Hey, Mark.
?
I got this same idea (contact mic + trains) but unpopulated PCBs still lay around and look at me accusingly.
The idea of guitar pickup seems great. As already mentioned above the rails may be to still for the pickup(s) but you could try to mount them on a thin piece of springy steel. If the rail doesn't move make the pickup vibrate.?
Affixing the contraption to the rail or the sleeper may be a kind of a challenge though. It shouldn't move, maintain small but constant distance from the rail etc.
The piezo you just stick in 2 seconds and you're set.
?
If you want to go the stealthy route (without asking for permissions etc) , I got a hint for you: do not hide microphones, cables and yourself in the woods. Do it in the open wearing a HiViz jacket, jeans and workboots (or some similar to).
No one should bat an eye.
A guy in regular clothes standing by the rails may be suspicious but this same guy in a HiViz jacket is doing his job, probably measuring noise levels.
Best get a used one in a second-hand shop. One that shows some wear (not too much! Just a bit) and a bit stained here and there.?
?
When I am recording city sounds, in regular clothes, there will always be a clown that thinks shouting something at the sight of the mics is so funny,? innovative and entertaining.
When I wear a HiViz jacket people just pass by.
Weird looks? I don't care.
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Re: Rode NT1-A requires 3 minutes warm-up time
On Thu, Oct 31, 2024 at 09:15 AM, Heinz wrote:
The meter dropped around 35.54%
?
I still don't fully understand what this means for the voltage measurements of the NT1-a circuit. Do I need to add about 35% to each voltage measurement to get the correct voltage values?
?
?
Using Henry's procedures, you've been able to establish that the impedance of your meter is around 1M, not 10M as I had originally suggested as a possibility
?
The 35% reduction in voltage measured at that point confirms that the correct polarisation voltage is being applied to the capsule.
As Abbey suggests, time to look elsewhere.
?
Significant reduction in measured meter readings will only occur at very high impedance points.... like the capsule end of a 4M7 resistor!?
Measuring voltages at the various points suggested by Abbey should all return readings pretty much as indicated ( those points are all at a lower impedance )?
?
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On Thu, Oct 31, 2024 at 10:02 PM, Mark Day wrote:
I was actually planning on approaching the company who owns the spur line near our house and asking permission.?
?
Hi Mark
It depends on who you talk to. I hope it works out and you succeed! Maybe you should ask Gibson for a set of classic pickups as well. I'm not kidding. ;-)
?
Your story reminds me of a night ride on a steam train in the black forest in Germany. The only one I took. One meter snow outside. All other trains had to stop that night until early morning because every railway company was afraid getting caught by the? "Year 2000 Bug". The steam train got a special permission to ride through the new years night. Two bands were playing on that train. There was food, good music, drinks and nice people. Somebody who really likes steam trains fulfilled his dream that night and got the permission. From 04:00 in the morning the party went on in a rock bar until dawn. What a great time we had! My friends and I really loved it! Some time ago...
?
and liked the tunes. Not so spectacular.
?
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Am 31.10.24 um 00:43 schrieb Mark Day via groups.io: I have been thinking about building a
set of contact mics using Jules' circuit and a flat piezo disk. One of
the things I want to record is a passing train. Don't. They have more than enough trouble already with people taking nude photographs of their girlfriends on the tracks. Railways and trains are inherently dangerous. Be safe and stay away. Ralf -- Ralf R. Radermacher - K?ln/Cologne, Germany Blog : Audio : Fotos :
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Good point about the rails not moving much through the magnetic field. I was actually planning on approaching the company who owns the spur line near our house and asking permission. My mentor in audio was a man named Jerry Frederick who in the late 1950's made several recordings for Audio Fidelity Records, an early adopter of the then new stereo format. He got access to a rail yard in Reading PA and hauled his Ampex 351 and a couple Neuman U47's out there and spent the day recording the vanishing steam locomotives.
I don't expect as warm a welcome as Jerry received, but I am a professional audio engineer, so who knows. I guess it's all in how I approach them.? Although I prefer the former, I could do it stealthily as well on this spur that sees one or two trains a day. The biggest problem would be hiding the mic cables, and myself in the woods, and.........waiting...
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Re: Rode NT1-A requires 3 minutes warm-up time
On Thu, Oct 31, 2024 at 07:45 PM, Jerry Lee Marcel wrote:
Can you check the various voltages circled in red in both cases?
I will try, but it will take some time. Many thanks!
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Re: Rode NT1-A requires 3 minutes warm-up time
Can you check the various voltages circled in red in both cases?
