True bypass switching using Boss flip flop circuit?

[Electron Tornado]

Has anyone used a Boss type flip flop circuit for true bypass switching? Is it even possible, or are the input and output buffers in pedals like the DS-1, for example, needed to use a flip flop?

The key to answering the question probably lies in understanding what requirements the FETs have in order to be used as switches. I plenty of references that explain the flip flop, but none that really give an explanation of using FETs as switches. Does anyone have a good reference for that?


Thank you.

[R.G.]

True bypass is not possible with JFETs.

True bypass IS possible with the Boss flipflop - you just have the output of the 'flop run a relay.

[Electron Tornado]

R.G., thank you very much for your reply, it will save me from heading down a blind alley. If I use a relay with a flip flop, I'm guessing that using pulldown resistors will help keep it from popping. Correct?

I also have a copy of the article "Bypassing and  Switching with the CD4053 CMOS Analog MUX"          http://www.geofex.com/Article_Folders/cd4053/cd4053.htm  .  Are the circuits described in the article quieter than a flip flop with a relay, about the same, or is there something they need to prevent popping when switching the effect?

Thanks again.

[R.G.]

Relays and CMOS switches pop for different reasons. Relays pop for the same reasons hard-metal contacts pop, plus the capacitively coupled coil voltage.

CMOS switches pop if they switch between two DC levels (not the CMOS' fault) or if they are not biased near the middle of their supply, or if they are driven too fast.

You'll also want to read about audio relays, there's an article on that, as well as how to drive relays quietly, there's an article for that.

ALL bypass switching, by whatever method, can pop if you get it wrong. You need to know the details of the method you're using and get that one right.

[Electron Tornado]

I read the article "Relays for Switching Audio Signals", looked at some relay data sheets and have a question. The article mentions using shielded relays to avoid coil voltage spikes being coupled to the signal. The datasheets I looked at did not mention shielding, per se, nor was it listed in the search filters on a couple of web sites I looked at.

Is being shielded something that's listed explicitly, or is it understood to be part of either the FCC Part 68 compliance, or one of the other standards such as CECC or IEC 60950? This being a hobby, I'm not familiar with the FCC Part 68 or any of those standards.

[Mark Hammer]

Let's turn this on its head a bit, shall we?

Some folks have no qualms about using input and/or output buffers and FETs for switching.  But what they REALLY like is the certainty of the CLICK when they step on a stompswitch.  In other words, what they like/seek from so-called true bypass is the tactile feedback, and if there are any electronic benefits accompanying that, well that's cool.

In fact, companies have used a standard stompswitch as a means of actuating switching FETs.  Take a look at the schematic (pg 4) of the venerable Boss BF-1:  http://hammer.ampage.org/files/BOSS_BF-1.pdf

You will note that a SPDT (well, half of a DPDT, actually; see pg 3) is used to turn a pair of FETs on and off.  It's simply a question applying the supply voltage to, or grounding, the gate of one or more FETs.  Were one interested in having complementary sets of FETs (these ones turn on whenever those turn off), it would be as simple as simply wiring up a set of FETs the same way as shown but lugs on the second set of contacts on the stomp switch would be wired opposite (i.e., the V+ lug for one half the switch would be where the Gnd lug is for the other set of contacts).

Normally, the flip-flop in the Boss and similar circuits is used to permit a momentary to behave as if it were a latching switch by feeding a steady voltage to the gates of some FETs.  It is always the user's choice to locate the stability in the actuating switch itself by using a latching switch.  That latching switch could be a footswitch or a toggle, or even a slide switch.

Works the other way too.  If there was something you wanted to switch that would normally require more poles/contacts than you can typically get at reasonable cost in a reasonable sized toggle package, there's no real reason why you could not use a Boss-style flip-flop and a momentary chassis-mounted pushbutton like these to accomplish that switching.

[Electron Tornado]

Mark,

Thanks for the info.

My reason for starting this thread is that I built a simple overdrive circuit around a 386 op amp. I gave myself the challenge of fitting the circuit into a spare BF-2 enclosure I have, making it true bypass, and using the original momentary switch from the BF-2. So, I need to learn about switching methods to do that.

The result is that I'm getting to learn a lot. 

[sevenisthenumber]

can someone help me make a blues driver true bypass. Ive seen posts were the sd-1 and ds-1 were made true bypass by drilling a hole for a 3pdt. i just need to know how to get it to stay on all the time and how to wire it up.

[Barcode80]

can someone help me make a blues driver true bypass. Ive seen posts were the sd-1 and ds-1 were made true bypass by drilling a hole for a 3pdt. i just need to know how to get it to stay on all the time and how to wire it up.

all boss pedals have the exact same switching mechanism. if you do a search on "boss" and "true bypass" together, you will find a million threads on this subject.