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Excalibur - help needed, headphone circuit.

H

Hopster

New member
Hi all,
I was wondering if there are any audio geeks here who have some knowledge of the Excalibur original style headphone wiring.
Background first: I threw away my old "NY" model phones years ago when they went bad but I did note they had little transformers potted to the backside of each piezo speaker/ transducer.
I built my own phones using 32 Ohm mini mylar speakers mounted in air chambers, waterproofed, with sound diaphram to transfer the sound to water while diving.
They sounded great on dry land----wide tonal range, but sucked underwater below about 4 feet or so.
So, now I want to build a piezo style because they are proven, and I have some 50 MM transducers on the way. At 3500 Ohms I don't think the Excal will drive these directly,
which explains the transformers I saw on the originals. From talking to Gary at Detectorpro, I gathered the originals used on the old excaliburs (red phones) were his company's design, and that the new Grey Ghost UW also uses transformers. So - below is the transformer I want to use as this is readily available from RS:

From Product description: "This audio output transformer is perfect for various audio/video projects.
Feature includes audio output and low-level impedance matching.

Frequency response: 300Hz to 10kHz
1,000-ohm center-tapped primary
8-ohm secondary
Low-level impedance matching

Model: EI-19 | Catalog #: 273-1380



I am looking to match the 3500 Ohm Piezo's to a 32 Ohm circuit on the Excalibur.
The end result is I will have everything I need to make my own phones although I will be buying some Grey Ghosts also.
There is also the question of the low pass filter or whatever it is that Minelab puts on their later phones in the end cap, but I need to tackle one question at a time here .....
Thanks,
DC (Orlando FL)
 
I was wondering the same thing, please keep us posted?

I built a couple of sets with the 50mm PUI (3500 ohm) and they will work however, I believe that the original 50mm's in the yellow headset are louder and cleaner. I've tried several different configurations to get a better sound but the transformer idea never entered my mind, I'm going to RS now before they close!

Search here and on the other forums and you'll find plenty of good information with regards to the excal headphones!

Here is link to Oldbeechnut he has a ton of good info out there!

Oldbeechnut stuff

Good luck!
 
endcap values, originals swords never used these

my reds from my sword, no transformer

Gold-Master uses the 50mm PUI Bender

Testing several, cool new way...stacking benders..turns your head into a sub-woofer.

transformer/inducer from GG UW, GG UW work better without transformer with the excal..Like a paddle wheel slowing down the flow with.........without...20 percent Louder and better audio

Looking for the perfect HP's..Got the best shell,,,%eltor's 105's
 
Stock Grey Ghost UW Head Phones Vs Stock Yellow koss. many I have talked to say the GG UW's they did not like....some do, A very well built set of HP's but to hear the faints..better without..
Before taking transformer out
http://www.youtube.com/watch?v=1r17l6MYaqg


After transformer removing from the circuit

http://www.youtube.com/watch?v=NqVLZLzheVs
 
OBN If I understood correctly - remove the transformer from the GG U/W phones for better / more amplification of weaker audio signals (faints).
Since I don't have my GG's yet - is each transducer paired with its own transformer ? Or is there one transformer driving both transducers ?
Yes - my early NY model excal had one transformer glued to the silicone on the backside of each transducer, and Gary confirmed those were built that way.


What is the HZ range of the excalibur audio? (Tonal range ) . It looks as if you may have some equipment for measuring this ?
Here is why I ask - I know from doing most of the detecting with mylar speakers as headphones (about 1200 hours with that type) that the audio "seemed" (subjective here) to sound so much more pleasant and smooth, and I let my buddy try it who was used to his piezo phones on his own excalibur,and he agreed, most noticably was the louder low tones (Bass, if you will).
I guess that is one difference between speakers and transducers but I have not sought out any other proof. I just know I loved using them as long as not scuba diving.
A thin ladies ring or bracelet would be loud low tone (as well as foil ). The only drawback is they were extremely hard to construct and reduced volume with water depth increases.
My Kirby Morgan EXO26 commercial diving mask uses mylar speakers each encased in a rubber molded "sock", but they transmit within the air inside the mask so the audio level does not change with depth. This is why I want to try piezo speakers again. I will still build another , hopefully better, set with mylar speakers - for comparison testing, but I want to build the best piezo type possible if I can.
Hopefully those 50mm transducers from Digikey are a good start.

