True Bypass switching: myths, pro's, cons, alternatives...

All frequent questions on switching: true or not true bypass, transistor-based or mechanical.

True Bypass switching: myths, pro's, cons, alternatives...

Postby modman » 19 Aug 2007, 00:37

In a different time, not so long ago, true bypass switching seems the standard. Well documented and archived on numerous forums and websites. But there no reason not to question it.

Now we see the Crowther Hot Cake and the Klon to deviate from blue 3pdt standard and I've heard some comments in this direction I felt like starting this thread. There was a time no stompbox was true bypass and that's called Vintage now..

just kicking the bucket... see what rolls out...
Last edited by modman on 23 Oct 2007, 23:43, edited 1 time in total.
"The whole point of diy is diy. It's not dsoiyathodtr - do some of it yourself and then have others do the rest" (paulc)
User avatar
modman
a d m i n
 
Posts: 4200
Joined: 19 Jun 2007, 17:57
Has thanked: 2669 times
Have thanks: 442 times

Postby soulsonic » 19 Aug 2007, 02:15

My personal opinion is that generally a "standard" true bypass is probably the best way to go. But...... I think if the overall circuit (and system in general) is designed with it in mind, a bypassing scheme as seen in the Klon or a Cornish system can work very well.
That being said; my weekend project is to convert a Behringer VP1 to true bypass..... this is a necessary operation because noise and crap from the LFO gets into the dry signal when it's bypassed.
User avatar
soulsonic
Old Solderhand
 
Posts: 3503
Joined: 27 Jun 2007, 04:38
Location: Ithaca, NY
Has thanked: 53 times
Have thanks: 245 times

Postby bajaman » 19 Aug 2007, 03:32

Here is something for you true bypass fans to try - connect 3 true bypass pedals together in a chain, then play your guitar through them, with them all set to bypass - OKAY.
NEXT, plug your guitar straight in to your amp (no pedals) :wink:
Well - i bet you heard the loss of tone :wink: :(

Okay know, if you have a KLON or Morley JD 1, or similar pedal with an TL072 op amp buffered bypass, put this first in line and you will hear no loss of tone :D

This is why smart manufacturers like Cornish, Finnegan, Ward et al. are using buffered rather than true bypass :wink:

Regarding "vintage" pedals such as the Dallas Arbiter fuzz face and Solasound (colorsound) Tone Benders etc., these circuits had very low input impedances by today's standards, and severely damped the guitar's pickups, even when bypassed because all those guys did was switch the output on or off, while the circuit input remained connected and thus loaded the guitar.

ALSO - I have never liked the Boss or Maxon / Ibanez input buffers. They are usually built around a bipolar emitter follower - many people vainly increase the 470k input resistor to 1M in the hopes of increasing the input impedance. This is sheer folly, because they are completely overlooking the very low impedance bass emitter junction that is effectively in parallel with the 470k resistor. One exception is those pedals with a jfet source follower at the input - the gate source junction is a very high impedance - Tech 21 use a 2SK 117 as an input buffer in their Classic Sans Amp pedal - also roland used it extensively in their early Jazz Chorus 120 and Cube 60 combos.
In my humble opinion, this is why these products sound so nice to my ears - I am a great fan of the 2SK117 and strongly urge others here to give it a try :wink:
Cheers
bajaman

For this message the author bajaman has received thanks:
davidmochen (26 Oct 2011, 12:42)
User avatar
bajaman
Old Solderhand
 
Posts: 3982
Joined: 26 Jun 2007, 22:18
Location: New Brighton, Christchurch, NZ
Has thanked: 281 times
Have thanks: 652 times

Postby bumblebee » 19 Aug 2007, 04:35

I agree, theres a lot of hype about switching around and so far i've found it to be just a sales gimmick in a lot of effects. Sure, theres a use for it and i use it in everything almost because its easy, but if i buy a new box and its non-TB and sounds fine in bypass i'll leave it non-TB.

I also notice the difference like ya said about plugging straight in to an amp.

I have a old 78 small stone and the bypass on that was awful,it wasn't too bad if the "color" switch was down but when it was up it ticked and made heaps of noise in bypass.

I put a 3PDT in it and it leaked even worse than before, it was doing my head in cause i couldn't work out how it could leak "phase" when bypassed, needles to say i grounded the input and it was fine.

