BD 2 Mod Issues. Fault Finding Help Needed

[Semperfidoe]

Hi all. Ive been watching these forums for some time now but this is my first post for help as I tend to find most of my questions answered in previous posts if I search hard enough.

Anyway im fairly new to modding. I've done about 5 boss pedals to date, but this is the first one ive had problems with.

Ive made a number of mods to a new BD2. Ive checked its function at several stages, so I guess the fault must lie in the last stage or two.

Basically the issue is that the pedal seems to have lost its gain. Turning the gain knob from 7 o clock all the way to 5 o clock now has very little effect.

So tracing back the last changes I made were;

c100 (on the tone pot board) changed to 0.047uF metal film
c20 and c25 changed to 100pF Silver Mica
c21 and c23 changed to 47pF Silver Mica
c22 changed to 220pF Silver Mica
c10 changed from 0.047 to 0.01uF metal film
c14 changed to 0.1uF metal film
removed r39 and installed a clear blue led.

One issue that worried me was C22. On the PCB it has a positive side marked, but unlike the tantalum caps I couldnt see any indication on the silver mica cap of any polarity. Does it have to go a certain way round? Might this be the issue?

Another issue I wanted to ask is that ive changed 6 ceramic caps to tantalum. However I could only get 3 x 10uF 35v so three are 25v. This shouldn't be a problem should it?

As I say im new to this so im not sure how to test or whether its a case of having to remove and replace each component one at a time. All other functions seem to work (tone and volume) though there is also a slight volume drop when the pedals engaged as well as the lack of gain.

Any help much appreciated.

Cheers
Matt

The diodes and other caps that I changed were done first and it seemed to work fine afterwards so im discounting that as an issue.

[R.G.]

Just a curiousity of mine. What are you trying to do by modding this pedal? Is there a goal in mind, or are you prospecting for gold nuggets?

First: do you have a link to the schematic for the pedal? That would help, as we could find out the function of the parts you've changed and that might point to what is not working.

Second: Caps in the pF range do not have polarity markings. It is highly likely that your 220pF silver mica is vastly too small a capacitance value. How did you determine the value of cap to put in there?

Third: Ceramic and Tantalum caps normally have very little overlap in value ranges. How did you determine the values of tantalum to sub for ceramic in the six you changed? A

Fourth: Why are  you changing ceramic and tantalum and vice versa?

Fifth: It is highly likely that either you have picked out the wrong value of cap(or other component) to sub, or that there is a solder flaw from the subbing or a broken wire from messing about with the board.

[Semperfidoe]

Thanks for your reply. The mods are based around a combination of Keeleys and Monte Allums changes. Main objective to smooth out the gain, reduce noise and soften the harshness of the treble (especially as I use it a lot with a strat with cs'54 pups.)

1) Link for schematic http://www.freeinfosociety.com/electronics/schemview.php?id=116

2) C22 on the schematic looks like 220p so I assumed that was 220pF - am I incorrect in this assumption? Like I say im new to this, learning as I go.Certainly there is a polarity marked on the pcb (a + sign next to one of the holes) which is odd because the capacitor there looks like a small tantalum or the like wheras the others changed for silver were ceramic and had no polarity on the pcb. This still confuses me so im tempted to replace the original cap in C22 and see if it makes a difference.

3) The six tantalums changed were all 10uF and as far as im aware straight swaps for the previous value.

4) Mostly for hi-fi improvements.

5) Is there any way to check with a multimeter etc the soldering joints for problems? Ive checked all the wires and they seem fine.

Thanks

[R.G.]

2) C22 on the schematic looks like 220p so I assumed that was 220pF - am I incorrect in this assumption? Like I say im new to this, learning as I go.Certainly there is a polarity marked on the pcb (a + sign next to one of the holes) which is odd because the capacitor there looks like a small tantalum or the like wheras the others changed for silver were ceramic and had no polarity on the pcb. This still confuses me so im tempted to replace the original cap in C22 and see if it makes a difference.

Well, that's one problem down. The shemo shows that as .22uF/35V. That one change cut your gain by a factor of about 100 or so. C22 is used for DC blocking on the gain setting feedback resistor of a discrete opamp. The 220pF is effectively an open circuit until you get up into radio frequencies, so it cuts the gain of the stage to one at audio.

3) The six tantalums changed were all 10uF and as far as im aware straight swaps for the previous value.

I don't know of any ceramic caps that come in values as big as 10uF. It's highly likely that these are wrong now, too.

4) Mostly for hi-fi improvements.

