Is this true bypass?

[SuperGeo]

hello

is this really true bypass? Those J-fets remind me Boss pedals and I believe they are not true bypass.

http://www.diyitalia.com/index/schematic/Guitar%20FX/FET%20True%20Bypass.gif

[Unbeliever]

No. True-bypass to me = wire only (when bypassed).

[NoFi]

If i'm correct, the bypassed signal goes through two caps (no values on the schemo), and a switching transistor (type not mentionned).
It's different than the usual boss bypass, because in most boss pedals, in bypass mode, the signal still goes through two transistor buffers.
I don't think i would call it true bypass, but it may well be very transparent.
Would the switching transistor really affect the sound ?

[bioroids]

That system can't be called true bypass in any sense of the word. I think it's supposed to have input and output buffers, but are not shown on the schem.

Luck

Miguel

[SuperGeo]

thanks for the replies

That system can't be called true bypass in any sense of the word. I think it's supposed to have input and output buffers, but are not shown on the schem.

what would buffer interfere in the bypass mode? It wouldn't be better to have not the buffers so I'd be able to put it before an fuzz face for example?

If i'm correct, the bypassed signal goes through two caps (no values on the schemo), and a switching transistor (type not mentionned).
It's different than the usual boss bypass, because in most boss pedals, in bypass mode, the signal still goes through two transistor buffers.
I don't think i would call it true bypass, but it may well be very transparent.
Would the switching transistor really affect the sound ?

That's what I'm looking for, just a way that don't suck my tone and be free of clicks.

[bioroids]

You have three 470k resistors in paralel as input impedance, that's about 150k, and will suck a lot of tone. That's why you need a buffer.

In my opinion, the worst part of electronic bypass is the distortion produced by the switching FETs. The buffers can be "transparent" if implemented right, but I'm don't think the fet bypass can.

Luck

Miguel

[Dave Eason]

True bypass isn't really a great thing; electronic switching is better when the bypassed effect is pretty near what went in.  I thought of sticking TL071 buffers infront of the DPDT switch; technically not TRUE bypass.. but when the effect is bypassed, the signal is buffered.  You cold even stick tiny surface mount, hi-fi op amp buffers in jack plugs, to buffer the signal in patch cords.. if you were a true tone maniac.  Pete cornish has some great stuff on it

http://www.petecornish.co.uk/

[The Tone God]

I'll see your Pete and raise you a Jack.

http://www.muzique.com/lab/truebypass.htm

Andrew

[Unbeliever]

True bypass isn't really a great thing; electronic switching is better when the bypassed effect is pretty near what went in.

Agreed, but it's easier to sell something with true-bypass to guitarists.

[Dave Eason]

yep, and it's well frustrating! people like dave gilmour and brian may go to pete cornish to get around the problems of true bypass; the player into ultimate tone looks for better alternatives.

[Mark Hammer]

People want true bypass for a number of things.  Primarily it serves as a replacement for the old fashioned way of switching using SPDT switches where only the output was switched but the circuit input always stayed hardwired to the input jack.  In many instances that always-connected circuit led to loading of the guitar.  If you had 2 or 3 such pedals in a row, then all their loading was in parallel, and your tone disqppeared before your very ears.  A "true" bypass system would assure that all those input terminating resistors would not inadvertently end up in parallel because they were separated from the audio path when you stomped on the switch.

Of course, if the guitar went into a buffer stage, and came out the other side, only to go into the buffer stage of another pedal, then the two inputs, even if they were never ever removed from the audio path would not be hanging off the signal in parallel as occurred in the traditional "vintage" pedal.  If the input capacitors to those buffers were not wisely chosen, or if the transistors were not wisely chosen, then you *might* lose a bit of bass with 3 or 4 plugged in series, and you might have some audible hiss.  Completely straight wire true bypass *could* eliminate those issues, but on a one-off basis, tone loss or noise acquisition should be pretty minimal from that lonely little buffer stage.

Which brings us to the more  pressing question of whether a FET-based or any electronic switching system could, in any sense, be called true bypass.  If one defines "true bypass" strictly as staright wire, then obviously they aren't.  If one defines true bypass as any arrangement which permits the disabling of an effect without hampering the unaffected sound, then they are.  This assumes, of course, that there is no audible leakage of effect into the clean output (as some folks have complained about the Boss SD-1's).

[wampcat1]

I don't know if there really is a definate answer...the term "true bypass" really has no concrete definition as mark H said above.
***A.D.D note: Wouldn't it be funny if Mark's middle name started with a "C"? Then, we could all call him MC Hammer. and under his screen name, he could put "can't touch this!" haah!!!






Yeah, I know..I'm corny. 

Anyways...My thoughts are this. A "True" bypass should be mechanical, and hardwire only. A virtual true bypass should be a transparent, highly effective bypass.