Has anyone done a silicon Buzzaround?

[digi2t]

No, I'm not talking about the Buzzaround-alike, I mean an all silicon Buzzaround. Right now, I have this on my breadboard;



It sounds pretty good, but I'm pretty sure it could use some tweaking to get it closer to the germ version. I'm using the piggyback trick in the last stage to tone down the gain. The only thing is that it still has that silicon "edge" to it that I would like to tame. I could increase the B/C caps, but I'm wondering what more experienced eyes can recommend. The odd-ball resistor values are because I have trimmers there, that's what the read right now.

I'll try to get a clip out this weekend. Have to demo the germ Muff, and the Holmes Spectrum too... not enough hours in the day dog gonnit!

[jubal81]

Cool idea.
Any reason you stuck with PNP?

[digi2t]

Cool idea.
Any reason you stuck with PNP?

Because it was there. 

Seriously, no special reason, other than that I was trying to remain as faithful to the original as possible. Most certainly can be NPN though. Gus has fed me a few ideas too, so it looks like it will be on the breadboard for a while more. 

[duck_arse]

that Ge diode, should it stay or should it go [now]? is Q3 C open?

[Derringer]

when you adjust the sustain pot, that changes the DC bias on the base of the 2nd gain stage transistor right?
Are all settings (except for zero ohms to pos-ground which would be no sound I suppose) useable or is there a definite sweet spot or range?

[Tony Forestiere]

when you adjust the sustain pot, that changes the DC bias on the base of the 2nd gain stage transistor right?

I am gonna guess that the base junction of the second stage is biased by the 285K to supply, and the Sustain pot presents  more or less of the output of stage one to stage two.
(but what do I know?  )

[digi2t]

Since I have silicon transistors in there, the 15K that was originally between the balance pot wiper, and the Q3 collector, had to go. I had to use the 285K to the base to get it to start working. Not a deal breaker, but I know there's gonna be a price to pay somewhere to convert this to silicon.

that Ge diode, should it stay or should it go [now]? is Q3 C open?

Switching back and forth on the diode tells my ears that there is some form of clipping going on there, so I would keep it. It sounds a tad buzzier with it. Yes, Q3 collector is open. Q3/Q4 is a piggyback arrangement to bring the gain down.

when you adjust the sustain pot, that changes the DC bias on the base of the 2nd gain stage transistor right?
Are all settings (except for zero ohms to pos-ground which would be no sound I suppose) useable or is there a definite sweet spot or range?

The timbre pot is not really wide ranging tone-wise, but neither was the original. The real tone controls are the sustain and balance knobs. The timbre pot only adds a bit more top end..

[midwayfair]

If you remove the Ge diode, it should make it sound a little fatter, which may help with the edge. It absolutely adds clipping; I can hear a distinct difference even just flipping it around backwards.

You can also limit the gain just a hair and you'll get less of an edge -- try 220R in series with your 4u7 in the first stage.

Finally, you may want to add a 4M7 or 10M between the base and collector of Q3 to simulate some leakage. It won't have a big effect on the bias (it's already got positive bias from the 285K), but it will add a bit of negative feedback that's otherwise missing.

That's at least where I'd start experimenting.

[digi2t]

If you remove the Ge diode, it should make it sound a little fatter, which may help with the edge. It absolutely adds clipping; I can hear a distinct difference even just flipping it around backwards.

You can also limit the gain just a hair and you'll get less of an edge -- try 220R in series with your 4u7 in the first stage.

Finally, you may want to add a 4M7 or 10M between the base and collector of Q3 to simulate some leakage. It won't have a big effect on the bias (it's already got positive bias from the 285K), but it will add a bit of negative feedback that's otherwise missing.

That's at least where I'd start experimenting.

Jon,

I hadn't thought about the resistor in series with cap yet, and it so happens that it is a bit too hairy right now in this section. Just to be sure; the 4u7 below Q2, or before the sustain pot? Added to the list, as is the collector/base resistor.

I'll report back soon....

[Derringer]

when you adjust the sustain pot, that changes the DC bias on the base of the 2nd gain stage transistor right?

I am gonna guess that the base junction of the second stage is biased by the 285K to supply, and the Sustain pot presents  more or less of the output of stage one to stage two.
(but what do I know?  )

yes, the pot does vary how much of stage one's output is entering stage two

but since the pot is DC coupled to the 2nd stage, I imagine the pot position should also affect the DC bias on the bases of the piggybacked transistors
I'm just wondering if there's a particular base-bias point that sounds best. Then that point could be isolated, a more traditional voltage divider could be put in place and the sustain pot could then be AC coupled to the stage.


... unless the diode there helps to stabilize any bias swing the way it was originally designed (but it's reverse biased since there's negative voltage on the anode so only positive swings of the ac signal will be clipped?) just thinking out loud

Digi2t, have you tried it without the piggybacked transistors?
My experiments with piggybacking silicon never really got rid of the silicon sound.

And I like the idea of the feedback resistor to simulate leakage.

[joegagan]

And I like the idea of the feedback resistor to simulate leakage.

ha, i was diggin this thread last night.  first thought is always making that first set of trans into a mini FF. could make it low gain ( higher than 100k feedback r and even try changing the 4.7 u to 3.3? a larger input cap to entire circ would let the first stage distort in a more fluffy way.

[midwayfair]

If you remove the Ge diode, it should make it sound a little fatter, which may help with the edge. It absolutely adds clipping; I can hear a distinct difference even just flipping it around backwards.

