Debugging the Sparkle Boost

[RjM]

Ground is a reference voltage for the circuit. All points ground, with battery connected should read 0v potential from ground.
 All points ground should read 0 resistance from ... or ... continuity to ground.

The reading from the DMM is near enough to 0 resistance to assume that the grounds are all fine, and I don't think that the effect would work at all if a ground was disconnected. What is your take on the crazy transistor voltages? >>>Do you care to share the DMM reading
 >>>What makes you assume that ? Connect ground to ground, and 0v potential between the two ground points should be found.
 Look for continuity, or alternatively 0ohms resistance between ground and GND. Try test clips on a wire to 'get' ground when in doubt.
D- 4.87
G- 4.53
S- 4.71

The transistor isn't within operational range.

Sure, I'll get some various ground readings and post them here later. Do you think a bad ground somewhere is causing the transistor to not be within operatinal range? What does a bad ground look like, or what is a bad ground, anyway? I guess I'll just have to use the DMM to pinpoint the bad ground, I probably won't be able to see the problem, right? I know these questions seem less than intelligent, but for me, this is all a learning experience, learning about everything as it comes up.

[RjM]

EDIT: Whoops, double posted.

I have an idea, should I disconnect all my grounds and re-solder them? I tested from ground to ground, at various points, and it all came up with .000 resistance on the 2M setting of my multimeter. Could there be another problem?

[puretube]

the best is, to get 0.0 @ the 200 Ohm setting.

[petemoore]

I dont' know where the meter stops beeping, but tried the smallest resistor I had and that didn't make it beep so...
 ...I use continuity checker to test for ground continuity all the time, if it beeps that's it...only next test is whether that does it's job making the cct work...which invariably i think it has.
 I guess I'm just dogmatic, but I always clip to ground the black DMM lead, touch the red to it so I hear beep', then listen for beep on Every Ground Point...once that's established I move on.
 This is one of the first tests I do, because of odds of finding something wrong there, and easiness of looking.
 To me ground is'nt a 'quantitative thing, you either have it or you don't, working with a circuit that calls for ground without ground where it's called for...I'll spare you the analogies, and just say make sure all grounds are made where specced by the schematic. It's as simple as a choice gets....I/O, either you got it or you don't. If you don't and it's hard to get...perhaps another pastime is in order.
 Another way to test is with the battery connected, and the pots turned anywhere but at either end of the range,...if you read 0 volt potential from ground to known ground you've established that ground is at 0v...THEN I'd start moving on to looking for 'problems'...
 I can't believe I just typed all that.

[Johnny Guitar]

This has been one of the best threads I've seen (and I'm not building a SparkleBoost yet). RG, I think you should think about cleaning this thread up a little bit and add it to one of the debuggin pages -- either yours or here.

It would be a great resource to pull a few of the detailed real life debugging sessions and put them up somewhere: one or two for the FF, this one, maybe a couple of others. Just giving newbies an idea what to see on different pins of transistors will narrow their search. Then we might ask slightly more  informed questions.

Great work RG and everyone.
J

[RjM]

I dont' know where the meter stops beeping, but tried the smallest resistor I had and that didn't make it beep so...
 ...I use continuity checker to test for ground continuity all the time, if it beeps that's it...only next test is whether that does it's job making the cct work...which invariably i think it has.
 I guess I'm just dogmatic, but I always clip to ground the black DMM lead, touch the red to it so I hear beep', then listen for beep on Every Ground Point...once that's established I move on.
 This is one of the first tests I do, because of odds of finding something wrong there, and easiness of looking.
 To me ground is'nt a 'quantitative thing, you either have it or you don't, working with a circuit that calls for ground without ground where it's called for...I'll spare you the analogies, and just say make sure all grounds are made where specced by the schematic. It's as simple as a choice gets....I/O, either you got it or you don't. If you don't and it's hard to get...perhaps another pastime is in order.
 Another way to test is with the battery connected, and the pots turned anywhere but at either end of the range,...if you read 0 volt potential from ground to known ground you've established that ground is at 0v...THEN I'd start moving on to looking for 'problems'...
 I can't believe I just typed all that.

Alright, I've done that, from ground to ground, I've checked all the ground points, and the problem isn't ground. What else could it be?

