IC Buffer Helps but a little harsh sounding

[sjaltenb]

Hello,

I am working on my FX chain right now, tryign to decide where in the multiFX board to put the Buffers. I only have 1 GGG IC Buffer built, and I put in in my Test rig (basically an FX loop with an in and out for guitar and amp and test leads for circuits)

So i was testing some circuits in my Cornsih board w/ and without the buffer. Strangly, after installing the MicroVibe in its new home, it will not accept a direct guitar signal well at all! It cut the volume in half along with all the other lack of bass and trebble etc. So i threw the buffer in front and voila no problem worked perfect (putting the buffer AFTER did nothing) . Same with the Phase 90. Probably has to do with all the shielded cables and switches it was going through.

Anyways, So yes the buffer is magic HOWEVER  its a little harsh sounding even just Guitar-buffer-amp. Yes it does bring back the volume and makes the lows deeper and clearer but it just seems a little trebbly and harsh sounding. Not quite organic enough for my taste. Is this just becuase Im not used to having it there?

BTW i am using a Peavey Classic 30 amp and Very high quality Evidence Audio Cables (only 20 ft total)

Should I try other buffers? Thanks!

Also--Since I have about 10 different pedals, which after quick research, some have different input impedences, Can I/Should I build different buffers to be placed infront of each one based on their input impedence???

[R.G.]

Anyways, So yes the buffer is magic HOWEVER  its a little harsh sounding even just Guitar-buffer-amp. Yes it does bring back the volume and makes the lows deeper and clearer but it just seems a little trebbly and harsh sounding. Not quite organic enough for my taste. Is this just becuase Im not used to having it there?

That is the most likely explanation. It is possible that the buffer is not working quite correctly, is oscillating at RF just a little bit, or has some other flaw. You can dial back the treble a bit by tinkering with the buffer's response.

BTW i am using ... Very high quality Evidence Audio Cables (only 20 ft total)

I don't know of any real information saying these are any better than any low capacitance cables. Do not succumb to the cork-sniffing that has plagued hifi.

Should I try other buffers? Thanks!

If you like - but going to something new without understanding what is happening here will not help much. If you find another one sounds just right, you will conclude that this buffer is bad, but with no idea how or why. This is how internet rumors start.

Also--Since I have about 10 different pedals, which after quick research, some have different input impedences, Can I/Should I build different buffers to be placed infront of each one based on their input impedence???

No. The output impedance of any good buffer is low enough to drive any pedal. You do not need to match buffers and input impedances. That's kind of the whole point of buffers.

[sjaltenb]

Thanks R.G.

Well I was not saying that EA were superior, I just wanted to state that they were good low capacitance cables, not cheapos.

I have taken the past few hours to read a lot about buffers and impedence issues..and did learn that any good buffer is good for all pedals, so that helps. I will tinker with some different designs and components to see if anything sounds better/worse.

Now, I know that PC is not at all the king of tone or design or anyting like that, so forgive me for referring to what he wrote:

I read that fe places a buffer at the input, then AFTER each effect in the chain in his pedalboards, so, this way the guitar, or the FX output is looking at the same principles of a Tube amp input which is 1Mohm, 20pf.

Are these the same typical specs in most of the buffer we find online, such as the GGG?

again, forgive me for referring back to him, this just seems to make sense that it should have the same input characteristics as an amp. THanks!!!

[cheezit]

Take a look at stage photos of Hendrix and you will see him usually using coil cables, which have gotta have a huge capacitance-per-foot.   This mania to have the lowest possible capacitance is silly---someone measures something, says "lower is better", and everyone assumes that if they aren't trying to have a low value for that thing they are doing something wrong.

Sounds to me like you prefer the unbuffered sound of your effects chain.  Great!  Don't second-guess your ears.  It's absolutely worth knowing what is going on, and trying alternatives, but this is guitar gear, where the most famous circuits were usually designed with the cheapest components available.

[Ben N]

Now, I know that PC is not at all the king of tone or design or anyting like that, so forgive me for referring to what he wrote:

I read that fe places a buffer at the input, then AFTER each effect in the chain in his pedalboards, so, this way the guitar, or the FX output is looking at the same principles of a Tube amp input which is 1Mohm, 20pf.

