Oscilloscope Advice

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Ray P
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#1 Oscilloscope Advice

Post by Ray P »

I still haven't bought myself an oscilloscope in spite of getting close previously and knowing I really ought to invest in some basic capability. My only use is really as a tool for this audio hobby so I don't think I need anything expensive/esoteric and don't want to spend too much. For that use case is it worth considering a cheap Chinese USB device, like this:

https://www.ebay.co.uk/itm/203509482565 ... 1438.l2649

or would I be better looking for a used integrated 'scope?
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Nick
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#2 Re: Oscilloscope Advice

Post by Nick »

I would say it depends on what you want to use it for,
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#3 Re: Oscilloscope Advice

Post by jack »

Nick wrote: Thu Sep 09, 2021 6:41 pm I would say it depends on what you want to use it for,
...and your budget 8)
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Ray P
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#4 Re: Oscilloscope Advice

Post by Ray P »

Nick wrote: Thu Sep 09, 2021 6:41 pm I would say it depends on what you want to use it for,
Perhaps you're exposing my lack of knowledge/experience Nick, I'm assuming basic measurement/troubleshooting of analogue audio projects - amplifiers and the like. I've had amp projects with issues before, oscillation and the like, and I guess I could have done better if equipped with better tools - more objective than trial and error.

More generally I see this as part of gradually getting a better equipped workshop together so I also want to improve on things like bench power supplies, multimeters etc.
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#5 Re: Oscilloscope Advice

Post by Ray P »

jack wrote: Thu Sep 09, 2021 7:15 pm ...and your budget 8)
The cost of the USB scope I linked to was £85 - that's not my maximum but clearly I'm not looking to spend hundreds or thousands for occasional hobby use.
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#6 Re: Oscilloscope Advice

Post by jack »

Ray P wrote: Thu Sep 09, 2021 7:23 pm
jack wrote: Thu Sep 09, 2021 7:15 pm ...and your budget 8)
The cost of the USB scope I linked to was £85 - that's not my maximum but clearly I'm not looking to spend hundreds or thousands for occasional hobby use.
Like all bits of kit (as t'other Nick alluded to) it all depends on what you're trying to achieve.

If you just want to look at the shape of waveforms and a bit of ringing etc., then a low-end solution may well be absolutely fine.

If you want to measure THD at low levels or higher harmonics/intermodulation component/spectral analysis etc., then something rather better is called for - better ADCs (with appropriate good internal design), higher sample rates etc.

if you are looking to capture one-off events, you may need some sort of storage capability. If you think you might look to do a bit of VNA, then having a device with a built-in tracking generator is a plan...

I find that an Analog Discovery II does 90% of want I need, both analogue & digital, but I do have a high bandwidth Tektronix 2465A for the gnarly stuff. YMMV.
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Ray P
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#7 Re: Oscilloscope Advice

Post by Ray P »

Thanks Nick, I think with my state of knowledge and experience I need to be realisitc and just aim for the former,
jack wrote: Thu Sep 09, 2021 7:48 pm If you just want to look at the shape of waveforms and a bit of ringing etc., then a low-end solution may well be absolutely fine.
I can always build capability from there.
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#8 Re: Oscilloscope Advice

Post by Nick »

IMHO I have never regretted spending as much as I can afford on test kit. But if you are not sure what you need it for then maybe you don't need it.
If you just want to look at the shape of waveforms and a bit of ringing etc., then a low-end solution may well be absolutely fine.
I agree, but you will quickly hit a 20Mhz limit if you are looking at solid state devices, and its entirely possible it would fail to see chirps of oscillation if you are playing with Mosfets. Also, don't underestimate the value of a scope with good and flexible triggering, its not just about bandwidth. BTW, to test the above, you will also need a good source of a square wave.

On the third hand, there is not much to lose with that linked interface. It may be worth it if for nothing else than to make you aware what you are missing (or you may not be missing, in which case its fine).
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#9 Re: Oscilloscope Advice

Post by jack »

https://www.ebay.co.uk/itm/Tektronix-24 ... 635-2958-0

£40+p&p at the moment. Almost tempted myself!

Note: this is a truly superb analogue scope - arguably one of the best ever made - there are three in the series 2465. - 300MHz, 2465A - 350MHz and 2465B at 400MHz. There are also storage scopes in the range, but they are normally expensive. In practice, they perform far better than their base spec. Triggering is also awesome and the on screen measurements are really useful too
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#10 Re: Oscilloscope Advice

Post by Max N »

Hi Ray
There is a section on choosing an oscilloscope in the latest version of MJ Building Valve Amplifiers which I found quite helpful. It was published in 2013 I think, so doesn’t include recent models obviously. But it does discuss features and why you might want them.
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#11 Re: Oscilloscope Advice

Post by Nick »

Yep, I agree, you get more bells and whistles with digital and I doubt I would go back now, but the only reason I stopped using my Tek 465 was the eht broke down because of damp in the workshop. That would be a cheap way of learning how to use a scope and would do the "see the waveform" just fine, and as Jack says, its got great triggering.
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#12 Re: Oscilloscope Advice

Post by Mike H »

I agree with Jack (Nick D), have just looked at eBay, a few used ones on there now for under or around £100, what they're like of course maybe another matter – I have two nice second hands, a 2-channel 15 MHz Gould Advance I got maybe 1990 -ish, refurbed for £250 IIRC, or somesuch, and a digital Tektronix, cost more than that (can't remember exactly) – neither are used much but I don't regret buying them – sometimes when you need it, you need it – the Tetronix does up to 100 MHz, and even in an audio circuit can be amazing sometimes how much RF crap is flying around, that you maybe need to investigate.

I have looked at things you can plug into a PC but was never convinced enough to go for one. This included kits and published DIY projects. Image
 
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Ray P
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#13 Re: Oscilloscope Advice

Post by Ray P »

I took the plunge and bought this one;

https://www.ebay.co.uk/itm/133903661184 ... 1113.m2108

Thanks to Nigel (vinylspinner) for the tip on the listing.

I'll dig around for a user manual later.
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#14 Re: Oscilloscope Advice

Post by Paul Barker »

50meg will do the audio stuff you can hear.
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#15 Re: Oscilloscope Advice

Post by jack »

Paul Barker wrote: Mon Oct 18, 2021 3:23 pm 50meg will do the audio stuff you can hear.
You don't even need 50MHz for audio - you're way above any noticeable harmonic or IM products at that point.

What is important is stuff at RF. Plenty of nominally audio circuits behaving badly can oscillate at"RF", meaning that 50MHz plus is perfectly possible - I've seen 120MHz in one of my more abhorant silicon designs and I'm sure that the penchant for using RF valves in audio means that such frequencies will be found there too...

When something gets unexpectedly hot or unstable, RF oscillation may be the cause and having a 'scope that can see that and assist in tracking it's origins can be a great help.
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