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Firepod noise floor, fixed!
Old 16th March 2010
  #1
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🎧 10 years
Firepod noise floor, fixed!

Hi There,

There is so much good information on this board, and I use it nonstop, so I figured I would add something I discovered after much pain.

I had been reasonably happy with my firepod, but had primarily been using it with condenser mics. I noticed a reasonable improvement when upgrading to the RNP, but found myself in noise hell once I picked up an SM7b for some audiobooks I am recording. Even at modest gain levels (+48db, which is modest for the SM7) I was hearing a lot of noise. Sweeping it with a high-q eq showed an enormous spike at 120hz.

I have spent days figuring this out. Ground lifting every piece of gear one at a time. Turning off every device that could be contaminating the ground. All the while grabbing a 15 second sample each time to see what, if any difference it made. (None of it made sense, I am on a decent power conditioner, and using a unified ground.)

So to cut to the chase, I'll avoid listing every step I took to eliminate noise over the last few days: the culprit was the firepod's power adapter. Mine came with an AC adapter. I noticed that the firepod had several different options for power input, so I swapped the 15VAC 2000ma adapter for a laptop power supply at 19VDC 3900ma and now the noise is gone.

Hopefully this helps someone else out there too.
Old 17th March 2010
  #2
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LeeYoo's Avatar
 
🎧 10 years
Hi,
All unregulated power bricks produce a ripple that is the strongest at twice the mains frequency. 100herz in our part of the world, but spikes of multiples of the mains frequency are also present. The gear should have enough filtering to minimise these frequencies, but...
A regulated supply (heavy one) is better. It removes most of the humm and regulates the voltage to a constant one, or..
A switch-mode power supply like the one you mentioned. It converts to the required voltage with a much higher frequency, so humm is not an issue anymore. Downside, price... Manufacturers like to cut corners.
A little warning. While this has worked for you, not all gear that runs on A/C bricks can be cured this way. Most gear needs A/C, because they make a negative and a positive rail from this. It might not work at all, or you loose things like phantom supply. Open surgury to replace the filter caps with bigger ones is the only option.
Old 17th March 2010 | Show parent
  #3
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🎧 10 years
Ya, the Firepod aka FP10 is somewhat unique in that it can run off of both AC and DC power supplies--don't see that very often. I am just glad that I found it before I had to spend too much cash troubleshooting. I still want to get a better ADC, but that is another thread I suppose.

The funny thing is I just found an adequate DC supply on Amazon for only $12 after shipping (my laptop will need its power supply back eventually.)
Old 17th March 2010 | Show parent
  #4
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LeeYoo's Avatar
 
🎧 10 years
Make sure is is regulated or switch-mode. BTW, a cheap switch-mode can add other (HF) noise.
Also, the DC voltage has to be higher than the AC rating on the unit, about 20-40%. It all depends what is inside the unit
Old 17th March 2010 | Show parent
  #5
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🎧 10 years
Hey Frameloss, I am not really affected by this issue, I just wanted to chime inand say thanks for offering something back to the community. This may indeed come in handy for others having a similar problem.

thumbsup
Old 17th March 2010 | Show parent
  #6
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🎧 10 years
This is info I have found a year ago... I just copy pasted it in a text file and do not have the sources... I believe it was on the presonus forum, you can probably google it.

Guys I thought some of you FIREPOD users might run into this problem and I finally found the fix after two times sending the unit back to Presonus and coming back from them with Problem Not Found:

Ok Folks!
here is the fix. it is an easy one and as expected, a ground loop (I know - I had to battle this in my amps...)
1. Take the case off your Firepod. You need a Phillips screwdriver and a 1/2" hex socket for the rear jack nuts.
- There are 2 screws on the top, 2 on the bottom and 3 on the rear (the S/PDIF and the two MIDI mounting screws) .
- Remove the 16 rear jack sockets with the 1/2" hex socket.
- remove the two side brackets.
- Disconnect the Power connector from the PCB board.
You are cleared now to carefully slide the case out:


2. Now... can you can see that S/PDIF socket? Can you see the metallic part that is between those two RCA connectors? BINGO!!!

THAT IS THE CULPRIT!!!
When the case is on, it creates a groundloop that induces the hum by touching the case and it needs to be isolated...
This is confirmed by Presonus as beeing an issue on older (2 years ago) Firepod construction that apparently was fixed at one point using an S/PDIF socket that doesn't have that metallic part, or something similar).
The metallic part does NOT have to touch the case by any means since it does not have any electrical use at that point.

--->>> continuing in the next post since I am allowed to only post 4 images per post...

continuation from previous post...

