TA Amulet lens experiment

[Cuki79]

Hi everyone,

I did not dare post that on SpruceTop's thread but this is totally related to his TA Amulet successful installation.

Inspired by SpruceTop, I have been trying to re-install my bass-side amulet lens... unsuccesfully. I could do better but not enough.

So before I run out of red tape, I decided to make a small experiment

I have a plastic plate with a surface exciter.

I sticked on it a K&K sensor (super glue) and an Amulet lens with red tape and over 12h clamping. Both sensor go into Hi-Z focusrite 2i2 inputs.

The exciter is fed with pink noise.



1) First experiment consist in comparing the K&K and the Amulet spectrum response. If you look at the left figure below, the K&K (Yellow) has more sub 100Hz content than the Amulet. The Amulet has more of everything above, expecially above 10 KHz.

2) Second experiment, I added weights to the Amulet (coins + double tape) or magnets to add pressure and improve bounds. I used all kind of neodymium magnets. (See pictures above)

My conclusion, is that the added weight effect on tone is minimal. I could get significant tone change by adding small neodymium magnets (5) to squeezet the amulet lens. Those small magnets are trong and lightweight, you can see on the right figure below, they added low and low mids... Exactly what my previous Amulet installation lacked.


NOTA BENE: The two spectra are different, because I pause the analyser at a different moment. Also I moved the plate between experiment 1 and 2 so the bundary condition for the hanging plate are different.

You can actually hear the difference



The sound sent to the exciter is pinknoise. Of course the plate response colors the tone already.

1) Amulet lens
2) Amulet lens squeezed by 5 small neodymum magnets

That is very consistent with what Spruce top has observed recently. A better bond provides better lows and low mids which eventually can make the tone control unnecessary...

The only question is: How can we get that great bond with red tape?

I have only 3 pieces left... I'd probably never get the answer.

[SpruceTop]

Cuki, You're A Mad Scientist! Thanks for doing this! You can order more red tape from Trance Audio and ask them to send a goodly supply as it won't cost any more for shipping a dozen sheets than it would for a couple of sheets.

Even with the epoxy bond, the Amulet M-VT preamp Tone Control still has an effect on the tone. As you've indicated the trebleness of the Tone Control when wide open with an epoxy bonding of the Amulets is much less brittle-sounding than when the Amulets are installed with the red permanent tape. I'll make a demo in which a listener can hear the effect of the tone control with an epoxy bonding of the Amulets. In the past, I made a demo that demonstrates the effect of the Tone Control when the Amulets are bonded with red permanent tape.

Here's that demo from July 23, 2017, it's of a permanent red-tape Amulet installation along with an explanation of what's going on:

Hi Folks, the following track demonstrates the effect of the Tone Control on the output of the Trance Audio Amulet M Dual Mono M-VT Acoustic Guitar System. NO EXTERNAL EQ OR EFFECTS WERE USED IN MAKING THIS RECORDING.

Signal Chain: 2014 Martin HD-28 with Trance Audio Amulet M Dual Mono M-VT strummed with BlueChip TD35 Pick > 10-Foot-Long Mogami Gold Instrument Cable > PreSonus Studio 192 Digital Audio Interface with PreSonus Studio One DAW outputting one input channel to a 24/48 Mono Wav File.

1) The first section of the track is The Trance Amulet M Dual Mono with Tone Control at FULL TREBLE which incorporates the full tonal-range from bass-to-treble of the system;

2) The second section of track is with Tone Control at FULL BASS;

3) The third section of track is Tone Control BALANCED tonal position as heard through AKG K240 Studio Headphones. This Tonewheel position can vary slightly depending on personal taste, the guitar in which the M Dual Mono M-VT is installed, and the room acoustics of a venue.

Remember: 10 to 15 feet of air between a loudspeaker and an audience will make any pickup/preamp system sound different (likely better) than a direct recording heard through headphones.




The following is a 2020 Martin HD-28 with Trance Amulet M-VT Phantom that demos the tone range of the Tone Control with the Amulets mounted with Henkel Loctite 6-Minute Epoxy. It's the same demo order scheme as the 2014 Martin HD-28 with Trance Amulet M-VT Phantom:

[Cuki79]

That's exactly what I usually can get.

From what I've heard so far, I think you (with the Epoxy) or Maury (with the red tape) can get better.

[Cuki79]

After few other expriments, I am pretty sure both lenses have different frequency response.

