Bosstone wierdness

[Mark Hammer]

Put a Bosstone clone together this past weekend.  I already have one I made and it works just fine.  The current one was made with a 2N3565 (hfe around 150) in the front, and a 2N3906 (hfe around 240) in the second position.  I also included a 3-position switch that would give me stock, stock with a treble-cutting cap in parallel with the clipping diodes, or a .1uf input cap added in parallel to the .022 unit.

At extreme settings, the unit behaves reasonably well, generating the expected tones.  The problem is that the unit frequently behaves very much like a mistracking octave divider, skipping around like a badly behaving Blue Box, and when the input sensitivity pot is turned down anywhere past 11:00 I get oscillation.  At first, I thought it may have somethng to do with the 22k resistor from V+ that I used as a Q & D substitute for the 18k value I didn't have handy (one of the posted schems shows a 47k value in that position), but changing that to an 18k unit didn't improve anything.

Is my transistor choice to blame?

[alex frias]

One of the higher points of my interest about this little circuit and the Harmonic Percolator regards to the weirdness they show and the capacity of being more than a fuzz/distortion boxes.
In my own experience, a lot of character is directly linked to the transistors hfe's.

Specificaly in Bosstone case, I've found that the input and output caps play a big role, directly dealing with some kind of  low frequency selfoscilation tuning. Anyway, when I used the "traditional" cap values and both trannies hfe's around 150, I"ve got very "normal" behaviour and "nice" distortion sounds. Inserting a 47R resistor to the first tranny emiter to the ground aproximates it more to the overdriven amp world.

But I confess I was in love with the weirdness of these babes... Bosstone with a kind of SAG control rules, IMHO.

If interested, give a look:
http://www.youtube.com/watch?v=78XVvOXcecY

[Mark Hammer]

A very impressive demo.  Some of the octaving sounded very familiar although certainly more predictabe than what I was experiencing.

I gather that what I have to change is the 2N3906 for a lower hfe unit ( I have some but thought for some strange reason that maybe a higher hfe would "help" - clearly it didn't).

The sag control interests me.  Should I asume that this is simply a variable resistance in series with the supply voltage?  What range of resistances have you used?

I also find the "trumpeting" effect very appealing.  A tiny bit of attack delay (swell) added in and Pat Metheny, here we come!   How is that done?

[alex frias]

Thanks for the gently words!

For trumpeting and octaving we need to use the Q1 as on the original, with no resistance from emiter to the ground. As you said, it's just a pot inserted between the positive powering point and the old point it joined the circuit. It was not my idea, I just follow this sugestion from another guitar forum. They suggested 100K, I've used that, but maybe 50K could be fine...

So the caps must be changed too. Not to very high values, more important is the output one. I used 1uF for the input and 0.068uF for the output. This way, when I don't want the sweet weirdness, it stays as normal as it can be.

When I put down the powering, rising the resistance, the trumpets are achieved at next to maximun gain and the octave down when lower gain setings are used. You can do it by yourself with the guitar volume knob. At the video I changed volume, tone and pickup setings.

[Mark Hammer]

I think I will try 15k in series with a 50k pot and see where that takes me.  I currently have a .033uf unit on the output instead of the stock .022, although you are suggesting something even lower.  The .022+.1uf arrangement I have right now seems large enough. 

[nokaster]

very cool alex!!!!

which transistors did you use?
which hfe?

those are amazingly cool sounds from a bosstone.
can't get mine to do the octave down.
i've got the normal 22nF input cap + a 220nF that i can switch in parallel to the 22nF.
maybe i should change the 22nF at the output to a higher value?
or is the sag really needed for good octave results?

[aron]

Best demo I ever heard for the Boss Tone. Now I want to make another.... how many have I made over the years and what happened to them??

[sengo]

Mine does the same funky oscillation when you turn the gain down. If you place a lower hfe transistor in the Q1 slot it usually disappears. When I finally box mine up I'm planning on making Q1 switchable so I can still get that weirdness.

Nick

[Barcode80]

holy shit. that sounds amazing.

[Mark Hammer]

Mine does the same funky oscillation when you turn the gain down. If you place a lower hfe transistor in the Q1 slot it usually disappears. When I finally box mine up I'm planning on making Q1 switchable so I can still get that weirdness.

Nick

That is good to know.  Here I was thinking it was the 2nd (PNP) transistor that was the problem.

[alex frias]

I would like to thank everybody for the kind words and the patience to listen to the vid!

I started another thread some time ago when I posted the vid in the utub:   http://www.diystompboxes.com/smfforum/index.php?topic=70080.0

The trannies I used on the demo were 2N3565 and 2N4125, but the important thing is the hfe's: ~ 150

[alex frias]

Mr Hammer, I gave you a mistaken info: the input cap I used on the vid was 0.1uF, not 1uF, as I informed you. I even tested that cap value but it was too much low frequency content for the circuit operates with good results, IMHO.

Here a schem with the values i used:

[GREEN FUZ]

Mark, for what it`s worth, I`ve just measured the hfe`s of my boringly normal sounding bosstone and they are respectively:

Q1 2N2222 = 200
Q2 2N3906 = 195


I followed Dragonfly`s layout and all the component values are stock.

[Mark Hammer]

That's pretty much what I used on my existing one that "behaves".  I think I'll pull the 3565 and stick a 2222 in there instead.  Lord knows I have enough of them.

[Gus]

Another fun thread

I have not built a bosstone but looking at the schematic links in schematics I see something to check

R.G.s and the factory one show R6 a 18K.  Using the factory schematic

R6 18K is the emitter resistor of the emitter follower Q2 section AND that node is the supply voltage for the Q1 gain section and bias

So the total current for the circuit goes "through" R16 the 18K and then divides up at the node of R6,Q2E, R5,R4,C3.  The output voltage signal is generated from the current in R6

So if one has a scope and signal generator.  I would set the generator to sine and/or triangle 100mV peak to peak to start with say a 10K series(might not be needed if the input drive control is not turn to max).  Do the tests with the diode clippers in and out of circuit

try 300 hz then 600 then 1.2K
Adjust the input from 0 to 500 mV P to P
and
Look at the nodes at Q1 collector and Q2 emitter and R7 at max
Note when the waveforms have parts cut out.  note the Level and also frequency

[DougH]

That really sounds cool, Alex! I love the trumpeting effect!

I've never played with this circuit. I'm going to have to give it a try, there have been so many good things said about it.

[Mark Hammer]

Well, I swapped the 2N3565 I had in there for a 2N2222A with a measured hfe of around 140.  The bizarre mistracking effect seemed to go away, though I still get the oscillation problem when I turn the input pot below about halfway. 

As an aside, I discovered an error last night on the perfed circuit that was behaving so badly.  I thought I had wired in a switchable cap to ground from the input of the volume pot (in parallel to the diodes).  But between my desire to have a tiny footprint for the circuit board, and the almost inevitable mental rotation errors that occur when you improvise a layout on the spot and flip the board back and forth, I inadvertently soldered the connection to the emitter of Q2, such that I would switch in a cap that went from emitter to ground (i.e., my treble-cutting cap was on the wrong side of the output cap).

So, for those of you who thrill to the surprising misbehaviour of simply circuits, try that out as a "mod".  FWIW, I uses a .027uf cap.

[Barcode80]

FYI, i whipped up an unverifed layout for the bosstone based on your schem...

[alex frias]

Great! But I think I found a mistake in your layout:

[Headshot]

Holy Crap was that demo cool!   I've got to whip one of these up.