Those observations of mine don't match at all. The initial observation of the HF loss was something I thought was very subtle. Have to admit now it seems I'd allowed myself to "observe" what I expected to happen. Can't believe that old chestnut caught me out, from now on I won't trust subtle perceptions of change!
Speaking of hearing what you expect - I've read over and over again that long cables from Hi Z pups before the buffer are a bad idea because of noise and signal loss of apparently various types but I'm just not hearing it! My cable doesn't seem to be picking up noticeable noise, it is only 3.5 metres and has both a braided copper screen and a conductive plastic shield?
What are the reasons you are biased against the cable? what problems would you expect it to have?
There'd have to be pretty good reasons to go to the effort of making, installing and carrying around a preamp and the box to send it phantom when a capacitor soldered inside a jack plug seems to be doing an excellent job.
I'm not sure it is a HiZ source any more, hasn't the added capacitance essentially lowered the impedance anyway?
I've done the same thing, and caught myself only by calling in a friend to administer a blind test. Even though not double-blind, after about 20 trials, the statistical results showed that I had been fooling myself.
The fact is that we cannot step back from our own extremely fallible humanity. Our senses and psychology will always be biased and error-prone. If we wish to be objective, the best we can do is use the tools of science to try and keep from fooling ourselves - but if you tinker with audio a lot, who can possibly test every perception with a proper series of double-blind tests?
Luckily for us, when it comes to making our own music, I don't think it's that important if we fail to be objective. We probably already think our kid is cuter, our songs are better, our driving skills are better, than they actually are; what does it matter if we also think our guitar amp / violin preamp is better than it actually is?
Then you are golden. IMO, if you don't hear any problems, there aren't any worth bothering with!
As an amateur musician myself, I have to constantly remind myself that an extra four or five hours of thoughtful practice time with my instrument will improve my sound far more than four or five hours spent tinkering with unnecessary electronics. Time is precious, why squander it chasing a supposed problem that you can't even perceive?
There is lower, and then there is low. Your 420 pF piezo started out with an impedance of nearly 2 mega ohms at 198 Hz, and your additional parallel cap dropped that to around 540 kilo ohms at the same frequency.
540k is much lower, but is still very high compared to the sort of output impedance we would normally expect to see in good small-signal audio gear - usually under 1 kilo ohm, never more than ten kilo ohms.
Still: if you aren't hearing any problems due to the high Z, that's all that matters!
-Gnobuddy
I misread your original post, thinking you had a Headway pickup, but see you have their direct box.
My daughter is a fiddler, and I built her a pickup mimicking the Headway "The Band", in appearance only. I read some years ago it has three piezos, so I assume they use ceramic type.
3rd try was a keeper. I didn't want to deal with ceramic piezo variables, so I started with a variety of polymer piezo products from MSI (Measurement Specialties).
The first two were unusable because I used such a short length of low capacitance piezo coax (I think someone uses this in a guitar bridge pickup) that I needed a 40 Mohm input impedance...which had so much hiss it was intolerable...there might have been a way around that but I just used a larger (higher capacitance) sensor for lower impedance. The smallest one (40 pF, IIRC) picked up hum no matter what...quite likely I didn't use intelligent shielding, as more & more didn't make any difference, and it had a very narrow field of hum pickup at the end...unusable...
I also got an MSI contact mic (CM-1 or CM-2?) with integral preamp...don't remember if it was JFET or MOSFET, but it's on line. It was awkward on a violin and required power.
I then went to the opposite extreme, using an MSI polymer ribbon sensor roughly 150 mm x 20 mm. I thing it came in two film thicknesses resulting in about 5500 pF and 11000 pF.
Talking to a local upright bass builder, I learned finishes in the violin family can range from polyurethane on cheapest ones to varnishes, shellacs, French polish oil finishes, and infrequently nitrocellulose. A local guitar luthier once told me he was wearing a blue polyester or cotton/poly blend shirt and it stained a blonde NC finish...so I decided safest approach was cotton.
As you surely know, The Band has a rubber tube-like construction, and I think hook/loop (Velcro) attachment.