I taped the two sensors in a similar manner. I made multiple recordings, feeding the exciter with pink noise. Changing the boundary conditions of the plate affects the tone but one sensor has consistently more low end and less high end than the other.


You can here them there


Those measurements are very consistent with all my install. Whatever the install tweaking I could do the "bass" sensor could nevevr made to match the "treble" sensor warmth.

Since the begining I can discriminate both with a white tape on the connector of the "treble" one.

Note that I can "tap" on both sensors and hear on headphones the tone being bassier on the good one...

I wrote Gary to ask if I could order a single lens "tone tapped" and selected for better bass response... He will probably just think I am crazy.

[Cuki79]

I am not so sure anymore.

today I sent some pinknoise and squeezed with my fingers the sensors while comparing the spectrum and I could make one bassier than the other...

Then bonding is the issue...

[SpruceTop]

Originally Posted by Cuki79

I am not so sure anymore.

today I sent some pinknoise and squeezed with my fingers the sensors while comparing the spectrum and I could make one bassier than the other...

Then bonding is the issue...

That's good, Cuki, that both Amulets seem to be similar in tone and output!

The ringing in my recordings is string-related and not Trance pickup or electronics-related as I can hear the ringing when playing acoustically only with both my Martin HD-28 and Martin D-18 with its Ultra Tonic 3.2 system.

[Cuki79]

Originally Posted by SpruceTop

That's good, Cuki, that both Amulets seem to be similar in tone and output!

The ringing in my recordings is string-related and not Trance pickup or electronics-related as I can hear the ringing when playing acoustically only.

I want to do your 5" clamp install but there are out-of-stock in Stew&Mac european distributor... and the shipping costs from the US for one clamp almost double the price.

I would have to either borrow one or make one myself...

[SpruceTop]

Originally Posted by Cuki79

I want to do your 5" clamp install but there are out-of-stock in Stew&Mac european distributor... and the shipping costs from the US for one clamp almost double the price.

I would have to either borrow one or make one myself...

I'm thinking the little turnbuckle clamp that comes with the Trance system should do what you want for tone but I guess you've been using that already, correct? Gary Hull urged me to try this Trance method after I told him I used epoxy to mount the Amulets and preferred that tone rather than using the tedious little turnbuckle clamp and red-tape method. Frankly, I don't know if the turnbuckle clamp method works as well or better than epoxy because I've never applied this method as I'm pretty happy with the epoxy mounting.

You should be able to buy a usable, deepthroat C-clamp from a tool supply or hardware store. Even if it's heavier than the Stewart-MacDonald clamp, you can put a support under the end near the soundhole to keep the clamp level on the Amulet.

[SpruceTop]

Originally Posted by Cuki79

Hi everyone,

I did not dare post that on SpruceTop's thread but this is totally related to his TA Amulet successful installation.

Inspired by SpruceTop, I have been trying to re-install my bass-side amulet lens... unsuccesfully. I could do better but not enough.

So before I run out of red tape, I decided to make a small experiment

I have a plastic plate with a surface exciter.

I sticked on it a K&K sensor (super glue) and an Amulet lens with red tape and over 12h clamping. Both sensor go into Hi-Z focusrite 2i2 inputs.

The exciter is fed with pink noise.



1) First experiment consist in comparing the K&K and the Amulet spectrum response. If you look at the left figure below, the K&K (Yellow) has more sub 100Hz content than the Amulet. The Amulet has more of everything above, expecially above 10 KHz.

2) Second experiment, I added weights to the Amulet (coins + double tape) or magnets to add pressure and improve bounds. I used all kind of neodymium magnets. (See pictures above)

My conclusion, is that the added weight effect on tone is minimal. I could get significant tone change by adding small neodymium magnets (5) to squeezet the amulet lens. Those small magnets are trong and lightweight, you can see on the right figure below, they added low and low mids... Exactly what my previous Amulet installation lacked.


NOTA BENE: The two spectra are different, because I pause the analyser at a different moment. Also I moved the plate between experiment 1 and 2 so the bundary condition for the hanging plate are different.

You can actually hear the difference



The sound sent to the exciter is pinknoise. Of course the plate response colors the tone already.

1) Amulet lens
2) Amulet lens squeezed by 5 small neodymum magnets

That is very consistent with what Spruce top has observed recently. A better bond provides better lows and low mids which eventually can make the tone control unnecessary...

The only question is: How can we get that great bond with red tape?

I have only 3 pieces left... I'd probably never get the answer.