I'll tell ya what has good non-TB....the SansAmpClassic, excellent bypass on that! And to be honest, i cant hear much, if any difference in quite a few non-TB effects.
User avatar
bumblebee
Cap Cooler
 
Posts: 591
Joined: 18 Aug 2007, 01:05
Location: Australia
Has thanked: 0 time
Have thanks: 4 times

Postby analogguru » 19 Aug 2007, 04:41

This is sheer folly, because they are completely overlooking the very low impedance base-emitter junction that is effectively in parallel with the 470k resistor.


As far as I remember it is the base-emitter junction plus the emitter resistance multiplied by ß (hfe) of the transistor what is in parallel to the 510k (470k) base resistor.

analogguru
There´s a sucker born every minute - and too many of them end up in the bootweak pedal biz.
analogguru
Old Solderhand
 
Posts: 3286
Joined: 26 Jun 2007, 14:58
Has thanked: 0 time
Have thanks: 110 times

Postby bajaman » 19 Aug 2007, 06:00

As far as I remember it is the base-emitter junction plus the emitter resistance multiplied by ß (hfe) of the transistor what is in parallel to the 510k (470k) base resistor

Maybe so - but it is going to be different in each half of the cycle and still way too low in impedance
I'll tell ya what has good non-TB....the SansAmpClassic, excellent bypass on that! And to be honest, i cant hear much, if any difference

Like I said - buffered bypass with a 2SK117 N channel Jfet - very nice transparent device.
bajaman
User avatar
bajaman
Old Solderhand
 
Posts: 3982
Joined: 26 Jun 2007, 22:18
Location: New Brighton, Christchurch, NZ
Has thanked: 281 times
Have thanks: 652 times

Postby analogguru » 19 Aug 2007, 07:46

Let´s agree first that a FET-Buffer has some benefits over a bipolar Buffer stage....no doubt

Maybe so - but it is going to be different in each half of the cycle and still way too low in impedance


This is something I don´t understand:
Assuming that we have a power-supply of 9V and that the base is biased at 4,5V we fil find at the emitter resistor a voltage of approx 3,9V. Assuming that the input signal is not bigger than 4Vss :!: (normally 100mVss) we have in the (most) positve cycle the situation that the transistor is more conducting leading to a "bias" at the base of 6,5V producing an emitter voltage of 5,9V. In the (most) negative cycle the "bias" at he base is reduced to 2,5V leading to an emitter voltage of 1,9V. In all cases the base-emitter junction is biased in the same direction....How this will produce a "different" impedance "in each half cycle" ?

Too low impedance:
Most of the input buffers are made with 2SC 1815GR or 2SC 1815BL or equivalent devices. The 2SC 1815GR has a ß of 200-400 and the 2SC 1815BL has a ß of 350-700.

The formula for the input-impedance of the transistor is:

Ri = ß x (Re + RE)

With an emitter resistor of 10k and the mentioned biasing we get an collector current of 390µA so Re is approx 25(Ohm)/0,39(mA). ß = 200

Therefore in the worst case the transistor impedance is
Ri = 200 x ([25/0,39] + 10000) = 200 x (64 + 10000) = 200 x 10064 = 2,012.820 Ohm or more than 2MOhm - with a beta of 500 it is more than 5MOhm.

So in the worst-case with an input resistor of 470k and a ß of only 200 we will get a total input impedance of 380kOhm loading the pickup. Much more than a FuzzFace, Rangemaster or Wah-Wah.

If this is not high enough you can use a "bootstrap"-circuit as shown and used for example in the univibe.

analogguru
There´s a sucker born every minute - and too many of them end up in the bootweak pedal biz.
analogguru
Old Solderhand
 
Posts: 3286
Joined: 26 Jun 2007, 14:58
Has thanked: 0 time
Have thanks: 110 times

Postby bumblebee » 19 Aug 2007, 14:14

bajaman wrote:
I'll tell ya what has good non-TB....the SansAmpClassic, excellent bypass on that! And to be honest, i cant hear much, if any difference

Like I said - buffered bypass with a 2SK117 N channel Jfet - very nice transparent device.
bajaman


i should read a little slower sometimes too, :roll:

bajaman wrote: - Tech 21 use a 2SK 117 as an input buffer in their Classic Sans Amp pedal
User avatar
bumblebee
Cap Cooler
 
