, I still can't do it with audio equipment. I gotta have my test equipment, white noise, pink noise, sweeper, distortion analyzer, and all important oscilloscope. However, I can do something like that with 2way radios. I've heard enough of them on the air to be able to diagnose problems by simply listening to the audio. Moral: Use your ears first, then use the scope. >The displayed traces on a DSO are often very misleading and hence useless >for many test procedures that analogue scopes do just perfectly. Oh? Misleading in what way? What measurements are misleading? How will using a digital scope produce a misleading diagnosis? I use a digital storage scope for doing the all important square wave test. Instead of the fuzzy blur of high frequency ringing and oscillations seen on the analog scope, I see the digital equivalent, which looks like a jitter infested trace in the same area (top of leading edges). By superimposing multiple stored traces on top of each other, ringing and oscillations are fairly obvious, even if they exceed the frequency response and resolution accuracy of the A/D converter. DC related phenomenon are a problem with a PC sound card based scope. There's no DC response, and the lower limit is about 20Hz. Low frequency display during the square wave test will show up as a "sag" in the horizontal part of the waveform even with a DC coupled audio amplifier. Scope probe compensation also shows the same "sag". I partly compensate with the scope probe compensation, and just remember what the "sag" looks like when the scope is directly connected to the square wave generator. In other words, I ignore the low freq sag. High frequencies are more of a problem. <http://en.wikipedia.org/wiki/Slew_rate> Slew rate testing is difficult with a digital scope, unless the scopes usable bandwidth is more than 5 times the highest frequency of interest. For a 2MHz bandwidth digital scope, that limits the maximum frequency to about 400KHz, which should be more than adequate for any slew rate testing. That's NOT the case with bottom of the line sound card based scopes, which are bandwidth limited to about 22KHz. The 96KHz 24bit sound cards are much better. There are probably other areas where an analog scope is better than digital. Tuning and tweaking in real time is much easier with a fast responding analog scope than on a more slothish digital equivalent. Seeing oscillations and ringing at tiny points during a frequency sweep is somewhat easier to see on an analog scope. Did I miss anything on why an analog scope is superior to digital? -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
From: Jeff Liebermann on 3 Apr 2010 23:46
On Sat, 03 Apr 2010 10:52:49 -0500, Jim Yanik <jyanik(a)abuse.gov> wrote: >A nice,simple,inexpensive used TEK scope would be the T922/T932/T935 or 442 >scopes;15MHz or 35Mhz. They don't use any custom ICs,have simple >attenuators,have a decent size CRT graticule,and aren't too old. >Negatives are the plastic case that allows chassis flex,easy to break knobs >that are no longer available. > >I'd avoid the T912 storage scope. Ummm.... I now have 3ea T922 (15MHz) scopes. One works, but the other two have blown flyback xformers. I've been unable to find a replacement or substitute flyback. Both failed while they were being used on my bench. The problem seems to be that the scope does not have a fan and the flyback was probably overheating. There's a perforated grill and location for a fan on the lower back, but no fan. So, I added one on my working T922, which seems to be surviving so far. There's not much air circulation in the upper section (where the flyback lives) so I added some holes in the top cover (under the handle) to improve circulation. >Next inexpensive TEK scope I'd recommend would be the 2213/2215/2235 >series (60 Mhz to 100 Mhz),but those do use a few TEK-made ICs that are out >of production. >But they have good reliability. I have a 2213. -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |