HH Build Clarification

[WesP]

I want to verify this part of the build instructions:

Short pad 1 of IC8 to a convenient
ground (simple to do when using IC
sockets — IC9 pin 4 is ground). This
should never be done with IC8
installed. R24-R26 is now a simple
voltage divider, the same as R25-R27.
A DC voltage can be applied to R23,
and if there is a mismatch in the two
dividers, R23 can be adjusted to null it
out. This should be done with the analog
gates turned on, which will be the
case as long as Q8 & Q9 are not
installed.
Use a voltmeter to measure the voltage
at TP4. Adjust R18 until this
voltage is maximum. Now measure the
voltage across pins 2 and 3 of IC8, and
adjust R23 until it is zero. Readjust R18
until the output of IC6 (TP4) is 0 volts.
Remove power to the board, remove the
ground short to IC8’s pad 1, and install
R5, IC8, Q8, and Q9. Set R31 to its
midpoint.
l
Is the second paragraph the proceedure described in the first paragraph or do you have to apply a voltage to R23, match the voltages, then do the proceedure in second paragraph? I'm am using 1.0 % resistors for R24,25,26,27.

Sorry if this is a bonehead question but I'm just learning.

[Molzar]

Hi WesP,

The first paragraph has some instrutions and some descriptions of what is happening in the second paragraph, do as below.

1) Make sure IC8, Q8, and Q9 are not installed
2) Short pad 1 of IC8 to a convenient ground (IC9 pin 4 is ground)
3) Follow procedure in second paragraph.

I think when I did this the zero volts was about +/- 15 mV on DMM. Using a scope may give you a little better null. Either way, should be close enough.

Molzar

[Molzar]

Nulling

Hi WesP,

The first paragraph has some instrutions and some descriptions of what is happening in the second paragraph, do as below.

1) Make sure IC8, Q8, and Q9 are not installed
2) Short pad 1 of IC8 to a convenient ground (IC9 pin 4 is ground)
3) Follow procedure in second paragraph.

I think when I did this the null (0V) was about +/- 15 mV on DMM. Using a scope may give you a little better null. Either way, should be close enough.

Molzar

[WesP]

Thanks Molzar. I'm working on assembling my second HH v2 board. The first doesn't seem to have any detection or audio. I'm trying to be very careful with this one.

[Carl-NC]

Wes,

You do not have to apply an external voltage. R18 adjusts the DC offset of IC6, and this gives you the needed voltage on TP4. It doesn't have to be max, but the more voltage you put on TP4 the better you can null the differential integrator.

- Carl