Germanium Diodes in Klon type projects

[Slidester]

i have been building different versions of Klon inspired overdrive pedals. I have read about component values in an original Klon Centaur in which the Germanium Diodes were said to have a value of .34V. I have been buying various Germanium Diodes and testing them - 1N34a, 1N270, various D9 variations.
My DMM has diode test setting. i cannot speak for its accuracy, but it is consistent. Most of the Germanium Diodes I have checked read around .23V or .24V. I have found a couple 1N34a that measure .32V. (I even had a couple 1N34a that measured .55V)
I'm curious about a couple things. Am I actually performing any kind of viable test by using the diode setting on my DMM? Is there another way I should be testing these? And has anyone tried checking the difference in a Klon type overdrive with Germanium Diodes rated at .24V versus .34V?
input will be greatly appreciated. Knowledge is power. Thanks

[PRR]

You never know what is inside a DMM.

A Known Test would be a 9V battery, a 10K resistor, and the diode, all in series. Measure the diode voltage drop. If it is anything like 0.3V, you *know* it was 9V-0.3V or 8.7V, in 10K, is 0.87mA, practically 1mA, and same near-enough for all diodes 0.2V to 0.5V.

OTOH: the Klon uses a 1K series resistor. The diode impedance crosses 1K about 0.03mA. That suggests 9V with a 300K resistor. As a second step, the diode will be down to 100r, heavy clipping, about 0.3mA, which is a 30K resistor. So you might try 9V and a 330K, with a switch to parallel 33K, and note both readings. Many diodes will be proportional (similar sound at slightly different level); a few will be outliers and may sound different.

But chasing the Sacred Diode may be a never-ending quest and maybe a unicorn hunt.

[Rob Strand]

Germanium Diodes I have checked read around .23V or .24V. I have found a couple 1N34a that measure .32V. (I even had a couple 1N34a that measured .55V)

If you do all the measurements on the same multimeter then the result is likely to be true.
As to the reason why it is higher you have to carry out more detailed tests.
Test at lower currents using the scheme PRR recommended.
DMMs usually have this type of circuit inside and typically the diode test feature tests using 1mA (you can check your DMM manual).  I'd test at 1/10th that so use 100k in PRR's setup.

You need to make sure you compare apples to apples.  That means doing the test on low voltage diode and high voltage diodes. If you decrease the test current on *any* diode the measured voltage will drop.    For a diode, reducing the current by 10 will give you about 100mV drop.   Now if one of diodes has a higher resistance you might see more drop for the same change in current but only for high currents. 

To do the test at two currents using 10k and 100k, calculate the change in voltage for each diode.
If the change in voltage is much higher in one you can conclude the higher voltage is due to diode resistance.   If then you were to test at even lower currents (say with 1MEG) you would expect the voltage change in each diode to get closer if the resistance is the issue.

Having said that  if you get a much higher voltage in one diode even at very low test currents that (usually) means the size of the junction is smaller.


Look at the second graph, and then look at the green and red curves.  You can see the red diode has a lower voltage at lower currents than the green diode.  However the red one has more resistance so at higher current the voltage drop becomes more than the green one.

http://www.lessmiths.com/~kjsmith/crystal/deyeball.shtml

[digi2t]

A great read;

http://www.diystompboxes.com/smfforum/index.php?topic=118007.msg1105187#msg1105187

[Ed G.]

I'm using 2n7000s as clipping diodes in my GGG clone.
I'm sure it sounds nothing like the original Klon but I'm loving the sound.

[italianguy63]

A great read;

http://www.diystompboxes.com/smfforum/index.php?topic=118007.msg1105187#msg1105187

I was just looking at some D9B's yesterday....  I think I am going to pick some up.

MC