[petemoore]

Typo time...here's what I do...
 Measure resistances in circuit that affect bias.
 If you get a reading at or above specified value, you have a resistor that's too large there.
 However if you get a reading of lower value than schem, you must either:
 Pull one end of the resistor...or
 Do the math and figure out what the alternative path through the circuit would make those two paths read as an R value...or
 Figure they're ok and Go by the color codes once again, and try to find other problems
 I've found mis-R values this way, also found faulty resistors, tho it is uncommon.
 Look at everything else, and try to find the new things to look at from the debugging page.
 The reason I typed this is as a last resort it works for me...time consuming and tedious yes, but how the heck else would I have found bias mishaps.
 The source and gate are up sorta near 1/2v of supply, I suspect there is a biasing issue around one of them.
 A cursory in circuit resistor check....skim over the 'funny' readings...IF there's another path available through the circuit for current across the test points.
 Lotta 'ifs eliminations' and some math, but this is how I track stuff down when I get tired of trying other ways. Also helps me to figure the way a given circuit 'ticks'...especially after I get it going... :idea:  ...realizing raising 'this' resistor value here also changes a transistor B and C value there, and should be larger by x amount than that resistor...some reading at GEO about transistor biasing is recommended...

[lethargytartare]

I'm a novice at the headier stuff, but I just did a quick build of the SB, using a J201, and I unwittingly used a perf layout that was actually for the NTE458 -- so my pins were in the wrong order -- but the symptom was the exact same -- when active, the volume dropped a ton, but the volume still "worked" and the gain's impact was not-apparent.  I also got no impact from the trim pot until I got the pins straightened out.

That said, my voltage readings were very different (D 3.93, S .472, G 0 -- after dialing in the trim pot to where I wanted it)...

Sorry if that's a "duh"...

Good luck!

ltt

[Dragonfly]

I'm a novice at the headier stuff, but I just did a quick build of the SB, using a J201, and I unwittingly used a perf layout that was actually for the NTE458 -- so my pins were in the wrong order -- but the symptom was the exact same -- when active, the volume dropped a ton, but the volume still "worked" and the gain's impact was not-apparent.  I also got no impact from the trim pot until I got the pins straightened out.

That said, my voltage readings were very different (D 3.93, S .472, G 0 -- after dialing in the trim pot to where I wanted it)...

Sorry if that's a "duh"...

Good luck!

ltt

how'd you like the Sparkle Boost once you debugged it?

[analog kid]

I have my sparkle boost working now , as far as everthing functioning. BOTH Pots now work `100k and 10k . signal both in bypass and effect BUT the volume drop is just HUGE.!!
TWO weird things that I'm getting:
the trim pot that is on the DRAIN of the transistor gives a very loud POP when it reaches turned all the way down
And the Voltages:( they can't be good)
 Drain =  4.5
 Signal=  3.87
 Gate  =  3.87   both s/g are the same but DO NOT have continuity !!
I know this means the transistor can 't be operating properly since the Gate is not high enough above Signal And the Drain is obviously not over 1volt above Gate ( if the rule does apply to JFET transistors as well)

All resistors are proper value , no subs have been made, Battery voltage is 8volts.
NOTE TO DRAGONFLY:  I have the 2N5457 oriented with the Flate side facing the 1 and 10uf electo. caps instead of the way your picture shows it facin BECAUSE when i looked up the pinout  http://www.nteinc.com/specs/400to499/pdf/nte457.pdf
And then tested in my hfe meter, It showed to be the other way . Being that FLAT SIDE- Left to Right is G S D  so that the rounded side of the transistor must be facing the to the right side of the crkt to get the D G S pinout. When I turned this around is when I at least got Both pots to start responding.
I also have a pretty low quality Push Button , not Stomp, DPDT switch in there for this project. and I used the GGG bypass layouts to wire it up. Maybe you could post a proper example of how you wire the DPDT's

[Dragonfly]

I have my sparkle boost working now , as far as everthing functioning. BOTH Pots now work `100k and 10k . signal both in bypass and effect BUT the volume drop is just HUGE.!!
TWO weird things that I'm getting:
the trim pot that is on the DRAIN of the transistor gives a very loud POP when it reaches turned all the way down
And the Voltages:( they can't be good)
 Drain =  4.5
 Signal=  3.87
 Gate  =  3.87   both s/g are the same but DO NOT have continuity !!
I know this means the transistor can 't be operating properly since the Gate is not high enough above Signal And the Drain is obviously not over 1volt above Gate ( if the rule does apply to JFET transistors as well)