Hi-fi improvements in a distortion pedal? ? ? ? ? ? ? ? ?

[Semperfidoe]

RG Thanks. Ill try swapping the C22 back then and see what happens.

Just to clarify - the ceramics were swapped for silver mica. The 10uF tantalums did not replace ceramic caps. Im also pretty sure I tested it after id added the tantalums so i dont think they are affecting it - my only question is whether three of them being 25v rather than 35v would be an issue?

As for hi-fi improvements - well yes. In terms of reducing hiss, improving dynamics etc. A friend of mine did some sound analysis in his work lab for me and it does make a difference on the previous pedals Ive done (DS1, MT2, CS3).

Thanks again for your help.

[Semperfidoe]

Ive just checked the four ceramics that came out. 2 are marked 47k (no other markings) and 2 are marked B 101k.
These four were replaced with 2 x 47pF and 2 x 100pF silver mica caps. Is this incorrect then? (sorry for the dumb questions im getting confused on markings)

Thanks

[R.G.]

Sorry - I misunderstood. I saw:

ive changed 6 ceramic caps to tantalum. However I could only get 3 x 10uF 35v so three are 25v.

Which caps were those that you changed? I'll check the circuit function. As I said, there's little overlap between ceramic and tantalum values, so which ceramic caps were changed to tantalum can make a difference.

No, the 25V rating will make no difference.

2 are marked 47k (no other markings) and 2 are marked B 101k.
These four were replaced with 2 x 47pF and 2 x 100pF silver mica caps. Is this incorrect then?

That's OK. Those are the right values.

As for hi-fi improvements - well yes. In terms of reducing hiss, improving dynamics etc. A friend of mine did some sound analysis in his work lab for me and it does make a difference on the previous pedals Ive done (DS1, MT2, CS3).

I'll maybe go with reducing hiss, perhaps by resoldering joints.

But if you want to reduce hiss, the simpler way is to replace the resistors in the input stage with metal fillm and replace any transistors in older pedals with new, low noise devices. Caps don't make hiss to any significant degree; only resistors and active devices do.

I'm not aware of any measurement device that will measure "dynamics" in a sound lab.

It may be that replacing caps changes the time constants of the frequency rolloffs in a way you like. Changing ceramic caps in the signal path for film does have a beneficial effect, but is not good at all for power supply bypass caps, which should remain ceramic. Ceramics also tend to have higher tolerances than films, so if there are ceramics involved in the audio band, replacing them with film does tend to change the sound.

Tantalum tends to sound a bit grainy as well, but again the solution is to go to film.

And all of these are subtle effects. They're easily covered up by any distortion at all. That's why my comment about hifi improvements in distortion pedal.

[Semperfidoe]

Thanks again RG. I've changed C22 back again and the pedal now works as expected thanks 

As for the tantalums I changed caps C1,6,7,12,13 and 15 all for 10uF (i think they were all 10uf to start with but electrolytic.

Im very interested in your comments on reducing noise through the resistors. From the schematic which do you think would have most impact? Also I noticed some have the five ban colour scheme - am I correct in thinking this only applies to metal film (ie they already are metal) or does it apply to carbon too?

I must confess having just done a quick head to head with a regular BD2 this is the most subtle of all the mods ive done so far. (the MT2 and DS1 were very dramatic improvements). I expect them to have a little more impact when I can raise the levels above living room though. The most important thing it that it does appear to have reduced the 'icepick' which is what I wanted.

[R.G.]

First things to worry about for hiss, in order. Make these 1% metal film. 1% is always five band, but there are carbon film 1%'s.
R18 - 10K
R15 - 1M
R19 - 10K
R17 - 100K
R23 - 100K
R23 - 220K
Q2/10/11 - 2SK1040A; if this is damaged, it can be high noise. Change the resistors first.

Might help
R30 - 4.7K
R28 - 2.2K
There are others, do these first, in order.

Change these caps as shown:
C22 to 0.15 polyester film
C1, 5, 6, 7, 12, 15, 24 to 1uF polyester film
The originals were either tantalum or aluminum electrolytic. Tantalum is electrolytic, just like aluminum. 1uF polyester in 63 V is available in small radial packages with will fit the board with some difficulty.

The icepick is coming from C23 and C25 not being big enough, or possibly from the treble booster in C9/C16/Q7/R10/R20/R21. You can defeat that by grounding the junction of R20/C9/C16.

Diddling with cap types is OK for subtle, cork sniffing kinds of changes, but changing the values of the major frequency response stuff will do much more. Tell me what you find.

