Sparkle Boost perfboard error??

[Pushtone]

I've built and am troubleshooting a perfboard Sparkle Boost from Dragonfly's gallery. While trouble shooting I noticed a difference between the perf version
and the schem and stripboard versions. I'm asking if this is an error or maybe it doesn't matter.

In the perf version...
9v+ connects to the wiper and pin 1 of the 100k trimmer.




In the schem and the stripboard version 9v+ connects only to pin 1 of the trimmer.





Error?

I altered my perf to match the schem but with no change in the symptoms I'm troubleshooting.
So maybe is doesn't matter and my problem lies elsewhere.

The problems I'm having are...

1. The Vol pot is working backwards, clockwise is less volume.

2. The level goes from null to unity gain, no boost, and sounds kinda weak.

3. The Gain pot is not working, no change in sound when turned.

4. I can't get anywhere near the 4.5v bias. I'm clipping the neg lead of the meter to ground
and the positive lead to the drain. Meter is set to read 20DCV. I'm getting 8.6v at one extreme of the trimmer and 7.1v at the other.
Here are all the voltages: D-8v, G-0.00, S-1.10 (S starts out at 4.5v but quickly drops as I meter it and stays there until the power has been removed.)


I'm using a 2N5457 with the G & S pins twisted round to match the perf layout.
The vol pot I'm using is linear not log.

I'll get the NTE458 and log pot tomarrow.

[Ardric]

The trimpot wiring doesn't matter.  It's being wired as a variable resistor.

Re your biasing symptoms, I'd look again at that 2k7 source resistor.  Maybe you've used a 27k by mistake?

[pyrop]

In the perf version...
9v+ connects to the wiper and pin 1 of the 100k trimmer.




In the schem and the stripboard version 9v+ connects only to pin 1 of the trimmer.

If you look closely the wiper is connected to the same pin in both layouts. It's just flipped around in the layouts. Makes no difference

4. I can't get anywhere near the 4.5v bias. I'm clipping the neg lead of the meter to ground
and the positive lead to the drain. Meter is set to read 20DCV. I'm getting 8.6v at one extreme of the trimmer and 7.1v at the other.
Here are all the voltages: D-8v, G-0.00, S-1.10 (S starts out at 4.5v but quickly drops as I meter it and stays there until the power has been removed.)
Sounds like the trimmer could be faulty or the wrong value

Just my 2c

pyrop

[Dragonfly]

Error?

nope...the layout is verified

The problems I'm having are...

1. The Vol pot is working backwards, clockwise is less volume.

you have lug 1 and lug 3 switched...looking at the bottom of the pot, with the lugs facing away from you, lug 3 is on the left

2. The level goes from null to unity gain, no boost, and sounds kinda weak.

a working sparkle boost DEFINITELY wont sound weak...either youve accidentallly used a wrong value part, or youve connected something incorrectly

3. The Gain pot is not working, no change in sound when turned.

once again, i'd suspect that something is wired wrong

4. I can't get anywhere near the 4.5v bias. I'm clipping the neg lead of the meter to ground
and the positive lead to the drain. Meter is set to read 20DCV. I'm getting 8.6v at one extreme of the trimmer and 7.1v at the other.
Here are all the voltages: D-8v, G-0.00, S-1.10 (S starts out at 4.5v but quickly drops as I meter it and stays there until the power has been removed.)

check your trimpots value, and check your ground connections....

I'm using a 2N5457 with the G & S pins twisted round to match the perf layout.

ive never truste "twisting the legs", but thats just me...too easy to damage the part....

The vol pot I'm using is linear not log.

wont matter

hit the debugging page...i suspect you'll find the error is either the trimmer is bad, or youve got something "miswired...

best of luck,
  AC
I'll get the NTE458 and log pot tomarrow.
[/quote]

[markm]

I don't know if this helps but,
In my gallery I have a version of the sparkle boost with the J201/2N5457 pinout.
Maybe you could use it as a guide 
Go here>>>>>>>>>>>http://aronnelson.com/gallery/album15

[KerryF]

Does anyone have a soundclip for the Sparkle Boost?  I am looking to build a nice clean booster, but want to make sure its not close to my other booster.

[petemoore]

  The 100k pot should adjust between 0k and ~87k [depending on what it's potwafer resistance 'actually' is...
  every other resistor on the board should measure within +/- ~10% of the shown values on the scehmatic.
  I'd just go through the board looking at resistances of every resistor measured, count the number of connections at each node on schematic [then verify the same # is securely connected on the board], and that no 'stray connections have been made.
  100k trims...can be finnicky, and not actually provide 'controllable resistances to provide bias on ...certain Jfets, I've had luck with tapering resistors on 100k pots...long story...
  I ended up with a 4k7/100k pot on a Jfet drain, that Drain Resistance jumped over the bias point when I tried adjusting the 100k, so I started by adding a 47k trim resistor on the pot, better but still jumpy.