You can also limit the gain just a hair and you'll get less of an edge -- try 220R in series with your 4u7 in the first stage.

Finally, you may want to add a 4M7 or 10M between the base and collector of Q3 to simulate some leakage. It won't have a big effect on the bias (it's already got positive bias from the 285K), but it will add a bit of negative feedback that's otherwise missing.

That's at least where I'd start experimenting.

Jon,

I hadn't thought about the resistor in series with cap yet, and it so happens that it is a bit too hairy right now in this section. Just to be sure; the 4u7 below Q2, or before the sustain pot? Added to the list, as is the collector/base resistor.

I'll report back soon....

The 4.7u hanging off the emitter of q2. That'll limit the gain without altering the sustain pot.

[duck_arse]

I thought the Ge diode in the orig was for temp compenstion for the following Ge dvice. as yr gone Si, it ?wouldn't be necessary? or ?it should be silicon?

is that -.85V on the open collector?

geeze, digit, open a can of burns worms, why don't you. [also: "frank burns eats worms ...."]

[midwayfair]

I thought the Ge diode in the orig was for temp compenstion f

That's its purpose, but it does affect the sound.

[kaycee]

IIRC, on Mictester's version he put a buffer on the output to get the full range of the tone control?

[digi2t]

IIRC, on Mictester's version he put a buffer on the output to get the full range of the tone control?

Yeah, but it still uses a Ge transistor. The purpose of this stupidity exercise is to go totally silicon, while trying to stay as close to the Buzzaround topology as possible.

Drawing on the ideas presented thus far, this is where I'm at right now;



The Meg range resistor on B and C of Q3 or Q4 did nothing to tone down the top end sizzle, but with a trimmer, I found at 120K, it was quite pleasing. The setup is similar to what's found in the GGG silicon Tonebender. I added a 0.047uF cap along side the diode, which tamed some really high frequencies, and further enhanced the buzz. The 100R limiting resistor really helped tone down the full on harshness too. Thanks for that one Jon!  

I've been doing a side-by-side shootout with my Burnski Buzzaroundski (Russian Ge equipped Buzzaround). and it's really, really close flat out. I had the wife do a blind taste test, and she said it sounded the same to her. The fuzz roar that comes out of this sucker flat out is unreal. Just brutal. The biggest difference is when you dial back the sustain, it simply gets less fuzzy, whereas the Ge version gates more. Also, it's much more "guitar volume user friendly" than the Ge version. Rolling the guitar volume back with the silicon cools down the fuzz to almost clean level. Like a very mild overdrive.

Can someone breadboard this and see if they hear what I hear? Probably nothing new here, but I think it sounds pretty awesome. Probably closer to Tonebender territory, but lots of fun.

EDIT: Recorded straight into a BR-600. Just a touch of reverb added.

http://www.soundclick.com/player/single_player.cfm?songid=13070336&q=hi&newref=1

[mac]

This is what I'd do, IMHO,

At the first stage I'd use only one 220p from B to C, or a bit higher.
That 63k can be a 68k for 5.0 @ C or 82k for 3.9v @ C.

I'd simplify the second stage a bit.
No q3, no 7k, no 120k.
Just one MPSA42 or something around 100-150 and a silicon diode.
And for testing I'd put a 1M pot instead of that 285k to tune to taste. Or you can use some negative feedback connecting on side of the 285k (or big pot) to the 10k wiper or after the 24k.
If the pot does not work as you would expect, (ie, below 5k there is no sound), you can change that 24k and/or the pot value.

mac

[digi2t]

Cool, thanks mac. I'll try that tonight. In any case, there's been some positive comments from the ilf folks about it, but they would prefer to see it NPN (for easier powering), so I guess I could swap the polarities at the same time I try your suggestions. You're spot on for the single 220p, I pulled the second one out, and it didn't make a lick of difference. Check on the 68K, I have a trimmer in ther now, and 5v is where it tends to emulate the original one the best.

Interesting take on the single transistor idea, I have a 1M trimmer in the now. There was some things that I didn't want to mess with, only for the sake of not getting too far from what the Buzzaround sports now, i.e. germanium diode, pot values, etc. Yes, I could change a pot value, as a last resort. The Ge diode I was hoping to keep, but what if I add a second diode in series? wouldn't that bring the voltage drop up? Then I could keep the Germanium vestige. I'll try it, hell, it's what makes this so much fun! 

So far, I'm liking the sound of it, so I think something good will come of this. Gus has also sent me some recommendations, including a sim. It's an even simpler set up, with only two transistors. I plan on testing that one on a clean slate though, after (if ever!) I'm done with this.

[mac]

Yes, I could change a pot value, as a last resort.

I saw germ schematics that use 5k, some 10k. My guess is that you just need to adjust the 24k if you want the pot to work in all the range.

Gus has also sent me some recommendations, including a sim. It's an even simpler set up, with only two transistors.

I did something like this in a simplified tonebender III, only two transistors. A MPSA13 darlington, or a 2N3904/5088/BC549C can do the job.

http://www.diystompboxes.com/smfforum/index.php?topic=84315.20

(The sound clip I recorded is horrible, but you can breadboard it in seconds and hear it for yourself )

mac

[thehallofshields]

I'm very glad people are still working on this.

The general idea out there is that Tonebenders can't be replicated with Silicon Transistors. I haven't succeeded in making a good one yet, but I'm glad people haven't given up.