I asked a couple of aircraft avionics technicians which wires would be source and which were output and they got into an argument, so I'm posting a photo of the package label with wire colors.
Can anyone look and discern which two wires hook to te speaker and which two are from the detector source? And what happens with the center tap wire or is it used at all ?
I will do some testing when the transducers arrive, but I dont want to hook it up in such a way as to damage the detector itself.
Regarding the stuff in the end cap, later I will try to contact an audio expert and get an explanation of how it is hooked up (cant tell from the blob of wires) and what exactly Minelab intended it to do.
The photos you have posted have been helpful so far and the videos were awesome ! Keep it coming OBN.
 
All of this suddendly trying to learn about "Capacitive circuits" and "phase mirroring" makes my head hurt.
A lot of it sounds like this gent :blink:

http://www.youtube.com/watch?v=oIS5n9Oyzsc
 
OBN If I understood correctly - remove the transformer from the GG U/W phones for better / more amplification of weaker audio signals (faints).. Yes.
Since I don't have my GG's yet - is each transducer paired with its own transformer ? Or is there one transformer driving both transducers ? One single on the inlet
Yes - my early NY model excal had one transformer glued to the silicone on the backside of each transducer, and Gary confirmed those were built that way. Guessing, but EX's were the first, so they were looking for the best results. So all the EX's had inducers/transformers, but they came to find out, they were not needed? Since they have not used them since the EX?
What is the HZ range of the excalibur audio? (Tonal range ) . It looks as if you may have some equipment for measuring this ? Yes, Software, but have not had a chance to sit down and figure it all out...
 
Made this up for a Dive friend..50mm PUI Piezo...almost like the one jw fisher uses...
Special thanks to lil john on the Pads
 
Here's what I found out this evening once I received my 50 MM transducers from Digikey :

1) The Early NY model of Excalibur will not drive the 3500 Ohm piezo on its own, zero sound, nothing.

2) When hooked to the primary side of the transformer it gets sound but very low volume. ( Speakers driven from secondary )

3) When hooked to the secondary side of the transformer it gets low volume when using the full secondary windings (Green and black)

4) When hooked to the center tap and either end of the secondary it gets full volume.

The answer is, and I don't know for certain whether this is harmful to the PC board or not - The red and white wires (primary winding, 8 ohm) hook to the audio out from the board.
The black and blue wires (secondary winding, center tapped, about 500 Ohms) hook to the speaker. The sound is about what I expect from a piezo. It "seems" to be missing the "bass" or very low tones that my mylar speakers "seemed" to produce,
but it is certainly good enough for the hunt. I think we can expect reduced battery life since the audio is "seeing" two 8 ohm windings in parallel rather than the 32 Ohms it "likes" to see.
And I forgot my theory regarding resistors in parallel so somebody please chime in here , but I thought total resistance is reduced below sum of both, whereas resistors in series would be additive..
Bear in mind this info applies only to the prehistoric excalibur models, and based on what OBN said earlier, not all of these have transformers.
I don't yet know how much power the newer ones output to the speakers. Also bear in mind we now have a capacitor hooked to a coil, so there is a possibility that when turning audio on or off we might get
a spike, but that part is way over my head - where is Steven Hawkings when you need him. On the newer models they apparently drive a piezo directly (capacitor) so I'm rough guessing the inline capacitor in the end cap absorbs "spikes" when the machine is shut off, and the resistor then bleeds off the capacitor - just a hunch and good chance I'm wrong.

I will build both types of headphones and try to improve on the design of the mylar speaker powered phones. After about 1200 hours using them I got used to the "voice" and it's hard to like the sound of a piezo speaker.
If I can get some leads made up I will try to take the old and a newer Excal to my workplace and try to get the output power measured to see what the difference is.

