Monday, 12 May 2014

A Pair o' Preamps - Echoplex and Tillman

Just a couple of little preamps that have been requested.  Some people swear by these little circuits and use them at the input of other effects because they like the way they colour the sound, so a quick build for people to experiment with.




A couple o' variations:

EchoPlex Preamp with charge pump for 18V from a 9V supply





Early version EP3 with volume control





Tillman with Gain Switch



76 comments:

  1. Tks!!
    But isn't this like regular buffers?
    Cheers!

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  2. Is there a difference between this type of circuit and a buffer?

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  3. They both boost the signal by some degree, buffers are usually unity gain.

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  4. They're not buffers, they're boosters with a fixed boost set approximately by the drain resistor divided by the source resistor. They do have a high input and low output impedance like a buffer, but they're not unity gain source followers.

    If you wanted you could omit the source resistors and put an appropriate pot in there instead so you could set gain, but I just wanted to post them in their raw form, so you can use and adapt as you want.

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    1. What would you recommend for a gain control on the Echoplex?

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    2. I'd try a 5K with both

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    3. ivlark
      5k pot? Log or liner? What source resistor are talking about? I am learning so much here on this site. What a great way to share! thank u for that! lol Cheers
      Vince

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  5. Cool. Thanks. Will try the Echoplex...

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  6. My first real build that wasn't a BYOC kit was the Tillman (with a knob). I made it for my girlfriend to use with her passive pickup ukulele. It fattens it up nicely.

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  7. The EchoPlex schematic work to 18v....... You have another schematic?

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    1. Put 18V into it then, as long as your capacitors are rated appropriately you can supply it with any voltage up to the maximum for the jfets.

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    2. Thanks for the layouts lvlark. Really nice and thanks for your time. I enjoy so much!
      lol
      Vince

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  8. Is the 3m resistor just a pull down?
    Cheers
    Dave

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    Replies
    1. No it also sets the input impedance, but you can still just use your closest resistor, it doesn't have to be exact

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  9. On the echoplex one, would the gain pot simply be a 100k lin pot replacing the 100k resistor directly after the input?

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    1. You could do it like that, but I don't particularly like the method of just increasing resistance in the signal path to affect the signal level going into the stage. I'd much prefer to leave the circuit true to the original and control the true gain of the stage by altering the ratio between the drain and source resistors, which I personally would do by replacing the source resistor with a pot.

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  10. The Tillman can be made high gain with a cap from source to ground (I use a 10uf) on a switch. I recommend replacing the 51k resistor with a pot in this case. Then you have a preamp & light overdrive- it's my go-to OD.

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  11. Do you have a link to a schematic for the Echoplex?
    Thanks!

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  12. Echoplex Verified. Tested it on a Strat. It also sounds surprisingly good on my cheapo Hadean EB-510 bass as well.

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    Replies
    1. Awesome, thanks for verifying matey

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  13. Total newbie here. Which resistors are the drain and source? The 22K and 3k3? Just want to make sure I'm understanding all this correctly. Just LOVE this site!!

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  14. Forgot to mention- audition J201s and play with the gain cap. Low values make a treble boost!
    Cheers

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  15. Hi,

    How must I connect the Gain Switch of the Echoplex on to the Veroboard?

    Cheers, Jan

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    1. If you want to add a gain switch in the same way Peeps described for the Tillman, solder a 10u cap from the 2nd from bottom to the bottom row, with a cut to isolate the cap from the other components soldered on the 2nd from bottom row. Then one wire from the switch goes to the JFET source, and the other goes to the 2nd from bottom row so it connected to the cap you just soldered in.

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    2. Hi Ivlark,

      Thank you for the explanation. Cheers, Jan.

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  16. Hi Lvlark,

    Can it also been done with a Gain Pot (not a on/on swith, but a turning knob)?
    I don't know the correct English word.

    How must this be connected? The same as your 09.11 post?

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    Replies
    1. Emitter to pot lug 3, lug 2 to the new 10u cap, lug 1 to ground

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    2. Excuse me Ivlark, could you expand on how to insert a gain pot? I'm just a novice and I tried replacing the 3k3 resistor with a b5k pot. the result was that the volume was practically zero. i took out the 220k resistor, but the effect volume still gets, at max, to 50% of the clean volume. Please help and thanks for your work!

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    3. (i'm referring to the first echoplex preamp on top)

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  17. You can verify the Tilman with gain switch. Sounds ok, just like a buffer type ciruit would, brings back the highs. The gain cap I'd leave in all the time, it makes the circuit a little louder so that you get just a little boost out of it.
    Cheers
    Dave

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    Replies
    1. Thanks for verifying that one mate

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  18. Hello ,

    Do you know any transistor replacement for the Echoplex?

    Thanks.

    Messbel.

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    Replies
    1. The original used TIS98's or maybe TIS58's which will probably be difficult to find. Try any other JFET, I've suggested the 2N5457 in the layouts above.

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    2. OK , thank you so much. I've got a Belle Epoch from Catalinbread , used as a preamp it sounds really great , I'm gonna look inside and try to locate the JFET. I'll tell you what I'll see.