3. So, I simply used masking tape to isolate it from the case:

4. I mounted the case back (don't forget to connect the power connector back in its place in the PCB board), using all the screws BUT THE S/PDIF one and VOILA!
NO MORE HUM! Problem solved!

Wanted to post this here knowing of the fact that there are Firepod owners that have the same issue, and hopefully this way providing an easy fix - enjoying this way a hum-free excellent piece of gear!
Cheers,
Gabi.
Old 19th March 2010 | Show parent
  #7
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🎧 10 years
Thanks!

Wow, thanks guys!

I noticed that my Presonus FP10 had a bit of a hum on the inputs, especially with the gain all the way up on a channel with nothing plugged in. The Presonus Firebox I used to have never had that hum. The output on both has always been totally fine though.

After seeing this post, I did a quick test recording of one channel turned all the way up with the gain maxed out and nothing connected, to maximize the ugliness. Sure enough, an EQ sweep in logic confirms that 120Hz is exactly where it's happening.

Since I only use balanced connectors, I thought the only way to fix this would be to upgrade to a different audio interface or use higher quality external preamps. I'm extremely happy to see this low cost improvement / fix that I can implement on gear I already have.

Do you happen to have a link or a make/model of the DC power supply that was confirmed to fix this issue? Does anyone have any thoughts on whether it's worth implementing both fixes in parallel, or just picking one method and going with it?

Finally, I know when I upgraded from the Firebox to the Firepod/FP10, the published literature said they had similar preamp circuits, but that the Firepod should sound a little better due to more voltage being available to the circuit. Along these lines, since the FP10 can take 12-24 volts DC, I wonder if a 24 volt power adapter would sound better than a 12 volt power adapter.

Thanks again to everyone here for these excellent bits of information! Truly news you can use
Old 19th March 2010 | Show parent
  #8
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Puffer Fish's Avatar
 
9 Reviews written
🎧 10 years
Quote:
Originally Posted by LeeYoo View Post
Hi,
All unregulated power bricks produce a ripple that is the strongest at twice the mains frequency. 100herz in our part of the world, but spikes of multiples of the mains frequency are also present. The gear should have enough filtering to minimise these frequencies, but...
A regulated supply (heavy one) is better. It removes most of the humm and regulates the voltage to a constant one, or..
A switch-mode power supply like the one you mentioned. It converts to the required voltage with a much higher frequency, so humm is not an issue anymore. Downside, price... Manufacturers like to cut corners.
A little warning. While this has worked for you, not all gear that runs on A/C bricks can be cured this way. Most gear needs A/C, because they make a negative and a positive rail from this. It might not work at all, or you loose things like phantom supply. Open surgury to replace the filter caps with bigger ones is the only option.
Interesting. I have never experienced any hum (that I noticed ) on either of the two Firepods that I have. So I will keep my fingers crossed that I never do. But now that I have read these comments regarding the power supply and this post regarding the filter caps I will be ready for unfiltered noise if it ever rears its ugly head! Thanks everyone.
Old 20th March 2010 | Show parent
  #9
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🎧 10 years
A/B

Just to show how dramatic the difference is, here is an A/B example. The samples were brought up 108db using multiple instances of the gain utility in Logic. With that much gain, I see a full 12db of difference.

As for which power adapter to use, I can't really say--the difficulty is going to be getting the right plug not getting something clean enough and supplying sufficient watts.
Attached Files

Output 1-2.wav (5.05 MB, 2943 views)

Old 20th March 2010 | Show parent
  #10
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🎧 10 years
Quote:
Originally Posted by tenkas View Post
This is info I have found a year ago... I just copy pasted it in a text file and do not have the sources... I believe it was on the presonus forum, you can probably google it.
Ya, that is on the presonus forums, I confirmed that the SPDIF bracket has the RF shield removed on my unit. I wish that was the problem! It would have saved me 20 hours running around trying a million different things trying to find this source of noise.
Old 20th March 2010 | Show parent
  #11
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🎧 10 years
Quote:
Originally Posted by robotsound View Post
since the FP10 can take 12-24 volts DC, I wonder if a 24 volt power adapter would sound better than a 12 volt power adapter.
Just make sure you have enough wattage available. My stock adapter is 15VAC @ 2000 MA which is 30 VA, multiply by .6 to get DC watts: the replacement will need 18W minimum.

Which seems REALLY low, I thought I had read somewhere that this thing needed 35 watts?! The one I hooked up can supply just over 60 watts.

