This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.

Monday, October 3, 2016

EchoPlex Preamp

The EchoPlex Preamp emulates the input stage on the old EchoPlex EP-3. It provides up to 11dB of gain and is mostly used as an always on pedal to sweeten the user's tone. If you want to add the volume control, use a 500k pot and connect lug 1 at the junction of the 100n cap, 220k and 100k resistors, and run lug 2 to ground. This also works really well when running at 18v. Schematic for reference can be found here.


57 comments:

  1. Hi! The volume control with 500k pot in your comment means GAIN of the product version?

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  2. Replies
    1. Probably. Though you may need to adjust the value of the 22k resistor

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    2. I've made one using J201 and worked fine. Yes, 22k needed to be adjusted. Question, if I want to use a trimpot, how should I connect it?

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    3. Just jumper lugs 1-2 of the trimmer, then connect lug 3 to the voltage and lugs 1-2 to the other pad from the 22k resistors.

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    4. I built a few ones, I used J201 in the last one.
      I adjust the 3k3 too for more output, 1k5.
      Which is the recomended voltage to get adjusting 22k?

      Thanks

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  3. Why isn't the underside mirrored like the rest of your layouts?

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    Replies
    1. Um... cuz I forgot to do it. :D Fixed now

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    2. I started soldering this together then realized it :(

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  4. Hello, first congratulate you on your work is really incredible, I subscribed to your youtube channel; ).
    Do you think it is feasible that you can make a layout of the multiplexer echo machine? (1776 effects).
    It would be amazing.
    Best regards
    JP

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  5. verified. I just made it on perf board. Really puts a nice sparkle to the tone.
    Thanks for another great layout

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  6. Hi
    What would be the best bias on this one? 4,5v or could I get more volume by increasing the voltage? Thanx for the great layouts

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    Replies
    1. 4.5v is probably best. Increasing that probably won't give you more volume, at least without increasing noise or altering the tone. If you want more headroom, use an +18v supply

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    2. If I have the bias set on 4.5v at 9vdc, then I should double that value at 18vdc, is that right?
      If yes, then In miss the point... What is the difference between having a higher bias at 9vdc and being already higher at 18vdc? Can I just alter the r22k at 9vdc instead of going to 18vdc?

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    3. If you increase the voltage to Drain, the voltage to Source will increase too, and the working headroom will be higher (less compression/distortion).
      The resistor to Drain (voltage to jfet) is setted to have the 50% of the overal voltage input: not 9v strictly.

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    4. Think in the 22k resistor like an X in a equation: if you move that resistor, the overall functioning will change.
      The 50% I've mentioned, is the "recomended" area to work in this circuit to avoid volume loss, or in another extreme: saturate.

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    5. Thanks a lot for your prompt reply! I understand and I agree with what you said.
      I wanted to know, if the voltage to Drain that you would get at 18vdc can be set to be the same when using 9vdc by simply adjusting the 22k resistor?
      If yes, then what the point of using necessary 18v?

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    6. This comment has been removed by the author.

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    7. You're welcome! :-)

      Not exactly: you have to re-bias the resistor that goes from Source to ground.
      This one is setted to avoid the "distortion" point: depends of each tipe of J-fet and/or design.
      As I said... it's an equation: the J-fet is placed in between.
      22k resistor is the value, that in conjunction with Rs (source resistor), made the Jfet work with ~50% of voltage.
      Using 18v will made the Jfet work more "relaxed", more headroom (volume after compress).

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  7. How can I bias the transistor?? The V in D is 7.4

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    Replies
    1. Adjust the value of the 22k resistor

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    2. The voltage of D is 7.23 with a 22k resistor, I have to put a 63k resistor to have 4.5v in D, I discover, with 7.23v the booster are nice and clean and with 4.5v. The sound are fatter and a little harsh. Is nice in both ways!! Thanks man!! You're the best!!

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  8. the sound is really low, what should I do?
    the diode 5817 can be replaced with 4007 or 4148 right?

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    Replies
    1. I'll try with 4007; it's like 4001 with more wattage

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  9. just finished the perf version and the very first 2n5457 I pulled out of the tray fired right up! this is one of my favorite preamps.

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    1. all 20 or so Jfets worked the same for me - Vgs .8 volts

      not a lot of db boost but sweet tone fattner similar to a good RM

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  10. Hi, im a real newbie here, is there any way you can upload the pcb with the volume control? Is it necessary for it to work with 18v?

