Something stirs in the Undergrowth

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IslandPink
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#2341 Re: Something stirs in the Undergrowth

Post by IslandPink »

That's a very noble suggestion .

Now, I have been getting this all set up. More or less there, hit a snag.
If I was using a voltmeter I could just clip red & black leads either side of the series resistor.
With the oscilloscope probe , as soon as I attach the earth clip to either side of the resistor, the signal dies, as it's shorted to ground.
So, just train of thought here, should be able to measure across the speaker terminals instead, the neg speaker side from the amp can have the probe's earth clip attached there.
Yes, I'll try that.
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#2342 Re: Something stirs in the Undergrowth

Post by IslandPink »

Ok, now my brain hurts :confused3:
See set-up picture below :
With 1kHz tone playing through the pair of FX120's, as before, I connected the Osc probe's earth clip to the yellow ( = black ) wire, at the speaker .
This is coming direct from the chip-amp's black speaker terminal.
The tone just stopped, same as before
??
Impedance_test.JPG
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#2343 Re: Something stirs in the Undergrowth

Post by ed »

are you sure the phase is not reversed in your chipamp?
is the chipamp output isolated?
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#2344 Re: Something stirs in the Undergrowth

Post by Nick »

Chip amps normally drive both terminals with a H-Bridge sort of output, so neither are ground. Lift the earth on the scope mains plug.
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#2345 Re: Something stirs in the Undergrowth

Post by IslandPink »

...err, OK, how do I do that ?

(ps, in other news, see this posting for comment on the 0.6mH value -
https://www.diyaudio.com/forums/multi-w ... ts-32.html )
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#2346 Re: Something stirs in the Undergrowth

Post by Nick »

Use a IEC on the scope with the earth disconnected (and safely out the way).
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#2347 Re: Something stirs in the Undergrowth

Post by IslandPink »

Sounds like something to do tomorrow evening, when I'm a bit fresher.
It has an IEC lead, I can disconnect the earth in the plug, but what do you mean by 'and safely out the way' ?
I will still have to operate the controls to get the gain/timebase sorted out.
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#2348 Re: Something stirs in the Undergrowth

Post by Nick »

I mean make sure the removed earth doesn't find a way to come into contact with a live pin.
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#2349 Re: Something stirs in the Undergrowth

Post by IslandPink »

Ah, righto .
I think HiFiCompass has admitted the 0.6mH is a red herring, so I have soldered-up a 1.5uF(close) + 18R combo to try as a 'fix' for tomorrow's tests.
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#2350 Re: Something stirs in the Undergrowth

Post by SimonC »

Nick wrote: Mon Apr 29, 2019 9:50 pm Use a IEC on the scope with the earth disconnected (and safely out the way).
https://www.picotech.com/library/oscill ... asurements

Back when I was a lad we used to have stand-alone differential amps that floated the probe and ground in the test labs where I worked. For some reason the management were not keen on us disconnecting the scope ground when working on 600v+ DC drives...looks like the current (swidt) method is to persuade you to buy expensive differential probes, but you can make up a simple one out of a couple of op-amps for low voltage use. (https://electronics.stackexchange.com/q ... cilloscope gives you the basics).

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#2351 Re: Something stirs in the Undergrowth

Post by Nick »

Or as you are driving via a 500R resistor just connect directly to your sig gen.
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#2352 Re: Something stirs in the Undergrowth

Post by IslandPink »

As Nick usefully pointed out .... also we checked Farnell LFM4 specs and it has about 60R output impedance, so could drive a decent-sized resistor and speakers OK at low level. So I've side-stepped the problem of having to disconnect the Oscilloscope earth.

I put together a 100R and 180R to get a higher series resistor.
This all went amazingly well. I have some data points to make a graph , but briefly ...:
Without compensation, starting at 1kHz and input adjusted to read 4 Divisions on the scope, taken across the speaker connections, the voltage then rises to 8 Div by 11kHz , so more than twice the impedance.
I then connected 18R and 1.5uF zobel across the speaker pair, ( calc from Le = 0.2mH was 18R/1.2uF )
This combination was more or less bang-on perfect at 3.9 to 4.0 divisions across the whole 1k - 10k range.
No need to look any further :)
I will try & rummage out the Avo later, while things are set up.
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#2353 Re: Something stirs in the Undergrowth

Post by ed »

way to go!..respect!
I'm of the opinion we should all get back to steam driven methods...

having said that, if you want to do much more of this Mark, I'm thinking of selling off my antiquated Clio system together with a like generation pc with the necessary pci card. I don't think I'll be building any more speakers now.
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#2354 Re: Something stirs in the Undergrowth

Post by IslandPink »

Right-on, I like to understand what I'm doing.
Well on this Clio thing I must say I'm more than a bit interested. I kept thinking I ought to round your place at some stage and tackle my measurement difficulties head-on.
So could you give me a run-down of the bits in detail or a photo of how much kit is involved ?
I should be able to find some space, ( and return Nick's test kit :D ) , but I'll need some serious tuition at some stage.
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#2355 Re: Something stirs in the Undergrowth

Post by ed »

here's the gist of it Mark

http://www.vitalstates.org/diy/misc/cliomanpci.pdf
http://www.vitalstates.org/diy/misc/clioreadme.pdf

I have the complete system as described in the manual, with the exception of the turntable. I've done all the off-axis stuff manually in the past so I can confirm the turntable is not necessary. It has Audiomatica mic01.

be aware, as mentioned in my previous post, I'm thinking about this...I haven't given it full consideration yet.
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