Electronic Bypass

[FunkyGibbon]

Hello,

I just thought I'd share my experiences on electronic bypass with you. There was a discussion in February on this, and there seemed to be some dissatisfaction that this method was a less than ideal compromise.

I used the 4053 CMOS bypass method from Laurier's website:

http://members.shaw.ca/roma/switching.html

I used the momentary switch version. This uses a 4011 flip flop to control the 4053. This circuit looks a little cumbersome just for bypassing, but if you rearrange the layout Laurier gives you can get it quite small (28 x 44mm). I initially used the components exactly from Laurier's design. It bypassed neatly and completely silently, but there was a considerable loss of treble frequencies in bypass mode.

I found that others on this forum had found the same thing. R.G. suggested changing the 100k resistors in Laurier's design to 1M for less treble loss, but the offset of this would be an audible pop.

I tried first 470k, and then 1M. I must say I am now VERY happy with the result of using the 1M resistors. By taking the pedal that I used this bypass on in and out of the chain, I am satisfied that I can no longer hear any treble loss. The other upside is that I get NO POPS or any kind of switching noise. It switches perfectly silently. I believe that R.G. was referring to the design with just the 4053, which used a latching SPST switch to control it. I suspect that the flip flop action of the 4011 in this version is somewhat ramped, thus overcoming popping problems.

I also removed the 2.2uF input and output caps. I have not heard any ill-effects yet, but my testing hasn't been extensive. This might have no audible effect, but might please purists who would prefer to have the least components possible in the bypass signal.

Please note if you do try this circuit that you must leave the 100k resistor that goes from pins 5 & 6 to pins 8 &9 of the 4011 as 100k. I initially changed it to 470k (owing to my limited electronics knowledge), and found the circuit had difficulty switching, and when it did, it made square-wave-wailing tones in effect mode!! Cool, but not very useful! Just change all the 100k resistors (6) that pull the pins of the 4053 to ground (if that's the right terminology??!!).

Overall I concede that this is not true bypass, and a little more work than using a 3PDT switch. However, I am very poor, so a few dollars saved per pedal will mean I can build more pedals!! It's no more effort than using a millenium bypass with a DPDT switch. It also allows you to use the momentary switch that may be in your piece-of-crap pedal that you never use, so that you can reuse that chassis, switch-and-all (that's what I did with this pedal - it was a Rocktek ODR-01). Also you can use the Mountain DS-412 momentary footswitches. These were the ones used on the ADA Midi Controller, and allow you to switch on your pedals with a smooth tap, instead of the metallic snap of a mechanical switch.

So, in conclusion, this method is not true bypass but, using the larger resistor values, SOUNDS exactly like it (so far as I can tell thus far), is cheap and, using momentary switches and the 4011, is convenient and pop-free!! Give it a go!!

Happy building!

[FunkyGibbon]

UPDATE:

Having now used the pedal with the electronic bypass through big amps and speakers at high volume, I still believe there is no audible tone loss, however, with the big bottom end that both the bass rig and the old Marshall guitar rig I used are capable of, a low, thuddy pop was audible, which was not audible at bedroom volume.

Can anyone with better electronics knowledge than I tell me if changing either the resistor or cap value, or both, on the 4011 section of this bypass will make the 4011 flip (or flop?!) slower, hence overcoming any pops? If so, could this then be used to allow even larger resistor values pulling the 4053 to ground, just in case there is some tone loss that is not obvious but that might make a subtle difference to the sound?

Thanks in advance.

[CS Jones]

Thanks for the write up. Good info.

Is the switching consistent? Not erratic or "buggy"?

I don't have the ability to read .pdf files right now so I can't double check with any data sheets right now. I have to go with a (very) poor memory.

I don't think the 4011 is a true flip flop. I think it's just a simple control gate. The "firing points" are different. Maybe you need to go with some kind of trigger or comparator to lock in the changeover points. This adds another circuit stage though to the switching which makes for even more work and expense, I know.


EDIT. My spelling needs work

[FunkyGibbon]

Thanks for the reply.

I have found the switching very consistent.

[bond]

hey mate, did you find a solution to your problem?

[no one ever]

what problem

[bond]

well, when the volume's up, there is quite an audible pop when using these circuits, i'm wondering if he found a solution, because i may be using a identical circuit for remote switching....

if RG reads this, is it possible to get PIC's for the asmop project to allow it to interface with more than 8 pedals? (i'd want about 20...)
they don't need to be available in any order, i'd just like patch's set up so i can hit 1, 2, then be in patch twelve with 3 or 4 effects on.

[bond]

mmm i found my pic programmer today ....