speedball upgrade causing delayed voltage spike at headphone jack [resolved]

[vafan13]

Hello all,

Basic Crack came to life after getting the proper fuse.  I then happily listened to it while assembling the Speedball upgrade.  I have installed it and voltages all checked out, however something odd is happening with the headphone jack voltage check.  It ticks up to .1v immediately after flipping switch and then stays there until ~5.5 seconds, at which point it spikes into the low 20s and then plummets back down, sometimes going negative on the multimeter before going back to zero.  Any ideas?  I can post pics if one tells me what needs to be seen.

And yes I know it's after 4am.  I was on a roll. 

 

[vafan13]

After getting some sleep I did a search, found a nearly verbatim thread from 2012 which lead me to the stick at the top for the mod to fix this.  doh.

Anyways, all is working and I'm now the proud owner of a Crack w/Speedball!

 

[LeSid]

Same problem here: I just have modded a working stock-Crack with the speedball upgrade. Voltages checked within tolerances, except for the jack's ring/tip voltage which rises to 25V before settling near 0. When turning the amp off and back on after maybe 30 seconds, the voltage rises even to 40V.

I understand that there is a mod to short the Jack to ground when there are no headphones connected. However that does not change the fact that the startup voltage spike exceeds the 9V tolerance.

- Is there a way to get the spike within limits?
- Does a 25V spike hurt the Sennheiser 650 if my old dad turns the amp on with them plugged in?

Thanks!
LeSid

 

[Paul Birkeland]

The spike goes a little higher, but also for a far briefer period of time.  As long as this spike dives back down to 0V, there is no cause for alarm here.  In the last revision of the Speedball manual, we have completely eliminated this check from the upgrade process.

(If you have headphones plugged in while turning the amplifier on, the voltage spike will be considerably smaller, as the headphone impedance is significantly lower than the impedance of the resistors used to charge these caps)  I leave my HD-800's plugged into my Crack when I switch it on.

 

[LeSid]

Thank you Blackplate!