Echoplex pre-amp

[Xplorer]

sweet ! thank you !

PM sent

[mightymike]

I know this is an old thread, but I'm looking at this 12000 Super Tremolo build. And I've wanted to use the little board to experiment with gain or boost mods. So many ideas, then I stumbled on this thread, and it made me think.

You know how George sells the Zero Loss Effects loop kit? What If you did the same thing, but with an EP3 Pre amp board that you could mount inside the amp? **Sure it would need a separate DC supply **, but how cool would that be? Even cooler if it was on the little board in my 12000 super tremolo project, in hardwired turret style, But even if you had a kit, that mounted to the chassis like the loop, with a foot switch.



** Maybe you could kill 2 birds with one stone and get DC heater out of the deal with a separate 18v tranny for the EP3 pre, with 6v spliting off some how for DC heaters. Then have a Delay pedal in you Zero Loss effects loop.

Just dreaming out loud, but I think that would be killer.

[spaceace76]

hell you could do it with a charge pump up to 18v from the 6v heaters. the only stumbling block there might be the amperage, not sure how much the chips can withstand or how much the amp would be hitting it with after all the tubes are spoken for. interesting idea mike!

http://geofex.com/circuits/+9_to_33.htm" onclick="window.open(this.href);return false;

[Xplorer]

hello,

thinking of building an echoplex preamp , to go with a fuzz ( as i liked my last fuzz clone, played with the echoplex ) ,
i noticed a lot of differences that i can't really understand, from an ep pre schematic posted by Peter somewhere, and the ep3 schematic, that i compared to my echoplex ( really the same, and i did a layout presentation some months ago, comparing the schematic and the boards, to be sure to correct anything wrong, even if i still have some noise i'd like to remove !!!!!!!!!! ) .

here it is :

- before R4 ( 22k ) there are 22 volts going into the ep3 preamp circuit, and 13 volts after R4.

- C2 ( 0,022uf ) doesn't exist on the ep3.

- R2 1M : both feature this resistor but i wonder if i should perhaps remove it, cause on a fuzz, it removes some signal or sustain, with a high input impedance, right ?

- C3 ( 0,22uf ) doesn't exist on the ep3

- R5 and R6 : well, i see 2x 100k on the ep3, between the 500k echo volume ( and output ) and C4 ( 0,1 uf )

- C1 is 100 pf on the ep3, and 220 pf on the ep pre supposed schematic.

- there's a 0,047 uf orange drop cap on the echoplex, between the input and R1 ( 100k )

is it to improve somethings ?

should i try this ep pre supposed schematic or directly the ep3 schematic ? then i'd need 22 volts and i wonder if i should follow the same thing as on the ep3 with these four pieces after C4 : 2x 100k , an output and a 500k volume pot.

thanks !

[Xplorer]

ooooh ... i see ... it's based on the early echoplex schematic, i understand now.
i have two echoplex, one isn't working yet and seemed to be a black early one, ( but judging the preamp board it's a later one ) and the other is more recent. so as i understand the preamp of the early units sounds better ? i think i'll mod mine ..

don't try to understand what these colored circles mean, it's nothing related to this subject.

now i wonder if this 220k going from the ground to C4 is playing the role of the 500 k record level pot. ( ?? )
and then the 100k R6 is from the later schematic as the early one had a 220k there... and there's still another 100k between the output lug and the first or third lug of the 500k volume pot, which is an audio pot i guess.

[Xplorer]

just for the eyes

this is the echoplex of brian may, found on regis's site. very cool !
i wish i could find a spare record head rail , and sliding piece for the record head, cause i'm missing one and can't use my second echoplex for now.

