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nathanscribe
Silver Member
United Kingdom
376 Posts |
 Posted - 12/01/2008 : 14:10:57
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Picked up an OC-2 lately, and the 2nd octave down is a lot quieter than the 1st - which is quieter than the dry level. To get them the same level, the 1st octave needs to be full and the dry about 2 o'clock. There's no way I can get the 2nd octave to be anywhere the same volume - it's super-quiet, and only adds a little padding to the background.
Is this normal? If not, what could be wrong?
Cheers in advance for any help,
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 12/01/2008 : 14:32:05
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quote:
Originally posted by nathanscribe
Picked up an OC-2 lately, and the 2nd octave down is a lot quieter than the 1st - which is quieter than the dry level. To get them the same level, the 1st octave needs to be full and the dry about 2 o'clock. There's no way I can get the 2nd octave to be anywhere the same volume - it's super-quiet, and only adds a little padding to the background.
Is this normal? If not, what could be wrong?
Cheers in advance for any help,
Hi nathanscribe! Same happens in both my OC-2 pedals. Octave 1 is fine, Octave 2 is very subtle and really there as a "fill". When I did the repair to mine, the signal levels on the scope were about 40% of the incoming signal for octave 1, and 10% of the of the incoming signal for octave 2 respectively.
I think yours is probably OK based on your description.
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nathanscribe
Silver Member
United Kingdom
376 Posts |
Posted - 12/01/2008 : 16:18:34
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| Hmm, interesting. Do you think these levels could be boosted? Perhaps a couple of resistor changes..? |
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sp-1
Platinum Member
Germany
1454 Posts |
Posted - 12/01/2008 : 17:12:33
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| Can it also have something to do with the lower sound of both octaves down ? Is the sound of the two octaves louder when you turn the bass up on your amp ? |
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nathanscribe
Silver Member
United Kingdom
376 Posts |
Posted - 12/01/2008 : 19:53:33
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quote:
Originally posted by sp-1
Is the sound of the two octaves louder when you turn the bass up on your amp ?
I'm going into a mixer/powered monitors, and there's no general problem with the bass (well, nothing a bigger pair of speakers wouldn't sort out  ). Playing a note 2 octaves up results in a much lower volume bottom note than achieving that note with either the 1 oct or direct settings. If you follow me.
Looking at the service notes, the OC-2 does seem set up to produce a lower volume at each stage. Around half the amplitude, I think, at each octave, which would suggest the 2nd octave produces a quarter of the original signal level. In practice, the 2nd octave is too quiet for me.
I'm guessing that replacing the gain resistors (R43 & R55?)in the divide stages would be something to try to boost those levels... unity gain makes sense to me - much more useful I think. |
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sp-1
Platinum Member
Germany
1454 Posts |
Posted - 12/01/2008 : 21:00:52
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Just hooked up my OC-2 OctaveR. When I set all the knobs at 12 O'clock I hear all 3 octaves when I dial in oct 2 it gets louder and definitely louder than the other two and so does oct 1 and direct level.
What year is your OC-2 ? maybe it's a problem with later version, I don't know.
Maybe you should use a psa adaptor instead of a aca or vice versa.
Just guessing  |
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nathanscribe
Silver Member
United Kingdom
376 Posts |
Posted - 12/01/2008 : 21:12:43
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quote:
Originally posted by sp-1
What year is your OC-2 ? maybe it's a problem with later version, I don't know.
May 2002 - KP82996.
I wonder if they changed the circuit to do this deliberately? I only have the schematic for the old version. |
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sp-1
Platinum Member
Germany
1454 Posts |
Posted - 12/01/2008 : 21:34:19
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| mine's november 1982 if that's any help, I also have a early MIT I'll see if I can hook up that one tomorrow. |
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sp-1
Platinum Member
Germany
1454 Posts |
Posted - 12/02/2008 : 20:59:43
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Hooked it up, also no problems.
