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OB-8 restoration Keyboard Synthesizers
Old 14th March 2018
  #1
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BM0's Avatar
OB-8 restoration

Recently finished my little OB-8 restoration project. Thought I would share some pictures.
  • Replaced all electrolytic capacitors on voice boards and power supply
  • Replaced all voice board, processor board and bend box trim pots
  • Replaced all VCO's with new CEM3340 rev G chips
  • Installed brand new keyboard rubber contact strips
  • New battery installed (coin battery socket installed by previous owner)
  • Performed calibration

Processor board


Lower Voice board close-up
For each trim pot highlighted here, you need 8x amount to replace for both voice boards, except for the voice board output trim, which you only need 2.


Upper voice board


Guess which is old and which is new contact strip!


Many trimmers to replace

Last edited by BM0; 14th March 2018 at 08:34 PM..
Old 14th March 2018
  #2
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seamonkey's Avatar
WOW! what a labor of love, CONGRATS!!
now some proper demos will be just fine thank you.
Old 14th March 2018
  #3
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BM0's Avatar
Well maybe this info will help someone else with a project.

I thought about doing a demo eventually, as I do not currently own a video camera. I can record with my DSLR photo camera or iPhone, but that would only provide crappy microphone quality audio. I may evenutally get a cheap HD video camera so I can make proper videos with audio from my USB mixer.
Old 14th March 2018
  #4
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Quote:
Originally Posted by BM0 View Post
Well maybe this info will help someone else with a project.

I thought about doing a demo eventually, as I do not currently own a video camera. I can record with my DSLR photo camera or iPhone, but that would only provide crappy microphone quality audio. I may evenutally get a cheap HD video camera so I can make proper videos with audio from my USB mixer.
Thanks for this - really appreciate it. Subjectively, how much of a difference do you feel it has made to the sound? Again - really appreciate the effort
Old 14th March 2018
  #5
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BM0's Avatar
Quote:
Originally Posted by dr_Jezz View Post
Thanks for this - really appreciate it. Subjectively, how much of a difference do you feel it has made to the sound? Again - really appreciate the effort
Overall, I think it provided more consistency between voices. For the raw sound, proper calibration of the filters is key in getting the full sound that the OB-8 is capable of. The VCO trim pots are only for v/oct scaling as the Autotune function will tune the frequency. Even the old VCO trim pots were good enough to properly calibrate scaling. Since Autotune does not tune the filters, manual calibration of the frequency and resonance is required. A while back, I realized that whomever calibrated the filters did not do a proper job. Even with the panel resonance knob at 100%, there was little resonance coming out of the filters. This was because the resonance trim pots were turned down too much. They need to set just below the point where they stop self-oscillating, as described in the service manual. This is where new multi-turn pots benefit as you can get more precise adjustments than the stock single-turn pots. Also, tuning the filter frequency is much easier with new pots. It was impossible for me to tune them all the same with the old single-turn pots as they were dirty and not precise. Improperly tuned frequency pots may also prevent the synth from getting as low of bass sound then what it is capable of.

In summary, a properly calibrated OB-8 is key to getting the best sound out of the OB-8. I don’t think the new CEM3340 VCO’s made much if any difference. The old chips were fine. I do feel there is more overall consistency between voices, which may be due to new capacitors, and that is not some huge difference. It may also just be in my head...lol. Also, every OB-8 has aged differently, so YMMV by doing a large restoration.

To note on the EG’s, there is no per voice calibration. The available EG calibrations are for the upper and lower boards offset, which is important to do as the timings may be mismatched between boards. There shouldn’t be huge discrepancies of ADSR timings between individual voices of one board. Subtle differences are fine and even desirable as it adds character. If the envelope timings have huge discrepancies between voices of a single board, something probably needs replaced, such as a CEM3310 chip.
Old 15th March 2018
  #6
Lives for gear
 

Quote:
Originally Posted by BM0 View Post
Overall, I think it provided more consistency between voices. For the raw sound, proper calibration of the filters is key in getting the full sound that the OB-8 is capable of. The VCO trim pots are only for v/oct scaling as the Autotune function will tune the frequency. Even the old VCO trim pots were good enough to properly calibrate scaling. Since Autotune does not tune the filters, manual calibration of the frequency and resonance is required. A while back, I realized that whomever calibrated the filters did not do a proper job. Even with the panel resonance knob at 100%, there was little resonance coming out of the filters. This was because the resonance trim pots were turned down too much. They need to set just below the point where they stop self-oscillating, as described in the service manual. This is where new multi-turn pots benefit as you can get more precise adjustments than the stock single-turn pots. Also, tuning the filter frequency is much easier with new pots. It was impossible for me to tune them all the same with the old single-turn pots as they were dirty and not precise. Improperly tuned frequency pots may also prevent the synth from getting as low of bass sound then what it is capable of.

