Transparent input / output buffers

[wcampagner]

Hello,

I'm testing some input / output buffers... the picture below shows the buffers:



I also put a DPDT to see the diference between the buffer and the direct sound.

What i noticed is that when the signal goes through the buffers, i can hear a small diference... the sound get a little louder and there is a little more treble too... i really enjoyed the sound... but i'm looking to the most transparent buffer possible...

I tried a lot of diferent parts...

output transistor: 2n5089, 2n5088, 2n3904
input JFET: 2sk30a, 2n5089

I also tried to change the values of the resistors and the capacitors... but nothing seems to change the sound... is there any mistake in my buffers?? Is there anything else i could try??

I also tried Amp-Op buffers, but i think the sound is a little diferent from this one.

I'm planning to put some effect between C1 and C4... that's why there is 2 caps between the in/ou buffer.

Thanks in advance,
Wagner.

[R.G.]

A good question to ask is - what is "transparent"?

If by that you mean "sounds just like my guitar without the buffer", then why would you need a buffer?

What i noticed is that when the signal goes through the buffers, i can hear a small diference... the sound get a little louder and there is a little more treble too... i really enjoyed the sound... but i'm looking to the most transparent buffer possible...

Of course you heard a difference. One of the main points of buffers for guitar is that they eliminate cable-induced volume and treble losses. The sound is a bit louder and a bit more bright - just like you found! And you liked it. Try this - compare your guitar sound with a 20 foot cable and a two foot cable. I bet the short one sounds a bit louder and a bit brighter.

I also tried Amp-Op buffers, but i think the sound is a little diferent from this one.

A typical opamp circuit has much less harmonic distortion at low signal levels than either of these buffers, both of which have a slight bit of distortion on their own. Many people LIKE the slight distortion, thinking it sounds warmer or sweeter. The opamp, not having as much distortion sounds less sweet or warm - but boy, is it ever transparent, in that the output is *exactly* like the input if you don't overdrive it.

[wcampagner]

Thanks again R.G. for answering,

What i mean by transparent is just what you said: sounds just like my guitar without the buffer.

I'm building this buffers because i'll be using electronic switch instead of DPDT or 3PDT... just like the boss, ibanez style.

I've also build the electronic switch and i'm very happy with it... very silent for me.

The problem is even if i use the shortest cable i have, the sound of the buffers are slightly diferent... i thought i could have made some mistakes, because i did the buffers project on my own...

I'll try again the Amp-Op version to compare both buffers...

I have one question: if i use... let's say 10 buffers in series like this, will the original guitar tone change a lot??

Thanks again,
Wagner.

[R.G.]

The problem is even if i use the shortest cable i have, the sound of the buffers are slightly diferent... i thought i could have made some mistakes, because i did the buffers project on my own...

I don't think you made a mistake. Buffers do tend to change the sound, in exactly the way you describe, by eliminating losses. It's not so much that the buffer changes things much, but that it prevents the losses. And there is that slight distortion of the non-opamp circuit.

If you use ten of them, the principal change will be that the buffers also preserve the build up of high frequency noise in each pedal as well as preserving the tone they got a the input. There will be a **slight** increase in hiss. This is again not so much the buffers adding noise as them preserving and preventing treble loss.

You are dealing with very slight changes in sound here. The tone will not change a lot - but "lot" is a relative term. I think that you'd be better served by seeing if it's a sound you like, not merely an accurate sound. That's what effects are all about. Transparency in the sense of incredible accuracy is something that's properly a hifi concept more than a musical instrument one. MI rigs make sound, not just reproduce it.

Note that it is possible to make the input buffer have a slight treble loss to fake the cable losses if that is what you're after.

[wcampagner]

Thanks again R.G.,

You are the Master!!!

I'm interested in making the input buffer have a treble loss... just to test it... and see how it sounds... but how can i do it? How can i implement it?

Everything is on my breadboard so now it's testing time... i like to test most of the combinations possible to see which one makes me feel happier... sorry... i'm the kind of people who like everything to be perfect... i can't avoid it...

Thanks,
Wagner.

[petemoore]

  Use a LP Filter...a small capacitor between signal path and ground.

[wcampagner]

Thanks a lot for all the advices,

Today i had some time to test...

I did the tests sugested by Petemoore (ading a small value cap. on the input)... there was a treble loss... but i think it didn't sound good... all the notes got a little more bass...

I also tested the buffers with Amp-Op instead of JFET and BJT... i liked the results... but as with the others buffer... it also got a little louder and a little more treble... but it didn't sound bad... in my opinion it got a better sound... but i really didn't notice the diference between the Amp-Op version and the JFET/BJT version...

Then i tested my Sansamp GT-2... and i noticed it was changing the sound just like my buffers did... i was thinking that i was doing something wrong... but now i know my buffers are OK!!

So i'll be using the Amp-Op version, because it is cheaper and uses less parts...

I read that it is a good practise to put the input far away from the output... so i'm thinking if it a good idea to use a dual Amp-Op like tl072 or two single Amp-Op... i prefer to use the dual... if there is no problem...

I think now things are starting to work... i also got the electronic switch working very good... very silent switch... it is missing now only the effect to put in the middle of the buffers!!!! 

Thanks again,
Wagner.

[Gilles C]

Just for your info, check what they say about adding a capacitor at the input of this buffer to simulate the loading of a guitar cable.

http://www.jensentransformers.com/as/as004.pdf

Gilles

[wcampagner]

Thanks Gilles C.,

Interesting article... i liked it.

But i'm enjoying the sound of the buffers as they are now... feels like the guitar is alive!!!

Thanks,
Wagner