Debugging the Sparkle Boost

analog kid · February 08, 2005, 12:40:57 AM

Also I assume it doesn't matter where that resistor comes off of the wire or lugs1/2 just as long as they're all connected between lugs one and two of the gain pot?

Dragonfly · February 08, 2005, 12:59:08 AM

Quote from: analog kidAlso I assume it doesn't matter where that resistor comes off of the wire or lugs1/2 just as long as they're all connected between lugs one and two of the gain pot?

correct....but it still sounds like something is wrong in your circuit...i'll post some voltages in the next day or two...i need to buld some more sparkle boosts, as im sold out currently....

analog kid · February 08, 2005, 02:33:03 AM

you may be right and I appreciate you putting those different test voltages up but It still may be working correct already. I haven't played it at more than a vERY low volume to my sick little boy sleeping, but I just tried some more with more subjective listening and I DO hear that when I back the volume a bit and use the gain boost instead of the vol. pot alone, there is a very slight amount of overdriven 'dirt' to the signal. Very slight! but there. the only thing that really makes me wonder that it's not functioning as meant to is that the Gainpot doesn't show ANY response on anything UNTIL it reachee the very end of it's taper!
That's what bothers me! still don't know if that's normal?

CAN YOU PLEASE POST A DIAGRAM OR SOME EXPLANATION OF HOW YOU WOULD ADD THE CLIPPING DIODES IN THIS CIRCUIT? aCROSS WHAT?

GreenEye · February 08, 2005, 08:47:47 AM

Quote from: analog kidCAN YOU PLEASE POST A DIAGRAM OR SOME EXPLANATION OF HOW YOU WOULD ADD THE CLIPPING DIODES IN THIS CIRCUIT? aCROSS WHAT?

I'm not very good at drawing circuits on the computer; I usually do it by hand. However, here is an example:
http://members.cox.net/dankpog2/SparkleDiodes.GIF

Basically, start with two diodes as shown; one pointing one way, and one pointing the other. Try two red LEDs and then try two silicons. Should give different results (silicons being harsher). You should see the red LEDs blink when they "are clipping." I only tried it in the position shown. Some people I guess like them closer to the end of the circuit, hanging off the pot or something. I never tried that...

petemoore · February 08, 2005, 08:58:46 AM

Well they're connected to the pot's 1 'n 3 lugs...'hanging off the pot'd' be the same.

Dragonfly · February 08, 2005, 09:08:43 AM

Quote from: analog kid
That's what bothers me! still don't know if that's normal?

...but thats what ive been telling you for my last three or four posts....the "taper" is clean for a long time, and thats why i posted the mod.....it "evens out" the taper.

RjM · February 08, 2005, 01:00:23 PM

I think I'm going to re-solder all my ground connections, and just any other messy connections. It still is having the problem, but I did something, and now at least my transistor voltages are normal.

Dragonfly · February 09, 2005, 09:19:36 AM

Quote from: analog kidyou may be right and I appreciate you putting those different test voltages up but It still may be working correct already. I haven't played it at more than a vERY low volume to my sick little boy sleeping, but I just tried some more with more subjective listening and I DO hear that when I back the volume a bit and use the gain boost instead of the vol. pot alone, there is a very slight amount of overdriven 'dirt' to the signal. Very slight! but there. the only thing that really makes me wonder that it's not functioning as meant to is that the Gainpot doesn't show ANY response on anything UNTIL it reachee the very end of it's taper!
That's what bothers me! still don't know if that's normal?

oh...AK...i thought of something else...iirc, you used a 5457 for the fet, right? if so, your gain knob might not be as effective simply because the fet doesnt have as much "internal gain" as the NTE458 does...

hope this helps,
andy

analog kid · February 09, 2005, 01:09:31 PM

Alright, that's something I had been wondering about and that's why I added that to the last post as a remider that's what I used.
would that also be why I don't notice that much of a difference when adding the Gain pot mod( as far as you saying that it improves the taper) it still stays 'clean' and the same level for just as far into the pots taper either way. SO besides that 458 what else would be better in there. would one of the '201' jfets work good??
ALSO : is this the way you recommend adding the clipping diodes into this circuit as well?? (see Greeneye's Post!)