In summary, a properly calibrated OB-8 is key to getting the best sound out of the OB-8. I don’t think the new CEM3340 VCO’s made much if any difference. The old chips were fine. I do feel there is more overall consistency between voices, which may be due to new capacitors, and that is not some huge difference. It may also just be in my head...lol. Also, every OB-8 has aged differently, so YMMV by doing a large restoration.

To note on the EG’s, there is no per voice calibration. The available EG calibrations are for the upper and lower boards offset, which is important to do as the timings may be mismatched between boards. There shouldn’t be huge discrepancies of ADSR timings between individual voices of one board. Subtle differences are fine and even desirable as it adds character. If the envelope timings have huge discrepancies between voices of a single board, something probably needs replaced, such as a CEM3310 chip.
Great feedback - thanks for this and it will definitely be valuable for others in future. Great job
Old 15th March 2018
  #7
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shreddoggie's Avatar
Nice job mate! I think the OB8 is such an underrated synth - everyone likes to go on and on about the OBX and OBXa as if the OB8 aint all that and I couldn't disagree more. I love the OB8 as much as the other 2 - each has its unique charms - the OB8 has the page 2 modulation that I make extensive use of, really great for movement and variety in those thick Oberheim pads.
Old 15th March 2018
  #8
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BM0's Avatar
^agreed. Particularly with the comparison between OB-Xa and OB-8. Everyone mentions about how the OB-Xa has more low end in its sound, which is true but that is it, and that tends to be an exaggerated difference. Nobody ever mentions how the OB-8 VCO’s can have mixed pulse+saw waves as well as triangle, neither of which is possible on the OB-Xa. And yes, page two offers things like unison detune, variable Portamento timings, LFO modulation, voice enable, etc. With the LFO, OB-8 can restart phase on trigger and has S+H that can be modulated by the 2nd LFO (vibrato) to get the staircase effect. And there is the arpeggiator that can have customizable transpositions which you can switch between while playing. On top of all the additional features, OB-8 is more reliable and easier to service. It’s all of these reasons as to why I decided to go with the 8 over the Xa. Don’t get me wrong, Xa is a great synth as well.

Edit: forgot one, though I am not certain if possible on the Xa, but the 8 can have independent pulse width adjustments for each oscillator.
Old 15th March 2018
  #9
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shreddoggie's Avatar
Quote:
Originally Posted by BM0 View Post
^agreed. Particularly with the comparison between OB-Xa and OB-8. Everyone mentions about how the OB-Xa has more low end in its sound, which is true but that is it, and that tends to be an exaggerated difference. Nobody ever mentions how the OB-8 VCO’s can have mixed pulse+saw waves as well as triangle, neither of which is possible on the OB-Xa. And yes, page two offers things like unison detune, variable Portamento timings, LFO modulation, voice enable, etc. With the LFO, OB-8 can restart phase on trigger and has S+H that can be modulated by the 2nd LFO (vibrato) to get the staircase effect. And there is the arpeggiator that can have customizable transpositions which you can switch between while playing. On top of all the additional features, OB-8 is more reliable and easier to service. It’s all of these reasons as to why I decided to go with the 8 over the Xa. Don’t get me wrong, Xa is a great synth as well.

Edit: forgot one, though I am not certain if possible on the Xa, but the 8 can have independent pulse width adjustments for each oscillator.
Word - you get all this goodness with the OB8, yet the comparison with the OBXa so easily drifts into that 'completely different sounding' delusional madness territory best suited for beard stroking hair splitters - until you hear the 2 together in the same room. I chose the OB8 quite intentionally when I had a chance to directly compare it with an OBXa - both in the same room, recently serviced an sitting right next to each other...
Old 20th March 2018
  #10
Here for the gear
 

I agree, I couldn't live without the extra functionality. You forgot to mention LFO envelopes where you can fade in or fade out the modulation, have it speed up/down or any combination of the above. Page 2 Voice detune is great for the supersaw-effect in Unison, or livening up brass, pads and strings.

You already mentioned the ability to switch between free-running and retriggering LFO so you can use it almost like an envelope with PWM for example. The sampled vibrato LFO waveform is also special in that it creates almost rhythmic patterns based on the combination of bend lever LFO speed and waveform, and the normal LFO speed.

But I have to say my favorite feature is programmable pedal release. I use a MIDI pedal and it adds so much expressiveness to be able to instantly stop a long-release sound with the pedal, or sustain a normally short sound, or anything in between. All the factory patches are beautifully designed with this in mind.
Old 22nd March 2018
  #11
Gear Nut
 

thanks for this excellent post. i wish that new analog polys sounded this good or had many of these page 2 features. even the dsi synths for all their mod matrix tricks don't let you accomplish much of this.

did any of you refinish the externals as well? i've always wanted to but never quite figured out how to touch up the pinstripes where they're scratched. and any solutions for a mod lever that seems to have a weirdly muted effect?
Old 22nd March 2018
  #12
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Rufuss Sewell's Avatar
I always preferred the OB8 to all the others. It sounds just as good to me, has the best features, is the most reliable... and inexplicably it’s the most affordable.

I would love a Matrix 12 though. But OB8 scratches that itch.
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