Second HH build trouble

[maca404]

Using a rev D board for second build and run in to a problem I am adjusting r18 and at tp6 I get +2.1v to -1v which is not right and when shorting pd1 of ic8 to gnd across pin 2 and 3 I always get 0 volts not matter the position of R23. All other voltages checkout as documented any ideas ?.

[maca404]

Issue was found to be a dry joint on R22, On a side note I will be mouting this in a metal case. I have the main delay, pulse width, threshold, volume and of course swithes and headphone jack as outputs, do these need to be isolated from the metal enclosure ?

[Qiaozhi]

Issue was found to be a dry joint on R22, On a side note I will be mouting this in a metal case. I have the main delay, pulse width, threshold, volume and of course swithes and headphone jack as outputs, do these need to be isolated from the metal enclosure ?

There should be no need to isolate the front panel controls from the metal enclosure, as none of the potentiometer pins are electrically connected to their respective cases. However, the headphone socket is a different matter. It is best to use plastic sockets with the HH, as the metal ones can short out the power supply.

[maca404]

one interesting thing I have noticed when running the scope over this is the secondary sample pulse width is shorter than the main, I know this will affect performance but I can see why this is happening ?.

[Qiaozhi]

one interesting thing I have noticed when running the scope over this is the secondary sample pulse width is shorter than the main, I know this will affect performance but I can see why this is happening ?.

I think this is due to a difference in the internal resistance between the external capacitor pins and GND on the 74HC221. The datasheet recommends shorting pins 6 and 14 externally to pin 8. See if this clears up the problem.

[maca404]

I tried this but still no luck, the secondary pulse withs is 10us shoter than the main, I also tried replacing the diodes which feed the pulse width to no avail. I will go out tommorow and get a handfull of new chips and see if replacing them helps.

[Qiaozhi]

I tried this but still no luck, the secondary pulse withs is 10us shoter than the main, I also tried replacing the diodes which feed the pulse width to no avail. I will go out tommorow and get a handfull of new chips and see if replacing them helps.

Also make sure the 74HC221s are from the same manufacturer.

[maca404]

Just a follow up to this after chaning the ic's the two pulses now have identical pulse witdth, And with the new coil I wound it is happily detecting a tiny gold piece the only issue I have now is finding something to shield the coil everything I have found so far ruins the coils performance.