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Re: Echoplex Gain Mod


The LED level indicator upgrade is:

R7 - 75k 5% 1/4w CF. changes clipping indication on input LED, good
idea to change, but not very important.

That is the comment I got from Kim some time back. 

Have you confirmed that this change is not in your EDP? You should
look at your PCBA to see the value at this location (and the
input/output gain changes.   I had a list of about 9 changes that had
occurred over time for the EDP.  I checked all the locations on this
older EDP to find that only 1 upgrade was not in my 96 vintage EDP. 
That was R75 change to 820 ohms (change from ~640 ohms).  This change
"optimizes a delay time", but I don't really understand it.

If you want the complete list that I got from Oberheim, I can send it
to you.  

22.1 k ohm is a "standard" resistor value.  Assuming a 1% tolerance,
the actual resistor could fall from 21.879 k ohm to 22.321 k ohm.  If
indeed you found a 22.0 k ohm 1% resistor (a non standard value), then
this should be OK for this application.  You can, of course, measure
(using a Digital Volt meter) the exact resistor that you plan to use
and confirm it is within 1% tolerance of 22.1 k ohm.  Kim, please
correct me if I am wrong here.

Having changed one resistor on my older EDP (R75) I would note that it
is a tad tedious to replace a resistor on the PCBA, without completely
dissasembling the EDP.  I did not completely dissasemble my EDP (I
feared I would risk more damage that not), but rather replaced the
resistor from the component side, without removing the bottom of the
EDP box.  This requires more care in removing the old resistor,
removing the solder from the hole with a solder sucker, trimming the
resistor legs before you insert it, and carefully soldering from the
component side.  Normally, you would do the soldering (for removal,
clearing the hole, and soldering in the new component) from the bottom
of the PCBA, and Trim the legs After you solder it in place.  With my
method, you risk making the legs too long, and they would contact the
metal case on the bottom of the EDP.  Make sure you inspect your work
carefully under good light and magnification after you remove the old
resistor (to insure you did no damage to traces or pads) and after you
solder in the new resistor (to insure the solder flowed down the via
well, and that you did not bridge extra solder to other traces or
vias).  My EDP works just fine following the change.

---Ed Drake <ejmd@erols.com> wrote:
> Hello loopers,
> Pardon my ignorance but I've got a question regarding  the resistors
to use
> for the Echoplex gain mod. I know you are supposed to replace R10
with 10K
> at 1%, and the R30 with 22.1K at 1%. I've checked a local
electronics store
> and they have the 10K and instead of 22.1K they have a 22K. Is this
> enough? Also, I remember awhile back someone mentioned exchanging a
> resistor to fix the LED(?) I think. This last one is not mentioned
in the
> FAQ at the website, so could someone please go into more detail
about this.
> Thanks!
> Ed

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