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    Replies
    1. Hope it help :)
      http://i.imgur.com/JGnYaIW.png

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  11. Hi, newbie here too, and it looks like an easy one to start with. I just have one question : how do I know what kind of capacitor I should use ? Is there a color code or something ?
    Thanks for your great work !

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    Replies
    1. There's a numerical code on capacitors. Just google capacitor codes. If you're concerned about the type of capacitor (ceramic, film, etc) in my layouts green = film, yellow = ceramic, grey = box, and black = electrolytic. Best of luck!

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    2. That's what I was looking for ! Thanks a lot !

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    3. Finally had the time to build it, sound awesome !
      I built it with a B500K pot. Passed the quarter of its course, it has no much impact. Any idea why ?

      Anyway, thank you for this blog. Up to the next build now !

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  12. I used 1n4007 instead of 5817.
    It's possible the 4007 lowers the volume due to voltage?

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    Replies
    1. I wouldn't think the voltage drop would be that dramatic...

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    2. I have there a few 1n5819... should I change the 4007 for this one?
      Which is the difference with the 5817?
      Thanks

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    3. The 5819 is in the same family as the 5817 (schottky diodes), but the 4007 will fine for this application too.

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  13. Is the same if I remove the 220k resistor, and put there a 1M pot as a variable resistor, for Master Volume?
    As I can notice, the 500k pot and 200k resistor are working in parallel to ground.
    Am I correct?

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    Replies
    1. No, the 500k pot and 200k resistor in parallel make the pot effectively 150k. Check out this calculator for parallel resistance:

      http://www.sengpielaudio.com/calculator-paralresist.htm

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    2. My bad...now I get it
      So, I'm doing the same if I remove the 220k resistor and put there 250k pot as variable resistor?

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  14. Newbie here. What can I do to get more bass out of this?

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    Replies
    1. Try increasing the value of the input capacitor (22nF right by the JFET). You can also play with the value of the output cap (100nF).

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  15. another newbie here, first thanks for the blog and the work ,when you say the 500k pot connect lug 1 to junction and lug 2 to ground the 3rd lug is jumpered with 2nd?

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    Replies
    1. It can be, but doesn't have to be. It should work the same either way.

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  16. Hello and thank you for this wonderful website!

    I have two questions, please:
    1. What FET exactly do you recommend?
    2. What is the real purpose of the diode and the 1000uF cap? Can I just adjust the 22k resistor instead, is it the same?

    Best,
    Y.

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    Replies
    1. Hi there! My humble oppinion:
      1. I've built several times this one; always used BF245 and 2N5457. J201 need to be rebiasing here.
      2. They're for reversed voltage protection. It's not the same to use that resistor.

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    2. Thank you very much for the prompt answer and help!
      1. Any experience with J202? Some swear on it saying it is the closest one to the original TIS58. I don´t have engineer´s degree, so I don´t know nothing about specs and stuff, sorry! :-(

      2. I understand. My question was actually going about the meaning of author´s sentence "works really well running at 18v" and about the debate 9v/18v. If there is only one specific voltage range for the right operation of every FET, I can not see how it will work on both voltages? When it works right on 9v, you have to adjust the 22k resistor in order to reach the same range when using 18v, does that make sense?
      For instance my build (w/ 2n5457) works good on 9v, but it is barely audible/ working when switching to 18v.

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    3. 1: not J202, but yes J201. It need to be re-biased! The last time I did it, replaced 3k3 res (from Source to ground) for 1k5: with this value I kept 22k, and 4.5v to Drain. I kept 4.5v to drain because...(point 2)
      2: Drain voltage is for design. In this case, it works with 4.5v (from 9v), and almost 9v from 18v. You have to see the mentioned Source res (3k3 or 1k5) to keep the Jfet 'balanced'.
      There's a looong way to understand it...a lot of equations and etc's.
      I keep it simple... I don't know if it es therical correct; but by ear, sounds really good.
      Less than that value, distort, and more than that value, reduce volume.
      More Drain voltage (+ 4.5v) gives more headroom, that's why using with 18v can help.
      Nothing works better than 5457's... but the closest one is BF245A.

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  17. Sry for newbie question, but it works with 9v?

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