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Old 9th May 2005, 04:14 PM   #1
sopapo is offline sopapo  Spain
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Default OP buffer for electric guitar

Hello to all,its nice to stay here with you folks,this is my firt topic in this great board here,I will to stay weeks reading all the existing topics that I have found,there are so many interesting things¡¡¡

First of all excuse for my english ...

but I would like to look for advice for a thing that ultimately I ve been around....

I would like to do an OP based buffer for electric guitar (or I must do discrete? )
the thing is to avoid tonal degradation for the use of cables and effects boxs..
I see that the design of Pavel Macura its veri interesting, I wonder if I could apply this topology (627+buf634) to electric guitar

There a few changes that I imagine that its basic to do

first of all the input impedance has to be around 1M or so because the impedance of the e guitar is around 9,5 -11k and they would like to see the impedance of a input of guitar amp (around 1M too)

another thing is that it could be powered by 4,5 V since it must be powered by battery or 9 volts the question is (this op work well withis tension?) in the pdf os 627 it says that the minimum tension supply is 4,5....

Its the opamp working in class A the thing to do for this case? (or the discrete in class A)

dos you think that I would go discrete? do you knos other designs for this?

I would like your opinions

Thanks for your time
Best regard
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Old 9th May 2005, 04:31 PM   #2
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Just some opinions.

1) Personally, I would recommend against this. The inconvenience of changing batteries in the guitar just for a buffer stage with no tone stack is not worth it IMO. If you are worried about your tone or gain or whatever, I would pursue something more traditional like a high quality buffer preamp as your first pedal in your chain. It will present a constant impedance to your guitar and your tone will not change as you move effects around and twist knobs etc.

2) I do not like your OPA + BUF idea. 2 opamps to just do buffering in a guitar is overkill and reward is short battery life, which is a pain to change in a guitar. I would try to extend battery life as much as possible.

2) You will find many guitar preamp schematic with a simple search. Many opamp chips will work with +/- 4.5V. I wouldn't worry about Class A bias and all that, you efforts are better spent on other details. If all you want is a buffer stage, then a discrete FET design will have low parts count and long battery life.
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Old 9th May 2005, 11:20 PM   #3
sopapo is offline sopapo  Spain
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Thanks for your answer leadbelly...but I didnt explain correct,sorry...mi idea is not to have the buffer built-in on the guitar, mi idea is to have the buffer in a stompbbox-like enclosure and in the first place on the chain,too......and with a dedicated power supply....not batterys

....the power autonomy isn't an issue....

In this case,do you think that the concept of 627+buf634 is right? Will I have some advantages with this over a single op design?

Thanks for all
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Old 9th May 2005, 11:49 PM   #4
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Quote:
Originally posted by sopapo
In this case,do you think that the concept of 627+buf634 is right? Will I have some advantages with this over a single op design?
Well, you seem to have it pretty much under control, and will likely be successful whatever I say, so this is all I can think of:

I doubt that figure of +/- 4.5V was coincidence, Burr Brown obviously wanted the OPA to be considered for 9VDC applications, so it should work.

I don't think you will gain anything over the single op design because in terms of tone, the tone imparted by the guitar and the amp themselves will swamp out the subtleties of a particular opamp chip or buffer stage topology, assuming of course that we are discussing low noise premium opamps. And I would say the same can be true of the subtle difference in impedance loading of the different topologies.

If it were me I would probably just use the BUF634 alone. It does what is needed most, and since it is rated for +/- 2.25V, you will have the long battery life of a commercial design. I know this is not very important to you, but I personally like the idea of building something that has the performance of commercial products when it costs nothing extra.
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Old 10th May 2005, 06:31 AM   #5
sopapo is offline sopapo  Spain
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ok thanks again leadbelly,I did think to try the buf634 alone,I was on the opamp thing,but I will try sure
I will tell you what happen

Thanks
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Old 11th May 2005, 12:06 PM   #6
Gerben is offline Gerben  Netherlands
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Hello,

IMHO the OPA627/Buf34 T is total overkill for a guitar. I had good succes with this one:

http://www.muzique.com/schem/mosfet.htm Very good/clear sound with very low need of power. Be aware that the BS170 is very sensitive to static so connect the power jack at the output.

Browse www.muzique.com for more boosters/buffers suitable for guitar of go to a more appropiate forum like www.diystompboxes.com

Regards,

Gerben
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Old 14th May 2005, 01:07 AM   #7
sopapo is offline sopapo  Spain
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Thanks gerben,I tried a simple buffer with opamps (OPA 2134,4558,TL072), a basic thing,the typical topology of a circuit only with a biased point of two resistor of 2 M in the + input and the raw feedback loop and 0,1 uF poli cap in the input and a 10 uF cap in the output...... and it doesn´t do the thing for me.....it colour the signal more than desirable...especially in the realm of dinamics.....it dampen the dinamic of the guitar.......

it for this that I am triyng something more to achieve the most transparent sound posible

I know that a little change ibn the sound there will be but in my tryings there are more than this.....

Thanks
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Old 14th May 2005, 12:40 PM   #8
Gerben is offline Gerben  Netherlands
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HI,

Offcourse going 'active' with a buffer means less loading of the signal and a change in tone. PLease keep in mind that in general you're already using a buffer when using a pedal since allmost all pedals '(eg.boss/ibanez etc) dont have true bypass.

I'm not a big fan of opampbuffers, it just sound to 'clamped'. I really like the extra clarity and the slight dirt that the mosbuffer brings. Since the partscount/cost is low just try it.

Gerben
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