Quad 34: Cutting tracks or not when reducing radio sensitivity?

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06-Mar-2019 12:07 AM

Fabian

Fabian

Posts: 74

I want to reduce the radio input sensitivity on one or both of my Quad 34 to 500mV (or 300mV). Following the advice on this forum I want to replicate the component values of the CD and tape input. This means changing C3 and C4 from 330nF to 680nF, adjusting the shunt resistors R11 and R13 from 100k to roughly 10k (or roughly 18k). Additionally 39k resistors have to be put in series with C3 and C4.

Unfortunately the PCB layout does not account for that, so the usual recommendation is to cut the tracks between the input sockets and C3/C4 and solder the 39k series resistors from the copper side instead.

This can be undone technically, but not without leaving obvious signs of modification. Also there are surprisingly few 680nF film capacitors available with a lead wire spacing of 7.5mm or 10mm so they can be used as a drop-in replacement. Or to put it the other way around: Better film caps are available with 15mm or 22.5mm spacing.

Somebody suggested (somewhere, can't remember) tonot cut the tracks, but to solder a "flying lead" R+C triangle and solder the open legs into the place originally taken by C3 and C4 alone. This could be reverted anytime without leaving a trace and a bigger and better film cap could be used. 

Is there any real-world disadvantage to this approach, apart from sloppy looks? Could this setup be more prone to picking up hum or anything else? It should be no problem to get this done in a mechanically robust way.

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07-Mar-2019 05:54 AM

EJP

EJP

Posts: 1589

I am about to do exactly that to a 34. Don't cut tracks.
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07-Mar-2019 07:18 PM

Fabian

Fabian

Posts: 74

Thanks for your confirmation, Esmond.

Way to go!

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