A Complex Technical Mystery Solved And Other Oddit

A complex technical mystery solved and other oddities.

Being an active Ham (Amateur) Radio operator and a vinyl person can make for interesting scenario's! Specifically, things like Radio frequency (RF) interference 'issues'. Thankfully I haven't had too many issues but there have been one or two slightly baffling issues! Putting things in metal boxes and properly 'earthed' is good engineering practice however RF can find sneaky ways of 'injection'. I have had instances of breakthrough on 'phono' caused by loose or partially 'open' RCA connectors (a lost earth connection), yet everything has worked fine at 'audio', as often an earth connection occurs through other 'incidental' circuit path's. However phono preamplifiers are quite touchy in terms of potential RF interference issues because of the high voltage gain in the amplifying circuit and the wide amplification bandwidth. Once again, proper earthing and shielding usually solves most breakthrough problems before they start, but not always!

Despite properly earthing and shielding my main audio system's phono preamp, I was frequently told that my Ham Radio transmissions were often heard over the Hi Fi system's loudspeakers when playing records! The other day I had another go at fixing the RF breakthrough.......with success and yes it came down to rearranged 'earthing'. In the end the earth wiring looked practically unchanged but there was a subtle difference as I included the phono preamp and power supply into the main earth wire bus, essentially 'star' earthing at a common earth point. This experience shows the value of this kind of earthing as originally there was 'earthing of sorts' through the braids of the signal leads, but it wasn't enough! Proper 'star' earthing provided a complete cure......well almost anyway!

Actually there is no RF 'breakthrough' now, but one little oddity. It is 'just' noticeable that my Ham Radio transmissions cause a slight change in the speed of the turntable giving an effect that sounds like a slow 'wow'. My investigations indicate that the cause of the problem is RF injection through a poor mains 'earth' stake but this is essentially out of my control as the 'authorities' need to remedy this issue. This has been brought to their attention, but in bureaucratic circles things move v-e-r-y s-l-o-w-l-y! I have wired in a separate stake which is a lot better than the official mains earth stake but it is only an interim and temporary measure. However it does help, thankfully!

Lost or 'open' earths are regrettably common especially in interconnects that are subject to flexing and/ or frequent movement. Fortunately though a 'missing' earth usually becomes self evident through resultant buzzes or hums! Occasionally though, the inner conductor also goes open circuit, and learning how to properly use a digital multimeter can be most useful as a means of diagnosing all manner of little electronic 'faults' such as broken or intermittent leads. Actually 'intermittents' have driven many a service technician to the point of a nervous breakdown and/or baldness. Look at my head......there's clear evidence. I could tell you some unbelievable yet completely true stories over the years in both home and work situations!

Whilst the average hi fi person can't be expected to be a technician, I think possessing a basic digital multimeter and learning how to properly use it is very worthwhile. However stay well clear of 'mains' or other high voltages. Leave those faults to those with appropriate authority and training. Many multimeters now also include a 'capacitance measuring' function. I actually own a good quality stand alone capacitance meter. It has been a most useful test instrument for measuring actual cable capacitance, something of considerable importance at least if using a moving magnet phono cartridge. Electronics....it's fun! More to come! Felix.