Pete cornish discrete buffer on class A

[sopapo]

Hello,Pete cornish in his page claim that he use discrete buffers in class A

What is the sense of a unity gain buffer with a jfet,fet,bip etc  (or opamp)biased  in class A?

its not limiting tha range of signal?

Thanks

[cd]

The "sense" is that you get a high input Z for no loading of the guitar signal, and a low output Z to drive long cables with no treble loss.  Provided the buffer is well designed, and the power supply swing large enough, whatever you put into the buffer, you get out.  There's no gain involved (buffer has a gain of 1) so unless you have superhero pickups that can put out say 7V peak to peak (99% do not), you won't be limiting anything.

[sopapo]

Thanks cd for  your answer,sorry I dont explain it correct.....my question was why class A for a buffer? its better in class A than A/B for a buffer? there is significant diference interms of sound between a buffer unity gain with class A or class A/B?

Thanks

[cd]

For a low level guitar signal?  There's a difference, but is there a NOTICEABLE difference, or is the mystique of "Class A" just a marketing term?  I lean towards the latter.  Try not to get caught up in the stupid little things, decide what your needs are and go from there.  For example, the Electro Harmonix LPB-1 booster works in Class A.  Is it the "best"?  Is it the "greatest"?  Nope.  It sounds good but not because of the sole fact it works in Class A.

[sopapo]

I think you are right cd,and I would like to add that a buffer shouldn't have a distintictive sound,in fact it must be transparent,no color,It should have no sound at all

so,its for this that I wonder the meaning of class A in a buffer,because class A its something that I see like implies coloration (for my level of knowledge)

I dont think a class A improve the transparency in sound of a buffer which the principal feature that it must have, or am I wrong?

[Mark Hammer]

In the world of amplification, especially power amps, and especially power amps of any real power, Class A is incredibly wasteful of energy and demands far more "stuff" (parts and current) to produce the same amount of power as many other classes.  It also tends to produce less of certain types of distortion (crossover), and many feel that when it distorts it does so in a pleasing way.  As a result, when people talk about "Class A", they are either referring directly to the mystique and "spare-no-expense" aspect of amplifiers, or else they are transferring the mystique to other circuits that also use a Class A design, but in a much more economical fashion.

Typically, when people talk about Class A in describing solid state preamps, they are talking about single transistor stages.  If someone uses a pair of 6L6 output tubes, an expensive transformer, and a top quality fan to keep the tubes from overheating in order to get 10 watts in Class A, clearly they have overspent considerably in search of getting a particular tone (a pair of 6L6's *should* be able to produce anywhere between 45-60W, depending on type of 6L6 and other design aspects).  The difference between Class A and the alternatives, when it comes to input buffers, is not even remotely in the same league, cost and effort-wise.  Indeed, if I've understood all this stuff correctly, isn't every Boss pedal equipped with a "discrete Class A input buffer"?

At the same time, a well-designed simple transistor buffer stage, that just happens to be Class A, can help a great deal in letting a decent pickup on a nice guitar send every nuance of its tone to an amplifier, 50 feet of cable, and oh so many picafarads, away.  If it does so without adding noise, so much the better.  Note, however, that there are Class A buffer stages that use FETs or MOSFETs with very high input impedances, and bipolar buffers that afford somewhat lesser input impedances.  There likely ARE cases where the second type actually subjectively improves the tone quality (for the same reasons that some folks will use lower-value volume pots on single-coil type guitars or seek out "curly cords" - namely to take away some of the brightness of those pickups).

There are some sound samples of different bypass types on the CD accompanyng Dave Hunter's recent effects pedal book.  The buffered bypass sample of a Visual Sound pedal is quite impressive, although I suspect that some folks are so used to the way that long unbuffered cables  roll off treble, that they might think of the VS buffer as being a bit of a treble booster!

Pete Cornish, like I suppose any manufacturer without a monopoly who is trying to sell their products, plays up the mystique aspect of Class A.  I'm sure it's decent, and I'm sure it helps, but we are not talking about the same sort of stuff as those $5000 12w/channel Class A tube amps you see described in audiophile mags.

