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PG506 standard amplitude output rise-time?
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The 1kHz standard amplitude waveform was a curious shape, traced to a dead or dying opto-coupler driving the 'standard' amplifier stages, fixed by replacing it.
I then noticed that the output waveform rise time was noticeably faster (~1us) at outputs of 20V and above than at 10V and below (~23us) this seems to be due to the 0.22uF in parallel with a 10k5 resistor that is present across the output connector when these lower voltage ranges are selected. I realise that this doesn't really matter as it is the amplitude accuracy that is important in this application but I have failed to find mention of the purpose of this filter in the service manual, can anyone enlighten me? Thanks in advance, Adrian |
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The standard amplitude output is driven in two different ways - the
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20/50/100V output is voltage driven with a current limit, whereas the lower voltages are current driven for a 50Ohm load. There's a discussion of this in the Theory of Operation section. On Thu, Jun 13, 2019 at 1:58 PM Adrian <Adrian@...> wrote:
The 1kHz standard amplitude waveform was a curious shape, traced to a dead |
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That's true Siggi, but it doesn't explain the presence of C315 0.22uF across the output.
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The 10V-and-below goes down to 0.2 mV. At that low amplitudes spikes produced by the switching power supply appear in the output signal and can be larger than the signal amplitude. I guess C315 serves to reduces these spikes. In earlier versions there was no C315 but the output was filtered by an LC network in the path to the BNC connector. The filter was by-passed in the 20-50-100V positions. Albert On Thu, Jun 13, 2019 at 11:51 PM, Siggi wrote:
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Thanks Siggi & Albert,
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Yes, that was my point and I think Albert is correct, lifting one end of C315 makes the fast noise worse at very low amplitude outputs, although hanging a .05 uF ceramic cap in it's place seems to pretty much get it back where it was in terms of noise but with a much improved rise time. Of course that may just be telling me the noise is way worse than it should be and I need to look at the state of supplies etc - will prod around some more! Adrian On 6/14/2019 9:18 AM, Albert Otten wrote:
That's true Siggi, but it doesn't explain the presence of C315 0.22uF across the output. |
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Adrian,
There have been several posts here about that switching noise. Maybe the B04-up version performs better in this respect, I don't know, my PG506 is B03something. With suitable setting of the scope time base unit you can trigger on the spikes in the signal, with the square wave appearing as noise. Albert |
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Mine is a B04 something and yes, I can trigger on the noise in that way too!
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On 6/14/2019 12:02 PM, Albert Otten wrote:
my PG506 is B03something. With suitable setting of the scope time base unit you can trigger on the spikes in the signal |
Mlynch001
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