Choosing an oscilloscope for amplifier testing

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rsumperl

rsumperl

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Joined 2009
#1
Good afternoon everyone,
I'm looking at an oscilloscope that is in really excellent condition and at a really decent price, however it is a 20MHz scope. I know "our" audio range is 20Hz-20KHz, so my gut tells me this scope will be fine. Any inputs???

Thanks
Ray
 
#3
scope bandwidth really needs to exceed worst case high frequency "features" you should want to see

that includes misbehavior, oscillations way beyond audio frequencies

audio PA may only have few MHz global feedback gain intercept - but to be able to diagnose that you want 10-20x scope BW

and you can have local RF oscillations in many discrete transistor subcircuits commom in audio PA from 10s to 100s of MHz

some used scopes can be a deal but today there are also awesome price performance low end scopes like Rigol 1052, 1102 for < $400
 
#6
even with Tek I wouldn't want an old sub Gs/s digital scope for any any money today given the modern options, low prices for guaranteed working, calibrated new product

I would consider a 100 Ms/s sampling digital scope a disposal problem - like my TDS460 (the fact that it didn't turn on last month after a decade in the closet contributes to that opinion too)
 
#7
rsumperl said:
Good afternoon everyone,
I'm looking at an oscilloscope that is in really excellent condition and at a really decent price, however it is a 20MHz scope. I know "our" audio range is 20Hz-20KHz, so my gut tells me this scope will be fine. Any inputs???

Thanks
Ray
Click to expand...

A scope is really a very handy thing to have. If it's an old analogue scope it'll be easy to drive which is important. Older digital scopes are a freakin nightmare to drive. Personally, I think 20MHz will give you plenty of good use even if it won't do everything. You'll learn how to use it and get the most out of using a scope for audio amplifier work. You can even make your own probes if necessary and a grid-dip meter for finding very high frequency parasitic oscillations in misbehaving amplifiers [Troubleshooting Analog Circuits Paperback – Jun 19 1991 by Robert Pease (Author) ]

If you find it lacking in the future you can always sell it and upgrade with a much better understanding of what you want before you spend bigger $.


Edit: just noticed you identified it as a Gould scope. The photo I attached I found on the internet. It looks like a disaster for a person like me ! - lot of push buttons and probably some difficult menus - not for me. Give me a simple layout with knobs I can twist. Please. 😛
 

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#9
I'd say, look at the price of a modern digital scope like DS1054Z or DS2072. They're quite cheap considering their possibilities.

Sorry Bigun... DO NOT BUY DS1052, it is obsolete. Newer scopes have intensity grated display, which makes all the difference.

Therefore, I think a used analog scope should be purchased for something like 100-150€. If you can get a Tek 465B... go for it!
 
#10
no worries, I'm not about to buy the Rigol but it's good to know about the display as I've not seen one in the flesh. I use a Leader 200MHz analogue scope in my hobby room - I was lucky that I got it at a good price and it performs fiine. It's fairly old, some times of the year when you first turn it on there can be a loud 'crack' from inside. Some kind of HV arc-over. Of course what happens is that you are delicately probing the leads on your power output device with a DMM trying not to let the probe leads slip and produce a short when the scope goes 'CRACK' and you jump out of your skin with probes flying where they may !!
 
#14
a possibility, I would check on EEVblog Electronics Community Forum - Index for Hantek, reputation, model comparisons

I think Rigol may still be the deal if that Hantek is sharing 1 Gs/s ADC between 2 channels, then you only have a couple of points at the "200 MHz BW" corner frequency

for a more "analog scope" look/feel, insight into the wave forms you really want more oversampling to analog BW ratio

"equivalent time" sampling isn't so hot for debugging wide BW noise, interference
 
#15
I have looked at some DSOs over the holidays in view of getting one. Sometimes these four are in the same price range for similar capabilities:

- Rigol
- Owon
- Siglent
- Hantek

I've read a few comments on Amazon. I've been mostly looking at the Rigol DS1054Z myself actually.
 
#16
The Gould 1604 is a dual mode scope. It has an analog section with 40ns max. horizontal deflection and a digital section with 20Ms/s and 7MHz bandwith. For Audio sufficient. For about 100-150§ it should be ok. A service manual is available on the web.
 
#17
jcx said:
even with Tek I wouldn't want an old sub Gs/s digital scope for any any money today given the modern options, low prices for guaranteed working, calibrated new product

I would consider a 100 Ms/s sampling digital scope a disposal problem - like my TDS460 (the fact that it didn't turn on last month after a decade in the closet contributes to that opinion too)
Click to expand...

Pfft! My Tek 340a is a bloody nice bit of kit. I could care less that it samples at 500Msps. That's oodles.

If you really want to dispose of your 460, I'll take it off your hands. Then I'll replace the power supply caps, which is probably all that's wrong with it, give it a quick clean, and be sure to show you lots of pics of it working beautifully.

Kids these days!

For the OP: buy something that does 100MHz, 2 or more channels, 400+Msps. Old Tek is incredibly good. LeCroy also. I have a personal gripe against HP CROs, as we had the worlds worst 1GHz one at work back in the nineties, that we dubbed the "one knob wonder".

Really old Teks, like the 465, are awesome, but will probably need a lot of work to get going reliably. Newer CROs are windows (or underpowered junk) and pretty-much disposable.

Just one thing. Buy really good probes, the best you can afford, and look after them. You'll need at least 250MHz probes to properly drive a 100MHz CRO.
 
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