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Passive Piezo UST and volume pot?

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Re: Passive Piezo UST and volume pot?

Postby Wonks » Thu Nov 28, 2019 10:00 pm

Last of the big spenders. Corbyn's got his sights on folks like you. :D
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Re: Passive Piezo UST and volume pot?

Postby Sam Spoons » Thu Nov 28, 2019 10:18 pm

Yeah, life's a bitch innit.....
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Re: Passive Piezo UST and volume pot?

Postby Sam Spoons » Wed Jan 20, 2021 11:32 pm

Just to recap and save you rereading the whole thread, I'm looking at replacing the Fishman Rare Earth sound hole pickup in my Brian Eastwood Custom with a piezo hopefully to make it work better with my Tone Dexter preamp as mag pickups are not recommended.

Anyway I'm resurrecting the thread as I had a little mind bomb earlier when I realised my NS Design Wav electric upright bass has what I believe is a piezo pickup under the bridge (the only others I can think of are B-Band type capacitive sensors but they'd need a polarising voltage) with tone and volume controls and a pizz/arco switch. It's passive, no preamp or battery, the pizz/arco switch just adds a second cap to the circuit (I'll try to draw it out tomorrow) and the volume pot measures around 1 Meg. It sounds great straight into the amp (in this case a little 1 x 10" Warwick bass combo). Granted it doesn't need much in the way of HF which may be why it works but a passive circuit would be much nicer on the Brian Eastwood and save the faffing with internal batteries (I'm not about to cut a hole in the side for a battery box) so I'm thinking I'll order up a 1 Meg pot and give it a try.
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Re: Passive Piezo UST and volume pot?

Postby Sam Spoons » Sun Jan 24, 2021 8:39 pm

Ok, that didn't work, so far, as the cheapo Chinese piezo elements appear to be dodgy, lots of hum and low output so I'm going to try the similarly cheap and cheerful active pickup I bought. It has no hum and plenty of output and a volume control on a sound hole mounted edge wheel pot. I want to use the existing hole for the volume so I need a standard guitar pot with a 6mm split/splined shaft. The problem is that it's a A50k log and I can't find a UK supplier with a split shaft. Any suggestions?
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Re: Passive Piezo UST and volume pot?

Postby ef37a » Sun Jan 24, 2021 9:20 pm

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Re: Passive Piezo UST and volume pot?

Postby Sam Spoons » Sun Jan 24, 2021 11:43 pm

Brilliant, ordered, thanks Dave.

I spent about ¾ of an hour searching for one, fine of you live in the US but none of the UK suppliers that Google 'supplied' had the combination of split shaft and 50kΩ log taper.
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Re: Passive Piezo UST and volume pot?

Postby ef37a » Mon Jan 25, 2021 11:05 am

Sam Spoons wrote:Brilliant, ordered, thanks Dave.

I spent about ¾ of an hour searching for one, fine of you live in the US but none of the UK suppliers that Google 'supplied' had the combination of split shaft and 50kΩ log taper.
Glad to be of service. I just searched for "splined shaft potentiometers" and that site came up PDQ. Just lucky I guess.

BTW even though they ARE in America, Stewmac get guitar related parts here extremely quickly.

Dave.
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Re: Passive Piezo UST and volume pot?

Postby Sam Spoons » Mon Jan 25, 2021 8:31 pm

I'm a step further down the road in that the piezo with the preamp sounded pretty bad* so I've had another go with the passive, better result this time, it's a funny install, the saddle is about 8mm wide to allow good intonation (initially done that way as I used a plain third but also 'cos I had planned to install an Ovation bridge and electronics at some point). The piezo goes in a deeper slot at the front side of the bridge slot and I think I didn't have a thick enough shim underneath it so the saddle wasn't making full contact with the element. I have sorted that and installed it without a volume control for the moment. It sounds much better than the active version and better matches the level of my Rob Aylward 'Selmer style' and my mandolin (both also passive).

Now the problem, neither the RA or the Mandolin hum but the new pickup does quite badly. Since the setup is very similar, passive piezo UST** wired straight to a jack socket the only thing I can think might be causing it is the open frame jack socket or the piezo element itself.

I will try swapping the socket for an end pin, enclosed/shielded type tomorrow.

* also the fitted/included volume control doesn't work well at all, no difference until the last few mm before off.

** the Mando and RA pickups are both encapsulated in the floating bridge, a Fishman and a BigTone respectively.
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Re: Passive Piezo UST and volume pot?

Postby Murray B » Mon Jan 25, 2021 8:51 pm

I don't know if this is related to your hum issue Sam, but some time ago I had a new bone bridge made for my acoustic. I discovered at the first gig I'd picked up a hum when it was amplified :( Replacing the bridge with the original plastic version made the problem go away. I never really worked out what was going on but assumed it was due to the bone not being as good an insulator as the plastic was?

I can't speak to the science of the situation and I'm sure that others will have been able to use a bone bridge without any trouble... Anyhow just thought I'd share it just in case it's relevant.
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Re: Passive Piezo UST and volume pot?

Postby Sam Spoons » Mon Jan 25, 2021 9:08 pm

Thanks Murray, the bridge on the guitar is brass but the shims are plastic, I tried to find a brass shim I had for it a fair while ago and see if earthing the strings helped, if I can't find it I'll try wrapping them in kitchen foil to make the connection when I next take it apart (probably tomorrow). Touching the sleeve of the jack socket reduces the hum but doesn't remove it entirely.
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Re: Passive Piezo UST and volume pot?

Postby Alba » Tue Jan 26, 2021 6:59 am

What i do for my piezo equipped guitars that have the strings through bridge is to solder a bit of wire to a strip of copper tape back to the jack ground and then copper tape goes under the bridge plate (all a bit tricky but this does work).

So now you can see the adhesive side of the copper tape when looking down through the bridge pin holes. Then i carefully punch through the tape of each hole and tidy up the hole from inside the guitar.

When the string goes through the hole it is pushed into the copper tape and grounded. Touching the stings silences the hums!

Got the idea from seeing this... Platemate

Not tried this on a passive mag pup but i think it would likely work.

The tape works for me but then i'm not out changing strings every day.
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Re: Passive Piezo UST and volume pot?

Postby Alba » Tue Jan 26, 2021 7:42 am

Spent ages going through this hoop by the way. I make my own preamps now based on this design.

http://www.till.com/articles/GuitarPreamp/

His cable works really well too...

http://www.till.com/articles/PreampCable/index.html

Veroboard layout http://tagboardeffects.blogspot.com/201 ... llman.html
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Re: Passive Piezo UST and volume pot?

Postby Sam Spoons » Tue Jan 26, 2021 9:53 am

FWIW this is a piezo under saddle jobbie, not a mag. What I'm struggling with is the fact that the Aylward and mandolin are totally silent... I'm not holding out any hope that shielding the jack will help as the problem doesn't seem to be EMI, it doesn't change when I move the guitar but I'll give it a go. The copper foil trick sounds like it might help too, thanks for that suggestion.
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Re: Passive Piezo UST and volume pot?

Postby Alba » Tue Jan 26, 2021 10:43 am

Might help someone anyway.
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Re: Passive Piezo UST and volume pot?

Postby Sam Spoons » Tue Jan 26, 2021 11:42 am

:thumbup:
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