Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

NPD X2: Ibanez TS7 & Boss SD-2

Discussion in 'The Stomp Box' started by ukepicker, Sep 19, 2017.

  1. 11 Gauge

    11 Gauge Doctor of Teleocity

    Mar 21, 2003
    Near BWI Int'l
    You probably want to decrease the value of C41 - stock, it's 470pF, and it forms a lowpass filter with a corner freq of ~3.4KHz (encroaches on your treble a bit). I dropped it to 390pF, which moves the corner freq. up to 4KHz, which is kind of my upper-end preference for drive circuits that are intended to be on the gainier side (and lots of speakers for our purposes tend to start rolling off the treble around that freq. anyway).

    ...If you prefer more "air," and you'll be keeping the gain/drive low on the lead channel, you might want to make C41 even smaller. Using a value of 330pF will move the corner freq. up to ~4.8KHz.

    IMO, it's worth taking the time to tweak the value and corner freq., because there's a clipping circuit at this point (it's the second of two), so you can somewhat finesse the harmonic content "right at the source."
     
    ukepicker likes this.

  2. 11 Gauge

    11 Gauge Doctor of Teleocity

    Mar 21, 2003
    Near BWI Int'l
    It looks like that puts 1uF parallel to C10, which forms a high pass filter with R28. The sans-C100 version has a high pass corner frequency of ~400Hz, which is already kind of on the low side, IMO. Adding 1uF drops the HP filter all the way down to ~30Hz, and there's really not much need to go very far below ~80Hz, because that's the 6th open string freq. with standard tuning (and the more gain you've got going, typically the higher you want the corner freq. to be).

    ...That filter also happens right at the "adjustable gain stage," e.g. the drive pot is in that part of the circuit.

    I'm going to find out if mine has C100, and I'm pulling it if it does...
     

  3. ukepicker

    ukepicker Tele-Holic

    656
    Oct 15, 2013
    East Texas
    Wow! Thanks, Keith!
    I glanced through the schematic I found last night (don't think it had C100) and decided that the tone control on the lead channel probably wasn't the culprit for the mud. I don't know really know my way around schematics and gain circuits, so at that point, I was at a loss.

    I socketed the location for a cap on an SD-1 once and was able to try multiple values before sticking with one. I might try that on this one.
     

  4. 11 Gauge

    11 Gauge Doctor of Teleocity

    Mar 21, 2003
    Near BWI Int'l
    Yeah, TTBOMK, there's only one schemo out there for the SD-2, and it's a little bit counter-intuitive (is in 'portrait' format instead of 'landscape,' and has the lead channel continuing in a second 'row.'

    IMO, the tone circuit is really good.

    Socketing C41 is a GREAT idea, because you can really fine tune it to your specific tastes and knob settings. If you want to calculate the lowpass filter corner frequency before popping in another cap, you might want to use this calculator. The resistor value is 100K, so you have to enter resistance as 100000 ohms, and the small value caps need to be expressed in microFarads, so 470pF (stock) is .00047uF, 330pF is .00033uF, and so on.
     
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  5. pictacado

    pictacado TDPRI Member

    67
    Oct 17, 2013
    Los Angeles
    I've found 2 schematics for the SD-2, didn't see the added C100 on either. And thank you for explaining what that does.
     

    Attached Files:

    ukepicker likes this.

  6. 11 Gauge

    11 Gauge Doctor of Teleocity

    Mar 21, 2003
    Near BWI Int'l
    It's not what I indicated earlier, after opening mine up. o_O Mine does have C100, and it turns out that it's in series with C29, which falls on IC3B's output (pin 7). So, it can't just be pulled, you'd have to put a jumper connection in its place.

    The bottom line is that the pre-C100 SD-2 actually has a slightly lower highpass filter corner freq. on IC3B's output - it's ~160Hz vs. ~170Hz on the ones with C100. That's very minor, and not worth the trouble to change anything (IMO).
     
    Last edited: Sep 23, 2017

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