USB Oscilloscope

[Fresh_Start]

Would this USB oscilloscope be adequate for amp debugging and design tweaking? Stingray list $220.

Anybody have suggestions about alternatives?

I've searched for "oscilloscope" here and most of the posts relate to old, tube powered 'scopes with a CRT.  While no doubt cool, I'm just interested in a tool to help me "see" what's happening at Point A and Point B in the signal path.  One concern I have is the voltage range - don't know what we need.  The documentation for this device mentions some kind of probe to allow measuring greater voltages, but I don't know if that would take me into the price range of a B&K, Protek, orTektronix bench-top oscilloscope.  Mouser lists some probes that cost more than the Stingray  :-?

Thanks for any help with this.

Chip

[panhead]

Try this for some good deals:

http://www.oscilloscopedepot.com

[Fresh_Start]

Wow!  Those are great prices.  Unfortunately, I still don't know what the key specs are other than dual trace.

In another thread, one of our most learned co-contributors referred to the need for "A real 'scope, not a PC-based toy".  I would never disagree with this gentlman, but it would help to know what the drawbacks of the "PC-based toys" are.

Also, what kind of probes would I need?  For example, the first B&K scope shown comes with two "PR-33A x1/x10" probes.  Does the "x1/x10" mean that the probes can multiply (or reduce) the input signal by a factor of 10 for certain applications?

Chip

[PRR]

> old, tube powered 'scopes

What will you be lookin at? An old (or old-type) tube powered amp.

It's a perfect fit.

Digital is crap for audio. Good digital can be acceptable to the ear, but always has problems for measuring.

You do NOT need or want a "good" 'scope for geetar amps. 1MHz bandwidth is plenty. I learned with "400KHz" (ha!), have a 20KHz 'scope. DC-coupled is nice, and now universal, but audio is not DC and my older scopes ignore DC.

'Scopes that old (one a mine is 1937) need more repair than a sick amp.

You want a tranny CRT, VERY basic, which won't be any slower than 5MHz just cuz it wasn't worth making them cheaper. The $400 Instek GOS-620 is too good, which is fine, though you can do better than $410 or $284 if you sniff eBay a while.

> some probes that cost more than the Stingray

PROBES? Don need no steekin probes. You need a 50 ohm BNC plug (the 75 ohm job found on hi-end video is not right) and some clip leads. That will do for all preamp work. If you are stupid enough to try to probe power tube plates, build a well-insulated 1Meg:10K divider to knock 1,400V peaks down to few-hundred volts which will not zap your 'scope input.

Such a cheap-trick divider will not pass 20MHz, but you do NOT need 20MHz. This isn't radar. This isn't even TV. It is mostly about frequencies which your ear-bone can shake at, or a bit higher. 5KHz, 20KHz, being able to see 100KHz squeal may be a bonus. That's 0.1MHz, so any MHz is more than plenty.

[PRR]

> one of our most learned co-contributors referred to the need for "A real 'scope, not a PC-based toy".

Oh, him. He just clings to the past. He thinks cause he spent years welded to 'scope knobs, nobody should use a mouse.

Aside from the fact that a well-learned knobset is faster than a mouse (do you adjust your amp with a mousy interface?), digital means chopping a repetitive (usually) wave with another repetitive wave, and trying not to hit multiples which give phantom answers.

An irrelevant, for our purpose, objection is that digital sampling must run twice, and more often 10 times, the audio rate to get any honesty at all. That Stingray must have 10MHz chips but can only claim 250KHz (0.25MHz) bandwidth. (Some of that may be the USB 1 interface, true.) Since that old grump already said that 20KHz is gravy and 100KHz is a bonus, 250KHz is not a problem.

The main thing on the Stingray is the 50V input limit. You MUST use a 10:1 or 100:1 attenuator for nearly all tube work. But it does not have to be precision compensated to many MHz. Couple resistors works just as well.

[Fresh_Start]

PRR:  Your comments are infomative and amusing as always!  The observation about needing analog to avoid slicing the data incorrectly makes lots of sense.  I didn't really like the idea of toting my laptop out to the workshop anyway...

I have looked on FleaBay but am afraid I don't know enough to get a good deal.  If that Instek GO620 is "too good", it may be just the ticket for this young (at least in terms of electronics knowledge) sprout.

Many thanks!

Chip

[billcreller]

Weber has a small new one for $275, 20mhz.  All the specs are there on their site under "amp tech tools".  Since I don't know jack about scopes, it's all I can pass on.

[FYL]

Digital is crap for audio. Good digital can be acceptable to the ear, but always has problems for measuring.

Hmmm. All of my stuff is digital except my trusty VTVM, a cap analyzer, a couple of tube testers - mainly used for gas and leakage measurements - and maybe a generator or two. Tube analyzer, curve tracizer, scopizer, FFTizer, all of the izers are digital.

[PRR]

> Weber has a small new one for $275

https://amptechtools.powweb.com/scope.htm

Same model, a nickle cheaper, and the fact that Weber says "it does everything I need" is worth something.

[FYL]

Aside from the fact that a well-learned knobset is faster than a mouse (do you adjust your amp with a mousy interface?), digital means chopping a repetitive (usually) wave with another repetitive wave, and trying not to hit multiples which give phantom answers.

Agreed with provisos: analog is perfect for some applications, digital for others. Using the right digital tools, you can measure and fully characterize an amp in a couple of clicks, doing the same using analog gear would take at least half an hour. Oh, and yes, I do happen to adjust amps using rodents...

