Sweet Thing booster and power section plus some whining noise

[Rob Strand]

I got that 47n/68n is to try for C9
And the 12n/15n is meant for C10, right?

Yes, that's it.

You can play with the values.  You will soon know what suits you.

[matopotato]

I finally got around to try this.
The change to add 47R/220uF twice and 100nF at the end did not seem to have much impact on the squealy noise.
Still If I go Guitar - Sweet Thing - Amp the squeal is gone, so I will put it down to my pedal board being what it is (have yet to find the offending pedal) and trust the recommendation along with the 1N5187 instead of the 1N4148.

As for the C9 100nF/68nF/47nF and C10 22nF/15nF/12nF variants I could detect only a very small difference, which left me unsure as to what to listen for.
Still, left to my own thoughts, I felt C9 68nF and C10 12nF sounded possibly a touch better.
Tried Single Coils and Humbuckers and this circuit seems to have most of its useful range with Single Coils. Humbucker kept things a little bit muddy.

Anyway, I plan to go ahead with the values I mentioned above.

Thanks for all the input and ideas to try! I really appreciate it 

[Rob Strand]

I finally got around to try this.
The change to add 47R/220uF twice and 100nF at the end did not seem to have much impact on the squealy noise.
Still If I go Guitar - Sweet Thing - Amp the squeal is gone, so I will put it down to my pedal board being what it is (have yet to find the offending pedal) and trust the recommendation along with the 1N5187 instead of the 1N4148.

Try moving the 22pF (C1) to the other side of the 33k (R2).    You could even increase the value of C1 to 47pF or 100pF.

As for the C9 100nF/68nF/47nF and C10 22nF/15nF/12nF variants I could detect only a very small difference, which left me unsure as to what to listen for.
Still, left to my own thoughts, I felt C9 68nF and C10 12nF sounded possibly a touch better.
Tried Single Coils and Humbuckers and this circuit seems to have most of its useful range with Single Coils. Humbucker kept things a little bit muddy.

I'm surprised there wasn't a larger difference as the mods push up the tone control frequencies quite a bit.   Nothing stopping you using smaller caps, especially C12.    It's always tricky getting this stuff right and people's preferences vary a *lot*.

As for the mud on the humbuckers.  Reducing the value of C3 to say 4u7 might help shave some mud off.  Again tweak to taste.

[matopotato]

Try moving the 22pF (C1) to the other side of the 33k (R2).    You could even increase the value of C1 to 47pF or 100pF.

OK, I tested with 22pF, 47pF and 100pF, each on each side of the 33k. And I am sorry to say, but the overall "breadboard and wire" squeal and disturbance with me just moving my hand over some of the JFETs sort of makes any difference hard to determine.
I recall that with my first pedals I felt it was sometimes difficult to separate different ODs (set similar) from each other, and a few years later I can better tell some differences.
So experience, to know what to listen for and what other settings to use on the pots and guitar and amp all come in to play. And I guess at this point I am still learning how to distinguish differences that more seasoned senior circuit designers and builders perceive as a bit more obvious.
Should anyone else build this circuit, which I do recommend, then I hope the suggestions in this thread will come in handy.
Also as you say, the line between "fixing" or tweaking something to get it to what you would prefer versus staying true to an original or vintage design trying to catch its "inner beauty" is not so easy to draw.

I'm surprised there wasn't a larger difference as the mods push up the tone control frequencies quite a bit.   Nothing stopping you using smaller caps, especially C12.    It's always tricky getting this stuff right and people's preferences vary a *lot*.

Again, I think this could be lack of having a more trained ear and setting pots, guitar, amp to reveal or emphasize such differences more.
I have full respect for your suggestions being the proper ones so I think it is more in me than the circuit 

I am guessing you mean the C10 here, currently at 12nF. I have only up to C11 as numbered caps in the schematic,

As for the mud on the humbuckers.  Reducing the value of C3 to say 4u7 might help shave some mud off.  Again tweak to taste.

I tried that as well, and sadly I could not tell any greater difference.
Watching a YT clip last night by Brian Wampler on different booster circuits https://www.youtube.com/watch?v=rWH_4nVvyy0, it seems that Sweet Thing is a Mu-Amp(?) type of circuit and does muffle Humbuckers a bit more. Btw I am using 2N5457s instead of the original J201s.
I think it sounds nice with Single Coils though so I can live with that.

Again many thanks for your suggestions, I appreciate it!

[antonis]

it seems that Sweet Thing is a Mu-Amp(?) type of circuit

http://www.geofex.com/Article_Folders/modmuamp/modmuamp.htm

I's try to turn it into cascode amps by grounding C2 and C7 negative plate..
(just for fun..)

[Rob Strand]

OK, I tested with 22pF, 47pF and 100pF, each on each side of the 33k. And I am sorry to say, but the overall "breadboard and wire" squeal and disturbance with me just moving my hand over some of the JFETs sort of makes any difference hard to determine.

If you can change things with your hand that usually means that external noise is getting picked up by the circuit and that you need to shield the circuit.

A good idea is to take an alligator clip and connect aluminum base-plate of the bread board to the circuit ground.   This can make an *enormous* reduction.  Another good practice is to connect the metal backs of the pots to circuit ground.

There's a few threads on this forum where people have L shaped metal chassis with holes for 6.5mm jacks, switches, and pots.   The chassis is connected to circuit ground.    This greatly reduces noise on breadboard setups.  You place the breadboard on the chassis.   I have had set-up like that for many years.