      Cheers,

      Messbel.

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  19. i see this is based on the ep3 later model. in the schem the 100K and 1M resistors are supposed to be a 500KA pot for volume. cheers

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    Replies
    1. Thanks for the info. Do you mean that the early model used a 500KA pot instead of the 100K and 1M?

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  20. I requested the early EP-3 layout a while back and included a late model EP-3 to early EP-3 conversion schematic if that would help.
    http://guitar-fx-layouts.42897.x6.nabble.com/file/n1472/ep3_conversion_schem.jpg
    The 220k and 100k resistors meet at lug 1 of the 500k pot - and lug 2 is going to ground.

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    1. That method with the pot wouldn't work very well when just building the preamp, because that is designed to ground the output from the preamp or the output of the echo head and by doing so alter the level of echo. So just a standard volume pot as we usually wire them would be the way to go. I'll add it. Now added

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    2. I found a few posts on various forums from Peter Clinch, who's EP-PRE is considered to be one of the finest EP-3 preamp pedals available. He addressed a couple of things that I'd like to share here as they appear to be important bits of info concerning output impedance and the 500k pot:

      "The output impedance of the Echoplex EP-3 is in the region of 200K. In designing the EP-PRE, I included a resistor network that would maintain an output impedance of 200K. I was aware that this may cause problems in some situations, but I tried a number of methods to reduce the output impedance, and found that they all detracted from the magic EP tone. Sadly, a number of EP pretenders have chosen to use those methods in their pedals."


      "I saw your Veroboard (stripboard) layout at FSB. You seem to have gone closer than anyone else to approximate the output impedance of the EP-3 preamp and you've used a 500K pot :) Without giving anything away, I suggest that you look at the Echo Volume pot on the original Echoplex schematic - I think you probably have a copy. Notice that the pot is not in the main signal path. The wiper of the pot is grounded, therefore the function of the pot is to control the output by bleeding signal to ground, not to pass signal to the output socket.

      There has been talk of "correcting" the high output impedance of the circuit, but the high output impedance is one of the things that sets the EP-3 preamp apart from a common JFET preamp. Your SPDT switch will give you more output and lower output impedance, but at the expense of some of the special sound of the real thing. As I said in an earlier post, the EP-4 has a low impedance output buffer, and it is not regarded as having that Echoplex magic."

      Here's a (as Peter describes it) snippet of schematic that he also posted:
      http://tinyurl.com/pp2js96

      Hope this helps and thank you for all your hard work with this blog!

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    3. this whole thing makes me laugh. i've owned an ep3 for over 25 years. the circuit these guys are claiming is some "secret boost used by the pros" is bunk. the gent in the above post indeed brings it up. the purpose of this part of the circuit was to get a good signal to noise ratio to the tape, NOT TO BOOST THE GUITAR. it would boost the recorded guitar LOUDER than the dry signal, but never ever ever actually boosted the guitar signal itself.
      at best, most of the plexes i've had (three so far) two were slightly below unity gain, and one just barely above.., which is my original one that i still have now.
      the output impedance is for saturating tape. being a preamp, yes, you can use it for a guitar but it's never going to make anything sound like an echoplex.
      echoplexes were never overdrives. ;) seriously. find someone that owns one, and put it in the loop of an a/b box.
      nice sounding overdrive.. but echoplex?
      still don't buy it. ;)
      peace out
      pjp

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  21. He's obviously wired it something like the schematic when it comes to the pot so that he can maintain the output impedance, but the snippet you posted doesn't match the EP3 schematic.

    In the schematic, after the output cap is a voltage divider with what appears to be a pot or trimmer to ground, and the 220K going to volume 1 and then a 100K from volume 1 to the output. The snippet has a 220K to ground and a 100K to the output.

    I remain sceptical that the subtleties that he seems to believe are crucial make the difference between having a "pretender" pedal and sonic nirvana, but I've posted a layout anyway :o)

    It's as per the EP3 schematic rather than the snippet.

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    1. Incidentally, if you do want it as per the snippet, then the first layout matches it. Cut the 1M pulldown resistor at the output if you want it exact.

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  22. Question: if I connect the ground from the input to the ground on the board there seems to be a shortcut (noise and no signal). But I can't find the cause.
    So just to be sure: the minus side of the 47u cap faces to the south right?

    My transistor (2n5457) values are:
    D 1.7V
    S 1.25V
    G 0V

    I'm using the bigger greenies for caps. Could it be that they don't work properly? (I wanted to try them because they look so cool :)

    So, when not powered I get a clean signal. When I power it, but not ground it, I get noise/hum and very lwo signal. When I power it, with ground, I get no sound at all.
    Still a newbie (this is my fourth attempt in building pedals, but so far with little luck :P But I really want to learn it!
    Is there something obvious I'm missing?

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    1. This comment has been removed by the author.

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    2. Hello!
      I've got similar values for the 2N5457:
      D 1,45 V
      S 1 V
      G 0 V

      Did you manage to make it work?
      I'm getting very low signal on the output and with the pot (500kA) to the max, the same level as the "dry" signal.

      Little help people? :)

      Thanks for the site btw, really cool!

