1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Hiss???

Discussion in 'Shock Brother's DIY Amps' started by RollingBender, Jun 9, 2020.

  1. RollingBender

    RollingBender Tele-Afflicted Vendor Member

    Posts:
    1,403
    Joined:
    May 14, 2011
    Location:
    SW Minnesota
    My most recent build I used only metal film resistors throughout. When cranked with nothing plugged in, there is a lot of hiss. What could be the source?
     
  2. King Fan

    King Fan Poster Extraordinaire Ad Free Member

    Posts:
    5,978
    Joined:
    Jan 1, 2013
    Location:
    Salt Lake City
    Tubes can hiss, as can other items. V1 especially suspect maybe. Gain makes it worse. What is the amp (is it high gain)? Diodes and other components can hiss. "Cheap components" are reputed to hiss. You can read that poor filter caps aggravate hiss (dunno myself.) Lower-watt resistors hiss more than large, even in MF. Input signal anywhere near power can do it. Shielded input runs and hanging the V1 grid stoppers right on the pins (and 1W or larger resistors in the input sector) are commonly suggested. Maybe even a sound sample could help the smart folks here.
     
    Last edited: Jun 9, 2020
    awasson likes this.
  3. koolaide

    koolaide Tele-Afflicted

    Posts:
    1,010
    Joined:
    Oct 11, 2009
    Location:
    south carolina
    I'm no expert, but in addition to what King Fan said, some designs have hiss. I am working on a TW Express clone build, and I have been told to expect hiss, and that they all hiss.-It is a high gain design.
     
  4. demon

    demon Tele-Meister

    Posts:
    486
    Joined:
    Jan 18, 2015
    Location:
    Northern Europe
    How much hiss are we talking here? Understood there is hiss when cranked with nothing plugged in, but is it still present and irritating when you're playing? Or does the hiss get lost under the guitar sound?
     
  5. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Resistors and tubes are your typical sources for Johnson noise. Like the fellas say.

    Merlin has a trick for lowering the resistance of the input grid resistor which he says is a big source of hiss. Maybe this will help a little.

    "However, the input grid stopper adds the most amount of Johnson noise (hiss) of any resistor in the amp. (A 68k stopper generates at least four times more hiss than a typical 12AX7!) Can we use a smaller resistor to reduce noise, but still keep the bandwidth the same? Yes, it's easy. We simply add a little extra capacitance to make up for the lower resistance. I recommend a 10k resistor, which will make the amp much less hissy, together with an extra 100pF to 470pF capacitor from grid to ground."

    http://www.valvewizard.co.uk/gridstopper.html
     
    King Fan and awasson like this.
  6. RollingBender

    RollingBender Tele-Afflicted Vendor Member

    Posts:
    1,403
    Joined:
    May 14, 2011
    Location:
    SW Minnesota
    It’s an AB763 with EL84’s in the power section. Most of the resistors (where 1/2 watt would be called for) are 1 watt... just a couple 1/2 watt but they are in the PI and later.

    I used the amp last weekend at a gig and the hiss really isn’t an issue at sane person volumes. Just wondering how I could tweak things a bit more. For what the circuit is, I feel that it is overly gainy and maybe some adjustments to bring the gain down under control would fix the hiss issue.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.