Hot Tubes

by gaussmarkov

Hot Tubes Build by stobiepole

I have revised the Hot Tubes clone. As it turns out, there was a capacitor missing from the factory schematic and another capacitor has a much larger value in actual builds. According to several reports on Aron’s forum (electrobuster, Bernardduur), the changes improve the sound tremendously.

Here’s the text from my original post:

First ever: stobiepole and gaussmarkov teamed up for this one. It’s coming out of the blocks verified, with no hum or oscillation issues in stobiepole’s build (pictured above).

So now we need a new picture! 😉

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23 Responses to “Hot Tubes”

  1. redstoneIII said:

    very cool. i had 2 of the original units, use of film caps definitely an improvement. also 9v in a bb enclosure, genius ! thank you !

    Posted 24.08.2007 at 4:19 pm

  2. plg said:

    mmm…. i have some problems !!! i have build this pcb but it doesn’t work !!! :((
    … i had change the r22 from 150k to 150R and the C2 from ceramic to electro as in the original schematic ….. may be this mod to do not work in it ?

    Posted 04.02.2008 at 3:08 am

  3. gaussmarkov said:


    you are right. R22 should be 150R. i will fix that. thanks very much for pointing it out!

    but that resistor value won’t affect whether the circuit works, just as you found out. nor will changing the type of capacitor.

    why don’t you try posting on aron’s forum, be sure to use the instructions for debugging that are linked at the top of the page. this includes things like measuring the voltages on the pins of your ICs and transistors.

    good luck!

    Posted 04.02.2008 at 7:11 am

  4. plg said:

    scuse me but … is there a specific page of the HOT TUBES in aron’s site ? can you make me the exact links ?

    Posted 04.02.2008 at 8:12 am

  5. gaussmarkov said:

    no, sorry, there isn’t a specific page. i am suggesting that you use the forum, specifically the forum about building. here is the link: Building your own stompbox. At the top there is a link called Debugging Page that I mentioned above.

    Posted 04.02.2008 at 8:19 am

  6. plg said:

    ok tnx … but … do you have any sample of your clone ?

    Posted 04.02.2008 at 8:37 am

  7. gaussmarkov said:

    everything that’s available is posted. 😉

    Posted 04.02.2008 at 9:47 am

  8. plg said:

    hi… i have fix my pcb … my cd4049 was going out 🙁 … now the circuit is OK!!! … but i have made this mod :
    – R22 150 R (as in the original) ;
    – C2 1uF electro (as in the original) ;
    – C10 1uF film (no electro as in the original !) ;
    – C17 180 pF ceramic ….
    …. and now the sound is REALLY great !!! much “mud” and tuby with more sustain …. TNX .

    Posted 05.02.2008 at 8:34 am

  9. gaussmarkov said:

    sweet. those 4049 are supposed to be easy to zap with static electricity. maybe that’s what happened to the first one?

    rock on … 🙂

    Posted 05.02.2008 at 4:23 pm

  10. diyer said:

    hi just built this! great sound, but i dont think it reacts well to neck humbuckers, i tried it on an lp and a js900, the sound seems too dark, and a bit fuzzy, how do i remedy that? and r22 supposed to be 150 ohms ryt? i have mine at 150k, is that the reason?

    Posted 24.06.2008 at 1:28 am

  11. diyer said:

    btw the changes that i made were 0.12 and 0.15 micro farad changed to 0.1, gain pot is 1m, everything else i followed in the project file, including the 150k instead of 150

    Posted 24.06.2008 at 4:07 am

  12. gaussmarkov said:

    u know, i would just yank the 150 (yours is 150K) resistor altogether. 150K is raising the output impedance of the circuit significantly. the 150 ohm resistor is probably there to keep RF noise down in case the next circuit is badly behaved. removing the 150K could brighten the sound significantly.

    Posted 24.06.2008 at 10:28 am

  13. diyer said:

    ahh, allryt ill try that, thx

    Posted 24.06.2008 at 2:16 pm

  14. diyer said:

    hi, just took out the 150k resistor, it still sounds too bassy, it boosts the bass more than any other frquency, what capacitor values could i reduce?
    and should c10 be 1 or 10 micro? because plg stated that he used 1 micro
    and is it possible that it became bassy due to the tl072 i used? thx and more power!

    Posted 25.06.2008 at 1:46 am

  15. gaussmarkov said:

    ok. a critical cap is C17 which has the value 39pF. if you raise its value you should get less bass. try 47pF and see what you think.

    this is a bottom heavy circuit. some bass players like to use it for that reason.

    Posted 25.06.2008 at 5:37 am

  16. gaussmarkov said:

    in an original hot tubes, C10 was 10uF. an old schem shows 1uF.

    the tl072 should not be making any difference to bass.

    Posted 25.06.2008 at 6:00 am

  17. diyer said:

    oh, ok thanks a lot! thanks for the great projects!

    Posted 25.06.2008 at 2:24 pm

  18. Anonymous said:

    Can you put a mp3 file of this effect?

    Posted 16.07.2008 at 3:30 am

  19. gaussmarkov said:

    i totally understand the request for mp3 files, but i have to limit what i do. so for now i am drawing the line at mp3 files. maybe later.

    Posted 17.07.2008 at 1:56 pm

  20. yoyo said:

    hello !
    somebody made this project, and I bought it .
    now I’m trying to modify a little the original schematics.
    1)R6 ( 75K) – replaced with a semi-variable 50k ( to much gain with 75K )
    2)now i want a to obtain low noise from the overdrive . i’m using it to maximum to get much better Tube sound , but it’s to much noise. how can i reduce it ?
    another value of C17 can change this ?
    3)I’ve eliminated the tone bypass switch( i don’t need it) , but i don’t like the tone corection. it becomes noisy in the low frequencies… can C10 change this ? it is a 10uF electro-pol in this moment . in spare-parts this is a film-box cap. wich one is ok ?
    thanks !

    Posted 25.11.2008 at 1:09 am

  21. Teddy said:

    Hello. Can you recommend a different op-amp than the LM4558N? The sad thing is that it is not available in Bulgaria and I really want to make this pedal. Here is where you can check if it is available here in Bulgaria. Cheers 🙂

    Posted 02.02.2009 at 6:35 am

  22. direx said:

    hi teddy,try to use tl072.hasta

    Posted 25.03.2009 at 2:24 pm

  23. joe said:

    I have built this circuit to no success and as you can imagine getting it working is driving me insane! i’m even dreaming about this project now 🙂

    I just seem to get a high pitch squeal, i can hear some sound with my amp turned all the way up?

    i have made some changes due to parts availability and they are as follows

    c4= 168pf (supposed to be 180pf)
    overdrive is 1meg (supposed to be 2meg)
    R5 and R7 22k (supposed to be 20k)
    c17 44pf (supposed to be 39pf)
    i also used a tl07 and i have tried a jrc4558

    i dont think any of these changes should stop the pedal working,

    pin voltages are as follows


    1. 9.2
    2. 0
    3. 9.2
    4. 3.7
    5. 3.4
    6. 3.7
    7. 3.4
    8. 0
    9. 9.2
    10. 0
    11. 3.71
    12. 4.08
    13. 0
    14. 3.72
    15. 4.05
    16. 0


    1. 4.51
    2. 4.46
    3. 3.76
    4. 0
    5. 4.5
    6. 4.59
    7. 4.56
    8. 9.21

    Thanks in advance for any and all help with this project

    and also thanks for a great web site there is some awesome info on here



    Posted 02.12.2010 at 3:00 am