EP-PRE revisited

[Coot Boy]

This is the Tillman FET preamp http://www.till.com/articles/GuitarPreamp/" onclick="window.open(this.href);return false; and here is how it sounds http://www.youtube.com/watch?v=RDeJXaxguqU" onclick="window.open(this.href);return false;
It's all very simple and nothing new but ends up sounding pretty good.

I just finished making one of these, when the guitar is on 10 it sounds just ok but if you turn the vol knob you get very loud scratchy sound, if you turn the guitar vol off the scratchy sound is horendous from off to one, the pickup switch made a huge noise (scratchy thump) as well when I switched positions, also doesn't boost at all, just rolls off some top end. Very disappointing, you couldn't use this seriously. Shame coz I had all the parts and it cost me nothing, maybe that's why it sucked.

[leadguy]

Don't throw it away. It sounds like your guitar electronics are not 100%.

The Tillman FET preamp has only slight gain (3 dB gain) but if you want more gain all you have to do is put a 10 uf capacitor across the 2.2k resistor.

http://www.marshallschematics.com/buffer.shtml" onclick="window.open(this.href);return false;

The Tillman FET preamp is not that much different from any other FET preamp including the Echoplex EP3 and the Xotic and the ClinchFX.

It is the FET itself that is responsible for the tone (as any experienced DIY pedal dude will confirm) and not the power supply (impedance) or minor FET spec spreads or certain frequency phase shift or whatever else pedal makers claim.

The Xotic EP Booster is almost identical in design to the Tillman but has more features like volume and filter switches and more adjustable gain, but both are just common source FET designs and so is the real Echoplex EP3 preamp. More features can be added to the Tillman circuit as well depending on simple design mods and more gain can be done easily with the 10 uf cap across the 2.2k resistor for a start.

[Coot Boy]

Nothing wrong with the guitar/s mate, trust me, all 10 of my home made strats work properly through all my amps. I used a J201, I have a bag of them. I'll have another look at it tomorrow, I'm sure it's wired right. Thanks for the responce bro.

[leadguy]

Well I'd check the wiring and try a different FET and do the 10 uf capacitor across the 2.2k resistor and see how that worked.

[Coot Boy]

I found a mistake in the wiring, I had the 51k on the + side of the 4.7uf cap. So I put it right, no diff, pot noise is on both ends of the volume pot, inbetween there is not much output, switch still thumps, I swapped out both caps, still no diff. Tried a heap of fets. I'm stuffed. The noises are the killer, if I could fix that I'd be happy. I just can't see what else it could be, it's a simple circuit

[spaceace76]

double, triple, and quadruple check your FET pinouts.
are you talking about a Tillman preamp build or an EP-Pre build?

can you post any pictures?

[Coot Boy]

It's the Tillman build. It's just all the parts hacked together on some perf board with a socket for the fet. I've tried the fet/s in both ways, the noise is the same, the output is hotter one way.

[spaceace76]

that's just the orientation, it could have a totally different pinout. depending on where you got the part, there might have been a datasheet that would clarify the pinout. the gate is not necessarily the middle pin, and the drain and source are not necessarily on either side.

this J201 datasheet demonstrates what I mean:
http://www.vishay.com/doc?70233" onclick="window.open(this.href);return false;

[leadguy]

Double check the wiring and polarity of the electro caps.
When something I've built doesn't work it has turned out to be my fault 99% of the time.

I'd say it looks like a FET pinout problem.

The 10 uf power supply electro can be ditched until it's working properly.

Here is a J201 FET stripboard/veroboard layout

http://johannburkard.de/blog/music/effe ... itter.html" onclick="window.open(this.href);return false;

[Coot Boy]

that's just the orientation, it could have a totally different pinout. depending on where you got the part, there might have been a datasheet that would clarify the pinout. the gate is not necessarily the middle pin, and the drain and source are not necessarily on either side.

this J201 datasheet demonstrates what I mean:
http://www.vishay.com/doc?70233" onclick="window.open(this.href);return false;

Yee haa dude, thanks a lot for that, it's working great now, I can't make any serious noise as it's night time now but tomorrow I'll run the amp up n see what we have here. The volume knob works great now and the pickup switch is silent. Now that it's works, I can experiment with adding some gain and maybe some top end, I'd like to add a true bypass switch as well. I'll post tomorrow after I crank up the vol. Thanks a million man.

[Staalhoofd]

I have a question (possibly a stupid one)

Ed used 2 Ep-3's and the idea is to have the guitar signal out of phase (for 3D effect). Correct? If you place 2 EP-3 in series, isn't the second EP-3 placing the guitar signal back in phase.

So, in other words, didn't Ed use the 2 EP-3's in parallel to maintain the out of phase/ 3d effect?

I'm asking because I want to buy an xotic ep-booster to go with my EP-pre. Do I place them in series or parallel?

[leadguy]

I don't know how all this phase stuff started but it's all barking up the wrong tree.

A transistor in a common emitter configuration shifts the phase of the input signal by 180 degrees or inverts the polarity of the signal and so does a FET in a common source configuration which is what the EP3 preamp is.

A 180 degree phase shift does not by itself do anything to the tone, it just inverts the polarity of the signal and another 180 degree phase shift inverts the signal again back to the original signal.

A 180 degree phase shift doesn't mean anything unless it is in reference to another signals phase which is not what we are talking about with the EP3 preamp as there is only one signal.

To make it simple, pickups can be out of phase but there needs to be 2 signals from 2 pickup coils to be out of phase, one pickup can not be out of phase.
Try getting an out of phase sound from a one coil pickup.

The EP3 preamp tone enhancement comes from the tube like behaviour of FET's and has been known for as long as FET's have been around.

With guitar effects, it turns out that not many of them used a FET preamp in the 60s and 70s and the Echoplex EP3 and EP4 did use a FET preamp.

So the Echoplex EP3 or EP4 preamp gives a tube like clean sound and is then getting put on tape and then read off tape and then going into the dimed distorted amp.
It's a bit like running a clean tube amp just before the dimed distorted amp and is like slaving in reverse

clean tube(or FET)->distorted tube

and slaving is

distorted tube->clean tube

They both have a clean tube thing and a distorted tube thing going on even though the placement is different.

The actual Echoplex EP3 preamp is very simple.
It has a filter at the input to set the high frequency cutoff and then it's just a FET preamp the same as the Tillman FET preamp but with a capacitor across the source resistor for a bit more gain and that's it.

[spaceace76]

the phasing stuff started with Peter's claim that the circuit shifted the phase in a way that was pleasing to the ear, which would not be 180 degrees. I'm not sure that 2 EP-Pre's in series would be in phase with the original signal, my guess would be that it's not.

[Staalhoofd]

So if I understand correctly, you could run a splitter cable into two ep-3's and run these two in parallel? What would that bring as far as sound goes? There was talk that Eddie possibly ran the two ep-3's in parallel, right?

[spaceace76]

I'm not sure there would be much of a point, and I'm not sure he even did that. In most of the live shot's I've seen he's just daisy chaining all the first channels together. The only reason to have multiple EP-3's would be to switch between multiple delay times, or to just have a backup. I don't think Ed was cooking up some weird tone recipe with them