Microphonic Starquad cable

[ccaudle]

not only that but the whole thing is now happy and hum free

I would love to understand what is different in that connection scheme that reduces the 60Hz noise. I don't have a good hypothesis at the moment.

capacitance to the sub frame which is grounded to the housing , that might be minimised further by insulating the tray ,

Basic capacitor physics is the capacitance is the conductive area multiplied by the dielectric constant divided by separation distance. Any insulation has a higher dielectric constant than air and will increase the capacitance.

 

[Tubetec]

I found a quick and simple way of electrically isolating the tray by adding small loops of insulated solid core copper wire for the support springs to attach to ,
It did reduce my capacitance , from 130pF per conductor to 123pF . Its not a major difference but I'll take the extra reduction in any case , the humble old TRS jack adds around 10pf on the tip and 5pf on the ring , no real way around that .


Ive only checked with my ears so far but the reduction in capacitance , and the reduction of the of the effects of that capacitance by placing lower load (120 kohms) across the transducer gives the spring a lot more sparkle , in contrast in line input mode ,which uses the same TRS jack the spring sounds a bit dull and lifeless with only 20 kohms load .


I dont know why the starquad totally messed up the CMRR of the SSL2 , Im glad I made the mistake and learned something about tribloelectric effects along the way . Now of course with twin coax the conductor to conductor capacitance is greatly reduced over what the starquad or even regular mic cable gives ,thats made all the difference in this case .

I can see the attraction of the FET booster circuit now , zeroing out all the extra cable capacity around the transducer and putting even more zing in the spring ,
Abbeys circuit would do perfectly , with a few additions , like HPF and Attenuation .

 

[Tubetec]

The tank on the left is the one Ive been experimenting with lately , The transducer core is mounted within the metalwork of the subtray and the springs are tied in so that explains the large capacitance I measure off the coil .
On the second example the core sits well insulated from the tray up on the yellow plastic mount , there is a tab which connects the transformer core and sub tray , but thats easily dissconnected ,the springs themselves remain insulated from the whole deal , unlike the other one .
My point here is that the type of transducer in the second picture can have very much less capacitance to ground .

I didnt take a look at things in REW today but if my ears and brain arent deceiving me I'm getting a whole lot more brilliance and clear usable HF content out of the spring ,not a spikey choked out mess above 10khz like before .

I have an identical pair of original Accutronics I can use for the next phase of tests once I dig them out .

 

[Tubetec]

I want to migrate this topic to one with a more suitable title ,
many cheers for all the views ,
look out for a 'Balanced/Hum bucking reverb recovery' thread very soon .