Yes, indeed, the superglue's hard and thin mounting of the piezo disk supplies more bass content than the thicker, more pliable, red permanent tape mounting of the Trance Amulet. The Trance's less intimate mounting does, however, have more treble content and a lot of it is what you don't want to hear in an acoustic-guitar amplified tone. My epoxy mounting of Amulets lessens much of the nastier treble tones while increasing the bass content of the amplified tone.

As an aside on tone: Michael Laiacona, president and founder of Whirlwind Music, and who was the "M" in the original MXR company, once said to me facetiously to make a point after I commented on the frequency range of a loudspeaker not going above 16 kHz: Kenny, if you can hear anything above 13 kHz the Army will hire you for a million bucks a year to do something for them! His point was a lot of the content in the human hearing audio spectrum of 20 Hz to 20 kHz, especially the very high frequencies, is not necessary for forming our favorable appreciation of a sound source, e.g., an acoustic guitar. I use the trebly brittleness of a red permanent tape mounting of the Amulets as an example of how some of its treble content adds some annoying tone to the amplified signal. The epoxy mounting of the Amulets attenuates a lot of the undesirable treble tones while increasing bass content.

[Cuki79]

Originally Posted by SpruceTop

I'm thinking the little turnbuckle clamp that comes with the Trance system should do what you want for tone but I guess you've been using that already, correct?

Yes I do

Originally Posted by SpruceTop

You should be able to buy a usable, deepthroat C-clamp from a tool supply or hardware store. Even if it's heavier than the Stewart-MacDonald clamp, you can put a support under the end near the soundhole to keep the clamp level on the Amulet.

I'll try to find one in my local hardware shop... but did not see anything like this on their website. Most clamp I see are very short.

[Cuki79]

Originally Posted by SpruceTop

Kenny, if you can hear anything above 13 kHz the Army will hire you for a million bucks a year to do something for them!

I doubt they'd hire a French guy

[SpruceTop]

I've added the new 2020 Martin HD-28 with Trance Amulet M-VT Phantom Tone Control Demo with Amulets mounted with Henkel Loctite 6-Minute Epoxy to my earlier post demoing the 2014 Martin HD-28 with Trance Amulet M-VT Phantom red-tape mounted demo in this thread at: https://www.acousticguitarforum.com/...25&postcount=2

[Cuki79]

Originally Posted by SpruceTop

I've added the new 2020 Martin HD-28 with Trance Amulet M-VT Phantom Tone Control Demo with Amulets mounted with Henkel Loctite 6-Minute Epoxy to my earlier post demoing the 2014 Martin HD-28 with Trance Amulet M-VT Phantom red-tape mounted demo in this thread at: https://www.acousticguitarforum.com/...25&postcount=2

Thanks Ken

[Cuki79]

Originally Posted by SpruceTop

I've added the new 2020 Martin HD-28 with Trance Amulet M-VT Phantom Tone Control Demo with Amulets mounted with Henkel Loctite 6-Minute Epoxy to my earlier post demoing the 2014 Martin HD-28 with Trance Amulet M-VT Phantom red-tape mounted demo in this thread at: https://www.acousticguitarforum.com/...25&postcount=2

Listened carefully and I think the Epoxy is less spectacular with the HD-28 than with the previous guitar (Larrivée?).

Luckily, the stewmac european distributor seems to have the 5" clamp avaiable again so I ordered one.

[SpruceTop]

Originally Posted by Cuki79

Listened carefully and I think the Epoxy is less spectacular with the HD-28 than with the previous guitar (Larrivée?).

Luckily, the stewmac european distributor seems to have the 5" clamp avaiable again so I ordered one.

Good News On The Clamp!

The only difference I can really hear is that the Martin HD-28 installation has a stronger bass level than the Larrivee C-03 TE. This may be because the Martin is a dreadnought versus the Larrivee's L-body shape? Both guitars are rich in bass content with the Larrivee being just a bit more balanced than the Martin. The Martin will likely need to be attenuated by a preamp by about -3 dB @ 98 Hz for most venues and for recording pickup direct to the computer. I look at the rich bass on both guitars as a positive as I don't have to try to get more bass into the signal, to begin with, because it isn't lacking.

My thoughts on Bass-signal content: Cuki, is it just me or have you also noticed that when bass is lacking in a pickup signal, that even after EQing in a goodly amount of bass with a preamp to compensate for the lack of bass, it just doesn't sound as full and distinct as having a strong bass content in the signal to begin with?