where to put buffer and preamp in a chain

[bent]

i have 7 pedal
and wish to build a buffer and preamp,
but where in the chain should they be put....

my first choice: buffer-pedal-preamp 
or
preamp-pedal-buffer
or
buffer-preamp-pedal
or
suggestion

is it good....?
bent

[markm]

I don't think the buffer really matters but I read somewhere (probably here!  ) that the buffer is better as first in the chain however, I can't be certain on that.
The preamp is a different story, what do you want the pre-amp to do?

[bent]

i read somewhere (me too probably here  ) that when you got on stage, the sound technician will love if your sound is preamp....

bent

[seanm]

Preamps are also buffers, so keep that in mind.

Where you put a buffer depends on what you want the buffer for, and what other pedals you have.

For example many fuzz pedals need to be before all buffers.

With a passive guitar, you put a buffer with a high input impedance first in your chain if the pedal has a low impednace input. Otherwise, almost all pedals have an input buffer and a second one is overkill.

You put the preamp before the pedal if you want to boost the signal going into the pedal. You put the preamp after if you need to add gain. And it doesn't matter where you put the preamp if it is just a booster and will be used with the pedal off.

[markm]

Preamps are also buffers, so keep that in mind.

I think he maybe terming a booster as a preamp.....not sure.
What is your use of the preamp??

[seanm]

I consider a booster as a buffer with gain. They may colour your tone more than a true buffer pedal should but usually they can be used as a buffer when set to unity gain.

I consider a preamp as a booster with EQ. But preamps will still have an input buffer stage, or an input buffer with gain.

A buffer is used to isolate parts of a circuit. A common use for a buffer in stompboxes is to provide a high impedance input. Another use is to provide a low impedance output. My blender uses buffers to prevent unwanted feedback. I have also used buffers on a tuner out so that you can connect and disconnect the tuner while the preamp is running with no noise.

If you want, I could walk through a simple preamp and describe all the buffers in it.

[markm]

If you want, I could walk through a simple preamp and describe all the buffers in it.

Sure 

[bent]

If you want, I could walk through a simple preamp and describe all the buffers in it.

cool 

[markm]

Hey bent,
What type of preamp are you using??

[bent]

Hey bent,
What type of preamp are you using??

i'm going to build the preamp of http://www.till.com/articles/GuitarPreamp/
with maybe the mod of this page  http://www.diyguitarist.com/Guitars/FET-CompactPreamp.htm  (at the bottom page)

bent

[seanm]

Ok, here is a simple preamp I designed. It works, but was not "optimized" since I switched to a different design (http://seanm.ca/stomp/preamp.html) It does not follow my definition of a preamp since there is no EQ. I consider this a preamp because it is meant to be connected to a power amp. It can provide 20V p-p of clean output.



I will number the transistors Q1 through Q5 going left to right.

Stage 1 is Q1. This is an input buffer. It provides a high impedance input. I play passive basses and they want to see a high impedance load.

Stage 2 is Q2 and Q3. This is a gain stage. Q2 provides gain. Q2 wants to see a high impedance load for maximum output. But the third stage is low impedance (100K || 15K). So Q3 is a buffer that provides a high impedance to Q2. Basically it buffers or isolates Q2 from the low impedance of stage 3.

Note that Q3 could be designed out, but this is not a commercial product and one extra transistor and resistor will not break the bank. And it makes the design so much easier since I can treat each stage in isolation.

Stage 3 is Q4. This is the second gain stage.

Stage 4 is Q5. The power amp I was using had a very low 10k input impedance. The output impedance from stage 3 was on the order of 4k. This was higher than I like. I generally use the 10x rule. You want the input impedance to be at least 10x the output. So Q5 is an output buffer that reduces the output impedance to 16 ohms. Much better!

So this preamp actually has more buffers than "amps".

[bent]

thank's for the info, 
for my case i'm going to try to find a "preamp for dummies"  , cause i was lost in the explanation, i'm far away of being a technician, so i could'nt follow....

bent

[markm]

Yes indeed seanm, very nice.
Impressive indeed. 
I think this may interest you bent;



There's a perf version and the PNP is in my gallery too.

[seanm]

Hey bent,
What type of preamp are you using??

i'm going to build the preamp of http://www.till.com/articles/GuitarPreamp/
with maybe the mod of this page  http://www.diyguitarist.com/Guitars/FET-CompactPreamp.htm  (at the bottom page)

bent

Talk about confusing! I use a circuit like that as a buffer. I called it a heater. At +6dB or so, it really can't be considered a preamp. But all circuits put into the guitar body are called preamps 

At the one practice space I am 20 feet away from the amp. But all my cables are 20 feet and that doesn't leave any slack to actually plug in. So I run a 20 foot cable from the bass to the heater and then 20 feet from the heater to the amp.

[bent]

thank's markm for the schematic,

i was going to build the ggg http://www.generalguitargadgets.com/pdf/ggg_buffer_jfet_sc.pdf
what is the difference between a buffer from another? i'm lost in all this...

mark hammer give me a good explaination on my other topic:  http://www.diystompboxes.com/smfforum/index.php?topic=48917.msg363174#msg363174

but with the notion of preamp....i'm feeling like going back to start.....

buffer,booster,preamp, argggggggggggggggggggggg!!!!!!!!!!!!!