[Satch12879]

Nothing is transparent.  Nothing.

And perhaps Pete is just using the proper name for the circuit in question.    Some people know what they are talking about and therefore tend to use the correct terminology.

That being said, here's some info on amplifier classifications from the NEETS manuals:

Class A: A simple transistor amplifier whose output is a 100% (or 360 degree) copy of the input signal and whose current flows for 100% of the input signal time.  The class A amplifier has the characteristic of good FIDELITY and low EFFICIENCY.  Fidelity means that the output signal is just like the input signal in all respects except amplitude.  It has the same shape and frequency.

Class AB: If the amplifying device is biased in such a way that current flows in the device for 51-99% of the input signal, the amplifer is operating in class AB.  Class AB amplifiers have better efficiency but poorer fidelity than class A amplifiers.  They are used when the output signal need not be a complete reproduction of the input signal, but both positive and negative portions of the input signal must be available at output.  (Many of the power sections of tube amps are class AB like Mesa/Boogies.  The characteristic distortion coupled with high output power of class AB amps explains the very pleasing phenomenon of power tube distortion which is particularly tasty on overdrive and lead settings.)

Class B: An amplifier that operates for 50% of the input signal.  The biasing of this type of amplifier only allows the negative portion of the input signal to be reproduced on the output signal.  It is used when there is a need for rectification and amplification.  The class B amplifier is twice as efficient as class A amplifiers.

Class C: An amplifier that operates for less than 50% of the input signal.  The output waveform is very small and bears little resemblance to the input signal.  It is the most efficient with the worst fidelity.

There you go.  Sounds like Mr. Cornish is completely in the right to say what he says with regard to his designs.

[davebungo]

Class B: An amplifier that operates for 50% of the input signal.  The biasing of this type of amplifier only allows the negative portion of the input signal to be reproduced on the output signal.  It is used when there is a need for rectification and amplification.  The class B amplifier is twice as efficient as class A amplifiers.

Class B reproduces both positive and negative going portions of the input signal, but with an amount of cross-over distortion where the two halves of the amplifier output stage switch.  Obviously not very good for low level signals.

[lovekraft0]

:roll: It's just more audiophool-crossover marketing - any single ended amplifier (ie, not push-pull) has to be biased  Class A, or it will clip on one peak of the waveform. Any discrete single transistor or JFET gain stage or follower that's not designed to distort is by definition Class A. In other words, the Ruby, the TS9/808 and the newer buffered wah pedals all have a "discrete Class A buffer" at  the input.

[sopapo]

Thanks to all for answering ,very interesting things are talked here.....

The tl072 is ok but I think-ought that is posible to achieve more transparency..

I thought that a op buffer with an chip like the opa 2134 it will give good results but there arent so noticeable...for me the sound is a little ....dull? In fact I think that the input buffer of the boss pedal is better,more transparent....

I think kthat the buffer of this pedals (boss) if are used only one in the first place of the chain,them are really good....the problem is when there are many....

another chip that give better results isthe opa2604,it is slighty harsh (very very little) but for a guitar sound its very ok...I would consider this like an another good option

I will do the probe with the opa 627 when I get it....

Do you think that for a guitar sound a discrete buffer is the way to go? given this results with opas..

Thanks

[cd]

Do you think that for a guitar sound a discrete buffer is the way to go? given this results with opas..

Do a double blind test where you're not "hearing with your eyes", and tell us the results.  I doubt you will notice any difference between 10 different opamps, or a discrete vs. opamp, etc.  ESPECIALLY when you're on stage and have a drummer bashing away behind you.  You'll be more worried about the stage mix than "oh the buffer in my pedal sounds harsh".

[sopapo]

Thanks cd for your answers,yes I am aware ot the things live-related,I was only trying to optimize the gear all the posible,which I think is sometihng all want to do as far as posible,independently of the moon,the stars and the heavy drummers,  there are time to practice,time to play live and time to tweak things which is something I think  this board is based... :wink:

apart of this I have found diferences between opamps,really,especially in the attack and dinamics more than the frecuency......

when I get the rest pf the opamps I tell you more...while I wnt to dive in the discrete...

Thanks  :wink: