AMZ Super Buffer question.

[digi2t]

Just a quick question on the Super Buffer. Can I use a TL074, instead of two TL072's, or is there some special isolation factor involved here? Just wondering.

[Sacorus]

U could also use four 741s!

It will work fine with the tl074, and I assume most other op-amps.

[GGBB]

Their PCB transfer is designed for two 72s, and the two-chip design makes it possible to remove one for less power consumption.  Otherwise a quad will work just as well as Sacorus stated.

[digi2t]

Thanks guys. It'll make my vero a bit tighter.

[R.G.]

Quick question - why do you need a "super" buffer?

[digi2t]

Quick question - why do you need a "super" buffer?

Well, I've got 40' of cable between my guitar and my switcher, with a true bypass tuner in the middle. I was thinking of adding the buffer at the end of the line, to reinvigorate the signal. Insofar as why I chose the "Super" version, I figured I could maybe try adding a switch into the mix, making a normal or super mode buffer.

Am I on track here, or has my cheese done slid off it's cracker?

[R.G.]

Well, I've got 40' of cable between my guitar and my switcher, with a true bypass tuner in the middle. I was thinking of adding the buffer at the end of the line, to reinvigorate the signal. Insofar as why I chose the "Super" version, I figured I could maybe try adding a switch into the mix, making a normal or super mode buffer.

Am I on track here, or has my cheese done slid off it's cracker?

Use Cheez Whiz under the real cheese. It's one of the best edible adhesives.

Put your buffer before the long cable. Once the treble is lost to cable capacitance, it can't be reinvigorated. It's gone forever. You'll have nice, well driven dull signal. The buffer needs to go as electrically close to the pickup coils as you can get it. And any buffer at all is incredibly much better than none at all.

There are ways to calculate how much drive you need, from the cable specs on pF/foot.

One thing starts to gnaw at me - maybe the super buffer needs those combining resistors. The TL07x family is (in)famous for not driving capacitive loads well without some series resistance. They can go mildly unstable, although they are far from alone in this regard.

The reason I asked is that even one TL07x buffer is pretty darned super compared to no buffer at all, and four of them is only 4x the available current of one TL07x. If you really need lots of current to drive loads, there are other and arguably better ways. Perhaps I should call this a "hyper-buffer".  

The TL07x family is fairly modest in how much current it can drive. It is specified to drive +/-10V into a 2k load per amplifier. The NE5532 and LM833, as well as others, will drive a 600 ohm load to +/-10.5V on each amplifier. So each section of the LM833 is about the current equivalent of three TL07x amplifiers, all by itself. It does this with 1/4 of the noise - 4.5nV/root Hz instead of 18.

If you want a super-er or hyper-er buffer, the LME49720 will output +/-13V into 600 ohms, and has an input noise of 2.7nV/root Hz. It's a DIP package as well.

So if you need the current, you can get more of it with one dual opamp instead of two duals or a quad.

[PRR]

> Can I use a TL074

The circuit could be made with a quad opamp package but it is more interesting to use a pair of dual opamps.

Not sure why "more interesting". Not as interesting as R.G.s' CheezWhiz factoid.

[PRR]

The four-TL07x array can drive 500 ohms to high level comfortably. It can face into true-600 ohm studio gear (very rare), or sixteen 10K line inputs parallel, without distress. It must be overkill for 99.44% of situations, though 47 cent overkill is no big deal.

What does digi2t really need? As mentioned, buffer *at guitar* to drive 40 feet cable. Cable is 30pFd/foot (sometimes less, rarely much more). 40 feet is 1,200pFd. 1,200pFd at _20KHz_ is about 6,000 ohms.

6K is a heavy load for naked guitar, but a real-easy load for nearly any opamp.

So just to drive this cable we could use ONE opamp 1/3rd as beefy as one TL071.

As R.G. says, most opamps get squirrely facing this much capacitance. Series resistor is by far the favorite fix. To maintain 20KHz response this must be less than 6K resistance. But it should be at least as big as the opamp's open-loop output impedance. TL07x has about 300 ohms inside. Pick a number between 330 ohms and 5.6K ohms. Anywhere in there will work.

There's other loading. INST inputs are usually very high impedance and can be neglected. LINE inputs can be as low as 10K. In this case we want the series resistor much-less than 10K. 1K is acceptable. So now pick a number between 330 and 1K. 470 560 680 are all suitable.

You may someday play a bigger stage. Designing-down from 6K for 40 feet to more like 600 also allows cable length to rise to around 400 feet. (At this point you have serious delay problems hearing what you played several notes back.)

So _me_, I'd skip IC1b IC2a IC2b, make R1= 470 (or whatever brown-stripe resistor I find in my pant-cuff), and do the rest just like AMZ Jack shows. (Or since TL072 is same-price and more generally useful than oddball TL071, maybe do IC1ab with R1 R2 = 1K each.)

[digi2t]

First off, thanks for the Cheese-whiz fix. A true «brick and mortar» approach, which my blue collar side can appreciate.

One of the downfalls of being technically disadvantaged where this stuff is concerned, I tend to over-engineer stuff, expecting the worse. I`m happy for the math lesson, and I won`t ever be on a stage of that scale, I`ll go with the one op amp, as recommended.

Thinking about it further, I`ve always used a 20`cable, and I`ve been happy with the tone. Adding another 20`was my main concern. I`ll stick the buffer just before the tuner in the middle, and things should be tickity boo.

Thank you gentlemen! I bid you all a great day, and may your cheese always be firmly afixed to your crackers.

[R.G.]

Seriously, think about how you might get a buffer right out at the guitar end. You'll be pleasantly surprised.

In my day job, we have a number of Japanese customers who are gaga over a strapmount buffer we make just for them.

... At least I *think* they strapmount it.

[digi2t]

Wow... a strap-on! Kinky little buggers.

I`m going to open up my tuner, and see if I can incorporate it into the same housing. I`ll save space on the pedal board that way as well.

[earthtonesaudio]

For when a "super" buffer is not overkill enough:

[digi2t]

Well, it so happens that I remembered the other day that I did have a buffer to test with already. When I built my Silicon Skyripper, I used the Klon buffer circuit in it. As a test, I plugged it in where I was thinking of using a buffer, and voila!, the tone perked right up. Not overly bright, and very clean, just like I remembered it. Very pleasant tone. I installed it right after my tuner, which is first in line.

I had a small enclosure hanging around (left over from the PLL build), and I put it to good use.







Finally used my first aircraft dash light bezel too, a la Spaceman effects. Yes, the bezel is dimmable.

For those who would like the vero, here it is;



Pretty much a rip-off of what I found on the net, but with the added LED resistor. I didn't use a 4.7K for the LED though, I opted for a 1K instead, with a super-bright red LED. Since I have a dimmer, I figured I could go with full warp.

Thanks to all for the buffer info.

[R.G.]

Good work. I kinda thought that even a modest buffer would be enough.

The Law of Diminishing Returns is one of Mother Nature's finest efforts. 

[mistahead]

Good work. I kinda thought that even a modest buffer would be enough.

The Law of Diminishing Returns is one of Mother Nature's finest efforts. 

So my DIY "Self-Sustaining Wetsuit with Microfine Filtration System" isn't a final solution to water shortages and dehydration after all?

Two weeks in and I thought I was doing ok now I'm used to the taste....