All resistors are proper value , no subs have been made, Battery voltage is 8volts.
NOTE TO DRAGONFLY:  I have the 2N5457 oriented with the Flate side facing the 1 and 10uf electo. caps instead of the way your picture shows it facin BECAUSE when i looked up the pinout  http://www.nteinc.com/specs/400to499/pdf/nte457.pdf
And then tested in my hfe meter, It showed to be the other way . Being that FLAT SIDE- Left to Right is G S D  so that the rounded side of the transistor must be facing the to the right side of the crkt to get the D G S pinout. When I turned this around is when I at least got Both pots to start responding.
I also have a pretty low quality Push Button , not Stomp, DPDT switch in there for this project. and I used the GGG bypass layouts to wire it up. Maybe you could post a proper example of how you wire the DPDT's

sounds like some "bad juju" going on there  :shock:

seriously though...i havent tried the 5457, but it should be fine...your unit is acting like a pinout issue, though i thought i remembered reading that you'd checked it.

keep in mind, that when checking NTE for a cross part, sometimes the NTE will have different pinouts than the parts they replace...doesnt seem like it should be that way, but it is.


heres what id do if i were you....in order to help you figure out the circuit, sometimes its easier to eliminate a variable or two....you might want to disconnect the "gain" pot, and just run the 10uf capacitor direct to ground..that way youre just trying to get a "clean" boost...you can always add it back to the circuit later, once youve debugged it.

your battery voltage is pretty low at 8 volts...id recommend a fresh battery.

i just looked again at your post...you stated that the 5457 (looking at the flat side) is GSD...and you turned it around to get DGS ...provided that you read the pinouts correctly on the 5457, that is incorrect. by turning the fet 180 degrees, you'd actually get DSG ...check that, as this could very well be the "heart" of your troubles.

check these out, and i'll check the thread later....

btw...heres how "i" wire a dpdt footswitch...

andy

[analog kid]

someone made a comment in another post about the sparkle boost project that asked something about the Trimpot Jumping past the Target Voltage. WELL...after doing some more troubleshooting on it. I had to turn my Jfet
around to get the Drain at the top ( round side facing left) , and now trim pot when turned  gives me just millvolts all the way up to almost full on and then at the VERY end of the taper it jumps past the 3-5volt range and goes straight up to battery voltage.  DID you know something about this, or did you have an experience the same??"
I still have it working but the Volume is just way low.

 :twisted: UPDATE ::: the voltages are very weird too... when you CAN get the trim nudges into the area of 5volts  It  evens out at  D 5.86 G 5.67 S 4.97
 
any idea

[analog kid]

Ya know what I just checked , when I checked that pinout I realized that I needed to twist the G/S legs and thought I did but when I just checked the transistor I forgot to twist them around and I did put it in As D S G, If that is the pinout from that side of the trans.  
AS Far as the cross reference discrepency, I also checked it with my hfe tester which gave me a 398 gain when plugging it in with D on the C side  and S and G turned around, into the C, B, E  sockets
BUT , as I type I  stuck another 54' in there to measure the gain and got a 336 gain reading but It seems like it's not in there the same way this time( Question, A meter  will not give an hfe gain reading UNLESS it's plugged in with the proper pinout , correct?? that's why I thought I had it verified. cause every other way I just got a (1) ) THIS TIME.. I just plugged  it in Flat side facing me , to the E, C , B pinout sockets as is without twisting anything around . So wouldn't that mean this trans. is a D S G pinout?
so you 're probably right , whatever the pinout ends up being , I'd say the problem now is a pinout discrepancy so I'll turn or twist after I hear back from you and try it again

[Dragonfly]

Ya know what I just checked , when I checked that pinout I realized that I needed to twist the G/S legs and thought I did but when I just checked the transistor I forgot to twist them around and I did put it in As D S G, If that is the pinout from that side of the trans.  
AS Far as the cross reference discrepency, I also checked it with my hfe tester which gave me a 398 gain when plugging it in with D on the C side  and S and G turned around, into the C, B, E  sockets
BUT , as I type I  stuck another 54' in there to measure the gain and got a 336 gain reading but It seems like it's not in there the same way this time( Question, A meter  will not give an hfe gain reading UNLESS it's plugged in with the proper pinout , correct?? that's why I thought I had it verified. cause every other way I just got a (1) ) THIS TIME.. I just plugged  it in Flat side facing me , to the E, C , B pinout sockets as is without twisting anything around . So wouldn't that mean this trans. is a D S G pinout?
so you 're probably right , whatever the pinout ends up being , I'd say the problem now is a pinout discrepancy so I'll turn or twist after I hear back from you and try it again

I dont believe that you can get an accurate test on a fet using a transistor hfe tester...i may be wrong, but im pretty sure it'll be innaccurate.

twist them legs around and tell me what you get

[analog kid]

Ok just to explain the way it's in there. From Top to bottom on the board and counting the legs from right to left looking at the front flat side of the trans. > I have leg 1 D (C) at the top ....Leg 2 G (B) is in the middle and Leg 3 Signal (E) is on the bottom pad of Q1.
The Volume IS NOW ALMOST EVEN!! I have never heard a booster pedal but I assumed that you should be able if desired with one, to get a level far above the Bypassed signal. If I turn the volume and gain both up high I still only get about UNITY> Also It seems that the boost is just A  BIT grittier and has less bass , kind of like a low cut filter.
What is normal of  all this. ? Why does this use a 100k trim?? A 10k is used for bias of the Transistor usually so can a 10k, 20k 50k be used here in place of 100k/?

