Echoplex EP3 Preamp Based Circuit Layout by Ulysses

[ulysses]

long time no see folks

i designed and built this today.

with so many versions out there i tried to keep it as original as possible.

sounds really nice.

i have added it to my layouts section so others can build it if they are interested.
http://www.aronnelson.com/gallery/main.php/v/ulysses/ulysses_layouts/

cheers

[FUZZZZzzzz]

Looks very nice! thank you for your time and effort! will try this

[Gus]

I don't see an output cap in the schematic at the posted link

Also you are using a Jfet why would you want a 1meg antipop input resistor?  you can increase R2s value try a 10meg. 
You might want low DA caps for C1 and C2.

[ulysses]

you are welcome fuzzzzzzzzzzz

gus, yes i left off the dc blocking cap. i built it and it works fine. i should really get around to adding a cap to block dc on the output.

the 1m seems to work fine for pops, having said that i do use grounded input on the 3pdt. is 10m really going to help any more?

why would low DA caps help for c1 and c2?

thanks for sharing your thoughts.

cheers

[Gus]

Think about what changes with the antipop resistor value.  I don't understand the use of a JFET when the input resistance is under 1meg.
What is the input resistance of the circuit with the 1meg anti pop?

A well designed JFET build can have 1000meg or more gate resistors, this can be found in some condenser microphones

[ulysses]

hey gus

im not sure what you are saying.

i made the circuit to be exactly as the preamp is in the EP3. i added a 1m pulldown resistor to stop pops. 1m seems to be what everyone likes to use for a pulldown resistor- it doesnt pop and sounds great so i dont see what the problem is.

if people want they can make it 10m i guess- or leave it off if they want.

cheers

[Gus]

A passive guitar or bass and the cable used between the amp or effect have an interaction.

It changes EQ with differences in input resistance and the cable used

It seems a waste to me to have less than the 1meg input resistance of the EP It also sees a waste to use a JFET at under 1meg input resistance when a BJT could have the same or higher input resistance and more predictable bias.

simple resistor maths two 1 meg in parallel = .5meg  The input of the EP did not have a antipop
Just because you see 1meg antipops on the web does not make it a good choice.

IMO you want the largest resistor value for the antipop that does not pop

Look for some of my posts that show the interaction

Also you can't just drop a jfet in the circuit and have it work correctly

[IvIark]

Gus he's done a layout for the preamp of the EP3, there may be lots of ways to do things "better" but it seems plenty of people like and want it as per the original so they must have done something right.  Thanks for sharing the layout ulysses.

[Gus]

It will not act the same as the original with the antipop being 1meg

I am trying to get people to think about this circuit.

In some of my posts I try to show the interaction or as some call it "feel" with a passive guitar or bass with the cable and amp or effect.  This is important to know about for good design IMO.

I am not going to post about DA people should look that up and learn about what it is , there web pages that show up with a search.  I am giving a hint I often don't post every thing, often doing a search on the terms I use will get some good sites.

[pinkjimiphoton]

i OWN an ep3. it's NOT a booster.

this is one of them bogus cases of some fool taking something out of context, using it wrong, and then proclaiming it's brilliance, imho.

not that it may not sound nice, but using it as a preamp is not doing the same thing as using an echoplex. at all. period.

the "boost" is nothing more than a way to get a good signal to noise ratio.

it doesn't improve the tone of the guitar, if anything, it buffers it a little and rolls off some high end.

that said, people like the sound of it when it's cranked up to the point of being a mild overdrive.

if it works for people as posted, why reinvent the wheel?

10m/1m does it really have an audible difference? no offense brother gus, but i sure as hell haven't heard one.

this SHOULD have a blocking cap at the end. any time you have an amplifying stage, you need a blocking cap.

[Gus]

Here is a simple sim of a single pickup guitar with a 2.5H 7K pickup
C1 is the cable and R5 is stepped from 10K to 10meg
Blue is 100K red is 470K
Sim is set volume max and tone full treble
The antipop being 1meg is less of an issue with some other inputs but for an effect that you want high input resistance it can matter

[bool]

so for that reason if you really want to keep up with the "hi-z tone", it's quite possible that a naked jfet input (only a resistor-to-gnd) or for that matter a naked fet opamp input may be the best choice. Implementation details .. your choice.