Le 31/10/2024 ¨¤ 11:08, Heinz a ¨¦crit?:
toggle quoted message
Show quoted text
On Wed, Oct 30, 2024 at 11:04 PM, Arjay1949 wrote:
If you measure the voltage at each end of the 4704
resistor (with reference to ground) it should remain the
same.? That is around 68v at the left hand end (viewing your
photo) and c.50v at the right hand end (assuming the meter
impedacnce of around 10M).
If that latter figure rises between not working on first
switch on, and the mic finally working, then that capacitor
is likely the cause of your problem.
?
?
Hi!
?
I measured? the voltage at each end of the 4704 resistor
and the capsule voltage in the working and non working state
(viewing from the photo).
?
When the NT1-a is in the warm-up phase (not working).
Capsules voltage: 10.1
Left hand end: 69.0V
Right hand end: 12.8V
?
When the NT1-a is working.
Capsules voltage: 10.2
Left hand end: 69.1V
Right hand end: 12.9V
?
Does it mean, that the capsule itself may be the culprit?
??
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Re: Rode NT1-A requires 3 minutes warm-up time
It really looks like the problem lies elsewhere, since bias
voltage is correct in both conditions.
If the capsule was leaky you would have significantly different
readings.
Le 31/10/2024 ¨¤ 11:08, Heinz a ¨¦crit?:
toggle quoted message
Show quoted text
On Wed, Oct 30, 2024 at 11:04 PM, Arjay1949 wrote:
If you measure the voltage at each end of the 4704
resistor (with reference to ground) it should remain the
same.? That is around 68v at the left hand end (viewing your
photo) and c.50v at the right hand end (assuming the meter
impedacnce of around 10M).
If that latter figure rises between not working on first
switch on, and the mic finally working, then that capacitor
is likely the cause of your problem.
?
?
Hi!
?
I measured? the voltage at each end of the 4704 resistor
and the capsule voltage in the working and non working state
(viewing from the photo).
?
When the NT1-a is in the warm-up phase (not working).
Capsules voltage: 10.1
Left hand end: 69.0V
Right hand end: 12.8V
?
When the NT1-a is working.
Capsules voltage: 10.2
Left hand end: 69.1V
Right hand end: 12.9V
?
Does it mean, that the capsule itself may be the culprit?
??
|
Re: Rode NT1-A requires 3 minutes warm-up time
On Wed, Oct 30, 2024 at 11:04 PM, Arjay1949 wrote:
If you measure the voltage at each end of the 4704 resistor (with reference to ground) it should remain the same.? That is around 68v at the left hand end (viewing your photo) and c.50v at the right hand end (assuming the meter impedacnce of around 10M).
If that latter figure rises between not working on first switch on, and the mic finally working, then that capacitor is likely the cause of your problem.
?
?
Hi!
?
I measured? the voltage at each end of the 4704 resistor and the capsule voltage in the working and non working state (viewing from the photo).
?
When the NT1-a is in the warm-up phase (not working).
Capsules voltage: 10.1
Left hand end: 69.0V
Right hand end: 12.8V
?
When the NT1-a is working.
Capsules voltage: 10.2
Left hand end: 69.1V
Right hand end: 12.9V
?
Does it mean, that the capsule itself may be the culprit?
??
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Re: Rode NT1-A requires 3 minutes warm-up time
On Thu, Oct 31, 2024 at 01:37 AM, Henry Spragens wrote:
Here¡¯s how to find out for yourself, if you have a resistor of around 1M. Measure the DC voltage of a battery or circuit around 1 to 12 volts. Now attach the 1M resistor in series with the red voltmeter test lead and measure the voltage again. If the input resistance of the meter is 1M, it will cut the voltage measurement in half, half of the voltage being dropped across the added 1M resistor and half across the meter itself. If the meter is 10M, the reading on the meter will drop only 9%. Total series resistance being 11M, and the meter being 91% of the total. (90.909090...% for the nit picky.)
The resistor doesn¡¯t have to be 1M, it can be any value above 330K or so, just enough to affect the reading differently for a 1M meter vs a 10M meter.
Hi Henry
?
Many thanks for link and the detailed instructions!
?
I bought the Mastech MAS830 in a real electronic shop about 35 years ago. The atmosphere in the shop was nice. Small boxes with countless parts everywhere. :-)
?
For the measurements you suggested I used a battery holder with 4 AAA cells.?
Measured DC-Voltage: 6.47V
As a resistor I added eight 68K resistors (SimpleP48 stock) in series to a breadboard.
Measured resistance: 0.542M
Then I attached the 0.542M resistor in series with the red voltmeter test lead and measured the voltage of the battery holder again.
Measured DC-Voltage: 4.17V
?
The meter dropped around 35.54%
?