[Dragonfly]

Ok just to explain the way it's in there. From Top to bottom on the board and counting the legs from right to left looking at the front flat side of the trans. > I have leg 1 D (C) at the top ....Leg 2 G (B) is in the middle and Leg 3 Signal (E) is on the bottom pad of Q1.
The Volume IS NOW ALMOST EVEN!! I have never heard a booster pedal but I assumed that you should be able if desired with one, to get a level far above the Bypassed signal. If I turn the volume and gain both up high I still only get about UNITY> Also It seems that the boost is just A  BIT grittier and has less bass , kind of like a low cut filter.
What is normal of  all this. ? Why does this use a 100k trim?? A 10k is used for bias of the Transistor usually so can a 10k, 20k 50k be used here in place of 100k/?

its still got issues...you should be able to get TONS of gain (probably 25-30dB's with the NTE, a bit less from other fets) from this circuit...but it sounds like youre getting closer....it should also be very "even" toned...pretty true to the sound that goes into it, maybe with a touch more sparkle on the high end.

a fet doesnt necessarily "bias" as easily as a transistor...there are often pretty wide variances in fets, so a 100k trim just helps insure that it can be biased properly. it is[/] possible to use a smaller trim pot, but depending on that particular fet, it may bias or it may not ....

have you used an ohm meter to verify the values of all the resistors?

[analog kid]

I have sir, I did sub a 2.2M for the 2.4 and a 2.2 for the 2.7 and ....DAMN!!!! I just caught something!! I found earlier that I somehow had a 100k in place of the 2.2 (2.7k) resistor  and I figured that was the problem at that point, WELL I just found out where the 2.2 went!! I had it where the the 100k should be, i  must have got them switched in my hand and when I measured them earlier I didn't check that one!
I am sure that's really holding things down in that area a bit huh? And there is probably no reason asking you why my Trimpot is Skipping over the bias point REALLY fast at the very last of it s rotation and staying in the 100's millV for the first 90%,  It is connected to that WRONG resistor.
My transistor values BEFORE changing this resistor error:
 D 4.60 V  G .04 Millivolts S .483 (shouldn't those last two be reversed? Maybe I still don't have the pinout right) It is louder when the booster is on and everything up all the way though

[analog kid]

Well I took care of that and trim pot biases a little better but still stays in mV until the last little bit of rotation. Makes it hard to hit between 4-5.5
I took the voltages again and it's still the same:
D = 4.65
G = 0.00 after settling
S = .465
So what do you think?? I"m going to try it now and see if it's LOUD

[Dragonfly]

I have sir, I did sub a 2.2M for the 2.4 and a 2.2 for the 2.7 and ....DAMN!!!! I just caught something!! I found earlier that I somehow had a 100k in place of the 2.2 (2.7k) resistor  and I figured that was the problem at that point, WELL I just found out where the 2.2 went!! I had it where the the 100k should be, i  must have got them switched in my hand and when I measured them earlier I didn't check that one!
I am sure that's really holding things down in that area a bit huh? And there is probably no reason asking you why my Trimpot is Skipping over the bias point REALLY fast at the very last of it s rotation and staying in the 100's millV for the first 90%,  It is connected to that WRONG resistor.
My transistor values BEFORE changing this resistor error:
 D 4.60 V  G .04 Millivolts S .483 (shouldn't those last two be reversed? Maybe I still don't have the pinout right) It is louder when the booster is on and everything up all the way though

im reposting the schematic here for clarity

sounds like youre getting closer....

[analog kid]

OH YEAH , Loud LOUD LOOUUUDDDD
still tell me though if anytyhing looks funny And if you could give me some ideas and sample settings for what you have used and heard this pedal used for. I have never used or heard a booster til now.  IF it ONLY boosts volume and that's ALL , I can't think of too many uses and benefits besides just setting it for a tad more gain and kicking it down for solos but most people use their overdrive boxes for that I think. I guess that would free up the overdrive for just your Gain and you could still get an extra boost on top of that.
But anyway I don't know about them , Some ideas are appreciated.