Hi can someone please help me with what scope I should get for Audio equipment repair? I need to have flexibility so I wont have to buy another for a while. A benchtop model is fine.
I want something specifically to cover tube/valve amps. I need to be able to check the performance of amp and see if my input signal is distorting, deteriorating, has interference or other types of problems that plague audio.
What the max MHZ range would I need to aim for? What other features would it need or be handy? Do you know a specific brand and model? Do you think I need any other equipment? Whats a good brand/model function generator?
Lastly I have read suggestions that I should get an older analog scope for this work. And then read the digital ones "can" do the job. It is a bit of conflicting information what do you think?
What would be best for audio and offer the most flexibility? Or has there been a scope that covers both digital and analog well?
I would recommend getting a dual trace scope. Minimum 20/30MHZ bandwidth. You should be able to get a used one reasonable. ($50 to $200 dollars) I like Tektronix, but a older BK, Hitachi, Kikutsi or such would be fine. There are some newer imports that MCM electronics carrys.
Since audio only goes up to 20Kilo Hz or so, you really don't need a lot of input bandwidth. But for looking at transients and other things it can be helpful.
I have little plastic boxed function sweep generators. You can also get CD's with audio tones and sweeps on them. For quick and dirty, download the CD to a small MP3 player and thats about as small as it gets. If your trying to do THD tests or such thats another ball game to get a low THD sine source. Depends on what your doing...
You should also get a potential divider for when working on the o/p area as you are bound to have the attenuator set on the wrong scale ,some time, and at least blow the first transistor. By the same reasoning an old 10 or 20 MHz scope with repair manual and usually no custom items in there, and make sure it easy to take apart for repairing it, plus perhaps a dead one of same model for spares. Get one that you remove one cover and almost everything is accessible. At least 10 or 20 M b/w usually means not a load of difficult to remove can screening involved.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
K Fodder wrote in news:4bb75ca6$0$14752$ snipped-for-privacy@news.astraweb.com:
He means blow the scope's input transistor/FET.
get a 10x probe; it divides the signal by 10 and givs a higher input-Z,for less circuit loading. it turns the scopes nominal 1 Megohm input Z into a 10 Meg input. Less capacitive loading,too.
you can also get switchable 1X/10X probes,but they cost more and are more trouble,IMO.
K Fodder wrote in news:4bb741a5$0$7727$ snipped-for-privacy@news.astraweb.com:
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.
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.
I don't do much audio work. Just the audio processing sections (mic amp -> compressor -> limiter -> modulator -> demodulator -> demphasis
-> speaker amp) of two way radios. The ability of digital scopes to do the grunt work of sweeping the frequency and amplitude range, measuring SINAD directly, and frame grabbing the results, have been a big plus. I may not be able to see distortions, high frequency ringing, and subtleties because of the dynamic range limitation of the A/D converter, but everything else is much better and easier. If I'm looking for high frequency oscillations, I use one of several 100Mhz scopes. If you have the money, I would get both a digital and an analog scope.
Article on the limitations of digital scopes:
So despite the unsubstantiated warnings of digital doom and disaster, I'll recommend Visual Analyzer:
for a (free) PC based software oscilloscope. This is what I use for most of my tinkering and light weight waveform sniffing. It should give you a clue as to the limitations of 8bit 44KHz (or 24bit 96KHz) sampling PC based scopes. With a 24bit sound card (Startech 7.1 for $20), I can see noise down to about -80dB (-120dB theoretical) below max input.
For a USB scope, this is my current favorite: $200. Note the open source software. The only problem is that I share it with a friend and don't quite own it yet.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Another consideration for valve stuff especially, ie big kit, is the ability to use the scope at the amp so being able to position it face up , floor standing, is useful. A valvetester and also for personal safety a variac plus isolation transformer and ELCB/RCCD/ GFCI
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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
------------------- ----- ---- -- -
** 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.
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:
I'm really tempted.
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.
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.
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@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
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.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
After a DVM the next most useful piece of test equipment is a crystal earpiece with a high voltage cap in tow, for audio repair work . Next comes a sig gen and then a scope (analogue not DSO and stand alone, not tied to a pc). Other useful pieces of test kit is a nose, eyes (with good magnifying inspection lamp) and ears.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I use a digital oscilloscope for audio all of the time. Although the view of the waveform may be different that an analog scope, there can be overriding benefits. Most digital scopes have measurement functions such as frequency and amplitude and FFT which is spectrum analysis. That is very handy for looking at distortion if you have a very clean audio oscillator for the source.
For me, the most useful item is a schematic. I don't have an earphone connector on my crystal ball, but I'll certainly check with my consulting sorcerer if it's an available option. The video on my crystal ball is working just fine and is able to devine the future and troubleshoot problems with amazing accuracy. However, without audio, the best I can do is lip read and guess what's happening. I'm not sure the other accessories will be very useful. My nose is always dripping. My reading glasses have morphed into surgeons glasses. My ears are fine, but haven't been the same since I bought an iPod Touch. I do have a magnifying glass, but find a microscope more useful for PCB work.
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.