Posts: 591
Joined: 18 Aug 2007, 01:05
Location: Australia
Has thanked: 0 time
Have thanks: 4 times

Postby CS Jones » 20 Aug 2007, 09:03

Maybe so - but it is going to be different in each half of the cycle and still way too low in impedance


I' m not quite getting this either.
If you keep the base at half the supply using a typical voltage divider with a cap at the node you'll have what *approximates* a ccs for a full, linear excursion on both swings. Both sides will feel an active pull, up and down; given the signal level we feed it and bandwidth we use. I can't see where current limiting becomes a problem here.

I'm not a buffer sniffer, btw. They are little more than current regulators to me. I don't consider them as tone controls.
CS Jones
 
Posts: 44
Joined: 05 Jul 2007, 07:31
Has thanked: 0 time
Have thanks: 0 time

Postby bajaman » 20 Aug 2007, 13:31

Sorry for the confusion - I merely meant that it is a bipolar device and one cannot ignore the influence of positive charge flow as well as negative electron flow - leakage, whereas the jfet is a unipolar device and does not suffer from this effect.
bajaman
User avatar
bajaman
Old Solderhand
 
Posts: 3982
Joined: 26 Jun 2007, 22:18
Location: New Brighton, Christchurch, NZ
Has thanked: 281 times
Have thanks: 652 times

Postby DougH » 20 Aug 2007, 21:49

IMO: I don't really care one way or another wrt true bypass or not. I have both on my pedalboard and it sounds fine. If you have long cable lengths, buffering somewhere in the chain is probably a good idea. Don't put buffers in front of fuzz faces, rangemasters, or other low Zin devices. Other than that, it's pretty simple to me.

Are there differences in sound between a string of true-bypass pedals in bypass and straight into the amp? Yes, probably. Is it enough to make me puke and demand that one way or another is the only "right way"? Absolutely not... I try to avoid the "vintage tone suck" style bypass (where either the input or output gets switched) but in all honesty, most of the time you can compensate for that somewhat with amp tone controls.

In most of these cases I find the differences subtle enough to not be worth arguing about. I suppose it makes good ad copy for some builders but like those that brag about what brand of components they use, I find it non-interesting... My setup can pretty much adapt to anything and still deliver a good sound.
DougH
Transistor Tuner
 
Posts: 1106
Joined: 18 Aug 2007, 05:53
Has thanked: 4 times
Have thanks: 21 times

Postby CS Jones » 21 Aug 2007, 17:59

Sorry for the confusion


No, no don't be b'man... I appreciate the info. I wouldn't have thought about it had you not brought that up. I thought what you said was interesting so it made me sit down for a bit and work through it just a little. That's one of the things I like about this site. You don't have to be 100% right all the time with this stuff. We can stray pretty far off the theory path and still find our way home without some ankle biting sheepdog incessantly directing us back on course. Most of what we do is experimental anyway and you can always do that with just a handful of tools. Pfft... this is stompbox building not medical research or life saving technology. We've all seen some pretty sharp guys disagree on even the most fundamental points. Throw in the fact that you can only listen to things through your own ears and all bets are off pretty much.

I use the blue switches to bypass only because I got a boatload of them a while back for cheap. 3USD per. It's just cheap and simple. At the front end of my board is a compressor then a state variable filter. The SVF is always on. That buffers my chain all the way through to the last pedal which is a Digitech Digidelay. This feeds into a Roland GR20 and then out to a stereo amp setup. One amp has a DI box to the mains. The whole journey is buffered. The only unbuffered portion would be from my non-Roland Ready guitar's pickups, through their vol/tone controls out the jack through the switch box and into the first pedal. The switch box let's me quick swap non-synth guitars. It's about 15 feet of cable and wire at the most from those guitar's outs to my first pedal in. I tried hanging a small buffer in a box from the jack out, through the 15 feet of wire. I made it switchable on/off. I couldn't tell any difference at all so it's sitting in my gig tool box. It's not much more than a novelty item. I'll pull it out on occasion to let someone demo.

