MPI 4: Scope traces at HF.

[62caddy]

I've been wondering why it's difficult for scope readings to register whe playing music at almost anything above 2K, (ie: when 200 - 2,000 Hz is selected, SWEEP control @ maximum).

This is only the case with music. With test tones however, I have no difficulty getting a bright clear trace at 20kHz. But with music however, the intensity must be turned way up and the readings are barely visible at anything approaching 1kHz and above. Trace readings are otherwise excellent when using the 20 Hz - 200 Hz range setting.

Has anyone else observed this with the MPI4?

I know special cables are supposed to be used with the MPI4 for preamplifier connections but this function is exactly the same whether the the readings are taken from the amplifier output terminals (for which no particular cabling is specified in the manual) or from the preamplifier outputs. Besides, the 20kHz trace readings come through clearly when using test tones so I can't see the ICs are at fault.

 

[Pio1980]

It's a natural result of the shorter interval of the beam on a point in the phosphor at higher freqs.

 

[62caddy]

It's a natural result of the shorter interval of the beam on a point in the phosphor at higher freqs.

So is this pretty much normal for all scopes?

 

[Pio1980]

So is this pretty much normal for all scopes?

Afaik, most if not all crt scopes. I don't know if any could comp for it.

 

[TSmith8605]

The test signal (I assume a sine wave) traces the same narrow line path across the scope screen concentrating its energy in that pass over and over again on each trace keeping the phosphor bright and so the trace remains bright.

When playing a music signal, the signal is more random-like and spread all over the scope screen (especially at higher audio frequencies) and the beam does not repeat its path trace-to-trace so the intensity is much lower.

I think this is normal scope stuff and turning up the intensity is the correct thing to do - and the reason the control is there.

More or less the same thing Pio1980 said but with a lot more words.