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Laurie
Double Platinum Member
Canada
4854 Posts |
 Posted - 11/15/2008 : 07:42:14
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This is a quick how-to for the CE-2 trimpot adjustment, or more correctly "how to set the BBD operating point".
Just done this to my MIT ACA CE-2 and it will work on any CE-2.
Tools
- You will need a scope. No way around it. I bought an old Tektronix 2215A off eBay for $100. A worthwhile investment...
- Phillips screwdriver to remove the base plate.
- Small flat-blade screwdriver to adjust the pot.
Procedure
0) Go get the service notes from here: http://www.godiksennet.com/images/sch/CE2.jpg
1) Remove the base plate and swing the board out
2) Obtain a 200Hz +3dBm signal source. I used CoolEdit on my PC to generate a 200Hz wave, then put it through a little Behringer mixer I have to boost it up to +3 dBm. Power the pedal with a known good battery (or the correct Boss power supply). Plug a lead carrying the +3dBm signal into the pedal input and turn on the pedal. Turn the "rate" pot fully anti-clockwise and the "depth" pot fully clockwise.
3) Set the scope to 500mV/division, 1ms/division sweep, and "AC" in. Use the service notes to locate Q3 on the board. It is quite near the trimpot. Connect the scope probe to the emitter of Q3 - it is leg of Q3 furthest from the trimpot. I just held my probe tip onto the solder pad on the solder side of the board.
4) Increase the incoming signal until you see one of the three waveforms on the service notes. If your signal is too low, the waveform will look like a perfect sine wave - wind up the signal until it starts to clip and looks like one of the three waves. Once you see a clipped waveform, "center" the waveform by turning the trimpot (i.e. until there is equal clipping on top and bottom of the waveform).
5) Once the waveform is centered, lower the incoming signal until one of the sides of the waveform stops clipping - this will look like either the top or bottom waveform on the service notes. When this happens readjust the trimpot until the waveform is again "centered" (there is equal clipping on top and bottom of the waveform).
6) Disconnect everything, and close up the pedal. You are done!
Note that at no point in the adjustment are we looking at DC-offset. Just leave the scope input set to "AC".
Looking at the CE-3 schematic, this same process will also work for the CE-3 (only change is the measuring point is Q8 in the CE-3, not Q3). You are on your own finding the emitter of Q8... 
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Edited by - Laurie on 11/16/2008 02:21:30 |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 11/15/2008 : 17:57:33
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Hi Laurie
Did you mean Q8 not C8?
Regards & Good night Dr. Bob |
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DeFrag
Moderator
USA
3409 Posts |
Posted - 11/15/2008 : 20:12:47
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quote:
Originally posted by Dr. Bob
Hi Laurie
Did you mean Q8 not C8?
Regards & Good night Dr. Bob
You can't get ANYTHING past these guys...  |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 11/15/2008 : 21:13:22
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Ye@h ye@h ye@h, b1ah b1ah... FIXED   |
Edited by - Laurie on 11/15/2008 23:53:23 |
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DeFrag
Moderator
USA
3409 Posts |
Posted - 11/15/2008 : 23:29:48
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I meant no offense Laurie.. just wish I had your mad skillz  |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 11/16/2008 : 04:03:21
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quote:
Originally posted by DeFrag
I meant no offense Laurie.. just wish I had your mad skillz
Hi DeFrag & Guys
It's a secret & unwritten code between Engineers & Tech's.
We do it to keep each other in check.
Now that I have told you, I will have to ask you to kill yourself.
Yes it's that big a secret..
(You know that old secret agent saying "If I tell you, I'll have to kill you")
Hey DeFrag. Seriously, did you see the time that I posted that?
Do the conversion, to Aussie time.
Regards Dr. Bob
4141
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Edited by - Dr. Bob on 11/16/2008 04:04:50 |
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DeFrag
Moderator
USA
3409 Posts |
Posted - 11/16/2008 : 05:08:08
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| I didn't mention time, you must mean another thread when you replied to Laurie in about 5 minutes. Its all good |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 11/16/2008 : 07:06:01
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quote:
Originally posted by DeFrag
I didn't mention time, you must mean another thread when you replied to Laurie in about 5 minutes. Its all good
Hi DeFrag
No, I meant what actual o'clock time it was, when I posted my last post,
regarding Laurie's minor typo.
It was 4AM here Melbourne time.
I was having a stay up all night (Sat) Insomnia can be such a bitch.
I had some new musical Ideas running around the old Cobwebs, & I just had to get the idea-s down before Zzzzz time.
Regards Dr. Bob
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DeFrag
Moderator
USA
3409 Posts |
Posted - 11/16/2008 : 08:44:52
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| OIC hehe, gotcha. |
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Topic |
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CE-2 trimpot adjustment (and CE-3)