[franee]

Hi,

How do i remove some of the bass of the BD-2? The stock one just has too much bass when im on the neck pickup and it gets really muddy. I've noticed that increasing the gain also increases the bass.

thanks

[R.G.]

Lower C18 0.1uF to 0.01 or 0.0047; even lower to your taste.

If that's not enough, there are other things that can be done.

[franee]

ok will try that. tnx:)

[Semperfidoe]

RG thanks for your ideas. I will definately try some of these and post back. Its working now and sounds nice but anything that can reduce any of the background hiss is always good (though its not bad to begin with tbh)

As for changing C1, 5, 6, 7, 12, 15, 24 to 1uF polyester film. Two questions. 1) Am I getting confused. I thought the existing caps were all 10uF. Is the change to 1uf an improvement or a typo? 2) Given that they were aluminium electrolytic in the first place and now tantalum what difference will poly film make?

Incidentally do you think changing D1 to an LED would have an effect on the sound?

Thanks.

[R.G.]

As for changing C1, 5, 6, 7, 12, 15, 24 to 1uF polyester film. Two questions. 1) Am I getting confused. I thought the existing caps were all 10uF. Is the change to 1uf an improvement or a typo?
2) Given that they were aluminium electrolytic in the first place and now tantalum what difference will poly film make?

It's different, and not a typo. You're off chasing capacitor sound improvements. I offered a different set of compromises on caps that is better suited to guitar effects than the ones you were trying, IMHO.

Tantalum has a reputation, deserved or not, for sounding slightly grainy. Aluminum electros can sound slightly harsh in some circumstances. Polyester film is much less noticeable, even in non-distorting audiophile situtations than either tantalum or aluminum at least by reputation. Changing to polyester will give you well over 95% of any hypothetical advantage of using ultra-fi, high-mojo audiophile caps, at a minescule fraction of the cost.
Yes, the originals were 10uF. The worst problems with electros of either kind happen when the cap in question is forming a significant part of the frequency rolloff of the circuit, and at least in the BD, these caps were all at least a factor of 10 bigger than they absolutely needed to be to pass the frequencies involved. I did a quick check of the rolloffs involved and found that 1uFs in these positions will probably not limit guitar signals coming through. That lets you use polyester which is available in 1uF 63V stacked film packages at low prices. So I recommended the 1uF. Try them - you may like them, you may not.

Incidentally do you think changing D1 to an LED would have an effect on the sound?

It will have no effect on the sound at all. D1 never conducts under normal circumstances, nor does D3. It's there to protect the inputs of that opamp from damage by rogue voltages. Read my articles "When good opamps go bad" ( http://geofex.com/circuits/when_good_opamps_go_bad.htm ) and "What are all those parts for?" ( http://geofex.com/circuits/what_are_all_those_parts_for.htm ) for some background in why D1 and D3 are there. The diodes that have an audible effect are D7, 8, 9, and 10.

[Semperfidoe]

Excellent - many thanks RG I will read your articles. This is all very enlightening. I will try the poly film cap changes and see what happens.

In terms of the diodes so far, D4 was changed to 1n4002 along with D7 and D8. D9 to 1n4001 and d10 removed for a jumper. In reality possibly at high levels I can hear a small difference - but then again it might just be me 'wishing/expecting' it. Im curious as to the differences with LEDs as these were my preferred changes in the DS1 where I had them on a 3 way switching. (and indeed on the MT2 also except for pure metal when I preferred the 1n34a germaniums)

[franee]

Lower C18 0.1uF to 0.01 or 0.0047; even lower to your taste.

If that's not enough, there are other things that can be done.

Did the mod:) i forgot the value. i had tried 3 lowered valued caps. no more muddiness:) before, i was limited at 9 o'clock in the gain position because it starts to get muddy from there. now i could go all the way to 3:) thanks R.G:)

[Semperfidoe]

RG

I did think about changing C34 from 0.1 to 0.047 - do you think this would make much difference?

Also I have already changed C18 but to 0.047. Would dropping it to 0.0047 make a significant further difference? and if so would itonly reduce the base or would it effectively boost treble too? (not something I want to do - I like the pedal balance now - however when I roll off the treble on my Strat it does seem to add a lot of extra bass which id like to counteract)

Im interested in anything that will add clarity without necessarily increasing treble any further.

Finally Im toying with LED('s) as clippers in D9 at least as my preferred position in the switchable DS1 I did used LEDs along with the other diodes (seemd to add a lot of sustain and clarity to the gain). Do you think this would work as well with the BD2?

Cheers

Matt