[bent]

hope that someone, someday, will do a very clear and simple topic explanation on that...

exemple:
a buffer is : somekind of capacitor that stuck the signal and release it equal....bla bla bla bla
a booster is : somekind of bla bla bla...
a preamp is doing: bla bla bla....

very very clear and simple....

a buffer/booster/preamp for dummies....

bent

[David]

Perhaps this might help:

Buffer:  Prevents treble loss due to impedance mismatch.  High-impedance input, low-impedance output.  No gain.

Preamp:  Provides slight boost to an input signal.  May also damp an input signal.  May or may not handle high-impedance inputs, depending on design.  May or may not invert the input signal.  Intended to be first unit in a signal chain.

Booster:  Gain stage somewhere in a signal chain.  By convention of this forum, not the first unit in a signal chain.  Generally considered to provide clean boost (which may or may not overdrive successive stages).  Amount of boost determined by circuit design and available input voltage.

[Ben N]

Bent,
Maybe you just need to take astep back.  Instead of saying, "I will have a buffer and a preamp, now what do I do with them?" , start by thinking about what you need.  After all, unless it is doing somthing useful, adding circuitry betwen your guitar and amp are more likely to hurt your tone and add noise than help.  So, Rule #1 should be, "If I don't need it, I don't want it."

So let's try and figure out whether you need a buffer and a preamp.  You say you have seven pedals, but we don't know anything about them.  Are they buffered?  True bypass?  Mechanical non-true-bypass? Do they include any old-school fuzzes?  Chorus or flanger?  What about your amp?  All of these things are relevant to answering your question.  Here are some guidelines:

1) Buffered pedals are, well, buffered.  That includes Boss and ibanez type pedals, that generally have both input and output buffers.  If the first pedal in your chain is buffered, then sticking another buffer in front of it is pretty much useless (assuming you are talking about use with conventional electric guitar magnetic pickups.  Piezos, which are high impedance, may indeed benefit from a higher impedance load than the 500k or so that many buffered pedals show.)  It also follows from this that if you have non-true-bypass pedals and buffered pedals, the benefits of the buffer at the begining of the chain only extend as far as the first buffered pedal.

2) True bypass pedals generally don't need a buffer in front of them, since they are designed to interact with a guitar as is.  However, if you find your tone with such a pedal becomes dark or muffled, adding a buffer may indeed be a solution.

3) Where buffers really help is with a string of non-true-bypass pedals, meaning old MXR pedals, Marshall pedals, or others which have either a SPDT mechanical switch or a DPDT switch where one pole just controls the LED.  If you have two or more of these in a row, putting a good low input impedance, high output impedance buffer in front of them will help save your tone.  Depending on what pedals you have, you may be able to accomplish this just by sandwiching single "tone-sucker" (like MXR) pedals between buffered (like Boss) pedals.  Here, a JFET or jfet-input opamp desig would be best.

4) Most amp inputs are high impedance, and do not really require a buffer ahead of them (after the pedals).  But, if you are running a long cable from your pedalboard to your amp, or you are splitting your sigal from the pedalboard to two or more amp inputs, or you are feeding a low impdance input like a mixing board or a Acoustic 360 amp, or the end of your pedalboard is high impedance, like a passive volume pedal, then adding a buffer at the end of the board is a good idea.  Here, the emphasis is on low output impedance, so a BJT or paraleled oopamp would be great (like the AMZ Superbuffer).

5) As mentioned above, certain things should not have buffers ahead of them, mainly old-school fuzzes like the Fuzz Face and its many variants.

6) Although buffers and preamps/boosters are similar, the big difference is that preamps/boosters are mainly intended to increase signal level, wheras buffers are intended to match impedances.  Preamps and boosters usually also have a buffering effect, but they may not do it as well as something designed for buffering.  Here again, the question is what you need.

7) In general, maintaining a higher signal level through your signal chain translates to a higher signal to noise ratio.  For this you would want a colorless, flat response preamp--probably an opamp design.  So, an always-on preamp at the beginning of your pedalboard would be good, right?  Well...

8 ) Most pedals have very little headroom--naturally, since they generally run on 9v unipolar power.  So boosting the signal coming into them more than a very little bit is likely to overdrive them, maybe in unpleasant ways.  If all you have on your board are overdrives and fuzzboxes this is not a problem, but for choruses, phasers, etc., it may be.  So it follows that preamping at the beginning of the signal chain may not be such a good idea after all.  Depends on your pedals, your guitar, your needs.

9) You may want a preamp at the end of your pedal chain if from there your signal goes to some kind of studio rack gear that is expecting to see a much hotter signal than pedals (or a guitar) would supply.  Here, too, your preamp should not color your sound, just make more of it, so go with an opamp design.  It should also have a lot of headroom, so an 18v or higher power supply would be a god idea.

10) Another way to use a preamp is as a boost--to increase your volume for solos, or to overload your amp's front end for distortion and volume boost.  For most, I think such a boost would go best at the end of your signal chain, especially if you have a tube amp, but this is an area for experimentation. Some people like boosting the input of a fuzz or overdrive to get a really saturated tone.  For this purpose, some like a flat boost, but others look for boosters that emphasize certain parts of the audio spectrum, or add some of their own distortion.  Season to taste.

HTH,
Ben

[Pushtone]

Buffer - a unity-gain amplifer. Same gain output as input. Used to buffer the signal before a significant load, like a long cable


Preamp - an amplifier capable of adding gain.


Did you read the text on the GGG buffer page and go to the Peter Cornish link? They're good info.

http://www.generalguitargadgets.com/index.php?option=content&task=view&id=69&Itemid=100

[Antero]

Why is it that certain fuzzes don't get along with buffers?