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    3. Hello
      Curious If you were able to get more output volume since I am experiencing the same issue?

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    4. Yes, kind of. I've posted a question on the forum and I was told to get the output resistor out or decrease the value. This got me a little more gain. Not tons of it though but now it's noticeable...

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    5. Have you solved the issue?

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  23. Hi All,

    I've built the first version Echoplex posted here and it works. Nice easy build, good for a beginner.
    I tried swapping the 3k3 for a 4k7 log pot but it didn't really work below half way, I got low level crappy sounding distortion, so I wired a 2k2 resistor in series with the pot and I now get a nice clean boost fully down and bit of crunch coming in at full vol/gain.
    Thanks IvIark!

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  24. For the Tillman with the gain switch is it ok to use 2 prong on off switch?

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  25. First and foremost this is one fantastic site, great job love the info and the helpful hints and etc..
    My issue is that I am still at unity gain with the pot at max position ? All the demos I have watched show at least a 10db volume increase with the pedal at max. How can I remedy this and get a bit more volume level, please help.. Thank you and you guys ROCK 👍

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  26. Built the early version EP with volume control. Used a 2N5457; volume only got back to unity at full volume.

    Also noticed my 2N5457 has a different pinout than the drawing; mine is SDG, not DSG like drawing.

    Any ideas how to fix? Has anyone built this version successfully?

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  27. Where does lug 3 of the volume pot go on the EP early version II?

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  28. Bit of a newb, but I had a question. I'm planning on building the Echoplex preamp, but from what I can tell, it gives a slight boost. For my application, I don't want any clipping. Is there a way I could add an internal trim pot to adjust the gain (to prevent clipping) without altering the tonal characteristics or volume of the circuit? Thanks!

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    1. this really shouldn't produce enough of a boost to cause any sort of clipping, but you can make a typical output voltage divider and remove the 100k resistor at the output, and place a trimmer with lug one to ground, lug 2 becomes your new output, and lug 3 connected to the junction of the 100nF cap and 220k resistor.

      another option would be to look at the echoplex ep3 version 2 layout, which has a volume pot, and put a trimmer in the same location on the other echoplex layouts.

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  29. Ahoy and thanks for some more great layouts!!

    Just one question - I used the first echoplex preamp vero and a 2n5457 FET but i had to clilmb up to 8 kOhm for the source to ground resistance in order to bias the fet to 4.5V (the other 2n5457 that i had available reached 4.3volts or so). Does this sound normal? The sound seemed to be OK though, clean and sparkly! Looking forward to your response, thanks!!!

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    1. The more FETs you use, the more you'll realise that they're horribly inconsistent, just as you've seen with your own batch. What you've done is fine and correct. Its getting evermore so important to learn how to bias FETs in some of these layouts that don't include trimmers.

      Just remember to bias by ear and not rely too much on the meter. A DMM will get you in the ballpark but only your ears know what you like the sound of.

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  31. Anyone put this preamp directly into their guitar? I'm playing with the idea.. I put a klon buffer in my strat, but am thinking about the echoplex!

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  32. nice pedal to boost an overdrive with :)

    here's my take,it's the pedal to the right:

    http://s29.postimg.org/g26u51m7b/IMG_0495.jpg

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  33. template as follows;

    http://s9.postimg.org/5tgm14qnj/echoplholes.png

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  34. Built the EP3 Early version with Volume and the volume does not change. Should lug 3 of the pot be connected to something? Thanks.

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  35. Lug 3 does not connect to anything, also omit the 100k output resistor and create a jump over the cut where the 100k would have been, so that there is no cut in the line going to the output wire

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  36. Thank you very much. That did the trick. It sounds a bit bright. Lots of top end. Is that normal?

    Thanks again.

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  37. It does bring back the top end much like a buffer would. You could also try A500k instead of the A100k pot and try a few different J201 transistors also

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  38. I did go with the 500K and the 2n5457. I do have some J201's. Would that make a difference?

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  39. I found that J201's work better, also keep in mind that this circuit was never meant to produce huge boost levels it's very subtle but noticeable, that being said it's a nice amount of bump in volume but most importantly the notes come to life.

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  40. I will give them a try, Thanks.
    Yes, it does add some "life" to the notes. I was not looking for a huge boost. I have an EP Booster clone and wanted to compare this one to that. The EPB has it's own thing going on, for sure.

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  41. Tried out the J201...huge difference! Tamed the highs quite nicely. The pedal is not quite the same as the EPB, but it is much better.

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  42. Maybe I'm wrong, but in the one with the 18V charge pump, pin 3 and 5 of the IC7660S shouldn't be linked for allowing pin 5 to be grounded too?

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  43. Built the "early version with vol control" EP-3 Preamp with a J201. Nice one indeed - not a huge amount of boost but definitely useable - doesn't seem to alter my clean tone so much either. I was waiting to find a nice boost to box together with another circuit and I think this is the one. Cheers!

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  44. hey people,
    I would like to build the echoplex with a gain pot. could you please explain me how can I add the pot to the first layout?
    thank you

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  45. Hi, How can I add a tone control to echoplex, thank !

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