[DuncanM]

Does anyone have a soundclip for the Sparkle Boost?  I am looking to build a nice clean booster, but want to make sure its not close to my other booster.

The SparkleBoost can be clean with the gain turned down and the output turned up but gets slightly dirty with the gain above halfway. Not quite as dirty as the Minibooster though. Halfway is nice as it sort of does the job of a limiter for clean funky rhythm playing with my strat, higher gain is good for lead breaks.
All in all, a very useful pedal.
Unfortunately, I can't do you a soundclip until midweek (pressure of work).

I would have though your MOSfet Booster would have been a good clean boost...?..

[markm]

I agree.
For squeaky clean, my vote is for the MosFet Boost.

[Gilles C]

Does anyone have a soundclip for the Sparkle Boost?  I am looking to build a nice clean booster, but want to make sure its not close to my other booster.

http://www.diystompboxes.com/smfforum/index.php?topic=37164.0

[KerryF]

Thanks guys I will think about building it.

[Fleetdog]

Is there a reason to build this with a trimpot rather than finding the needed resistance and just putting in resistors to get that bias?  For instance, would you need to adjust it periodically or does the bias have to be super precise for this application?

[markm]

I think the adjustment is easier with the trim and that's the reason for it.
The proper resistor put in it's place should be fine I would think.

[Dragonfly]

Is there a reason to build this with a trimpot rather than finding the needed resistance and just putting in resistors to get that bias?  For instance, would you need to adjust it periodically or does the bias have to be super precise for this application?

being that all jfets are a bit different, the trimmer makes it easier to "dial in" the proper bias for your particular jfet....

that being said, you could easily hook up a 100k pot in series, use it to find the bias, measure the resistance, and then use that value resistor in the trimmers place...i just think using a trimmer is much easier

AC

[Ardric]

The trimmers may need adjustment if the power supply voltage changes.  Try to trim it on the same sort of battery or wall wart that it'll be used with eventually.  Or add voltage regulation to the circuit.

A nice thing about substituting a fixed resistor for a trimmer is that you can use a lower noise metal film type.  Or alternatively, use a bigger metal film resistor and a smaller trimmer in series.  The drain resistance is probably the most useful place to put a metal film; I'm not sure where to get a 100K trimmer that isn't carbon.

[Pushtone]

I picked up a couple of NTE458 transistors on Saturday and got to try again Sunday night.

This time I went straight to the breadboard. Worked great and sounds exactly like DuncanM describes above.
This boost has more personality than a U of P cheerleading squad.

I was really digging the sound with the Epi Valve Junior head.
Got a little to a' rocking and took a stomp backwards onto the breadboard shorting out the whole thing out! 

I tried connecting the 9v supply in the two ways I saw on the layouts posted at top of thread.
I see now it doesn't matter. Just affects which side the trimmer needs to be leaning to.

But my perf job still has the same problems.
Won't bias, even after swapping trimmer with same value resistor as on breadboard trimmer.

I'll have to try it again, this time I'll go a few rows larger to it's not so tight for me.

Worth it. Very flexible and great sounding booster Dragonfly, thanks!
Worthy of top five ranking.

[KerryF]

I just finished putting the Sparkle boost on vero (minus Gain Pot).  It was a pretty fun and easy build (Probably the easiest one I have done).  I still need to get a 5k pot for the gain pot.  Anyone have one?

Thanks,
Kerry 

[Dragonfly]

..Glad ya like it !  its a really cool little booster...although "little booster" probably isnt a good way to describe it, as its pretty ballsy !

AC

[Dragonfly]

I just finished putting the Sparkle boost on vero (minus Gain Pot).  It was a pretty fun and easy build (Probably the easiest one I have done).  I still need to get a 5k pot for the gain pot.  Anyone have one?

Thanks,
Kerry 

if you have a 10k pot handy, you can strap a 4k7 resistor across it and get close to 5k....

or...you could use a 3k3 - 4k resistor in series with a 1k pot (most of the cool stuff is at the middle/top of the rotation...)

or...you could use a trim pot in series with a 1k pot...adjust the trimmer to a level where it sounds good clean, and then use the 1k pot to get a bit of "grit" into it....

just some thoughts....

AC

[KerryF]

SWeet!  Thats what I like.  I already have my Vintage Booster (MOSfet Type boost) which is nice.  Then I decided I wanted this to sparkle up my sound and add some balls when needed.  Then theres the germanium treble boost I did yesterday (waiting on my Germanium trannies and diodes I ordered from Yun ) so that I can test it.  Thats the Range Pig from petemore.  Then I will put both boosts in 1 box.