[Xplorer]

Guys, am i wrong or is this a correct echoplex preamp ?
i think that the ground between the 0,1 uf and the 220k is completely false, i've got it wrong. But i couldn't understand why this R5 - 220k is going to the ground on peter's schematic.
if talking about this particular preamp circuit seems irrespectful of Peter's ep pre's work i apppology, i'll stop it. i'm just trying to understand my ep3 and compare it with a home made circuit.
also on the ep3 schematic ,there's a node between the input, R1 100k and ... the ground ... it's wierd isn't it ? a ground at the tip of the input and a ground at the ring of the input ? so i erased it here.
i'm not sure about the role of these 2 100k at lugs 1 and 3 of the volume pot, going to the output tip.
also, the ep3 schematic shows 25 v . my ep3 shows 22v, and the ep pre is said to work at about 18 volts. i think i'll try at 22v-25v.

[fatihelloween]

Anyone try or compare with Xotic EP Booster ?

[firehand]

Hey people!

I was watching the schematic posted in the first page of the EP PRE and I was wondering where does the voluem pot go? And which is it's value? I want to build it for personal use, i'm no technician, but i got great soldering chops and can read most shcems.

Thanks!

[rgorke]

Hey people!

I was watching the schematic posted in the first page of the EP PRE and I was wondering where does the voluem pot go? And which is it's value? I want to build it for personal use, i'm no technician, but i got great soldering chops and can read most shcems.

Thanks!

here is how my pedal is wired.

[MackBurkes]

I've heard you've been in and out of commission due to heath reasons, and I'm always glad to hear about someone getting one of your pedals in the mail since that means you're doing better. I hear it a lot too, the pedal is a big hit!

Thanks for the info, and stay well!

Thanks spaceace,

I believe most of the health problems are well behind me now. During a recent trip to Carnarvon Gorge National Park, http://www.derm.qld.gov.au/parks/carnar ... index.html we walked about 15Km (nearly 10 miles) through some demanding terrain in one day, so I guess you'd say that we are both reasonably fit.

Mandy has Diploma qualifications in Electronic Engineering and years of practical experience both on the workbench and in management, so she is now doing a lot of pedal assembly and answering email enquiries.

Waiting time for an EP-PRE is currently no more than a month.

We're getting ready to travel throughout Australia, putting pedals together as we go. During our recent shakedown run, we sent pedals from Injune http://en.wikipedia.org/wiki/Injune,_Queensland, Emerald http://en.wikipedia.org/wiki/Emerald,_Queensland and Longreach http://en.wikipedia.org/wiki/Longreach,_Queensland.

Here's a photo of our caravan - I believe the Americans here would call it a Travel Trailer.



It's Solar powered with high efficiency LED lighting and carries enough water to remain away from civilisation for a number of days at a time. There is a good sized workbench inside.

We are at home right now finalising the design of a couple of new pedals before heading out again.

Peter.

Thanks for sharing desing and other information.. It is helpful while camping and going for long tours and will solve the power problem to an extent.

[bobtec]

why are they so much$$ Dunlop want $175.00..Just for a cool looking box

[Jeremy1283]

Hi Roger, it's quite a while since I last heard from you, but I guess this thread is getting old too

To answer some questions:

I use the LT1054 for the charge pump. It costs a little more but is a far more robust chip than the MAX1044. The pedal path is littered with broken MAX1044s because there was a small spike on the 9V supply A charge pump "Doubler" will never give double the input voltage, but. if you use Schottky diodes in the charge pump circuit, you can get close to double the input voltage. A charge pump power supply is a type of switch mode or switching supply. These generate a lot of high frequency electrical noise, requiring very good filtering.

There are very few JFETs that are an exact match for the original TIS58. If I hadn't worked in R&D as assistant technician to an analog design engineer, I would probably have never understood the significance of some of the data sheet parameters. Part of my job was to find components that could meet his specifications.

It's not easy to explain the need for capacitors and resistors that go to ground, without at least a few days worth of classroom study in electronics. The simplest explanation is that an electronic circuit must have a complete path from positive to negative, or vice versa. In this circuit, ground is negative, and these components complete the path. C3 affects the frequency and phase responses of the circuit. In later versions of the EP-3 it was not in the circuit.

Spaceace, we've talked before via PM. How are you?

