Making this Circuit more bass-friendy

Discussion in 'Effects [BG]' started by Thunderscreech, Jan 29, 2009.

  1. This is a Boss HM-2 Circuit. What do I need to to do to adjust the tone controls to make it more suited to the bass range?

    Edit: BLARGH!!!! Attached as PDF. :mad:

    Attached Files:

  2. Nyarlathotep

    Nyarlathotep Inactive

    Feb 5, 2006
    West Coast of Canada
    Subscribed :bassist:
  3. Is it worth it? I heard a jazz bass played through a humphrey modded HM-2 into an SVT and it sounded pretty cruddy. i'm sure somebody can do a better mod but i dunno, I'm not much of an HM-2 fan.
  4. I've never personally played one, but Spanky's video demo of the HM-2 certainly sounded pretty damn awesome to me. I'm interested to see if this thread goes anywhere
  5. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    I've been squinting at the teeny-tiny type on the schemo for a few minutes now, and I don't have any particularly intelligent suggestions. You could always try the gorilla approach and increase the value of some of the key caps, like the two 47nF's at the input could be replaced with 22 to 47uF's. Or I'm also looking at where it says "dist", and also near the diode arrays, and in the low EQ module, there are a number of spots where throwing in some different cap values would be worth the experiment. If you're feeling particularly adventurous, replace all the caps in the audio path with sockets, and then just swap values like mad with no further soldering.
  6. changing the 47 to a 47uf would make everything a bit full on gain wise and very squishy also more gain means less low end. I'd recomend changing the input cap to .068uf or greater .1uf being ideal.
    Also change the .047uf in parallel with the negative feedback to anything up to 47uf (negative to ground, positive towards the opamp) and also the cap in the negative feedback loop of the tonestack could be changed to a larger value
  7. ccpbass


    Aug 23, 2008
    Hair Noddles
    Doubling the input(47n) and output(10micro) caps will increase the bass freq going in to and out of the circuit. You can also replace ceramic caps with equivelent poly film. This will help with fedelity.
    Oh and don't forget to change the LED to a cool color.
  8. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Could you explain those statements a bit further? Not sure I understand what you mean.

    Edit: by "gain" do you mean distortion, i.e. the gain of the signal going into the diodes?
  9. Here Is a larger PDF. I seem to be made of fail lately. :atoz:

    Attached Files:

  10. pharaohamps

    pharaohamps Commercial User

    May 30, 2006
    Garner, NC
    Owner, Disaster Area Designs / Alexander Pedals
    The caps around the first FET are probably not going to make a huge difference. IIRC, the bypassed sound has plenty of low-end, and the bypass signal goes through the buffer, too.

    Your better bet would probably be to reduce the amount of clipping in the circuit. The HM-2 uses asymmetrical clipping in the main op-amp stage, then follows that up with a pair of series clipping diodes (the 1N270 germanium parts.) The Ge diodes are to simulate the "crossover" distortion of a Class-AB tube amp. Replace the Ge diodes with jumper wires and you'll immediately have a more bass-friendly effect.

    The tone controls in the HM-2 are implemented using gyrators (here used as simulated inductors in an LC circuit) and you can change the EQ centers by changing the cap values on them. Double the caps in the Low section to lower the lows to lower than low. Actually, just put an 0.068uf cap in parallel with the 68nf, and replace the 1.5uf with a 3.3uf cap.

    See the third gyrator there? IC2B actually makes a midrange control (IC2A is the treble control.) The stock HM-2 setup changes the Treble and Mids at the same time. If you break the connection there and wire in a third pot, you can have a 3-band active tone stack. I built a couple pedals with the exact same EQ setup a few years ago, and it works great.
  11. where IS the larger PDF?


  12. Under my second post in this thread....:confused:
  13. dannybuoy


    Aug 3, 2005
    The HM-2 has a very weird tonestack. It only sounds good with the bass on full and the treble at noon. With the treble any lower, all your upper mids and treble disappear, any higher, all your bass and lower mids are gone. Sounds good at the sweet spot though!

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