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Need Debug help on Boss CE3 modded to CE2

Started by Govmnt_Lacky, January 21, 2011, 08:30:23 PM

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geertjacobs

#40
January 25, 2011, 07:58:04 AM
QuoteI take it that the fact no one sees anything wrong with my posted voltages that there is NO PROBLEM with them.
The DC voltages (bias) seem ok, but there's no AC on top of it, so something is clearly wrong.
Otherwise your LFO would be LFO'ing.

What you could do is:
- post the layout
- post some pictures
- simulate the LFO in LTspice and check for differences between what is simulated and what's on your board.
Or juist build the LFO on a breadboard (if you have the parts, just a few minutes work) and see if you can get it to work there.
You have the great advantage to have an oscilloscope at hand.

Govmnt_Lacky

#41
January 25, 2011, 08:18:12 AM
Quote from: geertjacobs on January 25, 2011, 07:58:04 AM
What you could do is:
- post the layout

PM'd
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Govmnt_Lacky

#42
January 25, 2011, 02:57:22 PM Last Edit: January 25, 2011, 03:01:34 PM by Govmnt_Lacky
Simple question:

Does the 100K resistor on the LFO of the CE-3 (R51) have to be installed for the LFO to work?

I ask because the CE-2 has almost the IDENTICAL LFO set up without R51 and it works.

Could I try removing this 100K resistor and just short the contacts and see if this works?
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

geertjacobs

#43
January 25, 2011, 03:27:21 PM
Sim in spice:
changing the 100k to 1 ohm (almost short, zero resisotr is not allowed) makes the LFO start immediately instead of after about 4 seconds.
So do try.

Govmnt_Lacky

#44
January 25, 2011, 03:33:25 PM
Quote from: geertjacobs on January 25, 2011, 03:27:21 PM
Sim in spice:
changing the 100k to 1 ohm (almost short, zero resisotr is not allowed) makes the LFO start immediately instead of after about 4 seconds.
So do try.

Gotta wait until I get home. Gotta finish work for da' man!  :P

I will post results later this evening.

Thanks for ALL of your help geertjacobs  ;D
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Mark Hammer

#45
January 25, 2011, 03:50:40 PM
If you look at the Stompboxology explanation, when that extra cap (C29) is used, there is also a resistor between Vref and the inverting input.  Why, I don't quite know, but it is.  You'll find that same circuit (with only a few component-value differences) in the BF-2 as well.

Govmnt_Lacky

#46
January 25, 2011, 04:05:16 PM
Thanks Mark.

I am at the point where I need to just try things!  :o

Maybe modding the circuit to mimic the CE-2 LFO (removing C29 and R51)

You know.... just grabbing for the golden straw  :icon_biggrin:
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Govmnt_Lacky

#47
January 26, 2011, 08:11:17 AM
Finally at the shelving point  :icon_mad:  :icon_mad:  :icon_mad:  :icon_twisted:

Last night, I removed the 100K resistor between pins 2 and 5 of the LFO and hard wired them together: NO GO.

Reinstalled a 100K resistor. Then replaced C29: NO GO

Replaced.... one at a time.... the RATE and DEPTH pots: NO GO.

I just dont understand how the voltages could be spot on correct yet, the circuit will not modulate/oscillate  ???

I have some LM358 ICs laying about. Maybe I could try one of those in the LFO. Beyond that, I can only try replacing ALL of the trannys but the voltages all look good so why bother right?
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

Mark Hammer

#48
January 26, 2011, 09:06:17 AM
Thirty-seven years ago, one of my profs came in to class with a suitcase full of research papers.  He lamented that in our discipline (psychology), there was never enough hands-on experience at the undergraduate level, so he was going to try and simulate lab experience.  He described to us the very first paper ever published in a particular area, and we would tell him what we thought should be done next.  He would dig out the paper that had done just that (at this point the field would have been about 14-15 years old), tell us what they found, and we would then tell him what should be examined after that.  It went on for 90 very intense minutes, and we all left class exhausted, with our hair matted to our forehead.  I found the guy and wrote to him last year to thank him for that class, because it helped shape me, and I thought he should know that.

