It's promising that you are considering test equipment, you'll never regret having the tools to verify any builds or repairs.
While newer oscilloscopes can do bode plots (frequency response) in FFT, they are not particularly useful for measuring distortion. They are however well dispensed for finding faults, unwanted oscillation or for locating the origin of gross distortion in a circuit. Siglent makes some good four-channel models that can be paired with their signal generators for bode plots, even the 2-channel types are fine.
Good morning
Thank you so much for the very kind and valuable advice
I was impressed watching a video on Youtube that the square wave test was even able to highlight problems in the very cheap bnc to bnc cable supplied with a also cheap function generator so it means that that test is very telling.
It goes without saying that I would like to apply it to unbalanced audio cables that I already have and others that I would like to build myself
Then another absolutely fascinating topic for me are power supplies
For a small pre-line project that I have in mind I would like to start from an off-the-shelf SMPS and add filters
But I have to see the initial noise and the effect of different filters on it
Another good tool is the QA403. It is much like a sound card and can measure different types of distortion, but also has input protection. What it isn't, of course, is anything like the Agilent analyzers we use at work.
An LCR meter and digital multimeter are incredibly useful. I recommend having a the DE-5000 as an affordable LCR meter with good tolerance. For multimeters, I recommend keeping two close at hand. The bench meters are of course more precise and cost more.
Indeed I did, but the remainder were built to order using my specifications. I'm very precise and design most of the hardware, but sometimes it's better to have a craftsperson handle certain tasks.
I saw that there are very cheap oscilloscopes for PC like Hantek and perhaps I could try them first and see if i am captured
The one you mentioned is really excellent judging by the videos on YouTube but already in an enthusiast price range
About pots and attenuators: The noise through a pot is usually very low and gets swamped by the noise of the circuitry around it. Direct current traversing the wiper to the return path is the main concern. Resistor-based attenuators don't have that problem, as their contacts are done by switches. Either can be an ingress point for EMI noise pickup and should be in a metal case.
Some resistors are specifically noted as low-noise types, and as the designer or builder of your gear, you have to analyze the circuit or model its behaviors to determine where low-noise resistors are going to be of benefit. When you are choosing resistors, take careful note of the signal voltage and current for that part of the circuit where the resistor (or potentiometer/attenuator) is going. Choose based on rated power (higher is better, if available) and thermal coefficient (ppm, lower is better), as these are related. The ppm denotes the amount which the resistor can drift per °C thermal change in regards to the stated tolerance and value. I chose Susumu RR series simply because they met all the primary requirements, and they are not boutique audiophile nonsense. I could have specified any of a dozen other lines or brands and the result would have been the same. Don't overlook Yageo 50ppm 1% through-hole resistors, as they can save you a bundle if you need many. In a tape of 20 one is bound to find 6 that are within .2%.
thank you very much for the very helpful advice Caps are very usefull for dc locking but i have to see how much they degrade the square wave Maybe some less than others
Regarding resistors i have used in the past some from Welwyn Components bought from RS Components and seemed ok
Holco are good but a little rare I will keep in mind the brands you mention for sure
I have to try first to understand if there is passion. Not that I haven't already spent in the past but ultimately buying a device doesn't satisfy me fully. I like to modify or even build something.
I have downloaded hundreds of commercial units schematics
I also try to understand the circuit analyzes of the experts but when I hear that the circuit is far from optimal but has spectacular measurements anyway I am left puzzled
Another issue for me hard to understand is that i have found line preamps with just one mosfet and other with more than 20 active devices to do the same task i.e. some signal buffering and a little voltage gain
My main doubt is if it is so challenging to optimize a minimalist circuit it should be almost impossible to optimize a much more complex one i guess
In short, if we have to believe in measurements it is better to try to understand the measurements
I have some to study
Kindest regards, gino
