Ok gurus, answer me this

[R.G.]

Don Tillman's FET preamp is still around! I remember that from alt.guitar.stuff.and.nonsense way back there.

Transparent it's not, but it's sure better than an unvarnished pickup all by itself. And it does buffer enough, probably. I always though it added a bit of second-harmonic/asymmetrical amplification sweetening, but that's often not a fault.

To cut its gain by the 3db he mentions, split the 6.8K drain load resistor into half, maybe two 3.3K resistors, and take the output from the middle of the split. It might work OK just to lower the value of the 6.8K to 3.3k, too. I suppose you could make the entire 6.8K drain resistor be a 5K pot.

[daz]

Don Tillman's FET preamp is still around! I remember that from alt.guitar.stuff.and.nonsense way back there.

Transparent it's not, but it's sure better than an unvarnished pickup all by itself. And it does buffer enough, probably. I always though it added a bit of second-harmonic/asymmetrical amplification sweetening, but that's often not a fault.

To cut its gain by the 3db he mentions, split the 6.8K drain load resistor into half, maybe two 3.3K resistors, and take the output from the middle of the split. It might work OK just to lower the value of the 6.8K to 3.3k, too. I suppose you could make the entire 6.8K drain resistor be a 5K pot.

I did just that since i last posted. I got it to approximately unity, but you're very right...it is NOT at all transparent. Any suggestions for a very transparent and simple one? Even tho it's not a particularly good pre, i could see the potential if i could have one that IS transparent. I really like the way it retains the high end's tone when i roll off the volume. And i don't mean in keeping the highs, but it somehow just makes them sound more right. But the inherent voice it has isn't good. So a transparent one that does the same would possibly be a big deal for me. So anyone who knows of a definately transparent one, i'm all ears.

[Chuck H]

Did you say that you still need a bright circuit on the volume control? That surprises me. But the actual output impedance of that buffer circuit may not be low enough to squash the problems. Maybe a more transparent AND lower output impedance buffer?!?

[daz]

Did you say that you still need a bright circuit on the volume control? That surprises me. But the actual output impedance of that buffer circuit may not be low enough to squash the problems. Maybe a more transparent AND lower output impedance buffer?!?

Yes. My bleed caps are hooked to an unused tone control in series to lower thier effect probably 50% of the way to no cap at all. If i turn it all the way it's too muddy even with the preamp. But it IS less so.

[daz]

I just remembered i might have another box i built a few years ago and sure enough i found it. I can't remember what it is but i think it was a clean boost that i added a gain knob to and it also does some fairly hi gain drive. Might be one of those jack orman jobs but i'm not sure. Anyways, with the drive knob off and the volume at unity it's a lot better than the other one. It really makes those pickups much better. My other guitars it seems like overkill, like they don't need it. That would however i think speak to the likelihood those wide range buckers have some sort of bad design issue with impedance or something. But as good as it was it could be better so i still want to find a good truly transparent top notch circuit. If i can find one thats simple enough i may put it in the guitar since i don't think i'd want it with the others.

[Chuck H]

Do you have the NEW buffer set up after the volume control or after the pickup?

[daz]

Do you have the NEW buffer set up after the volume control or after the pickup?

Are you assuming it's in my guitar? it's in a project box. Maybe you mistook what i said about *thinking* i might put one in my guitar. But i wouldn't even consider that till i find a good one. This one isn't great, but better than the first one.

[frus]

if you've got a (long) cable between the guitar and the buffer, then it's doing nothing useful... it's meant to be installed in the guitar to be able to drive the cable length (or better, capacitance)
no wonder it's not keeping the guitar from loosing treble

[Steve Conner]

Yup. To get a better idea of what the buffer would do installed in the guitar, use the shortest cable possible between guitar and buffer. Maybe a patch cord from a pedalboard, and let it dangle in midair.

If you want transparent, it would be hard to beat a high-end FET input opamp like the OPA134 or OPA604 running off two 9V batteries for more headroom. The simple FET buffer circuits will all introduce some distortion. It's mostly sweet-sounding second harmonic, so you might well prefer it to the clean sound of an opamp, but you'll never know unless you try both.

Last of all: One of the pickup gurus (Possum?) says that the cheap screened cable used in budget guitar wiring harnesses sucks tone. I find that pretty hard to believe myself since the length of wire used in the guitar is so short compared to the cable between guitar and amp, but there might be something in it. Especially if the pickup switch is on the top bout a la Les Paul, with long runs of screened cable going to it from the control cavity.

[daz]

I'll give the short cable idea a try tonite, thanks.

[Chuck H]

Yup. Ideally the buffer amp would be installed between the pickup and the volume control. That way any inductive weirdness from the pickup/load relationship become moot and there is a lower impedance to the actual resistive divider and capacitive cable shield. Without doing it that way the point is missed.

You could actually test without installing it in the guitar. Just bypass the guitars circuit and wire the pickup switch straight to the jack, bypassing the pots entirely. Then include a volume control, post buffer, in the project box so you can determine how it will behave.

[daz]

Good point chuck. If i do this i will remember to use the wire from the switch to the pot input as my buffer in. But can anyone point me to a known good transparant buffer? (small simple circuit so it can be made tiny enough to fit easily)

[loudthud]

If you don't want to build the buffer into the guitar, duct tape the project box to your guitar strap and connect with a short cable.

I saw another simple buffer project somewhere that was built into the phone plug at the guitar end. It was phantom powered from the far end of the cable with just a pull up resistor.

I have a box I built during the Reagan administration. A JFET follower with a variable capacitance load.

[R.G.]

Getting a really transparent, really small preamp done is not an issue. The entire thing could be smaller than a fingernail. Probably less than a day from concept to ready-to-print PCB layout.

A JFET/bipolar cascade, a FET input opamp, bootstrapped bipolar, lots of choices, and many with low power requirements.

As noted, the ideal place for these is as close to the pickups electrically as your pickup switching arrangement can stand; definitely before controls in the guitar.

Getting the **DC power** to it is the challenge. There's room under the pickguard, even in a strat, for a stack of coin cells, but then you still have to remove the pickguard. That's why I came up with the coin slot battery. If you could find a place to run two small wires from the front (well, OK, or back) side of the guitar, you could disguise a couple of coin cells on the outside.

[daz]

Well, after what those Chuck said about putting it after the pickups it hit me that if i'm gonna do this, thats definately the way to go because it would eliminate the volume pot's effect on treble. My only concern is i really don't want to have to pull the cable out every time i put the guitar down. I often pick it up 5 or 10 times a day and would prefer to leave the cable in, nor do i want to put a switch in to cut the battery. So many important life decisions.....

If you don't want to build the buffer into the guitar, duct tape the project box to your guitar strap and connect with a short cable.

I saw another simple buffer project somewhere that was built into the phone plug at the guitar end. It was phantom powered from the far end of the cable with just a pull up resistor.

I have a box I built during the Reagan administration. A JFET follower with a variable capacitance load.