[robzy]

Hey guys,

I have been offered one a GOS-622 oscilliscope for a good price and was wondering what they were like for audio. Here are the specs:

http://www.flite.co.uk/gos-622g-20mh...illoscopes.htm

(Its the 20Mhz version)

Also - what does one look for when choosing an oscilliscope to use when building amps?

Thanks,
Rob.

 

[tangent]

Quote:

what does one look for when choosing an oscilliscope to use when building amps?

Something basic like what you pointed to can work fine. What you would get by moving upmarket:

1. A better chance that the thing can be repaired. It costs a lot of money to stock the parts for a modern scope long enough for them to be needed. If, 10 years down the line, that scope breaks, and the manufacturer has gone thorough two additional models since then, will they even have the parts to repair your scope?

2. Better quality all around, and more attential to detail. Just to give one example from a cheapie scope I have here: the markers on the knobs are almost impossible to discern from the anti-slip knurling. You have to actually study the knob to know what setting you've selected! A manufacturer like Tek wouldn't make that sort of mistake.

3. More speed. 20 MHz is plenty for watching sine waves, but if you want to see many types of oscillation or evaluate the amp's response to fast square waves, you'll need something faster. I would say 20 MHz is borderline useful. I'd prefer 60 to 100 MHz, and higher is even better. Just as an example, consider the now-popular AD8397: it's over a 60 MHz part, and is known to oscillate most easily at 40 MHz. You couldn't even tell that something was wrong with a 20 MHz scope, and even a 60 MHz scope might make things tough on you.

4. Digital sampling. Analog scopes are fine for watching repetitive waveforms -- test source waveforms, most oscillations, power supply noise -- but a DSO can capture one-shot events, too.

 

[bigcat39]

I agree with Tangent. "You get what you pay for" is very evident in test equipment. And, you get neat things like onscreen display of settings.
I have sole access to a $50K Agilent DSO, so maybe I shouldn't talk....

 

[jar]

I always run into this problem when I consider purchasing a scope. At work, we have a variety of scopes including a nice color 4-channel 100MHz Tek DPO. I'm pretty spoiled, having never really used an analog scope for more than looking at sine waves and stuff. So, I start thinking about getting a scope, usually because I see a cheap price on an older analog model. Then I think about the features I'm used to, and start climbing the price ladder, and then give up.

 

[deek]

What about a software scope? Where you can just connect the probes to different channels on your sound card?

Funny this topic showed up, just today I was asking my prof. about choices of what I could do for a scope.

 

[Francis_Vaughan]

Well all the talk of really lovely toys from Agilent or Tektronics is all well and good, but the rest of us mere mortals have to make do with much less. I have a 24 year old scope which is the direct predecesor of the GOS 622G. I bought it new. (The "G" in GOS stands for Goodwill). As scopes go these are very possibly one of the most popular cheap ones around, and are rebadged mercilessly all over the world. They have been made in numbers that Agilent or Tektronics could only dream of. But they are very much the cheap end of the market.

None the less, I have had great success over the years with it building and debugging all manner of stuff. An analog scope is easy and intuitive to drive, and, if anything, teaches you some fundamental things about the analog world that a digital toy shields you from.

Would I like a nice Tektronics digital scope? Sure. But for the money my ancient GOS622 has been great value, and has done 90% of what the Tektronics could have ever managed, given the relatively unsophisticated needs I have. Currently I seem to be moving in the direction of modding and building guitar amplifiers (no solid state here) and my old scope will be more than adequate for that.

 

[robzy]

Thankyou all for your replies.

I have decided to go for the GOS622 becaue it will be my first scope - will only be used really for headphone amps and maybe PSU's and for the price its being offered to me for - i cant say no.

(Thankyou for the specific info on that scope too Francis Vaughan)

Quote:

Originally Posted by deek What about a software scope? Where you can just connect the probes to different channels on your sound card? Funny this topic showed up, just today I was asking my prof. about choices of what I could do for a scope.

For some reason i would guess that could only read frequencies from 20Hz-20kHzish?

Rob.

 

[mikeblas]

If you don't already have a scope and the price is sensible, then I don't see any reason not to buy it.

 

[bigcat39]

It's actually a quite good looking scope. Better than what I have @ home, which is nothing.

 

[tangent]

Quote:

Originally Posted by deek What about a software scope? Where you can just connect the probes to different channels on your sound card?

Problems with that:

1. You're limited to the bandwidth of your sound card. You won't be looking for oscillation or square waves with this one. (In case you don't understand why square waves are out of the question: an ideal square wave is made of the fundamental frequency plus infinite harmonics. The more harmonics you can capture, the more accurately you see the wave. So, if you try to look at a 10 kHz square wave, you'll just barely see that plus its second harmonic with your average sound card, which will make the waveform look like a chunky sine wave. Also, the purpose of square wave tests is to look for ringing, which puts additional high frequency components into the wave.)

2. Unless the adapter between the probe and your sound card's input adds some kind of protection and scaling, you won't be able to capture signals much over 2V with most sound cards. It'll be fairly easy to blow up a sound card with overvoltage. A good hardware scope will have protection well over 100V, so with standard 10x probes scaling input voltages down by a factor of 10, it's pretty much impossible to kill such a scope accidentally.

3. Knobs beat mouse clicks for usability any day of the week.

4. It's easier to "float" a hardware scope if you ever need to. Because of the complexities of PC power systems, you pretty much have to resign yourself to a perpetually grounded scope.

5. Unless you have a laptop, a hardware scope is going to be more portable.


And there's one big, nonobvious adavantage of software scopes: 16 bit depth is de rigeur. With hardware scopes, you're lucky to be able to discern more than 8 bits worth of data. This is why I prefer software FFT programs over hardware spectrum analyzers, when only audio frequencies are under consideration.

 

[deek]

Thanks for the input tangent. I guess I am going to have to go out and find myself an affordable scope.