Jump to content

A/B Footswitch and cable capacitance


Recommended Posts

I have been used to using my own "long line" guitar cable with a head amp moulded into the cable near the guitar plug.  As would be expected I found that trimming the load capacitance on my guitar output via a small cap added into the guitar plug was necessary to keep it down at the top end.  I've just made myself a new TSR cable and realised that, if we assume the A/B footswitch is straight through for signal then we have a situation where the cable capacitance is now that of two cables added together, that's the guitar -> footswitch and footswitch -> amp.  That could be very dull for the standard magnetics at least.

 

Now I did wonder whether the footswitch may already have a buffer amp added to it in order to get around this problem.  Can anyone confirm or deny this?  If there is no buffer in the switch unit then how do the rest of you cope with this apart from using 1.5m cables?

Link to comment
Share on other sites

I didn't make things very clear in what I wrote originally.  When I mentioned using a buffered cable that was of course before getting my JTV59 and with standard type guitars.  But it isn't beyond the bounds that I may decide to design another one to match the JTV setup as my original unusual design works so well.  In that case, with a high impedance buffer amp about 15" from the plug there was virtually no load capacitance which shifted the pickup resonance way too high and the whole setup sounded very harsh and screechy.  After trimming, (I found a 470pF to be the best match for my own setup), it settled down to a beautifully controlled middle and top end which could be adjusted wonderfully with the amp tone controls showing the frequency of the pickup resonance was now in the right ballpark.

 

The issue is that I am worried that the present capacitance of my plain cables could be too high for the magnetics of the JTV59.  If the footswitch is straight through then using a slightly longer than usual cable (5m of 56pF per m ≈ 280pF) to the powered A/B footswitch will add to the capacitance of the (generic) cable from footswitch to amp and give me too high a value.  And without shortening the cable you can trim up but not down!  If the footswitch is buffered, (the signal passes through active electronics usually set as a x1 amplifier), on the way through to the selected output, then the second cable is isolated from the first and it is only the guitar TRS cable which needs to be taken into account in the trimming process.

 

Anyone give me a simple yes or no on this?

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...