I used (apparently) too many layers of fabric (piezo ribbon is copper-tape wrapped is stitched to a length of cotton web that is roughly 0.1-0.125" thick, then a muslin sleeve over it). It has a difficult EQ signature (EXCESSIVE midrange, which I blame on my construction...based on intuition only)...difficult for soundboard people...but the coolest thing about The Band's (and the imposter the wrap) attachment is that it doesn't kill the acoustic qualities, and doesn't suffer from a string-heavy or body-heavy sound, and damps feedback enough that it's usually everyone else's fault when there is a howling instrument on a stand somewhere). OTOH, the midrange imbalance could be related to string vs body sound, as it was just luck that got me as far as I did.
At about 3 years of use (no failures of the integral 3.5 mm jack), I had the opportunity to see three The Band specimens in person, but not to measure the capacitance of the alleged three sensors. My daughter played for some months with the large group that had the three Headway pickups & they never complained about her sound.
When she played as the sole fiddler with a guitarist, the EQ became a headache. I then bought a LR Baggs Para-Acoustic DI preamp, which made the violin presentable to the sound board EQ, but it was still a challenge for some people to figure out.
I then started exploring charge amps as mentioned above, and found a Sony lavalier mic I got in the 80's for saxophone but never needed...and bought a Rode violin mount...it holds a 4mm electret condenser mic. I carefully drilled it out to 6mm for the Sony. The rubber clip hangs from the dead end of the E & G strings between the bridge and tailpiece ('afterlength' is the proper name). It works great but has a lot of the typical microphone vs. speaker conflicts. I never looked very hard for a cardioid lavalier size ECM, but they apparently exist. I've also put a Shure ??-93 ECM on it with an old Shure VHF wireless system...one for violin and one for vocals, but usually only uses one & sings into the violin (which amuses some people).
I plan v.4 some day/year along with a bass version since the overkill (for violin) one has LF response down to about 20 Hz (based on capacitance and assumed 1M input impedance). I have used some industrial differential polymer sensors that were difficult to get, no support (answers) from the mfr., and not even what was on their datasheet. They were quiet no matter what I plugged into but it's a whole different approach for another day. (Emfit from Finland, who happens to own B-Band, a musical instrument transducer company, so they may not have been too interested in supporting a lone wolf pickup hacker). They call theirs an electret...further reading online lumps that concept into a quasi-piezo category... not something to split hairs over...but it's a 'foamed' material as opposed to a solid layer as used in MSI polymer piezo, so it has about 1/12 the capacitance and 12x the impedance. Some of the B-Band preamps are 50 Mohm input impedance because the electret has such low capacitance/high-Z, and they apparently design their preamps properly - the few people I have met that use their systems had no noise complaints.
Back to your original question, I bought an acoustic guitar preamp with under-saddle guitar pickup (cheapest I could find, op-amp based), opened it up & changed a 2.2 M feedback resistor (I think the 6-chip ceramic piezo assembly it came with was around 650 pF) to 10 M. I plugged a couple bass wrap prototypes into it just to make sure it still worked and that was as far as I pursued that. 'It worked'.
The microphone approach is hard to ignore for ease of standard connections at most venues...I picked up some mic-centric looopers and so one, but we haven't done anything with them...she plays unpiugged most of the time anyway (outdoors or solo indoors), so as usual, it's my project, not hers.
My daughter is a fiddler, and I built her a pickup mimicking the Headway "The Band", in appearance only. I read some years ago it has three piezos, so I assume they use ceramic type.
3rd try was a keeper. I didn't want to deal with ceramic piezo variables, so I started with a variety of polymer piezo products from MSI (Measurement Specialties).
The first two were unusable because I used such a short length of low capacitance piezo coax (I think someone uses this in a guitar bridge pickup) that I needed a 40 Mohm input impedance...which had so much hiss it was intolerable...there might have been a way around that but I just used a larger (higher capacitance) sensor for lower impedance. The smallest one (40 pF, IIRC) picked up hum no matter what...quite likely I didn't use intelligent shielding, as more & more didn't make any difference, and it had a very narrow field of hum pickup at the end...unusable...
I also got an MSI contact mic (CM-1 or CM-2?) with integral preamp...don't remember if it was JFET or MOSFET, but it's on line. It was awkward on a violin and required power.
I then went to the opposite extreme, using an MSI polymer ribbon sensor roughly 150 mm x 20 mm. I thing it came in two film thicknesses resulting in about 5500 pF and 11000 pF.
