Cherrybomb doubts to be undone

[garfo]

Hi everyone, I know there's a lot of people on the forum who have been trying to figure out what's on with this circuit. I've made one before and want to make another one. I'm  just wanting to avoid going all through it again figuring out about the splattering sound that everyone talks about and I have experienced as well.
But first things first.
Someone was saying that found one or more schematics that showed C9 facing the other way around, and I found one as well.
It would be great to check which one is right. Would it make any sense to flip that cap!?
I've made a yellow circle around the cap.
I've found another circuit for the Vox Power boost that show the exact same Cap configuration.

[Bret608]

I went over to DIYSB and asked anyone over there with an original unit to check the orientation of that cap for me. Electric Warrior, who does have one, answered me. This factory schematic shows correctly what is in vintage units. Fuzz Central and a lot of the DIY community after that have it oriented the opposite (including the Cherry Bomb).

Basically, the positive side should be facing the Q3 collector, not the negative side.

Now, what I don't know is if it actually makes much difference in the sound!    I think Rej and others are also right the transistors with the correct gains make a difference as well. I have not built one yet, but since I have the parts, I wanted to make sure and explore this before doing so.

[garfo]

When you say opposite, you mean as in shown on the original schematic?

[garfo]

The cherry bomb still has it facing the opposite from the factory original. That's why I ask!!!
Cherrybomb has C9 positive facing the 10n cap and the 4k7 res, and the negative side connected to the .22 cap and Q3.
The original I've posted is the opposite...

[Bret608]

Right, I mean the Cherrybomb has it backwards compared to the original schematic and original vintage units.

I almost feel like socketing C9 on my upcoming build to see what the difference is in sound when you change the orientation.

[garfo]

I did try changing it on my first built, and from what I remember, I think it made a slight change.it improved the way the splatiness behaved.
By the way, trannys gain, d'you think lower hfe would be a better feature for this project?

[madbean]

I'll check into this. On second look, the positive side to the collector makes the most sense because it is the higher voltage source. But, I have built mine the other way and did not have any splats. To me that sounds more like a transistor bias issue.

In any case, I have two builds around I think. I will have a look at those tomorrow and let you know what I find.

[bordonbert]

This circuit uses a standard Baxandall tone control circuit.  I don't know how it would sound in this application, (I wouldn't have picked it myself), but it was designed for hifi amps as it gives a gradual slope to the range with both cut and boost.  It's hardly ever seen in tone controls in guitar based circuits which it does not suit, they generally sound better with the tone stack concept which works with cut.

As far as DC levels are concerned, the ringed cap is between the collector of Q3 and the emitter of Q1.  Follow the DC path through the resistors and ignore any paths which meet any capacitors which block DC of course.  Q3 collector would be expected to sit just above half the supply voltage to give the best output swing and the emitter of Q1 would sit very low at around 0.5V.  I think the picture has values on there but they are not distinguishable at its resolution I am afraid.  The cap MUST be placed with it's positive end to Q3.  Incidentally the cap from Q2 collector must be the same way round for the same reason.  The diagram you have posted is absolutely correct with its orientations.

Turn it the other way around and you will reverse bias the cap by about 4V.  It's wrong and it won't like it!  And reverse biasing electrolytics does not give you a better sound!

[kothoma]

This circuit uses a standard Baxandall tone control circuit. [...] It's hardly ever seen in tone controls in guitar based circuits which it does not suit, they generally sound better with the tone stack concept which works with cut.

That's a strong claim in need of proof.
This curcuit uses a passive version of the Baxandall tone control actually called James tone control which of course works with cut only.
While it is true that many tube amp designs prefer a tone stack Ampeg is known for using a James/Baxandall circuit.
There are many pedals that use it in passive or active configuration. Even the Klon uses half a Baxandall.

[garfo]

So, you mean that as Brian also suggests it should have the plus side facing Q3, right?

This circuit uses a standard Baxandall tone control circuit.  I don't know how it would sound in this application, (I wouldn't have picked it myself), but it was designed for hifi amps as it gives a gradual slope to the range with both cut and boost.  It's hardly ever seen in tone controls in guitar based circuits which it does not suit, they generally sound better with the tone stack concept which works with cut.

As far as DC levels are concerned, the ringed cap is between the collector of Q3 and the emitter of Q1.  Follow the DC path through the resistors and ignore any paths which meet any capacitors which block DC of course.  Q3 collector would be expected to sit just above half the supply voltage to give the best output swing and the emitter of Q1 would sit very low at around 0.5V.  I think the picture has values on there but they are not distinguishable at its resolution I am afraid.  The cap MUST be placed with it's positive end to Q3.  Incidentally the cap from Q2 collector must be the same way round for the same reason.  The diagram you have posted is absolutely correct with its orientations.

Turn it the other way around and you will reverse bias the cap by about 4V.  It's wrong and it won't like it!  And reverse biasing electrolytics does not give you a better sound!

[bordonbert]

That's a strong claim in need of proof.

You're quite right there Kothoma, but I would maintain the proof is in the simple circuit action.  All of this circuitry has been around in exactly this form for 40 years!  You are doubtless right that the Baxendall tone circuit is used by named guitar electronics manufacturers like Ampeg, that is domain knowledge which I do not possess, but in its passive mode as they usually use it it is ground referenced.  The difference is that here it utilises feedback from the collector of the third transistor.  It is not in any way in passive mode, it is an active Baxendall control setup exactly as it is used in hifi.