The small boards I use are pretty much the same idea leaving out the Roland synth. 1 pedal in front is always on buffering the rest of the chain. Most, if not all, pedals are TB (for the same reason, viz. cheap) with the only unbuffered signal from guitar through 10 to 15 feet of low capacitance cable into the first pedal.
CS Jones
 
Posts: 44
Joined: 05 Jul 2007, 07:31
Has thanked: 0 time
Have thanks: 0 time

Postby Jim777 » 30 Aug 2007, 03:27

Hello fellas great site I've seen alot of good stuff on here. I think for true bypass it depends on your setup. Sometimes it's good sometimes bad. If you use something like a fuzzface you need to watch what you put in front of it or it won't interact with the guitar in the same way. Lots of other old timey effects have low input impedance and thats part of how they work. If you use alot of those type of effects you have to be careful where you put your buffered effects. I think idealy you would have to look at an individual setup to decide what was buffered and what was not. Probably an electronics engineer would look at it and go 'gasp that's all wrong'. A guitar player is never going to be worried about the 'electronic correctness' of a circuit as long as it sounds good to his ears. Probably the best way to choose a buffer is by the way it sounds. Don't get me wrong, I like knowing the theory and maths but with stompboxes it's almost moot. It's usefull only up to a point. Certain people come out with some very good sounding stuff with just some transistor sockets and a bunch of trimmers.
Jim777
 
Posts: 32
Joined: 20 Aug 2007, 03:21
Has thanked: 0 time
Have thanks: 0 time

Postby R.G. » 25 Oct 2007, 14:54

I do a regular column called "Tech Views" for Premier Guitar, and a couple of them have hit on true bypass versus other stuff. The bottom line is, as it should be, trust your ears.

A guitar needs a good high impedance load to avoid treble loss - unless what you WANT is treble loss, and there are some situations where you do. Like the song says, every hand's a winner and every hand's a loser.

With the exception of the original sounds of a Fuzz Face and a few other pedals, most guitarists vote for keeping the treble in, and that says do a good, high impedance through the effects, and do not load the guitar when the effect is not being used.

True bypass avoids loading while in bypass by mechanically disconnecting the effect input. Buffered bypass comes in two versions: a buffered input that stays connected while the incoming signal is switched to the rest of the chain, and a buffered input that PROVIDES the signal to the rest of the chain in bypass. This second version avoids loading by making the effect load high, all the time and never forcing the guitar to drive what's after the buffer.

The first form, where a buffered input remains on the signal line and the guitar signal is switched to the output jack, can cause its own form of tone sucking when there are many similar effects on the signal chain because the buffer loading is cumulative, and even a high impedance ten times in parallel gets much lower. The situation gets more complex on pedalboards with many different types of pedals and bypasses.

One thing that works nicely is to have a well-designed buffered bypass of the second form as the first effect in the chain. This keeps the guitar from being loaded down as it only ever drives one input. The low impedance output of this buffer then drives the rest of the chain, with input impedances and cable loading, without treble loss. The ultimate form of this is to put the buffer in or on the guitar. There is a commercial effect called "The Redeemer" that does just this. It's a high quality buffer put on or near the guitar that prevents the guitar from being loaded down by the cables to the first effect. It sounds very nice, I've tried it.

Once you have one buffer attached to the guitar as the first and only thing the guitar drives directly, the choices get less critical. The first buffer doesn't care much what it drives if it's well designed. After that first buffer, whether you have many paralleled buffer inputs or true bypass pedals doesn't bother the buffer much and doesn't bother your guitar signal at all. Putting many good buffers after and initial buffer only causes problems if the sum of their input noises add up to give you problems. I've seen that happen occasionally, but it's not a huge problem, just something to watch for.

As to the few effects that want a guitar impedance driving them directly to sound the way we expect them to sound: they can usually be faked into working properly with a resistor in front of them to add some source impedance back into the signal they're fed. In hard cases, you may want to put both some resistance and some inductance in series with the signal. This last can be very convincing, even in front of a picky Fuzz Face. There will always be certain cases where only the guitar into a certain pedal will do, but in a world where we seem to want full-loaded pedalboards, we owe it to ourselves to figure out how to make the pedals do what we want as easily as possible.
R.G.
Resistor Ronker
 
Posts: 339
Joined: 22 Sep 2007, 03:24
Has thanked: 0 time
Have thanks: 41 times

Postby DougH » 25 Oct 2007, 16:01

The formula for the input-impedance of the transistor is:

Ri = ß x (Re + RE)


This is true.