I did buy it used, so maybe it got paired with the wrong power adapter somewhere in its lifespan.
Old 21st March 2010 | Show parent
  #12
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🎧 10 years
Tip size

One more note, if you decide to try a replacement supply the tip on the original power adapter is 5.5 x 2.5 mm.
Old 21st March 2010 | Show parent
  #13
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LeeYoo's Avatar
 
🎧 10 years
Not sure if I should post this, because I don't know the Firepod. But I do know supply's. First of all, I downloaded the user manual and saw two different pictures of the supply input on the back of the unit (in the same user manual!). One looked like a proprietary type multi-pin socket and the other one like a normal DC socket. Multi-pin's are usually for AC in. You all seem to have the DC socket one.
So, how about voltage. It would be easier to tell if somebody had a service manual, or knew the type of regulator inside. Most units have the voltage regulator right behind the DC socket. Printed on it "78xx" and mounted on a little heatsink. The xx stands for the voltage, usually 12 or 15. Regulators like this need 3 volt MORE to work, so a 7812 needs 15 volts minimum. Any more than this is only heating up the regulator more and does nothing to the sound. Too hot and it will fail eventually.
Most units also have a "79xx regulator. Same, but for a negative rail. If the unit has a 79xx, it will need AC supply input, not DC!, to make both positive and negative rail voltages.
About the brick (the power adapter). The voltage of the UNREGULATED type varies a lot with the load. A brick with 12 volt written on it might give you 18volt or more when you measure it WITHOUT load. The rated voltage is under full load. These simple supply's have a big ripple under load, and the dip in the ripple could well be lower than the regulator in the unit needs, thus giving you a strong 100/120herz humm. Better to use a REGULATED supply (standard or switch-mode). These supply's have a fixed output voltage that does not change under load.
The power: If the unit has standard 78xx regulators on board, the supply need not to be bigger than 1AMP. That is the current limit of these regulators.
If the design runs on an AC brick AND the design has a flaw, like the dual grounding in tenkas's post, then the AC humm can enter the sound circuitry.
May have confused you a bit more with this post.
Old 24th March 2010 | Show parent
  #14
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🎧 10 years
Compatible DC adapter

I found a compatible DC adapter on Amazon in case anyone is interested:

Amazon.com: 12V DC 2000MA Regulated CCTV Power Supply PW2000R 1LC: Electronics

I can't say I experienced a full 12dB improvement in the signal to noise ratio, but the 120Hz hum is most definitely gone, and it knocked at least 2-3dB off of the noise floor, as measured by the channel VU meters in Logic Pro 9.

As a practical matter, when I turned up the gain all the way on a Shure SM57 that is sitting across the room and turned the master volume on the FP10 all the way up, the cars driving by outside were higher than the buzz-free noise floor
Old 25th March 2010 | Show parent
  #15
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🎧 10 years
I have noticed this problem on the firepod but I mainly record loud sources so it was never a problem.

I would like to know if this AC adapter from Amazon would be as good as the one Frameloss used (19v).

Is it possible that Frameloss got a better noise floor reduction because of the increased voltage?
Old 31st March 2010 | Show parent
  #16
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🎧 10 years
Noise floor

tenkas,

To put it in perspective, let me describe the practical real world results of this change.

I have my system calibrated so that if I turn the PreSonus FP10 volume all the way up, it will hit a maximum of 105dB in the mix position. I calibrated it using -20dB pink noise at 85dB, somewhat in accordance with Bob Katz's K-system.

If I turn the mixer knob to the inputs and turn the gain all the way up on a channel with nothing plugged into it, I can hear some noticeable hiss.

If I instead turn the gain knob all the way up (again, with the master volume all the way up) on a Shure SM57 that is across the room, I can hear room noise and the tiniest little bit of hiss below the room noise. Using headphones, I would say that the sound of me rubbing two fingers together 8 feet away from the Shure SM57 pointed 90 degrees away from me comes out at about the same volume as the hiss I'm hearing.

If there is demonstrable evidence that I can get another 10dB knocked off the noise floor by buying a second adapter, I suppose I would go for it. However, I have a feeling that this is about as good as it gets. Unless you are recording distant whispers with large diaphragm dynamic mics, you will almost certainly be OK with the adapter I ended up getting.

Last edited by robotsound; 31st March 2010 at 06:39 PM.. Reason: corrected information about decibels
Old 2nd April 2010 | Show parent
  #17
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🎧 10 years
Thanks for the answer. I will give the adapter a try.
Old 3rd February 2011 | Show parent
  #18
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🎧 10 years
DC power : Which polarity?

