questions about jordan bosstone

[taillie]

I'm building a friend of mine a jordan bosstone and have a few questions, two general questions and one trouble shooting question.  I'm using the Arron nelson schematic.  I have built a few bosstones and really like them,  this one is on my breadboard still, It is working as its supposed too.  But before i build it I would like to figure a few things out. 
Question one; Where does the strange character  tone of the bosstone come from? the octave type sound.  On paper it looks basically like an Electra except it has a complimentary pair instead of one transistor, and a few extra caps to get rid of treble. So what gives it that unusual sound?
  Question two;  has any one tried different transistor combinations, and if so are there any combinations of hfe that sound particularly good? I have tried a few and basically get the same sound. right now both transistors are in the 150 ish hfe range.
Question three;  In an old post about bosstones Rg says that in addition to adding the power filtering electro cap, you should also add a "monolithic ceramic cap" of .01 micro farads for to eliminate rf.  Is there any reason why it should be ceramic or will any material cap work?
Question four;  this is the question I most want answered.  So I've got the new bosstone on my bread board,  and by itself it sounds fine and as its supposed to.  I wanted to compare it to one of I have built in the past, so I hook up the older bosstone before the new one.  they are on the same power supply, when the new bosstone is on it begins to make a high pitched whine even if the old one is off.  If I disconnect the power to the old one the whine stops.   If I change the order so the old one is after the breadboard it stops. If I put any other pedal before the breadboard it does not whine.  So I am pretty sure the problem is definitely in my older bosstone.  So I try the old one before some other pedals,  same problem,  even when its off whatever follows it amplifies the buzz.  Now the wierd thing is If I mess with the output volume on the pedal it lessens the noise as I turn it down,  If I turn the  attack pot at all the buzzing stops and doesn't come back at all.  Then I discovered If i hook the pedal up and the attack pot is any where in the middle it wont start with the buzzing, only when you start with it turned all the way in either direction. Also turning the volume on my guitar will increase or lessen the whining.  I have never seen this before in any pedal,  especially because all this happens when the pedals is off.  I really don't want to repeat this in the one I am building for a friend so I am trying to make sense of it.  My theory is it must be something screwy with the off board wiring, something with my grounding, that noise is getting out and getting amplified by whatever is following it.  I don't have a camera to take a decent picture of it so I cant show the guts,  but I used the madbean style wiring layout, without a battery, but with the 3pdt switch and led ect.  the only things I did differently with this bosstone is I used pots with detents, but I don't see what difference that would make.  Then Instead of wiring the pots grounds directly to the board individually,  I have got The pot grounds wired together and then to the ground point on the 3pdt.  I think this may be the cause but I can't see why it would be, being all the grounds are connected any how. 
   any way I am sorry for the long post and so many questions.  but thanks in advance for any help\advice you guys may have.  I really appreciate it.   

[taillie]

 I guess that was 4 questions, sorry.

[R.G.]

The bosstone seems like it is quite sensitive to power supply decoupling and wiring issues. The ones I've built nearly all required some tinkering to suppress oscillation, including RF oscillation up to the FM band - about 100MHz!

Being so touchy, breadboarding is going to be challenging. Try putting small ceramic caps - 10pF to 100pF - from collector to base of each transistor, and inserting a 10R to 100R resistor directly in series with the base of both transistors.

Also be sure you're bypassing the power supply with a 0.1uF ceramic cap as close as you can get the cap to the transistors, and

[thermionix]

, and

RG passed out on the Post button again.

[taillie]

thanks Rg,  I believe  I have seen you give this same advice to some one else with bosstone noise issues.  The strange thing is I am not having any problems with my breadboarded version.  I built one in the past and hooked it up before the breadboard so i could do some comparing and I am fairly certain the noise is coming from the older one.  If i take a small cap and hold across the collector and base it does get rid of the squealing.  I don't understand   how exactly the noise is escaping into the next pedal in the chain because it is bypassed.  I think i must have something wired strangely.  regardless I do intend to incorporate your mods into my finished build just to make certain I don't repeat this same problem in my new pedal. one last question the power supply bypass cap what is the reason it should be ceramic? do they work better for radio frequencies than other materials? or is there another reason?  thanks again your advice is greatly appreciated. 

