"Softening" the clipping on a Buzzaround

[MordechaiBenZev]

I'm building a Burns Buzzaround clone, and I'd like the diode before Q3 to clip just a **touch** more softly, for a just a little bit smoother a sound.  I remember reading that inserting a low value resistor between the diode and GND can help with this -- but the stuff I've read relates other circuits, and the values suggested were 10R-47R.

I still would like the effect to sound authentic, so I only want to take a very, very slight amount of bite off of what the diode is doing.  Can anybody suggest a resistor value that would work best here? (I don't have access to a breadboard right now, otherwise I'd experiment on my own.)

[Rob Strand]

The other way to approach it is with filtering.  Cap across where the diode is maybe 470p to 1n.   Small caps across the BC junctions maybe 22pF to 47pF.    You will soon work out the value by experiment.

[pacealot]

Please correct me if I'm wrong, but my understanding is that the diode in the Buzzaround functions not as a clipping device, but as a temperature/leakage stabiliser for Q3. Adding resistance* there might defeat that protection.

Greater minds will have better suggestions as to where in the circuit to target to affect the clipping character, but I'd probably start with either the bias network on Q3, including the "balance" pot, or else adding a limiting resistor after the sustain pot (or perhaps tweaking the gain of the Q1/Q2 Darlington pair at either collector or emitter).

{* — edit to remove capacitance, as I characteristically didn't think through the DC path (or lack thereof) there — thank Rob for pointing that out}

[Rob Strand]

Please correct me if I'm wrong, but my understanding is that the diode in the Buzzaround functions not as a clipping device, but as a temperature/leakage stabiliser for Q3. Adding resistance and/or capacitance there might defeat that protection.

I saw the diode a clipping in the opposite direction as the BE junction making the clipping more symmetrical and resetting the 4.7uF cap before it.   The signal out of the first stage is strong so it will clip the diode and junction.

The pot before the diode/transistor will act like a BE resistor and that will swamp most of the leakage.  The diode might help temperature stabilization.  I haven't thought about that.  You would need to do some tests and it the results will depend on the specifics of the diode leakage and transistor leakage - if the diode is doing something it's very easy to get large variations in results.

Adding a cap won't affect leakage since it doesn't pass DC (and cap leakage is very small).

[idy]

Looks like it wold only clip if signal went *above* 9v, because it's cathode is going to positive ground. Backwards, it leaks, it is the biasing arrangement, yes temperature sensitive.

[idy]

And welcome to the forum!
Generally softer clipping is not what one builds a buzzaround for. It has a tone control, and two other knobs, and the guitar has a volume knob, and a tone control.

Articles about diodes as clippers are about something else....

[MordechaiBenZev]

Looks like it wold only clip if signal went *above* 9v, because it's cathode is going to positive ground. Backwards, it leaks, it is the biasing arrangement, yes temperature sensitive.

I'm glad you brought this up.  In a previous build that was essentially stock, I socketed the diode and placed it both in the stock position and then with the anode to ground, and it imparted a slightly smoother characteristic that was quite audibly distinct from the stock configuration -- which is buzzier and harder.  I would like to find a sort of happy medium between the two...leaning more towards the stock configuration, but with a smidge of the smoother character dialed in.

Maybe a different Ge diode would help.  I was using a typical 1N34A with a forward voltage of about .3V.  I have some Russian Ge's with a higher forward voltage of about .45V -- so presumably, they'd clip a little less dramatically...right?

[idy]

In stock circuit, the forward voltage never comes into play, only leakage.

Reversing it your are biasing to 9v minus the diode drop...if you like it go for it. Try other diodes, you are creating a different circuit.... Without the possible temperature compensation of the original.

So it may sound great.... but only in your man cave with its year round 65F temperature, and may sputter and splat when exposed to the sun. Experiment. Knock yourself out. (not literally.)

[iainpunk]

i don't think the buzzaround is designed to be smooth or soft, but more like the famous Japanese fuzzes, bright, harsh, where sustain was an afterthought.

if you want a bit more smoothness, the transistor needs bias. the transistor is currently un-biassed, or atleast biased near cutoff. putting some current into the base would place it more towards normal function, and thus a more conventional tone.
i would place a 470k resistor between the base and the collector of the transistor.

cheers

[MordechaiBenZev]

i don't think the buzzaround is designed to be smooth or soft, but more like the famous Japanese fuzzes, bright, harsh, where sustain was an afterthought.

if you want a bit more smoothness, the transistor needs bias. the transistor is currently un-biassed, or atleast biased near cutoff. putting some current into the base would place it more towards normal function, and thus a more conventional tone.
i would place a 470k resistor between the base and the collector of the transistor.

cheers

That's a great idea.  It reminds me of the bias adjustment mod in the Fulltone Soulbender.  I'll give it a try, thanks again.

[Steben]

All tonebender mkIII style fuzzes actually are the lesser harsh fuzzes around.

[iainpunk]

All tonebender mkIII style fuzzes actually are the lesser harsh fuzzes around.

if the transistors in use are leaky enough, yes really quite smooth, but if they don't leak enough, they can be gated and harsh. the only buzzaround i had the pleasure to play was a clone which was a little bit gated, and started to really gate if you turned down the guitar volume. it was done with Ge transistors, but not leaky enough. to simulate the leakyness, i suggest that 470k resistor between base and collector. also, more leakage is more smooth, as its closer to the softer ''saturation'' side of clipping, instead of the ''cutoff'' side which is often quite a bit harsher.

cheers

[Rob Strand]

if the transistors in use are leaky enough, yes really quite smooth, but if they don't leak enough, they can be gated and harsh.

There's no bias resistors on that circuit so leakage is the only source of bias.  Without leakage the transistor is completely cut-off and no doubt will sound harsher.