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Tuesday, 2 May 2017

Hornby Skewes Bass Boost

Another super rare Hornby Skewes pedal, so rare in fact I can't even find a video for it. Similar to the treble booster, but boosts the bass frequencies instead of the treble. I'm certain just like any other vintage Hornby Skewes pedal it's gonna sound great.

Layout 1: Original PNP


Layout 2: NPN Version



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22 comments:

  1. NHTMF3 May 2017 at 06:14

    built the NPN version on breadboard with MPSA18 and it works, though I had to leave out the 1k to ground 8F to get decent volume. I ultimately built with a few value changes - 100nf to 82nf and 125uf to 100uf. Sounds great on bass guitar, less so on 6 string..I guess it works like clean boost with more bass in it as described.

    Fun circuit to experiment with as I am just trying to teach myself how to set gain in a circuit.

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    1. Zach3 May 2017 at 16:05

      nice. leaving out that 1k to ground takes out the filter network at the output, and makes the 100nF go nowhere, so i don't think it would sound the way it should. how low was the output with that 1k to ground attached? i don't think it gives much of a boost, just a little bit. i mean there's not output control, so i can't imagine it being all that much.

      Delete
    2. NHTMF4 May 2017 at 00:12

      I put it back in and it's way less than unity with it. I put 10k in and it increased the volume to above unity.

      Delete
  2. Unknown3 May 2017 at 14:08

    I built the PNP version with a 2N3906, I used a 100uF electrolytic instead of a 125uF. Tag it, it works!

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  3. NHTMF4 May 2017 at 00:44

    https://drive.google.com/file/d/0B1xf8RhQa21vcnVUY0pMVjljZWs/view?usp=drivesdk

    Short sound clip playing bass recorded on my phone

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    1. Zach4 May 2017 at 03:08

      hmm, sounds pretty good to me. to me it sounds like without the resistor, and 100nF to ground it sounds fairly woofy to me, but with the 10k resistor it definitely boosts the lows, but retains some articulation. i dig it. since you have it on the breadboard, and you don't need to try and record another clip if you don't want to, with the 1k vs 10k does it have same tone?

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    2. NHTMF5 May 2017 at 01:22

      I agree it sounds better with the resistor in but with the 1k it's just not possible to compare against the 10k due to the large volume drop.
      I've been experimenting a bit and have a pot from 9v to the collector (and a 27k ~roughly~ resistor which was about the max increase in volume before it distorted in a not nice way), I assume this adjusts the bias?

      Anyway here is a clip on guitar on an already pretty crunchy amp thst I forgot to record, you can hear me fiddling with the pot/bbias/gain

      https://drive.google.com/file/d/0B1xf8RhQa21vTDdubzg5cW44TEU/view?usp=drivesdk

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    3. Zach5 May 2017 at 03:01

      yep, that's playing with the bias. i'm sure the reason for the lower output comes down to the transistor that's being used in place of the 2n3702 in the original.sounds pretty damn good to me.

      Delete
  4. Unknown29 November 2017 at 19:07

    This comment has been removed by the author.

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  5. Unknown29 November 2017 at 19:08

    I can provide pictures of the Hornby Bass Booster if you're interested. Didn't even realize it was a rare thing, since i just got it for free off some stranger on FB.

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    1. Nick S18 August 2019 at 21:18

      Hey Lasse - still got that Bass Booster? I'd love to see photos of it, if you have a spare moment.

      Delete
  6. gfp19 December 2017 at 21:43

    I've already built it three times with different components to make sure it's not a stupid mistake. It always make a big volume boost, but it attenuates bass and treble leaving only useless midrange. I used 100nf and 100uf, tried both 1k and 10k, also tried different bias resistors and tried many npn transistor and some pnp too. No idea what's going on.

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    Replies
    1. dvhx1 June 2024 at 14:46

      If you change input cap to 1u and output cap to 10u and increase 1k resistor to 3k3 it will boost 82Hz 2x

      Delete
  7. jack dias5 November 2018 at 11:28

    Thank you for sharing this information, Its has help me to know more about Sound Effects Free

    ReplyDelete
  8. Anonymous16 November 2018 at 11:11

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  9. jack dias10 December 2018 at 12:34

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  10. Unknown29 March 2019 at 18:26

    Hi everyone, I've just finished building one of these, it works well but despite being at the highest level, the output volume is anyway lower than the volume in bypass

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  11. D Russ6 January 2022 at 15:46

    Built the NPN version with 10k at 8f and a 2N2222. Sounds great, very loud and a good round tone, not woofy. I'm going to box this as a boost switch with a preamp, I think it's going to be great.

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  12. j-pee22 August 2023 at 18:47

    just to add the obvious:

    if anyone would like to have 125uF, you can have 100uF + 22uF...
    one of them can go 6g and 6i...
    and you'll add a jumper at 1f and 1g

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  13. gasboss77521 January 2024 at 02:51

    If anyone is planning to build the PNP version with the 2n3702, please note that the pinout above is wrong for that particular part, the 2n3702 pinout is: E-C-B when looking at it facing the flat edge.

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  14. gasboss77521 January 2024 at 22:44

    Rebuilt this on Breadboard with correct pin out for the 2n3702, works great with bass, I don't have a 6 string so can't comment on that. There was good gain even with the 1K resistor. I did change the collector resistor from 3K9 to 6K8 to even out the bias point as with 3K9 the collector was sitting close to -9V (-8.9V) This would also produce a small increase in signal gain, but with much more headroom.

    ReplyDelete