[PRR]

Ceramic (with very short leads) does work better for radio frequencies.

[Rob Strand]

The strange thing is I am not having any problems with my breadboarded version.  I built one in the past and hooked it up before the breadboard so i could do some comparing and I am fairly certain the noise is coming from the older one.

Breadboards have a lot of capacitance between the rows.   In some cases the added capacitance limits the frequency responds and suppress oscillations.  In other cases the extra coupling it causes between parts of the circuit can cause oscillations.   You can only know what is going on by looking at the fine details.

If i take a small cap and hold across the collector and base it does get rid of the squealing.  I don't understand   how exactly the noise is escaping into the next pedal in the chain because it is bypassed.  I think i must have something wired strangely.

If the Bosstone has strong oscillations the high-frequencies that jump over wiring and switch contacts (because of capacitive coupling) will also be strong.  That can affect things that otherwise look disconnected.   I don't know if that's what is going on here - I'm only giving a possible mechanism.

[taillie]

Thanks guys. When i think about it, your explanations make sense.  I have had many circuits get quieter after taking them off the breadboard and building them, because the long leads and extra metal would pick up noise.  But i forget that breadboards also add capacitance.    The different layout,  wiring and what not could very well enplane why my bread boarded version doesn't have the same problems.   I found that holding a 50 pf cap across the base/collector  did do the trick in my old bosstone.  so I may take it outa the box and add it at some time.   For the bread boarded version I decided to try all off Rg's suggestions, both the extra resistors and extra capacitors.  I drew up a layout that should make it fairly easy to remove and tweak those parts should the soldered version start acting differently.  I was thinking i might shield the input as well as an added precaution.  Any way thanks Its been very helpful.

[Rob Strand]

he different layout,  wiring and what not could very well enplane why my bread boarded version doesn't have the same problems.   I found that holding a 50 pf cap across the base/collector  did do the trick in my old bosstone.  so I may take it outa the box and add it at some time.   

There was a long thread on this group regarding this effect;  maybe "Let's talk about the Jordan Bosstone.".  Perhaps around the end of last year(?).  Here,
https://www.diystompboxes.com/smfforum/index.php?topic=78321.0

The existing cap in the circuit is quite ineffective at reducing HF gain.   I think the best value was 1nF but it still wasn't that effective.   That circuit has high gain so you have to watch out that adding caps across BC doesn't affect the tone (as the cap value gets multiplied by the gain due to the Miller effect).   Maybe a good place to start is simply put a 100pF to 220pF cap across the input terminals.

BTW: There's two possible scenarios:
1) The circuit itself is oscillating due to an *internal* feedback mechanism.  This type of thing is hard to analyse (and solve) for most people.
2) The circuit is oscillating because of capacitive feedback around the whole circuit due to wiring and the bypass switches.  This is easier to solve because you just need to roll-off the high frequencies anywhere in the circuit.

[R.G.]

, and

RG passed out on the Post button again.

Weird. That's the second time that's happened (that I know of). I actually typed a good bit more as I remember. But the posts after mine picked up most of it.

The bosstones I built were sensitive to power bypassing and lead dress, as Rob points out. Breadboards do add capacitance, for better or worse.

I had to do some combination of bypassing and lowering the frequency response of the transistors on the ones I tinkered with. A small cap - 10 to 47pF from collector to base helped a lot. One of them would pick up AM radio stations if I moved the leads ... just... right.

[Rob Strand]

One of them would pick up AM radio stations if I moved the leads ... just... right.

Actually now you mention it.  I remember when the old thread was running I was thinking it might be a good idea to add a 1k to 10k "stopper" resistor in series with the line after the input pot wiper.   That would form a fairly well-define low-pass filter against the existing collector-base capacitance of the first transistor.