extending millenium 2 bypass

[cpm]

so, adding a second mosfet you can have two alternating LEDs, for both ON and OFF positions of the switch. It's useful for those 3 legged red/green LEDs, for example.




Another one would be used to mute the audio path when the effect is off. Some high gain pedals tends to oscillate and leak into the bypassed signal when its input is not grounded. In this case a DPDT with mill byp must be discarded and use a 3PDT instead.
So, this knid of solve the issue, showing the first stage from a big muff:



this seems to work fine, but the point where audio is shunt to ground must be above above 0v, otherwise the mosfet body diode would clip when the effect is on.


what do yo think? any drawbacks on these?
the main point is avoiding the need of a 3PDT in those situations.

[cpm]

no love for DPDTs here 

[WhenBoredomPeaks]

no love for DPDTs here 

I would drop in a question related to DPDT-s:

Can you use Millenium bypass and input grounding with DPDT-s?

I guess it could be easy, you just have to connect two wires to the same leg of the switch  but i don't know how and where.

[R.G.]

Thinking about extending the Millenium to other functions was the line of thinking that led to the Millenium Extensions and the Millenium-C. the Millenium C gets the switch signal out of the analog realm into digital, and from there it can do anything that digital is good for.

See http://geofex.com/Article_Folders/Mill2extn/mil2plus.htm and http://geofex.com/Article_Folders/Millenium/The%20Next%20Millenium.pdf

The reason I went with a CMOS logic circuit instead of more MOSFET devices was price. A CMOS logic chip costs (or did at the time) about the same as one discrete MOSFET transistor. So in my mind, it was more cost effective to go with the chip as soon as you had to use a second MOSFET.

Good work Carlos! Keep on digging!

[earthtonesaudio]

Cool stuff!

[Auke Haarsma]

Nice, bookmarked!

[pqt_bach]

I don't think this should be in a new topic - as my question is super-related

Could one use this same Mosfet-as-shunt on the OUTPUT as well in order to cure the popping noise created when two different potentials are shorted?

Cheers

[R.G.]

Could one use this same Mosfet-as-shunt on the OUTPUT as well in order to cure the popping noise created when two different potentials are shorted?

Somewhere between maybe and probably not.

Switching between two different DC potentials is always going to pop. All you can do is change how fast the transition is. If you slow it down enough, the transition is so slow that it's below either human hearing, the bass response of the speakers, or the bass response of the circuit to reproduce. LDRs are good for not producing pops because they are inherently both slow switching and soft switching, so the sudden transition is a slow, sloppy process - electronically speaking  .

JFETs are good for switching as used by Boss and Ibanez because they can be slowed down by those R-C networks on their gate to any degree you want.

MOSFETs are a problem. If you could get MOSFETs without a substrate diode, they would be better for this. But you pretty much can't. So you're stuck with the internal diode if you use a MOSFET. There are ways around this, but it gets complicated fast. The internal diode either allows big signals through if you use the MOSFET in series, or clips big signals if you use the MOSFET in shunt. Since the output of a pedal is very often a large signal - more than a diode drop - it's especially a problem on pedal outputs.

There is an ideal device for signal muting like this. It's the LED/Photo-FET module, the H11F1/F2F3 series. LED on, about 200 ohms. LED off, as near infinity as a FET can get. They're just expensive.

The real cure for popping on outputs is to not let there be two different potentials to switch between. That takes capacitors and resistors, and is much cheaper than FETs.

[pqt_bach]

RG - that was a wonderful read - thank you.

Now, I have built a tube screamer pedal that has 3pdt true bypass with pull down resistors and no LED indicator and yet it pops... Tried different switches and the problem is still there. I have used the well known and used commercial PCB and all the voltages and connections are just fine. When using the pedal with the Volume pot set high it pops (especially when used with other pedals in series - both DIY and commercial). I know that there isn't any DC on that out put and it's not the lack of pull down resistors or Led current... So - I'm a bit baffled 

Could AC differences cause that pop?

[R.G.]

Now, I have built a tube screamer pedal that has 3pdt true bypass with pull down resistors and no LED indicator and yet it pops... Tried different switches and the problem is still there. I have used the well known and used commercial PCB and all the voltages and connections are just fine. When using the pedal with the Volume pot set high it pops (especially when used with other pedals in series - both DIY and commercial). I know that there isn't any DC on that out put and it's not the lack of pull down resistors or Led current... So - I'm a bit baffled 

Could AC differences cause that pop?

Yes. The sudden onset of signal from a mechanical switch can cause popping on AC signals. This is a phenomena known well to organ builders who worry about the  start of a note. In some organs, the sudden step is filtered and used for "chiff", a simulation of the sound of air starting into pipes.

You have found (one of) the Achilles heel(s) of true bypass. Mechanical switches cause conduction instantly. If there is signal on the wires, the connection causes the *instant* diversion between one signal and the other. Unless the signal on both wires (i.e. input and output of the effect) are at nearly zero the instant when the switch transfers, there is a sudden change in signal level. This may be between unnoticeable and really, really bad depending on how much amplification follows the switch. The only absolutely certain way to get rid of this is to use a soft switch, like the Boss and/or Ibanez systems, or an LDR, or some other way to fade between the signals over a time slow enough so that the change is below audio; one other way is a "low impedance" mute, the temporary connection of a low impedance, maybe 1K-10K during the switch make interval. Of course that's impossible with only mechanical switching.

The bigger the following gain, the worse the transient may be. The higher the following load impedance is, the worse the transient is.

It's there, and how bad it is depends on the specifics of the signal and what drives and follows the pedal.

[pqt_bach]

All of these sound very interesting to try out. I guess I would start with the JFET and LEDs - It's bread boarding time for me!

Thank you for a great reply, R.G.