The true purpose of the 1M input resistor (R2) from the gate of the JFET to ground is to provide a ground reference for the gate. It's a coincidence that it also sets the input impedance, in conjunction with R1, C1 and C2. At normal guitar frequencies, the input impedance will be very close to R1+R2 = 1.1M. At radio frequencies, the input impedance will be determined by R1 and the capacitive reactance of C1. Capacitive reactance http://www.tpub.com/neets/book2/4c.htm is the effective resistance that a capacitor will present to an AC signal. R1 and C1 create a filter to prevent radio frequencies from getting into the preamp. C1 will bleed any radio frequency signals to ground.

The output impedance is very important to the phase response of the EP-3 preamp. There's another guy selling PCBs for what he claims is the same thing as an EP-3 preamp, but he just connected a 50K pot to the end of the snippet of schematic that I posted, and that just doesn't cut it.

The Xotic EP Booster is effectively just a generic JFET Booster that has very little in common with the Echoplex EP-3 preamp. The cosmetics of the box come a lot closer to the EP-3 than the circuit inside

There are also other pedals around that use a buffer to reduce the high output impedance of the EP-3 preamp. One of the changes that came in with the EP-4 was an output buffer, and it just doesn't have the EP-3 tone.

I hope this helps.

Peter.

So the Xotic ep3 boster I have isnt the same as the original pre amp echoplex!

[rgorke]

Hi Roger, it's quite a while since I last heard from you, but I guess this thread is getting old too

To answer some questions:

I use the LT1054 for the charge pump. It costs a little more but is a far more robust chip than the MAX1044. The pedal path is littered with broken MAX1044s because there was a small spike on the 9V supply A charge pump "Doubler" will never give double the input voltage, but. if you use Schottky diodes in the charge pump circuit, you can get close to double the input voltage. A charge pump power supply is a type of switch mode or switching supply. These generate a lot of high frequency electrical noise, requiring very good filtering.

There are very few JFETs that are an exact match for the original TIS58. If I hadn't worked in R&D as assistant technician to an analog design engineer, I would probably have never understood the significance of some of the data sheet parameters. Part of my job was to find components that could meet his specifications.

It's not easy to explain the need for capacitors and resistors that go to ground, without at least a few days worth of classroom study in electronics. The simplest explanation is that an electronic circuit must have a complete path from positive to negative, or vice versa. In this circuit, ground is negative, and these components complete the path. C3 affects the frequency and phase responses of the circuit. In later versions of the EP-3 it was not in the circuit.

Spaceace, we've talked before via PM. How are you?

The true purpose of the 1M input resistor (R2) from the gate of the JFET to ground is to provide a ground reference for the gate. It's a coincidence that it also sets the input impedance, in conjunction with R1, C1 and C2. At normal guitar frequencies, the input impedance will be very close to R1+R2 = 1.1M. At radio frequencies, the input impedance will be determined by R1 and the capacitive reactance of C1. Capacitive reactance http://www.tpub.com/neets/book2/4c.htm is the effective resistance that a capacitor will present to an AC signal. R1 and C1 create a filter to prevent radio frequencies from getting into the preamp. C1 will bleed any radio frequency signals to ground.

The output impedance is very important to the phase response of the EP-3 preamp. There's another guy selling PCBs for what he claims is the same thing as an EP-3 preamp, but he just connected a 50K pot to the end of the snippet of schematic that I posted, and that just doesn't cut it.

The Xotic EP Booster is effectively just a generic JFET Booster that has very little in common with the Echoplex EP-3 preamp. The cosmetics of the box come a lot closer to the EP-3 than the circuit inside

There are also other pedals around that use a buffer to reduce the high output impedance of the EP-3 preamp. One of the changes that came in with the EP-4 was an output buffer, and it just doesn't have the EP-3 tone.

I hope this helps.

Peter.

So the Xotic ep3 boster I have isnt the same as the original pre amp echoplex!

Nope. That doesn't mean that some folks don't think it sounds good, just not exactly the same.

[Jeremy1283]

So i gonna sell that pedal. Lol
Any ideas on how do obtain a nos tis58 jfets?