Talking to a local upright bass builder, I learned finishes in the violin family can range from polyurethane on cheapest ones to varnishes, shellacs, French polish oil finishes, and infrequently nitrocellulose. A local guitar luthier once told me he was wearing a blue polyester or cotton/poly blend shirt and it stained a blonde NC finish...so I decided safest approach was cotton.
As you surely know, The Band has a rubber tube-like construction, and I think hook/loop (Velcro) attachment.
I used (apparently) too many layers of fabric (piezo ribbon is copper-tape wrapped is stitched to a length of cotton web that is roughly 0.1-0.125" thick, then a muslin sleeve over it). It has a difficult EQ signature (EXCESSIVE midrange, which I blame on my construction...based on intuition only)...difficult for soundboard people...but the coolest thing about The Band's (and the imposter the wrap) attachment is that it doesn't kill the acoustic qualities, and doesn't suffer from a string-heavy or body-heavy sound, and damps feedback enough that it's usually everyone else's fault when there is a howling instrument on a stand somewhere). OTOH, the midrange imbalance could be related to string vs body sound, as it was just luck that got me as far as I did.
At about 3 years of use (no failures of the integral 3.5 mm jack), I had the opportunity to see three The Band specimens in person, but not to measure the capacitance of the alleged three sensors. My daughter played for some months with the large group that had the three Headway pickups & they never complained about her sound.
When she played as the sole fiddler with a guitarist, the EQ became a headache. I then bought a LR Baggs Para-Acoustic DI preamp, which made the violin presentable to the sound board EQ, but it was still a challenge for some people to figure out.
I then started exploring charge amps as mentioned above, and found a Sony lavalier mic I got in the 80's for saxophone but never needed...and bought a Rode violin mount...it holds a 4mm electret condenser mic. I carefully drilled it out to 6mm for the Sony. The rubber clip hangs from the dead end of the E & G strings between the bridge and tailpiece ('afterlength' is the proper name). It works great but has a lot of the typical microphone vs. speaker conflicts. I never looked very hard for a cardioid lavalier size ECM, but they apparently exist. I've also put a Shure ??-93 ECM on it with an old Shure VHF wireless system...one for violin and one for vocals, but usually only uses one & sings into the violin (which amuses some people).
I plan v.4 some day/year along with a bass version since the overkill (for violin) one has LF response down to about 20 Hz (based on capacitance and assumed 1M input impedance). I have used some industrial differential polymer sensors that were difficult to get, no support (answers) from the mfr., and not even what was on their datasheet. They were quiet no matter what I plugged into but it's a whole different approach for another day. (Emfit from Finland, who happens to own B-Band, a musical instrument transducer company, so they may not have been too interested in supporting a lone wolf pickup hacker). They call theirs an electret...further reading online lumps that concept into a quasi-piezo category... not something to split hairs over...but it's a 'foamed' material as opposed to a solid layer as used in MSI polymer piezo, so it has about 1/12 the capacitance and 12x the impedance. Some of the B-Band preamps are 50 Mohm input impedance because the electret has such low capacitance/high-Z, and they apparently design their preamps properly - the few people I have met that use their systems had no noise complaints.
Back to your original question, I bought an acoustic guitar preamp with under-saddle guitar pickup (cheapest I could find, op-amp based), opened it up & changed a 2.2 M feedback resistor (I think the 6-chip ceramic piezo assembly it came with was around 650 pF) to 10 M. I plugged a couple bass wrap prototypes into it just to make sure it still worked and that was as far as I pursued that. 'It worked'.
The microphone approach is hard to ignore for ease of standard connections at most venues...I picked up some mic-centric looopers and so one, but we haven't done anything with them...she plays unpiugged most of the time anyway (outdoors or solo indoors), so as usual, it's my project, not hers.
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This is well known as expectation bias - and you're one of rather few people here who admit of being cheated by it. Thumbs up!
Sadly, we have several threads (e.g. the Funniest Snake Oil thread) and topics (e.g. the parts rolling thread in a Quad 909 amplifier) where some participants totally ignore and, even worse, deny of being cheated theirselves by this phenomenon. That's really a severe PITA.
Best regards!
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