But one of the problems I see with bjt buffers as they are implemented in a lot of these circuits is the use of the 1M/1M resistor divider to bias the base. This may raise Zin but at the same time it starves the base of current and pulls the bias voltage down into the ~2v range. They get away with it because you usually find this as an input stage and with a typical 100mv-1v guitar pickup signal, the "misbias" has a negligible effect.

But it is poor design nonetheless (just use a jfet instead) and demonstrates a basic lack of understanding of electronic design. (This is spelled out really clearly in the early chapters of the Art of Electronics, for example.) And when I see this kind of stuff created by people "in the business" who should know better, it kind of irks me.
Last edited by DougH on 25 Oct 2007, 17:11, edited 1 time in total.
DougH
Transistor Tuner
 
Posts: 1106
Joined: 18 Aug 2007, 05:53
Has thanked: 4 times
Have thanks: 21 times

Postby R.G. » 25 Oct 2007, 16:41

Yep - Noiseless biasing is so much more adaptable as well as quieter, and at the cost of one more $0.02 resistor.

A good emitter follower will also use a current source load on the emitter - runs the input impedance even higher and eliminates one source of distortion in the emitter follower.

Buffers are really simple, even to do them right! 8-)
R.G.
Resistor Ronker
 
Posts: 339
Joined: 22 Sep 2007, 03:24
Has thanked: 0 time
Have thanks: 41 times

Postby bajaman » 25 Oct 2007, 21:02

Thanks RG and DougH
I'm a buffered man of the second type for sure :lol:
bajaman
User avatar
bajaman
Old Solderhand
 
Posts: 3982
Joined: 26 Jun 2007, 22:18
Location: New Brighton, Christchurch, NZ
Has thanked: 281 times
Have thanks: 652 times

Postby guiltyspark » 06 Nov 2007, 14:44

I have about 6 TB pedals in series on my board. I've been thinking about measuring the capacitance and resistance of the chain when off. This should tell me something, not sure what though. I'm sure there's some capacitance, I guess I'll know how much high end I'm losing.

Guiltyspark
guiltyspark
Solder Soldier
 
Posts: 198
Joined: 18 Aug 2007, 06:24
Has thanked: 2 times
Have thanks: 33 times

Postby solderboy » 07 Nov 2007, 10:54

Hi,

does it count, where in the FX Chain a Buffer is placed?

Yesterday i tried out the A/B comparisation by plugging the Guitar directly into the Amp and... wow.wow.wow... YES... better Signal !!!
But in my FX Chain are Buffers....

My FX Chain is as follows:

Guitar -> WahWah(TrueBypass) -> DIYOverdrive (TrueBypass) -> ZoomUltraFuzz (has Buffer(s)) -> Boss CE-3 Chorus (Buffer) -> Boutique Phaser MEK (Millenium Bypass) -> Amp

After the Zoom there was placed a RogerMayerClassicFuzz (DIY), but i didnt need it anymore, so it flow out of the Chain..
The Zoom seem to have quite good Buffers, because there is no hearable influence to the Signal...

But i think the Boss is sucking Signal ... I tried some changes
and throw out the Boss, than the Zoom and at least the Phaser..

The Tone only with the Wah and DIY Overdrive was than the same as it is with guitar directly into the Amp.. no Buffers... (but only few TB Effects)

makes it a difference, where a Buffer or good buffered Pedal is placed into the Chain??

Thanx

Solderboy
solderboy
 
Posts: 33
Joined: 04 Nov 2007, 13:09
Has thanked: 0 time
Have thanks: 0 time

Postby polarbearfx » 07 Nov 2007, 11:13

DUMB QUESTION ALERT!!!!

if you have a buffer in a circuit does this make everything after it in the signal chaning buffered? Or does this stop once you have another pedal after it? Lastly I heard cornish buffers are supposed to be amazing. I guess the klon is in the same league. They must sound good or else I would imagine TB would be easier for them.
polarbearfx
Resistor Ronker
 
Posts: 312
Joined: 27 Sep 2007, 12:14
Has thanked: 5 times
Have thanks: 4 times

Next

Return to Switching & Wiring

Who is online

Users browsing this forum: No registered users and 2 guests