Well, if want a REALLY authoritative opinion that you can definitely trust more than Cornish's  , I will go ahead and second him: That is THE solution for consistent sound without excessive cascaded buffers to muck up your sound. When everything is bypassed there is exactly one buffer between your guitar and your amp, but every device that is ever in the chain will also see the same lo-Z signal feeding it, no matter how much or how little is on. This does pose its own challenges in terms things like vintage fuzzes, but PC can deal with that, too, I'm sure, and his clients will happily pay for him to get it right.

As for Cornish being "the expert," AFAIAC he IS the man when it comes to building over-engineered, road-worthy, super-reliable and tonally consistent pedalboards. Doesn't mean that is the only way, or even the best way for weekend warriors/inveterate tweakers like most of us who prize modularity so they can swap stuff in and out, and don't need to be 100% sure that everything will both last and sound absolutely right for 100 shows in front of tens of thousands of people. But for what he does, he is absolutely the best.

[cheezit]

The buffer is counteracting a number of different types of loading that happens to your signal.  But if you are bothered by the spiky highs, one thing you can do to restore the "warmth" is experiment with tacking a small capacitor (10pf - 50pf or more) from the buffer output to ground.   You could put in a mini switch to control it, or wire a pot as a variable resistor in series with the cap to vary the effect.

With the right value, you should get an approximation of your previous tone's high frequency content, but much clearer, cleaner and more dynamic due to the buffer preventing impedance-related artifacts from the following effects.

[sjaltenb]

well i must be finally learning somethign around here! I was going to try a small cap at the output. That sounds like a good idea to me...

Ben, Yes I have to agree that this concept does make a lot of sense... I tink this is how I will setup my board. Of course, that is going to take a lot of buffers, but at least they are cheap/easy to build once I find a design I like.

thanks!

As a side note,

I read that for David Gilmour's all tube pedalboard, cornish replicated the input stage of davids amps, the DR103. David always linked the briliant and normal inputs of his HIwatt, so im guessing that was incorportated into the design. he was also quoted as saying that the tubes were double triodes, so i take taht as they had similar characterisitcs as the ECC83s of the Hiwatt.

Heres the hiwatt layout:
http://mhuss.com/Hiwatt/Layouts/PreampLayout1.gif

SO is this something that could be done using a low voltage tube, like the Huffer incoroporated, or no?

seems pretty interesting!

[Ben N]

Interesting. I was under the impression that DG uses a modified Alembic F2B as his preamp, and bypasses the preamps in the Hiwatts. Of course, that could just be outdated or plain erroneous information.

As for the "dual triodes"--that is the package that triodes most commonly come in, and ECC83s and their US equivalents, 12ax7s, are the most commonly used preamp tubes in guitar amps of all makes, along with lower gain variants like ECC81/12AT7, commonly used as phase inverters and reverb drivers. Unlike more exotic varieties, these tubes are available pretty much anywhere there is a Guitar Center or a Sam Ash, and are therefore easily replaceable. So I would be very surprised if PC used anything much different.

As for doing this with low voltage tubes--hey, interesting question. Check out the various threads here dealing with miniature and low-voltage tube applications, like the Valvecaster. What will not work is trying to run high voltage tubes (like the aforementioned ECC83s) at low voltage, like you sometimes see in distortion boxes.

[aron]

Well I was not saying that EA were superior, I just wanted to state that they were good low capacitance cables, not cheapos.

Please tell me you have a capacitance meter and have measured these cables? These are the solid core cables that -- because of the solid core, the electrons travel better and there's more definition and clarity right?

Please measure and let us know!

Aron

[sjaltenb]

Well I was not saying that EA were superior, I just wanted to state that they were good low capacitance cables, not cheapos.

Please tell me you have a capacitance meter and have measured these cables? These are the solid core cables that -- because of the solid core, the electrons travel better and there's more definition and clarity right?

Please measure and let us know!

Aron

Hey sorry the first time i read this i took it the wrong way! No i have not measured it, I do not have a metter. I really do like the cables, they sound amazing. the solid core makes them a little stiff but well worth it...