I still don't fully understand what this means for the voltage measurements of the NT1-a circuit. Do I need to add about 35% to each voltage measurement to get the correct voltage values?
?
?
?
?
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I would think that the steel rails aren't moving enough for that
to really work well (guitar strings move through the magnetic
field, causing the signal... I don't know what the displacement of
rails when they are making noise are but it can't be much, at
least in the audible frequency range; I'm sure they deflect
significantly when train goes over them) and I would expect a
contact mic to work better.
That said, rail companies certainly wouldn't look kindly upon
discovering some electronics wired up to their rails (at least in
the US/Canada.)
If using a contact mic, I would think you could attach it to a
sleeper or something driven into the grade a further distance away
and probably pick up a solid signal there, too, and possibly incur
a shorter jail sentence. :-) That said, there might be
weird/interesting sounds coming through the steel (including from
long before the train arrives.)
-c
On 10/30/24 18:50, JAMES B wrote:
toggle quoted message
Show quoted text
But seriously, cool idea, I'm
guessing you would not directly attach the pickup as you would
with a piezo. I think the pickup needs a slight gap from the
vibrating "steel".
I actually experimented using
various guitar pickups as the transducer for my plate reverb
project.
On Wednesday, October 30, 2024 at 09:42:30 PM EDT, JAMES
B <guardtech@...> wrote:
On Wednesday, October 30, 2024 at 07:43:29 PM
EDT, Mark Day <neowalla@...> wrote:
Ever since I built a few pairs of Jules'
hydrophones, I have been interested in new
ways to make recordings with things other than
traditional diaphragm microphones. I have been
thinking about building a set of contact mics
using Jules' circuit and a flat piezo disk.
One of the things I want to record is a
passing train.
Then I got to thinking...I also having been
tinkering with electric guitar builds and I
have a few cheap pickups from kit guitars
where I replaced them with better ones. Rails
are steel. Like guitar strings.
What about putting a pickup on each rail.
Run them through direct boxes and into my
Mixpre and record a passing train?
|
But seriously, cool idea, I'm guessing you would not directly attach the pickup as you would with a piezo. I think the pickup needs a slight gap from the vibrating "steel".
I actually experimented using various guitar pickups as the transducer for my plate reverb project.
On Wednesday, October 30, 2024 at 09:42:30 PM EDT, JAMES B <guardtech@...> wrote:
On Wednesday, October 30, 2024 at 07:43:29 PM EDT, Mark Day <neowalla@...> wrote:
Ever since I built a few pairs of Jules' hydrophones, I have been interested in new ways to make recordings with things other than traditional diaphragm microphones. I have been thinking about building a set of contact mics using Jules' circuit and a flat piezo disk. One of the things I want to record is a passing train.
Then I got to thinking...I also having been tinkering with electric guitar builds and I have a few cheap pickups from kit guitars where I replaced them with better ones. Rails are steel. Like guitar strings.
What about putting a pickup on each rail. Run them through direct boxes and into my Mixpre and record a passing train?
|
On Wednesday, October 30, 2024 at 07:43:29 PM EDT, Mark Day <neowalla@...> wrote:
Ever since I built a few pairs of Jules' hydrophones, I have been interested in new ways to make recordings with things other than traditional diaphragm microphones. I have been thinking about building a set of contact mics using Jules' circuit and a flat piezo disk. One of the things I want to record is a passing train.
Then I got to thinking...I also having been tinkering with electric guitar builds and I have a few cheap pickups from kit guitars where I replaced them with better ones. Rails are steel. Like guitar strings.
What about putting a pickup on each rail. Run them through direct boxes and into my Mixpre and record a passing train?
|
Ever since I built a few pairs of Jules' hydrophones, I have been interested in new ways to make recordings with things other than traditional diaphragm microphones. I have been thinking about building a set of contact mics using Jules' circuit and a flat piezo disk. One of the things I want to record is a passing train.
Then I got to thinking...I also having been tinkering with electric guitar builds and I have a few cheap pickups from kit guitars where I replaced them with better ones. Rails are steel. Like guitar strings.
What about putting a pickup on each rail. Run them through direct boxes and into my Mixpre and record a passing train?
|
Re: Rode NT1-A requires 3 minutes warm-up time
Re: Measuring capsule bias voltage, how and why ¡ª
Some info here:
As for the input resistance of the Mastech MAS830, I can¡¯t find it listed anywhere, and in the ~ $45 price range, it could be either 1M¦¸ or 10M¦¸. More likely 1M¦¸, like most inexpensive multimeters.