DC, Orlando FL
 
Good to know, and interesting news. Wonder if Gary would know what they added to pump up the volume, and eliminate the transformers....Thanks for sharing that info.................
 
Tried to measure audio output last night. The oscilloscope could not pick up a clean signal so we were not able to measure frequency.
Audio power output when a simulated 50 ohm load applied was about 100 Milliwatts at full volume, about 50 Milliwatts at half volume.
I am curious to find out if the newer machines have a higher output.

I may have to add a resistor in the circuit to bump the impedance up - unless I wire both transformers in series, but even then I am loading up the audio too much with only 16 ohms.
Once I find a 20 or 30 ohm resistor to put in series with the main audio wire, I will post the results.
With two 8 ohm coils in parallel right now I think I'm asking for trouble along with shorter battery life.
I want to have at least 30 ohms in the circuit, or 30 to 100 total ohms.

An idea on the capacitor /resistor combo in the end cap : I mentioned I thought it was a "spike" absorber and I'm wondering, for anyone that has that configuration - do you get the loud blast of audio when you first turn on (or off) the Threshold /Power switch ? I always got a loud "WOW" when turning my unit on and a similar "ZZZUP" when switching it off.
If the newer units don't do this then that is what the capacitor is taking care of (I bet). Absorbing the audio "surge" or "spike" when powered on and off. Still just a guess .........

DC
 
A few more notes/ corrections :
My original NY excalibur had green headphones if I recall ( Serial no EX112, PCB Rev 2.2), and I can only be sure of there being one transformer on the back of one of the transducers.
I did the end cap mod on my newer excal 1000 and noted what looks like a capacitor on the PCB next to the audio output pins. My NY model PCB does not have this.

I will try the PU50mm transducers from Digikey but will use micarta/phenolic sheet rather than ABS plastic for the bulkhead, as I think it will sound better.
I tested and one transformer will run both piezos just fine. (NY model , PCB Rev 2.2) and no transformer needed for the newer ones of course.
I gave up on trying to find the exact pins that are .025" square female to mate with the .025" square , 2.54 mm pitch mini connector on the PCB (audio).
I found the new connectors at frozencpu.com but the female pins they sell are too large for the male pins on the PCB.
The watertight strain reliefs are Heyco 3237 and 3464 - depending on which cord diameter you use, 11 bucks for a package of 10 on amazon.

I just got a new batch of 40 mm mini speakers 16 ohm and will build the ultimate speaker-type phones.
The inner cups of the Peltor's are perfect air chambers if lined with accoustic material, and that was the shortcoming of my previous phones, but that is a subject for a different topic.
(When those are done I hope OBN will test them for me;) )
And speaking of OBN - what a wonderful thing those Peltor hearing protectors are ! Thanks for discovering them.
 
Keep it coming as I experimenting with headphones as well. I made couple sets without the hi pass filter and found that over a large object like a beer can it will blow your head off! I'm working on a limiting circuit now.
 
I don't know if it's a high pass filter or not, or where this notion got started, but would like to know for sure.
I looked at mine the other day and it's hard to see exactly how it's wired but it looks like a capacitor in series with one output line and a resistor shorted across both output lines.

I don't expect any revolutionary improvements in making my own piezo headphones other than cost savings and control over durability.
But the speaker powered phones are more "voicelike" to me (subjective) and I think my latest attempt will give me more depth (able to hear in deeper water) than the others I built.
If you are bound to using piezo and want better sound quality and you can't get phenolic sheet - you might want to get a scrap of marine grade 1/16 inch mahogany plywood, soak it with
thin (low viscosity) epoxy resin and then bond the transducer to that, rather than mounting to the ABS plastic. I predict a more smooth sound with a tiny bump in volume needed
to compensate for the wood resonance vs plastic. Just a thought.

