4 simple, unrelated questions

[Ell]

1. If I am to use LEDs instead of diodes in a Distortion +, what kind of effect will this have on the sound and do I wire them up with resistors, or not?

2. On a Ruby amp, I have added an on/off switch which works using an SPST switch. How can I add an LED indicator as well?

3. If you link up two capacitors, what effect does this have to the joint value? I believe with resistors if you put two together, it just adds them. What does it do with capacitors?

4. Does anyone know anywhere in the UK where I can get Davies #1510 replica knobs in Yellow?

Thanks


(EDIT: Sorry, I don't know if I'm allowed to post pictures from the layout gallery here so I won't, but doesn't anyone know if Andrew Carrell's distortion + is verified?)

[BAARON]

Using LEDs instead of silicon diodes will result in a much louder pedal with smoother clipping.  (Silicon diodes clip at about 0.6-0.7 volts and they clip hard, whereas tinted LEDs clip at about 1.5-1.8 volts and they clip "soft."  Crystal clear LEDs will often clip at even higher voltages.)  You do not need to add any extra resistors to the circuit: the 10k resistor after the electrolytic coupling cap (on the output of the op-amp) is already doing that job.

Ruby: Your on/off switch probably turns the POWER to the effect on or off, so you don't need a switch for your LED: just wire the LED and a resistor in series, and put them on the board's power lines, because the power on the board is already being controlled by the switch!

Capacitors: ...are basically the opposite of resistors.  If you put them in parallel, they add like resistors in series.  If you put them in series, the value falls like resistors in series.  http://www.allaboutcircuits.com/vol_1/chpt_13/4.html

Knobs IN the UK?  Beats me, but you can order lots of knobs from Smallbear and have them shipped to you!  http://www.smallbearelec.com/Detail.bok?no=610

[Andi]

Banzai do yellow 1510 copy knobs too.

[ianmgull]

Ruby: Your on/off switch probably turns the POWER to the effect on or off, so you don't need a switch for your LED: just wire the LED and a resistor in series, and put them on the board's power lines, because the power on the board is already being controlled by the switch!

Correct me if I'm wrong but wouldn't putting an LED in series with the power supply cause a significant voltage drop? I don't know much about the Ruby but unless I'm misunderstanding you it sounds like the best way would just be to use a DPDT to keep the LED out of the power circuit.

[Andi]

It would, but I think he's suggesting an LED and resistor in series, which would then go between the power line and ground. Thus when the switch is closed and power fed to the circuit the LED would light.

[Ell]

Originally my Ruby had an LED in series, straight after the SPST switch with a resistor. The LED worked when I turned on the amp, but the rest of the amp didn't. When I desoldered the LED and had the SPST straight before the circuit, everything worked.

I've actually been buying my Davies 1510 copies from Banzai, it's just that the shipping is expensive and I'd prefer to start buying them from the UK. However, I will just continue using Banzai then.

So if I were to put two DPDT on-on-on switches with 3 different types of diodes on each to the distortion +, would there be any point in having 1N914's, Ultrabright 3mm leds and then 3mm standard leds? Or, would the Ultrabright leds and the standards just sound very similar?

Thanks for the responses!

[Mark Hammer]

This is why batteries are generally connected in such a way that one "turns on the power" by connecting the battery to ground via a stereo input jack.  This allows you to connect +9v to a status-indicator subcircuit, the effect itself, etc., and not have any current flowing until the black lead to the battery goes to ground.

would the Ultrabright leds and the standards just sound very similar?

Yes.  I suppose there are going to be visible differences on a scope, but the audible differences will be negligible.  The biggest impact of LEDs will be simply in the raising of the clipping threshold to over 1.5V for each half-cycle.  Note that this is a 3V swing, and that boosting the signal enough that you'd still be over that critical level even after the first 10msec of the attack peak, means that you'd likely be applying enough boost that you'd be inducing clipping simply by virtue of reaching the limits of what the chip can do with a 9V supply.  Only some of what you hear is the LEDs themselves.  Another portion would be the chip and its headroom limitations.

If you really want to hear more of what the LED itself delivers, you should probably consider a charge pump chip to kick the supply voltage up a bit ( http://www.geofex.com/circuits/+9_to_33.htm )...within sensible limits, of course.  This way, you could have a signal that was 8v p-p or more for enough of its lifespan that you'd hear the effect of the LED.  Keep in mind that the peak on a note only lasts for a brief period, and quckly subsides after that.  In order for you to hear any clipping from whatever you use, the signal has to remain above threshold long enough.  You can achieve that by compressing or boosting the signal first, by setting the gain high in the distortion circuit itself, or by setting the clipping threshold lower (via Ge diodes).