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Thread: Can anyone ID this component please?

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    Valvulados.com jmaf's Avatar
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    Can anyone ID this component please?

    Hi, can anyone ID this component please?

    It's part of a preamp and seems to be somehow in shunt with a SPDT switch. Is it just a resistor with a cap as to avoid pops? I can't take the board apart and the trails are covered in black gook, I can't see what the connections are exactly...





    Thanks in advance for any pointers.

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    It would help to have a little more information (what does the switch do?), but I have seen at least one three-terminal double capacitor used for power supply noise filtering. That one was a triple-layer disc capacitor with the center plate grounded.

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    Valvulados.com jmaf's Avatar
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    Quote Originally Posted by Rhodesplyr View Post
    It would help to have a little more information (what does the switch do?), but I have seen at least one three-terminal double capacitor used for power supply noise filtering. That one was a triple-layer disc capacitor with the center plate grounded.
    Thanks.

    The switch commutes between wires 1 and 3 right behind the component. Simple SPDT. I just assumed it's shunted to the switch, but I don't know really. I don't have this piece in hand and have no physical access to it to be able to test continuity from the exposed terminal to the base of the component, so this info is all I can provide. Thanks again for your suggestion, already searching 3 legged caps but found none similar on google and bing images.

    Any idea what that brand is? CM? MC?

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    Old Timer J M Fahey's Avatar
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    I would also like to help, but
    The switch commutes between wires 1 and 3 right behind the component.
    is not the answer to rhodesplayer's question:
    (what does the switch do?)
    What we need to know is *what* does that switch do?, meaning: does it switch DC/low voltage AC/110/220V/EQ/gain/channel? .... etc.
    Thanks.

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    Valvulados.com jmaf's Avatar
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    Quote Originally Posted by J M Fahey View Post
    I would also like to help, but is not the answer to rhodesplayer's question:

    What we need to know is *what* does that switch do?, meaning: does it switch DC/low voltage AC/110/220V/EQ/gain/channel? .... etc.
    Thanks.
    This circuit is on a bass guitar preamp. The switch commutes between active / passive outputs. I know I have little information to offer, I thought maybe by just looking at this thing folks would know what it is.

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    Supporting Member Jazz P Bass's Avatar
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    It looks like an EMI filter.
    Why it is in that circuit, I do not know.
    Google Images: http://www.google.com/search?hl=en&x...og&sa=N&tab=wi
    Attached Files Attached Files

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    Valvulados.com jmaf's Avatar
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    Quote Originally Posted by Jazz P Bass View Post
    It looks like an EMI filter.
    Why it is in that circuit, I do not know.
    Google Images: dss6nz82a103q55b - Google Search
    Nailed it, JPB, thanks very much.

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    Old Timer J M Fahey's Avatar
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    Interesting..
    Now that we know what it is, we can easily see the not-fully-dipped ferrite beads on the external legs.
    It's incredible how much hindsight we have *after* the fact !!
    I can only guess that the preamp maker must have had a *terrible* RF problem, specially considering it appears to be on the output.
    And I also guess that:
    This circuit is on a bass guitar preamp
    explains the goop.
    Oh well.

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    Lifetime Member Enzo's Avatar
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    Well, it is a commercial product, the amp maker didn't dip them himself. I see these all the time, especially around high gain inputs and anywhere where RF immunity is desired. Look for example it the input jack circuit of recent Marshall products like the AVT150.

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    Valvulados.com jmaf's Avatar
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    Quote Originally Posted by Enzo View Post
    Well, it is a commercial product, the amp maker didn't dip them himself. I see these all the time, especially around high gain inputs and anywhere where RF immunity is desired. Look for example it the input jack circuit of recent Marshall products like the AVT150.
    I had never seen one, so good lesson for the day. Does it noticeably attenuate the high end? I guess for a bass guitar this will pass, but it probably loads guitar high end? Just curious, I was unable to tinker with it at all.

    Edit: I would assume 102 means a 1 nF capacitor for each leg, shared middle leg? If so, it'd definitely muffle guitar output...

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    Lifetime Member Enzo's Avatar
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    We don't even know where it is in the circuit yet, do we? It mught roll off some highs if it were in series with the input signal, but it could also be in a control switching circuit and have nothing to do with the signal path. And consider that it is part of a whole circuit, so even if it rolls off some high end, in the overall picture that may be desirable. Most amps have a tone stack, and if you think about it, tone stacks roll off highs too.

    What preamp is it? Perhaps we can come up with the schematic for it and answer these questions.

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    Old Timer J M Fahey's Avatar
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    According to JazzP's datasheet, they are all "Pi" (don't have the symbol) type filters, series inductor/grounded capacitor/series inductor.
    The inductors are the part leads going through ferrite beads.
    The generic schematic shows a single capacitor to ground (through the center leg).
    Besides the effect on audio signals we can expect from a 102 (1000pF) capacitor to ground, they also post the attenuation curves at Radio Frequencies for the whole enchilada.
    They show dips at varying frequencies, I guess the designer chooses them according to expected interference trouble (FM?, TV?)

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    Valvulados.com jmaf's Avatar
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    Quote Originally Posted by Enzo View Post
    We don't even know where it is in the circuit yet, do we? It mught roll off some highs if it were in series with the input signal, but it could also be in a control switching circuit and have nothing to do with the signal path. And consider that it is part of a whole circuit, so even if it rolls off some high end, in the overall picture that may be desirable. Most amps have a tone stack, and if you think about it, tone stacks roll off highs too.

    What preamp is it? Perhaps we can come up with the schematic for it and answer these questions.
    Thanks, Enzo. I don't recall the name. I'll make sure to ask next time I visit the luthier who was working on it.

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    Quote Originally Posted by J M Fahey View Post
    According to JazzP's datasheet, they are all "Pi" (don't have the symbol) type filters, series inductor/grounded capacitor/series inductor.
    The inductors are the part leads going through ferrite beads.
    The generic schematic shows a single capacitor to ground (through the center leg).
    Besides the effect on audio signals we can expect from a 102 (1000pF) capacitor to ground, they also post the attenuation curves at Radio Frequencies for the whole enchilada.
    They show dips at varying frequencies, I guess the designer chooses them according to expected interference trouble (FM?, TV?)
    Thanks for that. On the schematic there's also one without the inductors, and another with the inductors, I think they vary the kind of filter with the model(C, LC, whatever).
    It was good discovering what this component is and getting feedback from experienced members, appreciate that.

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