notes to self

Author: abram

  • sqrt() reverb…

    sqrt_reverb4

    this was the final build before it shipped out. circuit is a simple MOSFET (BS170) driver stage followed by two JFET (J201) recovery stages. i’ve included a sound sample of a similar reverb i built later without the second recovery stage and clipping diodes. it makes for a much more subtle reverb, but also tames the noise floor from the Belton module.

    [audio:http://abrammorphew.com/notes/wp-content/uploads/2013/02/sqrt_reverb_demo_02.mp3|titles=sqrt() reverb demo #01]

    this is the actual first build. the “dirty verb” comes in towards the end which just switching on a pair of germanium clipping diodes. you get more reverb for your buck with the second JFET stage, but i haven’t found a way to cool down the noise just yet. that’ll be revision 5… maybe 7. [audio:http://abrammorphew.com/notes/wp-content/uploads/2013/02/reverb-test02.mp3|titles=sqrt reverb demo #02]

  • Mistumin Valve Caster build…

    a tube overdrive build for Anthony of the The New Diet and The Regular Fucked Up People. it’s my take on the Mitsumin valve caster with the values i tend to use and a Telefunken 12AX7. excuse the ugliness for this one is just the prototype.

    four sections of clean vs. effected total.
    [audio:http://abrammorphew.com/notes/wp-content/uploads/2013/02/tube_overdrive_sample_long_02.mp3|titles=Tube Overdrive sound sample]
    1) high volume, no tone roll-off, and low gain
    2) mid volume, high tone roll-off, and mid gain
    3) mid volume, mid tone, mid gain
    4) high volume, low tone, high gain

    tube_od_proto_02

    tube_od_proto_03

    tube_od_proto_04

  • no. 5 re-appropriation…

    no5_redesign

    this is a re-appropriation of a Fender Frontman 15-B. it’s one 8″ speaker in a closed cabinet primarily designed as a really cheap bass amp to be included in starter packs. having gutted the amp a few years ago and replaced it with the contents from the No. 5 tube amp project, i got some time to rework the circuit into something more usable.

    the additions include a tone stack, second gain stage, and a stand-by switch. the power amp is now wired as a pentode instead of a triode, and i didn’t feel it necessary to have a switch between the two modes. it still needs a little work to keep it from self-oscillating at high volumes. thanks to those guys who run AX84.com for their P1 project. it definitely helped the way i thought about redesigning the amp.

  • work in progress

    early stages of a reverb effect pedal for guitar.

  • goodbye

    he’ll be missed by many. i consider myself fortunate to have known him.

  • Fender Bassman AB165 filter replacement

    some bad caps on a beautiful black-face AB165. i almost felt bad pulling the original parts out of it. forty-five years is a good run though.

  • 5W single-ended EL84 amp (before)

    insides of a Fender 15B solid-state bass amp that i gutted and converted into a simple tube circuit. i constructed this several years ago, and it’s not been very functional as of late. it definitely needs a better chassis ground, and i’d like to add in a switch for triode/pentode operation as well as a tone stack. i’d also like to play around with some of the filtering design as a practice.

  • Carvin Pro Bass 200 iPod-Mod

    And here we have a solid 160W solid-state bass amp with an RCA input on the front. this amp was brought to me with the complaint of really low volume on the RCA input. upon further inspection, this definitely seemed to be true. a reasonable listening volume could be obtained with the volume knob all the way up. definitely not a practical option if attempting to play live.

    looking over the schematic (this one being Revision I) you’ve got 22k resistors at each input (left and right) mixed together for mono delivery into a 33k resistor all before the first gain stage. that’s definitely a hefty signal drop. to boost the signal, i simply removed the 33k SMD resistor on the preamp board pictured below and replaced it with a small piece of copper wire between the pads resulting in a significant volume boost. cranking up the tweeter pad on the back basically turned a mediocre bass amp into a portable DJ amp.


    and if you’re not familiar with solder surface mount devices, you should really check out this extremely informative video.

  • magniscope


    a quick way to light the helping hands.