Use 20-22 gauge aircraft wire if you an get it (I do) because the conductors are plated with tin - less prone to corrosion if saltwater gets drawn in by capillary action.
Seal each wire end where you stripped it and after soldering - use the thin cyanacrylate (super glue) avaiable at any model airplane supply (ex "Zap CA" thin type).
The super glue will run down into the wire ends and help seal against water getting in.
Use "pro-seal" 2 part sealant if you can afford it, also called "PRC" by old hands in the aviation/aerospace field. It's about 4 to 8 bucks per ounce but well worth it.
Here's the data on their potting compound:

http://www.flamemaster.com/Technicals%20PDF/CS3100.pdf

And heres the data on the sealant I use for just about everything:

http://www.flamemaster.com/Technicals%20PDF/CS3201%20%20rev%2003-2011.pdf

Use the "Type B" as it is thicker.

These are 2 part sealants and don't need air to "dry", and they resist most chemicals and water too of course.
You might try somewhere like aircraftspruce.com to see if it's any cheaper than direct from manufacturer.
It is the most expensive component of any headphones I will build. But I still come out cheaper than Minelabs or Grey Gosts when I'm done...
 
Added a link to a passive RC filter tutorial.

Hopster said:
I don't know if it's a high pass filter or not, or where this notion got started, but would like to know for sure.
I looked at mine the other day and it's hard to see exactly how it's wired but it looks like a capacitor in series with one output line and a resistor shorted across both output lines.

High Pass Filter 101

I don't expect any revolutionary improvements in making my own piezo headphones other than cost savings and control over durability.
But the speaker powered phones are more "voicelike" to me (subjective) and I think my latest attempt will give me more depth (able to hear in deeper water) than the others I built.
If you are bound to using piezo and want better sound quality and you can't get phenolic sheet - you might want to get a scrap of marine grade 1/16 inch mahogany plywood, soak it with
thin (low viscosity) epoxy resin and then bond the transducer to that, rather than mounting to the ABS plastic. I predict a more smooth sound with a tiny bump in volume needed
to compensate for the wood resonance vs plastic. Just a thought.

Use 20-22 gauge aircraft wire if you an get it (I do) because the conductors are plated with tin - less prone to corrosion if saltwater gets drawn in by capillary action.
Seal each wire end where you stripped it and after soldering - use the thin cyanacrylate (super glue) avaiable at any model airplane supply (ex "Zap CA" thin type).
The super glue will run down into the wire ends and help seal against water getting in.
Use "pro-seal" 2 part sealant if you can afford it, also called "PRC" by old hands in the aviation/aerospace field. It's about 4 to 8 bucks per ounce but well worth it.
Here's the data on their potting compound:

http://www.flamemaster.com/Technicals%20PDF/CS3100.pdf

And heres the data on the sealant I use for just about everything:

http://www.flamemaster.com/Technicals%20PDF/CS3201%20%20rev%2003-2011.pdf

Use the "Type B" as it is thicker.

These are 2 part sealants and don't need air to "dry", and they resist most chemicals and water too of course.
You might try somewhere like aircraftspruce.com to see if it's any cheaper than direct from manufacturer.
It is the most expensive component of any headphones I will build. But I still come out cheaper than Minelabs or Grey Gosts when I'm done...
Click to expand...
 
Thans for posting that !!

Well, that circuit matches what I think I saw - a capacitor in series and a resistor across the two leads.
So, what was Minelab trying to accomplish by this ?

I , personally speaking, want all of the lowest tones possible as well as the high ones.
I love that deep "foil gum wrapper" low tone because I've also found tiny thin gold bands that way.
This is also why I like using speakers due to wider Hz response although I don't now if that matters ie; whether the piezo's are limited in that way or not.
I haven't seen any specs yet on what the Hz range of output is from the detector, would love to know.
But again, what the heck was Minelab trying do accomplish with the filter ?

There was an essay I read regarding piezo speakers and "balancing" the capacitance produced in the circuit by "mirroring" an opposite value
, and I'm probably not describing it correctly at all, way over my little sore head...... and a responder to the article says that the resistor creates a "low pass" filter, leaving lower frequencies unaffected.

http://eetimes.com/design/audio-design/4010013/Amplifier-considerations-for-driving-ceramic-piezoelectric-speakers-Part-2-of-2-

So I was wondering if the gizmo was something to do with that, or also whether it was for "impedance matching".
But I think you are probably right, just wondering why it was needed.
 
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