Friday, 4 July 2014

EHX Hot Tubes

Another one that was missing from the library. Original units call for 2M pot for the overdrive control, but as the demo below suggest, the middle position of that knob should be mild enough. So i see no harm in using 1M pot for that instead. That'll give you the latter half of the sweep.

...aaand i built one for myself. 1M lin pot for the drive works really well. At minimum setting the effect is slight overdrive with a nice tube sounding overdrive going on. When maxed it's a very high gain driver and sounds really nice. I think i may need to get myself an original nano version to compare them. But yes. This sounds very good. One more thing. I usually sub log volume pots for linear as i like the sweep better. On this one. Nope. You'll definitely want it to be logarithmic.



16 comments:

  1. Nice !
    Sould I Try this one during my holidays in a few days !

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  2. I just happen to have a few 4049s lying around. Thanks for the layout. I think you might need to relabel the 4049 on the layout to IC2 though.

    Thanks

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    Replies
    1. Thanks for heads up! Label fixed.
      +m

      Delete
  3. Cool. This was my FIRST distortion pedal... WAAAY long ago. I had a Sunn Coliseum SS amp... just for the volume, with a Hardtrucker 2x12 and heavy-heavy Altecs... anyway - this was how I got distortion before I bought a HiWatt Half-stack (used a DS-1 with that sometimes too, lol...). But the Hot Tubes - special, back then for sure.

    QUESTION: One thing about that pedal - it did not use a battery or an adapter. It plugged in to AC directly & only. I knew nothing about electronics back then (I was 15 - it was 1980...) so I don't know why they did that. It was in the early days, for sure... and - perhaps the current draw was high enough that they didn't offer a battery option? But why have the transformer/reg/rectification inside the box? Seriously. Are we certain that this was originally a +9v circuit? Since it was pulling from the wall, might they have run it at 12 or 18? Not doubting you for sure - just curious why this was a wall-socket/no-wall-wart pedal back in 1979.

    CHEERS and felicitations - Stephen ;-)

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    Replies
    1. EHX used to have a lot of units with internal transformers. No idea why they did that as many units from other manufacturers had spots for two batteries if the circuit wanted more than 9V. In this case, the NJM/JRC4558 sets the limit. Its maximum voltage is rated at 18V and CD4049UBE has maximum of 20V, so it may have been running on 12V. But if you're building this, you could try it with higher voltage. I don't think it will affect the overall sound too much. There's more than enough of gain and output level with running the circuit at 9V.
      +m

      Delete
  4. Forgot to tick notify... guess I might as well say THANK YOU for the premiere DIY effects website, tagboard... Not only for the spot-on, killer content, but a site with such a clean, elegant design as well - easy to read, navigate, etc.. Heads above the rest. Just sayin... cheers. Stephen

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  5. If massive distortion is wanted with this circuit, try feeding ONLY the 4049 with about 4 Volts.

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  6. could you explain the double links please? I could assume that blue links to blue, but on the left side there is only one blue dot.

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    Replies
    1. The hole has two links in it, one going up, one going down

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  7. Got the original EHX Hot Tubes nano in the mail today and compared it against my clone. Very much the same sound. You won't be saving any money building this though :)
    +m

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    Replies
    1. Didn't open it up yet, but i suspect the drive pot in this Nano is also 1M.
      +m

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  8. Finished mine up tonight.

    I used a dual 1 meg linear wired in series for the overdrive pot. Ton of gain in the 2nd half of the rotation. And used a HFC4049UBE and JRC4558.

    Has a low hum with drive turned up, hoping to find a fault and quiet it down.

    Here are some pics:

    https://lh4.googleusercontent.com/-s0Biu749gUI/U-7BYHf0E3I/AAAAAAAAAHc/xK5lQWsWyxo/w291-h510-no/Groovy%2BTubes.jpg

    https://lh5.googleusercontent.com/-KqDPoCKOidw/U-7BYBK4PJI/AAAAAAAAAHU/I9nNyZBo_nI/w258-h459-no/Groovy%2BGuts.jpg

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  9. The hum turned out to be the adapter, unexpected as it was fine a few days ago. 1st time I heard a hum is when I fired up this pedal, thought it was the pedal for sure.

    Just wasted a couple hours troubleshooting because I skipped hum troubleshooting 101... powering it up with a battery! Keep it simple stupid comes to mind.

    It's just 5 weeks old, bought new on ebay from julytechusa. We will see if they will replace or refund. Beware.

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    Replies
    1. Just an fyi, julytechusa offered a refund for the adapter.

      Pedal sounds great btw, thanks for another great layout!

      Delete
  10. Thx for another excellent layout ;) I've built this and found that an A100k pot works much better as the Drive controll. But even so I found that the Drive turned down had a weird fizzy decay. I decided to control the gain diffrerently: removed the current Drive pot and replaced it with a link (so Drive3 and Drive1&2 are now connected). Then I removed the 75k resistor from the second opamp stage's feedback net and replaced it with a pot. Best is to use it in series with a 20k resistor, so with the pot turned all the way down you will still get some crunch. The pot can be anything from 50k to 500k, logarithmic taper is the best. With 50k you will get about the same amount of distortion as in the original, with 500k you get a fair amount more, almost like a fuzz. Above that the circuit starts to oscillate, so I'd not recommend that. 250k might be a good compromise.

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  11. Dears,

    CD4049UBE = HEF4049B?

    Regards.

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