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Thread: taming a Rod Piezo

  1. #36
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    plan #1 is leaving the Alumitone set up as is , piezo to a 10k pot both sent to a TRS stereo out jack , stereo Y cable out, send the piezo through a pre-amp(tech 21 is on the way) to one amp , Alumitone out to another amp . I have more than one build, so I'd still like to have an internal blend set up , haven't decided which way to go on that yet. JM if you are still contemplating on providing a sketch please do , this is not a push!! so please don't feel it is , would like to try a DIY/w help something.

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    Last edited by shortcircuit; 03-15-2019 at 08:15 PM.

  2. #37
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    Quote Originally Posted by shortcircuit View Post
    plan #1 is leaving the Alumitone set up as is , piezo to a 10k pot both sent to a TRS stereo out jack , stereo Y cable out, send the piezo through a pre-amp(tech 21 is on the way) to one amp , Alumitone out to another amp . I have more than one build, so I'd still like to have an internal blend set up , haven't decided which way to go on that yet. JM if you are still contemplating on providing a sketch please do , this is not a push!! so please don't feel it is , would like to try a DIY/w help something.
    It is no good idea to connect a 10k pot to the piezo. A piezo PU is a high impedance capacitive source, a typical capacitance value being 1.5nF. Connecting this to a 10k pot produces a high pass filter with a corner frequency of above 10kHz! This means that all frequencies below 10kHz will be strongly attenuated.

    The minimum load resistance should be 1M. But a 1 M pot will noticeably reduce highs at lower vol. settings.

    There is actually no good passive solution to your problem.

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    Last edited by Helmholtz; 03-16-2019 at 04:10 PM.
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  3. #38
    Old Timer J M Fahey's Avatar
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    Ok, hereīs the very low consumption (0.2mA meaning 4000 playing hours from a typical 9V alkaline ) chopped to the bone Piezo/magnetic preamp.

    Fails safe, IF battery dies (which by itself will take Months or Years ) you simply turn Balance pot fully towards the Magnetic pickup and continue playing.

    Click image for larger version. 

Name:	PiezoMagnetic.gif 
Views:	30 
Size:	9.6 KB 
ID:	52978

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    Juan Manuel Fahey

  4. #39
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    Thank you JM , very nice design, I will start gathering components , will have to order a few , I'll give it a go and let you know.
    Thanks again really appreciate it.

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  5. #40
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    Quote Originally Posted by J M Fahey View Post
    Ok, hereīs the very low consumption (0.2mA meaning 4000 playing hours from a typical 9V alkaline ) chopped to the bone Piezo/magnetic preamp.

    Fails safe, IF battery dies (which by itself will take Months or Years ) you simply turn Balance pot fully towards the Magnetic pickup and continue playing.

    Click image for larger version. 

Name:	PiezoMagnetic.gif 
Views:	30 
Size:	9.6 KB 
ID:	52978
    Nice circuit!

    One remark: The 100k balance pot will load the magnetic PU. With typical high impedance PUs this results in reduced highs, similar to partly engaging the tone pot. I am not familiar with the Matchbox PU, but it might make sense to experiment with higher pot values (250k or even 500k) to preserve most of the treble response.

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  6. #41
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    Quote Originally Posted by Helmholtz View Post
    Nice circuit!

    One remark: The 100k balance pot will load the magnetic PU. With typical high impedance PUs this results in reduced highs, similar to partly engaging the tone pot. I am not familiar with the Matchbox PU, but it might make sense to experiment with higher pot values (250k or even 500k) to preserve most of the treble response.
    I will breadboard the circuit before I assemble anything permanent , will keep this in mind,as well as your #37 post for the other project, thank you for the input.

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  7. #42
    Old Timer J M Fahey's Avatar
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    Quote Originally Posted by Helmholtz View Post
    Nice circuit!

    One remark: The 100k balance pot will load the magnetic PU. With typical high impedance PUs this results in reduced highs, similar to partly engaging the tone pot. I am not familiar with the Matchbox PU, but it might make sense to experiment with higher pot values (250k or even 500k) to preserve most of the treble response.
    True, but real life decisions force us to compromise.

    The preamp I make commercially uses a TL062 (double Op Amp) and both the piezo and the magnetic pickups are buffered (1M the magnetic, 3M3 to 10M the Piezo) *BUT* this one is simplified for shortcircuit, specially avoiding him the trouble of printing and etching a PCB.
    As shown it needs no PCB at all, not even perfboard, can be built point to point or even dead bug style.

    When choosing the balance pot value, I had to compromise, because "half the circuit is active, half is passive" and to boot, since I chose NOT to use Op Amps here, maximum "gain" I can hope for is unity gain (source follower).

    * A 250K and even worse a 500k pot will attenuate signal way too much, specially because Volume and Tone pots are 250k each.

    * a 10/25/50k one will load Magnetic too much and even more at higher frequencies.

    * so I chose halfway 100k as a "least bad" compromise: signal loss is reasonable (a couple dB) and treble loss in practice is irrelevant .... since the Piezo will provide a Ton of highs anyway .... way more and specially way higher range than anything a magnetic pickup can even dream of.

    In general I try to see circuits not as a bunch of independent parts but as a whole system

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    Juan Manuel Fahey

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    Makes sense, thanks.

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  9. #44
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    Quote Originally Posted by J M Fahey View Post
    True, but real life decisions force us to compromise.

    The preamp I make commercially uses a TL062 (double Op Amp) and both the piezo and the magnetic pickups are buffered (1M the magnetic, 3M3 to 10M the Piezo) *BUT* this one is simplified for shortcircuit, specially avoiding him the trouble of printing and etching a PCB.
    As shown it needs no PCB at all, not even perfboard, can be built point to point or even dead bug style.
    And shortcircuit appreciates it !!!!!!! Will build as posted , out of respect for you taking time to post it, hopefully it isn't bug ugly .

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    Last edited by shortcircuit; 03-20-2019 at 03:22 PM.

  10. #45
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    Oh, donīt worry, "dead bug" because parts are usually mounted "legs up" is a tried and true build technology for minimalist projects or even to fit a non-pin-compatible IC replacement, in that case itīs mounted legs up and thin wires connect legs to proper holes.




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    Juan Manuel Fahey

  11. #46
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    Thanks very interesting , glad I haven't placed an order yet . I was thinking I'd be tar and feathered for something like that.
    My version I would be Those a work of art

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    Last edited by shortcircuit; 03-20-2019 at 11:39 PM.

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