Ben, thanks for the reply! I will search around. David does not use the Alembic F-2B anymore, that was in 94 during his Pulse Rig. (a great tone). With the All Tube Cornish Board he is back to using a typical Guitar-FX-Amp setup with the DR-103s

[PerroGrande]

The GGG circuit uses a TL071 -- is that the chip you're using?

I ask because the TL071 (actually, the TL07x series) can be a little bit  "difficult" to work with. 

It *does* have a nasty habit of oscillating even in a simple buffer configuration.  The oscillation *will* make it a little harsh sounding, not at all unlike what you've described.  Interestingly, the output will look clean when only a scope is connected, but when a mild load is connected (even a guitar amp with substantial input impedance), the oscillation begins. I've read several articles on the subject, and have experienced this personally -- and it isn't fun.

The good news is, there is a fairly easy cure that might be worth trying. Stick about a 220 ohm resistor in series with the output.  On the GGG wiring diagram, the "blue" wire that runs from the PCB to the switch should be unsoldered from the board.  Solder one end of a 220R resistor in the hole where the wire went, and then solder the blue wire to the other side of the resistor.  See if that cleans up the sound... If it does, your board was oscillating. 

[sjaltenb]

The GGG circuit uses a TL071 -- is that the chip you're using?

I ask because the TL071 (actually, the TL07x series) can be a little bit  "difficult" to work with. 

It *does* have a nasty habit of oscillating even in a simple buffer configuration.  The oscillation *will* make it a little harsh sounding, not at all unlike what you've described.  Interestingly, the output will look clean when only a scope is connected, but when a mild load is connected (even a guitar amp with substantial input impedance), the oscillation begins. I've read several articles on the subject, and have experienced this personally -- and it isn't fun.

The good news is, there is a fairly easy cure that might be worth trying. Stick about a 220 ohm resistor in series with the output.  On the GGG wiring diagram, the "blue" wire that runs from the PCB to the switch should be unsoldered from the board.  Solder one end of a 220R resistor in the hole where the wire went, and then solder the blue wire to the other side of the resistor.  See if that cleans up the sound... If it does, your board was oscillating. 

Thanks, I will try this as well! Yes, I am using the TL071.  Yes I forgot to mention that Pete says he uses the Miniature double triodes, but does say that the power supplies for these are pretty large, so that leads me to believe that he is not running them at 12v....I have pics of the tube buffers and power supplies for them, I dont know if i can post them but maybe if somoene is interested i could email them?

[earthtonesaudio]

The TL07x datasheet recommends a 100pf capacitor to ground at the output when used as a buffer like in the GGG schematic.  If you add this capacitor, place it before the output cap.

[sjaltenb]

hmm I will try this as well..

[rnfr]

i think Jack has a germanium buffer design over at AMZ.  that might do you ok.

[R.G.]

i think Jack has a germanium buffer design over at AMZ.  that might do you ok.

Simply rubbing germanium on something is not a cure for anything particularly. A buffer is one of those circuits which, by design, hides any information about what's inside the buffer, so a germanium buffer isn't any better than another style.

It just sounds mojo.

[dschwartz]

i think Jack has a germanium buffer design over at AMZ.  that might do you ok.

Simply rubbing germanium on something is not a cure for anything particularly. A buffer is one of those circuits which, by design, hides any information about what's inside the buffer, so a germanium buffer isn't any better than another style.

It just sounds mojo.

ahhaa, try using Tube-o-Lator laquer on the IC, that will give warmth...

now, seriusly, try that 50-100pF cap to ground to the output..
and other thing..are you sure you are not clipping the buffer? is it
correctly biased?..when buffers clip, they sound just awful...

[sjaltenb]

i added a 100pf cap (its all i had) to the circuit. It is VERY close to the sound of my guitar directly into my amp. I forgot that not only did I have the signal running through my FX test rig, it was running through my rack tuner. So i plugged straight in and compared it that way, and its much better than with the 100pf.

however it is pretty noisy, but its not in an enclosure and next to my computer and all that...the experiment continues!