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Switching out 1N4007's... Is there a benefit?

Discussion in 'Shock Brother's DIY Amps' started by tubedood, Nov 10, 2020.

  1. tubedood

    tubedood Tele-Holic

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    A lot of folks say that the tried and proven 1N4007 diodes that have been used as rectifiers a long time are slow and noisy. The general consensus now is to use a fast switching version, a UF4007.

    Would you pull out 1N4007's to replace with the UF version? Would my ears even notice at the speeds those things switch at?

    Thanks as always for your time and thoughts,
    Dale
     
  2. Tom Kamphuys

    Tom Kamphuys Tele-Holic

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    No. The uf diodes are faster and have less ringing. This is ultrasonic, so I don't think you will hear it.

    IMG_20200729_215931524.jpg

    We are talking about the small jump and (blurry) oscillation at the right. This is right after the (uf) diodes. Subsequent filtering will filter it out, but the signal can be transmitted through the air and be picked up by other parts of the circuit. The chassis won't block it, as it is created inside.

    Also, have a look at this:
    https://electronics.stackexchange.com/questions/323507/bridge-rectifier-4-diodes-vs-single-chip
     
    Last edited: Nov 10, 2020
    tubedood and Lowerleftcoast like this.
  3. gusfinley

    gusfinley Tele-Afflicted

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    I have used UFs for new builds, but I don't see a benefit to swapping existing diodes unless you are having problems with the ones you have.

    The UF series give you a recover time of 75 nonseconds instead of the 2 microseconds of the 1N variety. Hex FREDs bump that up to 28 nanoseconds, but you loosed the form factor and they cost more.

    I might use the UF5408 ( 3A 1000V ) diodes in Future builds, simply due to their larger size.
     
  4. LightningPhil

    LightningPhil Tele-Meister

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    Rather like Schottky diodes which avoid this issue. Anything should do at signal level. Silicon carbide for higher voltage power goodness.

    While the noise generated by silicon diodes is almost always a negative, there is at least one use for it. The silicon opening switch. Here’s a non paywall article:
    https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.12.1187&rep=rep1&type=pdf

    This is relevant as it shows that massive voltage spikes can generated when trying to do so - and thus they can be accidentally generated too.

    Silicon diodes generate the spikes as when in conduction, the junction is populated by a number of charge carriers. When voltage is reversed, these charge carriers must be removed before the device stops conducting. As such, current can flow through the diode backwards, somewhat unhindered till this charge is depleted. This current stores energy in the inductance of the diode’s leads and the circuit feeding it. When the charge is depleted, the diode suddenly stops conducting which causes the inductive energy to make a voltage spike across the diode. It’s rise time is often very fast, so RF noise results. Most of the inductive energy will generally be dissipated in the junction, but that which escapes can cause problems elsewhere.

    Schottky diodes don’t operate in the same way as silicon, and do not generate noise by this particular method as they have do not build up a reservoir of charge while conducting.

    So that’s why I prefer Schottky diodes. Not that big spikes aren’t fun. Highest voltage silicon opening switch system I’ve meddled with was operating around 80kV. It was horribly built so decommissioned it and replaced with a completely different PSU.
     
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