Check out here:  http://makearadio.com/tech/tone.htm  They confirm,

Independent adjustment of bass and treble frequencies in high fidelity  audio amplifiers is usually accomplished utilizing specially designed tone-control networks. There are versions for these tone controls based only on passive components, such as the ground-referenced  (my bold underlining) James network shown in fig. 1. Among those versions using active devices we must make mention of P.J. Baxandall´s proposal, in which the tone control was devised as a feedback amplifier. 

This is irrelevant to my claims about the DC conditions for the capacitor polarity issue however.  That is without question.  If you get a clear enough version of the circuit it even shows DC voltages posted on it.  Here is a copy for reference:



Anyone with experience of designing with transistors, (yes I go back that far  ) will be able to see what the DC voltages would be.  They aren't even close to being questionable.

The emitter of Q1 is low, it has to be. Notice Q1 DC reference is the emitter of Q2 and its emitter has to be about 0.6V lower than that.  Q2 emitter must be significantly lower than its own collector to allow it headroom to work and prevent it from bottoming out on signal swings.  So Q2's output capacitor DEFINITELY should have its +ve to C2 collector just as the schematic shows.

Q3 is set up similarly.  It's base DC point is defined by the two resistors at around 1.63V.  It's collector will then be around 5.1V.  This capacitor also has to have its +ve terminal to the collectors.

I'm sure someone else with design experience will come in to either confirm this or tell me I'm a dipstick.  (That may definitely be, but I don't think so in this case  ).

[kothoma]

That's a strong claim in need of proof.

You're quite right there Kothoma, but I would maintain the proof is in the simple circuit action.  All of this circuitry has been around in exactly this form for 40 years!

Hm, I still don't see how that would prove that a Baxandall isn't "suited" as tone control in guitar related circuits.

I've heard that the tonestack is prefered because it has less volume drop than a Baxandall, and that it needs less components.
This would explain the continued use from an engineering stand point.
And I like it in guitar amps to shape the basic sound.

As for pedals, now that's something completely different. Here I prefer a Baxandall from a musicians stand point. Just my personal choice.

it utilises feedback from the collector of the third transistor.  It is not in any way in passive mode

Ups. You're right. Pardon my confusion.

[bordonbert]

Absolutely with you there Kothoma, if you try it and prefer it then use it.  Personally I have always used the tonestack approach only because it does what I want with little fuss.  Consequently I have little experience of using a Baxandall setup in this area.  I have used them many times in other non-guitar related audio equipment where they are a standard and do a great job.  I have heard it said that they sound too smooth and "sterile" for guitar work, possibly because of their reliance on negative feedback, but that would not account for using them in passive mode as you have pointed out.  You have more experience than I do as to whether that is true as you have used them.  I should have made it clear that I was speaking mainly from the point of what I had been told regarding that matter.  My apologies.

Let's not forget that the original point I was really wanting to address was whether the caps were the right way around and my comment on the Baxandall was only intended as a throw away remark.  (Teach me to keep my mouth shut  ).  The cap polarity is a technical matter and incontrovertible, and in this area I do have 40 years of designing complex electronic equipment to fall back on.  The caps are shown in the schematic originally posted and the higher res version which I posted THE CORRECT WAY AROUND.  Using them the other way will not give any possible improvement in sound and will destroy the capacitors and possibly other components as well.

Why do people think that electrolytic capacitors come with a clearly marked -ve if their polarity is somehow optional?  They can explode if they are used with reverse polarity!!!!  Using them the other way around is not an option to try out just to see if there is any improvement, it is a fault.  Any circuit of the above, including the mysterious Cherrybomb, which shows the caps the other way around is WRONG, it will fault, and it is potentially dangerous!

Incidentally I can't find any reference to the Cherrybomb at Fuzz Centrasl and a Google search returns nothing. 

[kothoma]

Absolutely with you there Kothoma, if you try it and prefer it then use it.  Personally I have always used the tonestack approach only because it does what I want with little fuss.  Consequently I have little experience of using a Baxandall setup in this area.  I have used them many times in other non-guitar related audio equipment where they are a standard and do a great job.  I have heard it said that they sound too smooth and "sterile" for guitar work, possibly because of their reliance on negative feedback, but that would not account for using them in passive mode as you have pointed out.  You have more experience than I do as to whether that is true as you have used them.  I should have made it clear that I was speaking mainly from the point of what I had been told regarding that matter.  My apologies.

No need for apologies. Perhaps I should add that one thing to consider with Baxandalls for guitar pedals is that it is often a good idea to shift the center from the standard 1kHz down a bit towards say 700Hz.  Maybe that's why the hi-fi version sometimes is considered inappropriate?

[garfo]

Is it normal for this circuit to experience so much noise?
This circuit is working but experiencing huge levels of noise( ground?)
Not very normal. Even when I roll back the guitars volume knob there's some noise introduction.
Any idea?
I've A/B'd it with an original and the original sounded fatter, with much less gain, less noise and also, it appeared to have an extra section on the circuit with an F245A fet.