One of the things I learned that day was that, in science, there are some things you figure are going to pay off big time, so you pursue them and they end up leading down a long corridor to what seems like a dead end, or at least an unbreakable locked door.  Other things appear to be random wanderings with no hope of valid payoff, and they can end up leading you to the other side of that locked door at the end of the corridor, where you can simply flick the lock and continue the journey that was stymied earlier.

Put the CE-3 on the shelf, and work on something else.  Chances are good that you'll unintentionally learn some things via your other builds, and keep your eye open for things, that will ultimately lead you to open that door from the other side.

Govmnt_Lacky

#49
January 30, 2011, 10:06:03 PM
Eureka!!!!  :o  :o  :o  :icon_lol:  :icon_lol:  :icon_lol:

So, as it turns out, this particular CE-3 circuit DOES NOT like the TL072 OR the NE5532 dual op amps in the LFO section. It does however, like the LM358 that I put into it today. I simply removed the TL072 chip and installed the LM358 and the LFO started to oscillate!!

Now.... off to the interwebs to understand the differences between TL072s, NE5532s, and LM358s!!!
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

SISKO

#50
January 31, 2011, 08:26:08 AM
Congratulations!!

That was wierd! I tought for a moment that the ic could be the problem as it has hapenned to me when i built my Small Clone. It only works wit a LM358.
But this LFO is similar to the Zombie Chorus`s LFO and it works with a TL072 on it.
Anyway, enjoy your new build!
--Is there any body out there??--

Mark Hammer

#51
January 31, 2011, 09:37:26 AM
Quote from: Govmnt_Lacky on January 30, 2011, 10:06:03 PM
Eureka!!!!  :o  :o  :o  :icon_lol:  :icon_lol:  :icon_lol:

So, as it turns out, this particular CE-3 circuit DOES NOT like the TL072 OR the NE5532 dual op amps in the LFO section. It does however, like the LM358 that I put into it today. I simply removed the TL072 chip and installed the LM358 and the LFO started to oscillate!!

Now.... off to the interwebs to understand the differences between TL072s, NE5532s, and LM358s!!!
Simple.  Current.  The LM358 is a low-current chip.  Since you now know how to reinstate functionality, if you have a TL062, try that.  Or a TL022.

The other thing I'm wondering is whether the 100k resistor from Vref to the inverting pin on the first op-amp of the LFO is too high a value for the circuit when a 72 or 5532 are used.  That is, the circuit will "work" with those chips, but the current feed to kickstart the oscillaton has to be higher when using them, necessitating something smaller than 100k.

Govmnt_Lacky

#52
January 31, 2011, 10:25:42 AM
Quote from: Mark Hammer on January 31, 2011, 09:37:26 AM
The other thing I'm wondering is whether the 100k resistor from Vref to the inverting pin on the first op-amp of the LFO is too high a value for the circuit when a 72 or 5532 are used.  That is, the circuit will "work" with those chips, but the current feed to kickstart the oscillaton has to be higher when using them, necessitating something smaller than 100k.

I was going through the same ideas when I was troubleshooting Mark. Although, I had no grasp on this theory at the time, I wondered why the CE-2 (which has almost the EXACT same LFO stage as the CE-3) would work with a TL072 or NE5532 and the CE-3 would not. The only differences between the two is that the CE-2 does NOT include the 100K resistor(R51) and the 10nF cap in the first stage. (C29) All other values are identical.
In the service notes, both circuits use a TL022 for the LFO but for some reason, it is CRITICAL that you use a low current chip in the CE-3.
A Veteran is someone who, at one point in his or her life, wrote a blank check made payable to The United States of America
for an amount of 'up to and including my life.'

geertjacobs

#53
January 31, 2011, 01:01:21 PM
Congratulations!
And how does your CE-2.5 sound?
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