[pinkjimiphoton]

look at the original circuit. THAT is what people seem to like the sound of.

just cuz something looks good on paper, how does it sound? i built up some knobless SHO's recently.

i found they sounded better with 1 m voltage divider than 10m.... 10 m was too bright for my taste.

echoplexes are not bright, if anything they tend to darken the tone slightly.....so i gotta agree to a point.

it all comes down to what sounds good.

as an input pulldown/amti pop resistor? 1 or 10 m isn't gonna make that big a difference to the tone i don't think. you could probably go smaller to eliminate pop in some circuits, tho ya may bleed a small bit of gain to ground.

since resistors are also filters when tied to ground, ya gotta think about the frequencies involved too. the bigger the resistor, the less bleed, the less bleed, the more treble gets thru. it may or may not be what you're looking to do.

again, i'm a hack, not an EE, i am more interested in what stuff sounds like than what it looks like on paper.

this reminds me of the TC electronic thing a couple years ago.... one of their multi pedals was getting modified by some shop, on PAPER it said it should sound inferior, but in reality it sounded better... so they did the mod themselves to their own product and sold it for MORE money.

use a breadboard and your ears, and try it a bunch of ways to see how it reacts/interacts, but let your ears decide. in the end, that which sounds good, IS.

not trying to argue or besmirch gus, he knows his shit!! but a lot of times he doesn't ultimately build the designs he posts. they almost always sound good, but i don't know if they sound like what he's hearing in his head when he's designing them.

actually, knowing gus a little, i am pretty sure he can hear it in his head EXACTLY right.

[Gus]

I built and adjusted a good amount of effects over the years.   I have not built that much since hurricane Irene.  I do post if they are builds or sim ideas.
If you build enough and do tests you can "know" the interaction and what it might sound like.  Some sims are circuits I have built.

Now the SHO with 1megs tone change is because there is a 1meg drain to gate, remember as the gain goes up the input resistance goes down with a circuit like that.  The max input resistance at a gain of one would be about .5meg 1meg and 1 meg in parallel.  
The input resistance goes down as you turn up the gain and the input node at the gain starts to act more like the - input of an opamp set up as an inverting amp.

So you might be happier with a BJT gain stage (BMP like bias)instead of a easy to damage mosfet.
Have you tried the NPN boost ver2?

The IC diode fuzz I posted has the RC input I like for the high pass and loading of the guitar for a distortion I like a different RC etc.  For the most interaction of the resonate peak due to the guitar ,cable, input resistance I tend to like 1meg and greater input resistance

Found the sim I made some time ago

[pinkjimiphoton]

thanks bro, that makes sense....

but i think what i mean is, if these guys LIKE this circuit, why not just let this one be, and design a BETTER one as an alternative?

that's the rubber hit the road part... if ya like something build it, if ya don't like it modify it!

[Pojo]

Going back to the EP3-like circuit the OP put up, I would think if the goal was to be as close to the original as possible that the LAST jfet I'd use would be a j201....especially with no changes to the biasing resistors. The datasheet for the TIS58 shows me that a higher IDSS, lower gain part like the mpf102 would be much more suitable. Then there's the source voltage...if I'm following this schem correctly (and I could very well not be) the original fet has 22V to work with. Not saying the circuit displayed here doesn't sound good, but if the goal is to capture the 'magic' of the EP3 then fet choice and source voltage should be top considerations IMO.

[pinkjimiphoton]

that's why i say all this is is an overdrive circuit, with nada to do with an echoplex or it's "tone".

it's smoke and mirrors, people will buy fuggin' anything and swear it's the grail, dude.... if they read some other idiot says it's cool for 'em.

sorry.... not rankin on you guys for digging this circuit, but it has a bout as much to do with an echoplex as the computer i'm typing on does.

a REAL echoplex, at best, is a tone sucker. not a booster. it just don't work that way. i'll have to put my plex in a t./b looper and see if it's even unity gain... i bet it's a shade below.

[ulysses]

man..

what happened to you guys? whole lot of dick measuring going on here..

1m 10m 100m who gives a @#$%?

i stated on the layout this is based on the original circuit, i added a pull down and changed the tranny to one i thought "sounds really nice" (stating i had changed the tranny AND listed the tranny the circuit originally had)

i even called it a "BASED" circuit ffs.

so if you want to try it.. go on and try it.. i think it sounds really nice. it'll only take you 20mins to give it a go and if you think its shit - desolder it.

cheers

[ulysses]

so if i'm reading your graph correctly low e string at 82hz shows bugger all difference between 10m and 1m pulldowns?

[Gus]

so if i'm reading your graph correctly low e string at 82hz shows bugger all difference between 10m and 1m pulldowns?

The first graph is to show what happens with the higher frequencies.
The second graph is to show what changing the input cap does with a guitar. If you are playing loud in a band with an open back speaker cab sometimes you want to reduce the lows to reduce the speaker cone excursions.
The forum is not a face to face interaction so maybe the posts can sound harsh. 

The real Ep-3 does not have an antipop resistor
Some forum readers might build what you posted and had issues with no output cap going into a tube preamp without an input cap and changing the bias on the input tube.  At 9VDC often you need to select your jfet carefully for the bias. 
What happens when you apply 4.5VDC to the grid of the input 12ax7 tube in a preamp?

Now for Jfets assuming you want the bias at 1/2 the supply and will use a 22K drain and need to change the source resistor for biasing.

For this circuit VDCsupply/22K=the min IDSS I would use. I would use an even higher IDSS

9VDC/22k=.41ma so some J201s might not bias
18VDC/22K= .82ma
22VDC/22K= 1ma
You don't want to change the drain resistor value if you want to keep the same output resistance.

I left a note on the sim about the RC time constant in the source leg.