[jjasilli]

Agreed with provisos: analog is perfect for some applications, digital for others. Using the right digital tools, you can measure and fully characterize an amp in a couple of clicks, doing the same using analog gear would take at least half an hour. Oh, and yes, I do happen to adjust amps using rodents...
 
Searching 'scopes on this forum should be informative.  It's another recurring topic.  Checkout http://www.tone-lizard.com/

One issue with old tube analog test equipment, even a mere voltmeter, is that it's a whole new hobby just learning to use (and calibrate) them!

[phsyconoodler]

It is NOT the way to bias an amp.The crossover notch will likely be where the tubes are melting down.
  

[PRR]

> set the bias using it and to watch for the notch.

If you have an actual notch, you are grossly over-driving the amp, and bias does not matter.

What you get, with "too cold" bias, is a dead zone. Very small signals hardly come through, medium signals are flattened where the wave "crosses over" the zero line.

In the picture:
Yellow is clearly starving (30%THD)
Green is a little "lame" through zero but you can hardly see it (3%THD)
Red is mighty near perfect (0.3%THD)

Real amps are never this pretty. The "up" and "down" flatspots may be below and above zero. The "flat" usually slants. Etc.

> The crossover notch will likely be where the tubes are melting down.

I bet you meant to type "NO crossover notch will likely be where the tubes are melting".  

When you over-volt and heavy-load an amp, to get the most noise out of the least bottles, you can't make crossover "go away" until you idle the tubes VERY hot, often past the melting point.

Moderate voltage, moderate load amps can usually be trimmed for negligible crossover distortion without melting, though you may get only half the Watts from the same bottles.

At another extreme, over-geeked Class A Hi-Fi can "Gm double", which means more gain around zero than on peaks. The opposite of conventional crossover distortion.

[loogie]

There's one on Ebay for fifty-eight bucks:  190166195819

You can download this for free:

http://www.zeitnitz.de/Christian/Scope/Scope_en.html

It includes a signal generator and frequency analysis.  I've played with it a little.  Interesting...

[gregolson65]

I have a couple electonic folks tell me to get an analog O'Scope and not digital for amplifiers. So they pointed me to an Tektronix 465 or any model of that type on e-bay. That is all you need. Like someone said your not tuning an radar installation just a plain old amplifier. E-bay has tons of tektronix O'Scopes dirt cheap and they will do the job.

[DummyLoad]

Would this USB oscilloscope be adequate for amp debugging and design tweaking? Stingray list $220.

Anybody have suggestions about alternatives?

I've searched for "oscilloscope" here and most of the posts relate to old, tube powered 'scopes with a CRT.  While no doubt cool, I'm just interested in a tool to help me "see" what's happening at Point A and Point B in the signal path.  One concern I have is the voltage range - don't know what we need.  The documentation for this device mentions some kind of probe to allow measuring greater voltages, but I don't know if that would take me into the price range of a B&K, Protek, orTektronix bench-top oscilloscope.  Mouser lists some probes that cost more than the Stingray  :-?

Thanks for any help with this.

Chip

a decent scope.. more than you'll ever need for audio, price is decent..

ebay item # 110218979669

[RickRS]

Would this USB oscilloscope be adequate for amp debugging and design tweaking? Stingray list $220.

Factor in the cost of scope probes, as I don't see any included.

And concerning 10:1/1:1 probes, Tektronix's (one of the best) are only rated for 300 volts max and that the same for everybody else.  If you want to check plate voltages and output tubes, think of a x100 probe, which are rated for 1000 volts or more.  

As suggested, you can create a divider circuit to use for higher voltages, so there are ways around the cost of having both a x10 and a x100 probe in your kit.

I would have no problem with the digital vs. analog, as sample rate looks ok, but real knobs make for faster/easier use.

[Nigel]

Wow!  Those are great prices.  Unfortunately, I still don't know what the key specs are other than dual trace.

In another thread, one of our most learned co-contributors referred to the need for "A real 'scope, not a PC-based toy".  I would never disagree with this gentlman, but it would help to know what the drawbacks of the "PC-based toys" are.

Also, what kind of probes would I need?  For example, the first B&K scope shown comes with two "PR-33A x1/x10" probes.  Does the "x1/x10" mean that the probes can multiply (or reduce) the input signal by a factor of 10 for certain applications?

Chip

You would need to be careful with a USB scope in regards to grounding.
I can remove the ground on my scope and it can then used to reference to voltages above or below ground.

I have both a serial port and a normal scope and always use the normal scope.

[bnwitt]

My two cents?  analog, 40mhz and the biggest screen you can get.  This is what I have found to allow my old eyes to truly see the nuiances of an audio waveform.  And as said, the Tektronix 465 is a good one but beware of ebay scopes.  You'd have safer buy with Weber and the 20mhz new scope would probably have a nice crisp screen over an old scope.  You might want to buy an audio signal generator while you're at it if you don't have one.

[Fresh_Start]

bnwitt - thanks for the advice.  eBay makes me very nervous anyway, so I just got the Instek GOS-620 from Test Equipment Depot.  (Weber was out of stock or I would have added the oscilloscope to an order for speakers and a Mini-Mass that got here just today.)

Any further advice re: a signal generator?  I haven't even fired up the oscilloscope yet but am sure that my tuner output isn't going to do everything I'd like to try...

Cheers,

Chip

[bnwitt]

tubes and more has one for $159.95

http://www.tubesandmore.com/scripts/foxweb.dll/moreinfo@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=S-MAFGEN

[tubesornothing]

if you are getting a signal generator make sure you have one that has low harmonic distortion.  That messed me up for a long while.  Maybe also one that generates white noise and sweeps are fun too.