Dragonfly · February 09, 2005, 02:34:43 PM

Quote from: analog kidAlright, that's something I had been wondering about and that's why I added that to the last post as a remider that's what I used.
would that also be why I don't notice that much of a difference when adding the Gain pot mod( as far as you saying that it improves the taper) it still stays 'clean' and the same level for just as far into the pots taper either way. SO besides that 458 what else would be better in there. would one of the '201' jfets work good??
ALSO : is this the way you recommend adding the clipping diodes into this circuit as well?? (see Greeneye's Post!)

yep...that would explain the "taper" as well....

the J201 works quite well...not as nice as the 458, but very close, IMO....

i'll check greeneyes post regarding the diodes....

andy

RjM · February 10, 2005, 02:56:41 PM

I've triple checked the grounds, and they are not the problem for the transistor not biasing correctly. Right now, D,G, and S are all around 4.5v, and I don't know what to do. Could subbing a 2.4M resistor for the 1M have anything to do with it? Either it's that rather large resistor, a short, a cold solder, or just a bad transistor. I have a new MPF102, but I'm not going to replace the old one until I know that it's not a short or a resistor. I have a 3K9 instead of the 2K7 as well, although I don't think that difference could cause the transistor to be so saturated. I just got to thinking, it'd be a cool thing to try an IC instead of a transistor in a booster or another related circuit. I might end up trying that sometime after I get the bias fixed.

analog kid · February 11, 2005, 03:40:20 PM

Ok I tried the diode at the output idea and although I kind of liked what it gave the pedal it totally changed what I would be using it for completely. IT went from having that little bit of dirt only when the gain was totally full up to having a bit more of a dirty sound when up and no matter if the gain was turned totally off still retained a good amount of the dirty signal! SO no CLEAN boost at any setting because of it.
Is this the intent of the diode mod. ? I did onlyl try one type of diode, I'm ashamed to say I don't know what kind., I pulled them out of something and they look exactly like the germanium N34a's but with only one black stripe rather than two. and they tested almost the same for the voltage drop. (about 2.38v) I don't have two extra leds that I'm not using for pedal indicators , I have some silicon's NT1004's or something like that ? so is it worth trying others or is it pretty much the same result you get with any?

RjM · February 11, 2005, 04:29:47 PM

I'm thinking there is still a small problem somewhere, or rather a big problem, since there is some background hum, and when I turn the volume knob down, the hum increases, but at least there is no sound with the volume knob at 0. When I try to put the Sparkleboost before other effects, (My MT-2 and EQ pedals) no sound comes out. I'm thinking it is a ground problem, but I don't know how to fix it! Have any of you ever had this problem?

I can hear some guitar signal through the middle to beginning part of the taper where it hums a lot. It does boost the clean signal quite a bit, and the gain knob definately adds some subtle grit. Turning the gain knob down finally doesn't effect the volume, so the new tranny has fixed some things. I'm not quite sure what is wrong. Also, how much distortion should I expect from the clipping diodes? I put two silicons in series, and on the other side, I put a germanium and a silicon, and there really isn't any change in sound, so I think there is still something wrong, but the main problem was that bad tranny, but still... with that many diodes, I should be getting quite a bit of distortion, or I would think so anyways. I used 4 freakin' diodes! I'll check the diode connections later

What do you guys think? I'm closer than ever to having this thing completely working. I made an audio probe, where should I poke around with that? What should I measure with the DMM to find the problem? Is it that maybe the MPF102 is a lower-gain FET, and that is why I'm not getting distortion from the diodes? Hmmm.. regarding the problem with not being able to hear any sound from the sparkleboost when plugged in before another effect. (I should try putting it after an effect...) Anyways, when I have the effect bypassed with the power supply plugged into the DC jack of the effect, I get no sound out of the sparkleboost when before another effect. When I unplugged the power supply, I got sound.

analog kid · February 13, 2005, 02:33:03 PM

'dragonfly' I am having problems with the pinouts on the Jfet for the sparkle boost. I got some J201 s from aron for this to replace my 5457 but I can't get it to work when putting it in flat side facing left OR when reversing the G and S legs. THESE are the proper D G S pinout right/? also a got some BS170 do these work or not cause they're mosfet??
I would liek to get something aelse in there to see how it affects the Gain knob.
BTW I don't like the diodes that I've tried , TOO MUCH dirt at all settings.

Torchy · February 13, 2005, 04:10:12 PM

crp

RjM · February 13, 2005, 04:32:21 PM

My sparkleboost is working perfectly now! The problem was incorrectly wired jacks. The jacks I have are different than others. The first lug connects to the sleeve (ground) and the second lug is for signal. Anyways, it works perfectly, except for some weird crackling noise, which could be a loose wire or something of that sort, but I don't know how I could pinpoint the problem.

I definately need to eliminate the crackling, since it can be heard too much with my distortion pedal on. I definately want to try different transistors. What transistors could I try? I want to get a high-gain transistor, unlike the MPF102 I am using right now. The diodes I have in it just change the voicing right now, since the MPF102 doesn't push them hard enough for an overdrive tone. They do add some grit, though. It really doesn't boost the volume that much, if at all. It just changes the tone, so I want a transistor capable of more output and/or more gain.

Since I have a 3K9 resistor instead of the 2k7 that goes to the source lead, do you think that lowered the gain a little bit?

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Debugging the Sparkle Boost