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 12/02/2008 : 21:27:05
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quote:
Originally posted by nathanscribe
quote:
Originally posted by sp-1
Is the sound of the two octaves louder when you turn the bass up on your amp ?
I'm going into a mixer/powered monitors, and there's no general problem with the bass (well, nothing a bigger pair of speakers wouldn't sort out ). Playing a note 2 octaves up results in a much lower volume bottom note than achieving that note with either the 1 oct or direct settings. If you follow me.
Looking at the service notes, the OC-2 does seem set up to produce a lower volume at each stage. Around half the amplitude, I think, at each octave, which would suggest the 2nd octave produces a quarter of the original signal level. In practice, the 2nd octave is too quiet for me.
I'm guessing that replacing the gain resistors (R43 & R55?)in the divide stages would be something to try to boost those levels... unity gain makes sense to me - much more useful I think.
Everything you have described seems correct to me. (this is how the pedal works)
To increase the volumes would be easy, but the schematics on-line do not have component numbers!
There is an opamp in the OC-1 signal path with a 27k feedback resistor between pins 6 and 7 (IC "B" on the dodgy schematic). Increase this to 47k to increase the OC-1 signal.
There is an opamp in the OC-2 signal path with a 27k feedback resistor between pins 2 and 3 (IC "A" on the dodgy schematic). Increase this to 47k to increase the OC-2 signal.
The dodgy schematic is here:
http://www.freeinfosociety.com/electronics/schemview.php?id=135
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Edited by - Laurie on 12/02/2008 21:29:03 |
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nathanscribe
Silver Member
United Kingdom
376 Posts |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 12/02/2008 : 22:11:18
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Righto then - I didnt have access to my schematic archive (I'm at work).
The resistors are R55 and R43. Try them at 47k and let us know how it goes? |
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nathanscribe
Silver Member
United Kingdom
376 Posts |
Posted - 02/19/2009 : 18:22:24
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Finally got round to trying this!
Firstly, the PCB layout is different on my late OC-2 to the older models. Pics in the "internals" thread for comparison. But the part numbers on the board seem to match those on the (old version) schematic I have, so it's still necessary to swap R43 and R55 to get the boost. I used 47k resistors to get unity gain at each stage.
It works - kind of. I initially tried just R55 (for oct 2) and it definitely seemed louder - followed by R43 (for oct 1). That too seems boosted. The caveat is, they're not louder by much.
What seems to be happening is there's a filter, which mellows the signal and limits the frequency of its response. So high notes are barely affected, and there's a range of 2 or 3 octaves where the effect works well. But the octaves are not as bright as the dry tone.
Looking at the schematic, it appears there's filtering at each stage of the octave effect (around ICs 4 & 5) and something's going on with IC1 before the divider.
I'm wondering if it would be possible to brighten the sub-octs a little.
Laurie, et al? Any ideas? |
Edited by - nathanscribe on 02/19/2009 18:25:57 |
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IM28
Copper Member
26 Posts |
Posted - 02/26/2009 : 19:37:17
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Refering to the schematic http://www.godiksennet.com/images/sch/Boss_OC2_Oktave.jpg
The easist way to increase the audio level of the OCT/1/2 signals would be to decrease the 100k R60 and R61 respectivly.
The OC-2 uses an interesting chopper circuit to generate the octave down signals. The 47k in the FB loop of the chopper may not produce the change you want. There is significant low pass filtering after the signal is created, probably to limit the harmonic content so the octave voices are always "under" the direct signal. I find I always want addtional distortion added after the OC2. the drawback is you distort the clean signal too, unless you are mixing the dry signal externally.
I think a useful mod for this pedal would be a send/return jack for the octave voices allowing processing them separately. |
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nathanscribe
Silver Member
United Kingdom
376 Posts |
Posted - 03/01/2009 : 14:19:00
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Thanks for the info... I don't know why that never occurred to me. Replacing R43/55 definitely had less effect than I expected, so I'll go back in when I get chance and swap out R60/61.
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OC-2 volume drop