Here¡¯s how to find out for yourself, if you have a resistor of around 1M. Measure the DC voltage of a battery or circuit around 1 to 12 volts. Now attach the 1M resistor in series with the red voltmeter test lead and measure the voltage again. If the input resistance of the meter is 1M, it will cut the voltage measurement in half, half of the voltage being dropped across the added 1M resistor and half across the meter itself. If the meter is 10M, the reading on the meter will drop only 9%. Total series resistance being 11M, and the meter being 91% of the total. (90.909090...% for the nit picky.)
The resistor doesn¡¯t have to be 1M, it can be any value above 330K or so, just enough to affect the reading differently for a 1M meter vs a 10M meter.
On a related note, the NT1A is an example of a mic designed around an op-amp made of discrete transistors, resistors, capacitors, etc. Unfortunately, I don¡¯t see anything in the circuit diagram which shouts at me, ¡°Look here first!¡± But replacing the guts with one of Jules¡¯ OPA Alice circuits or one of Matt¡¯s DIY circuits is an option along side returning to R?de for repair. Watch out, though, micbuilding is addictive ¡
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Re: Rode NT1-A requires 3 minutes warm-up time
On Wed, Oct 30, 2024 at 11:04 PM, Arjay1949 wrote:
If you measure the voltage at each end of the 4704 resistor (with reference to ground) it should remain the same.? That is around 68v at the left hand end (viewing your photo) and c.50v at the right hand end (assuming the meter impedacnce of around 10M).
If that latter figure rises between not working on first switch on, and the mic finally working, then that capacitor is likely the cause of your problem.
Ok. I will check it tomorrow and let you know the results. Thanks!
|
Re: Rode NT1-A requires 3 minutes warm-up time
It seems likely that the meter will have an input impedance of c.10M ... most modern DMMs do.
?
Yes, that is the capacitor.? It's physically smaller than the one fitted to the NT1 (C8 in this photo)
?
 ? ?
but it performs the same function.... My probelm was dirt in the area under tha capacitor.?
?
If you measure the voltage at each end of the 4704 resistor (with reference to ground) it should remain the same.? That is around 68v at the left hand end (viewing your photo) and c.50v at the right hand end (assuming the meter impedacnce of around 10M).
If that latter figure rises between not working on first switch on, and the mic finally working, then that capacitor is likely the cause of your problem.
You can replace it with non SMD version, if that is easier?? ( The replacement cap needs to be rated at 100v rather than 63v). An mlcc type should do the job.
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Re: Rode NT1-A requires 3 minutes warm-up time
On Wed, Oct 30, 2024 at 08:06 PM, Arjay1949 wrote:
It's more likely to be the the primary 0.1uF (100nF)? capacitor, fitted between the 4M7 series resistor and ground, rather than the resistor itself.
Why do you think it's more likely the primary 0.1uF (100nF) ?capacitor? Do you mean this one? The whole area seems to be sealed.
?
 ? ?
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Re: Rode NT1-A requires 3 minutes warm-up time
On Wed, Oct 30, 2024 at 08:06 PM, Arjay1949 wrote:
Firstly though you need to confirm:
? the impedance of your DMM and?
? that the volts across the capsule are even lower at switch on
?
- The Multimeter I own is a Mastech MAS830. I had a but I couldn't find any information about it's impedance. I have sent a request to the manufacturer via Mastech's contact formular.
- I will check the voltage on the capsule tomorrow. If I remember correctly, it was 0.00, but I might be wrong. That's why I would like to do the measurement a second time.
I also looked under the capacitors with the eyepiece and a bright white light in the background. The area looks really nice and clean. Anyway. I cut one of my lense cleaning papers and pulled it underneath the caps several times. There was nothing unusual to be seen on the white paper strips.
?
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Re: Rode NT1-A requires 3 minutes warm-up time
On Wed, Oct 30, 2024 at 09:19 AM, Heinz wrote:
?
Hi! I'm back in town and did the measurement.
Across the two capsule wires it's 10.2V when the microphone is working.?
To check the voltage when the mic is not working, I have to wait until tomorrow morning. Then it usually doesn't work and needs the warm-up time.?
?
?
?
A DMM wil normally have an impedance of around 10M¦¸. Can you check the make and model of your meter, to confirm that ?
If 10M¦¸ is true , then a reading of 10V is low. The mic will work, but sensitivity will be much reduced.?
If it measures even lower than that when first switched on,? then that would suggest a faulty component in the voltage multiplier output filter.?
It's more likely to be the the primary 0.1uF (100nF)? capcacitor, fitted between the 4M7 series resistor and ground, rather than the resistor itself.
Or - as I suggested earlier - possibly dirt underneath the capacitor itself???
Firstly though you need to confirm:
? the impedance of your DMM and?
? that the volts across the capsule are even lower at switch on
?
|
Mark Day