Look here, post #5,
https://www.diystompboxes.com/smfforum/index.php?topic=116423.msg1077832#msg1077832

When things get really tough you can place a metal shield or some aluminium foil connected to circuit ground over the top of the whole structure.

I am guessing you mean the C10 here, currently at 12nF. I have only up to C11 as numbered caps in the schematic,

Yes, sorry.

I tried that as well, and sadly I could not tell any greater difference.

You might need more drastic measures like increase R3 to 1k or 4.7k then use much smaller cap like 100nF or 220nF.   You need to experiment and also find balance between not losing the single-coil sound and shaving some mud off the humbuckers.   A good plan is to make large changes to the point where you hear something then start backing off the amount of change to suit what you like.

[matopotato]

OK, I tested with 22pF, 47pF and 100pF, each on each side of the 33k. And I am sorry to say, but the overall "breadboard and wire" squeal and disturbance with me just moving my hand over some of the JFETs sort of makes any difference hard to determine.

If you can change things with your hand that usually means that external noise is getting picked up by the circuit and that you need to shield the circuit.

A good idea is to take an alligator clip and connect aluminum base-plate of the bread board to the circuit ground.   This can make an *enormous* reduction.  Another good practice is to connect the metal backs of the pots to circuit ground.

There's a few threads on this forum where people have L shaped metal chassis with holes for 6.5mm jacks, switches, and pots.   The chassis is connected to circuit ground.    This greatly reduces noise on breadboard setups.  You place the breadboard on the chassis.   I have had set-up like that for many years.

Look here, post #5,
https://www.diystompboxes.com/smfforum/index.php?topic=116423.msg1077832#msg1077832

When things get really tough you can place a metal shield or some aluminium foil connected to circuit ground over the top of the whole structure.

I have a base plate from an old metal sheet cupboard. But it is painted so it does not conduct unless I scrape some paint off.



Then the breadboard itself is on rubber feet, so that would also need some fixing.
I discovered that on its bottom there are 6 small screws that all conduct with each other. So I am taking that as they fasten the black plate (also painted/isolated) and in doing so go through the aluminum bottom plate of the breadboard. So I took a wire from one of the screws and brought it to the front and the common ground.
It did not have any huge impact on the noise though.


When I test out builds I am often lazy enough to just add them in last on the pedalboard. And as Tom pointed out earlier in this thread, the main contribution of noise is likely to come from some pedal in that chain. So connecting guitar directly to the build is very different. Most, if not all of the noise is now gone. It makes swapping guitars etc messier, but once the circuit is doing what it should, I guess getting the others out of the way is needed for tweaking and experimentation.
I still would have thought that the noise would be more reduced by shielding than it was, regardless of where the new breadboard build is placed.

You might need more drastic measures like increase R3 to 1k or 4.7k then use much smaller cap like 100nF or 220nF.   You need to experiment and also find balance between not losing the single-coil sound and shaving some mud off the humbuckers.   A good plan is to make large changes to the point where you hear something then start backing off the amount of change to suit what you like.

I did some testing with R3 at 1k and C3 down to 100nF, and at that point it does remove some mud from the Humbuckers but it makes them sound a bit too nasal. (There is just no way of pleasing some people...). And the Single Coils even more. So I went back to 100R and 4u7F, which feels good enough. Putting back the original 22uF is not any clear difference to me, perhaps a tiny one, but I might stick with 4u7F anyway.

And yes, experimenting and taking things a bit far first and then gradually move back is a very good practice.
I just have to learn a bit more as to where to make changes and what values to use when more than one component needs tweaking.

Again, many thanks!

[Rob Strand]

When I test out builds I am often lazy enough to just add them in last on the pedalboard. And as Tom pointed out earlier in this thread, the main contribution of noise is likely to come from some pedal in that chain. So connecting guitar directly to the build is very different. Most, if not all of the noise is now gone. It makes swapping guitars etc messier, but once the circuit is doing what it should, I guess getting the others out of the way is needed for tweaking and experimentation.

If you can change the noise by waving your hand over the board it goes against the noise coming from elsewhere.

I did some testing with R3 at 1k and C3 down to 100nF, and at that point it does remove some mud from the Humbuckers but it makes them sound a bit too nasal. (There is just no way of pleasing some people...). And the Single Coils even more. So I went back to 100R and 4u7F, which feels good enough. Putting back the original 22uF is not any clear difference to me, perhaps a tiny one, but I might stick with 4u7F anyway.

Yes, there's no easy win.  It's a game of balancing good and bad and never being happy with either!

[matopotato]

If you can change the noise by waving your hand over the board it goes against the noise coming from elsewhere.

Yes , of course.
I just noticed when swapping wires to different cap selections that when I passed mybhand over a transistor (Q1) there was an increased noise.
But the overall "stable" noise changed with placement in the chain or alone.
Can't remember if my hand movements affected when alone.
So I would suspect there are two issues.
Placement with a possible pedal offender in the chain makes up for basic noise.
Then unshielded build with my hands flying around is the other.
Together both are quite obvious, but separate I think the lack of shield has less overall impact.

Of course, I am not in any lab conditions so probably loads of disturbance sources, myself included cause different noise.
All in all I  am thankful for the tips and tricks learned in this thread.
Will hopefully post back when finished.