Mr. Haible's OB-Xa sound mod for OB-8

[j.dilisio]

I just tried the OB-8 mod as described here..
http://machines.hyperreal.org/manufacturers/Oberheim/OB-8/mods/OB-8.mod.txt
.. but rather than opening up the sound what I got was muted low frequencies.
It looks so simple. A resistor and a capacitor in series- in parallel to another resistor.. and this is supposed to offset the 22Hz highpass.

I don't really understand the electronics enough to know if he might have made a mistake listing a value or not.
Has anyone else had good results from this mod?

Thanks,
J

[j.dilisio]

I never did get this to work but I did successfully manage Jurgen's multimode filter mod..
http://www.jhaible.de/hjob8mod.html
.. and it rocks! I would highly recommend this to any OB-8 owners.
The high pass filter really opens up a new sonic spectrum for this instrument.

[radek tymecki]

i've managed to do audio mod and there was a diffrence to me! i did it on one board and compared 2 voiceboards. the one with mod had low freq boost

i always wanted to make a multimode modification but i was afraid I could not handle i was speaking bout it with Juergen but suddenly he passed away...

do You have photos how did You performed multimode filter mod?

[j.dilisio]

Sure, I can post a picture although this picture lays it out pretty clear..
http://www.jhaible.de/hjob8mmf.gif
Here's a photo of Jeurgen's modifications..
http://www.jhaible.de/ob8/jh_ob8_voice.jpg

I'd like to see a photo of your bass boost modification too when you get a chance.
I must be doing something wrong.

[radek tymecki]

i'll be back in poland in one week i think. now i'm in NL. then i'll take the photos

can u post some audio examples?

[j.dilisio]

I uploaded a few photos of the filter mod here..
http://jdilisio.com/ob8/

[j.dilisio]

Here's a demo of the four filter modes. I just calibrated the resonance so that it's a little higher than specified. You'll hear this on the 2-pole and highpass modes.
2-pole > 4-pole > 6dB > highpass

http://jdilisio.com/ob8/OB-8Filters.mp3

[radek tymecki]

oh man! this shit rocks!

tomorrow i'll try to look after spare 4052 and try to mod ob8!

anyway... i'll keep ya informed in progress!

[j.dilisio]

Here are a few tips..
-You don't have to cut the traces to the cx21 capacitors. Just cut or desolder the leg leaving enough of the lead so that you can solder a connection to it later.
-It is much easier to make the connection to pin 14 of ux07 before you mount the chip and solder pins 8 and 16.
Good luck.

[radek tymecki]

i've noticed that you dont have to solder a wire to pin 14. you can also solder it info hole after desoldered cap. anyway i'm in a half way. one of 4052's got damaged and i have to buy new one. then i'll be able to finish it

anyway. do you know how to calibrate arpeggiator? mine acts weird. when i press a note - C for example, ob8 arpeggiates it and later changes transposition etc

[radek tymecki]

i just finished this mod! KICKS ASS!

[j.dilisio]

Cheers! You should check out the arpeggiator section in the manual. It's pretty complex. You can program up to 5 transpositions.

Post a photo of your bass boost mod when you get a chance.

[radek tymecki]

tomorrow i'll make hi res pictures. these were made using my cell. anyway as far as i can remember i changed 4 resistors and made a network... another resistor and 47+10 nf cap.

[j.dilisio]

I just realized I was using 120ohm resistors instead of 120k

[radek tymecki]

haha good eye man!

is it working for you now?

[radek tymecki]

ps. do you want to build polymod?

[j.dilisio]

It's working now! The difference is more subtle than I expected but definitely noticeable.

I'm interested in the polymod but I'd like to hear a sample of how it sounds. I get the feeling I wouldn't have much use for it.