Hi guys,

I see some have succeeded on having the Firepod/FP-10 powered by DC power supply.
Can you please confirm which polarity is to be used to funtion properly? Should the center pin (tip) be negative or positive?

Thanks in advance,
Jorge
Old 3rd February 2011 | Show parent
  #19
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🎧 15 years
Quote:
Originally Posted by yuri1973 View Post
Hi guys,

I see some have succeeded on having the Firepod/FP-10 powered by DC power supply.
Can you please confirm which polarity is to be used to funtion properly? Should the center pin (tip) be negative or positive?

Thanks in advance,
Jorge
If the unit is designed to operate from an AC supply, there will be a bridge rectifier inside that will create correct internal polarity, so it doesn't matter which way round you polarise an external DC supply.

I've struck quite a few gadgets in the past which did benefit from a cleaner DC supply instead of the originally supplied AC unit... and yes a few extra volts is often useful in reducing noise. Just be aware that if the voltage is MUCH higher that your device may run a bit hotter. (onboard regulator chips)
Old 7th February 2011 | Show parent
  #20
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🎧 10 years
Quote:
Originally Posted by audioboffin View Post
If the unit is designed to operate from an AC supply, there will be a bridge rectifier inside that will create correct internal polarity, so it doesn't matter which way round you polarise an external DC supply.

I've struck quite a few gadgets in the past which did benefit from a cleaner DC supply instead of the originally supplied AC unit... and yes a few extra volts is often useful in reducing noise. Just be aware that if the voltage is MUCH higher that your device may run a bit hotter. (onboard regulator chips)
Thanks audioboffin!
Right! I thought it made sense as the power input stage was AC-ready, but I wanted to be preventive to not harm the unit; I was confused after I read another thread in which negative tip was said was the way to go, while Presonus support told me to use positive tip.
Will try DC, unless hum testing reveals no unwanted noise on my unit, in that case I'll keep the AC USA power supply, after converting [email protected] to [email protected] with a heavy transformer as I live in continental Europe.
Cheers!
Old 8th September 2011
  #21
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🎧 5 years
Frameloss - I was just wondering if the 19VDC 3900ma power supply was Ok on the firepod after long term use? I am worried that I will damage my firepod with too much voltage. I have a power supply with these specs (DC 19V - 3.16A ) and hope it will be safe to use.

Also will a fw800-400 9 pin to 6 pin cable work for the firepod to a macbook pro with the newer fw800 port?

thanks!
Old 19th September 2011 | Show parent
  #22
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🎧 10 years
I think you can't really hurt the Firepod... and worst case is you damage it, they cost next to nothing these days... You can get one that looks brand new for 200-250$.

I haven't tried the upgrade of Power supply, but I might since I am noticing a lot of noise compared to the cheap Steinberg 2-channel interface.
Old 20th September 2011 | Show parent
  #23
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🎧 5 years
My firepod is working great with the laptop power supply.
I am using a LaCie external HD that has FW800 and FW400. Right now I have the drive hooked up to the computer and the firepod hooked up to the drive.
I wonder if it matters which one is first when daisy chaining firewire devices?
Old 22nd September 2011 | Show parent
  #24
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🎧 10 years
I used to daisy chain HD with Firepod, you would want the firepod first (thats what they say in the manual). I have tested both ways and it is fine. Just don't try putting 3 HD and 3 firepods at the same time...

By the way, which laptop power supply did you get? Will they ship to Canada?
Old 22nd September 2011 | Show parent
  #25
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🎧 5 years
Quote:
Originally Posted by tenkas View Post
I used to daisy chain HD with Firepod, you would want the firepod first (thats what they say in the manual). I have tested both ways and it is fine. Just don't try putting 3 HD and 3 firepods at the same time...

By the way, which laptop power supply did you get? Will they ship to Canada?
I did a little test of the drum mics last night and everything worked and I was able to record 7 tracks around 4 minutes long with no issues using Logic. If I swap the drive and fp then the drive will have to use the fw400 cable instead of the 800 from the macbook. Ill see how that setup works as well.

Heres the link to the power supply I got from ebay. They Ship worldwide it says. I was using one I borrowed from work that was slightly higher and they worked the same.
Firepod noise floor, fixed!eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices

The adapter is actually a little too long it seems and sticks out the firepod a little. Still works just doesn't snug all they way in.
Old 22nd September 2011 | Show parent
  #26
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and did you notice an obvious noise floor reduction? Is it worth $10?
Old 23rd September 2011 | Show parent
  #27
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Quote:
Originally Posted by tenkas View Post
and did you notice an obvious noise floor reduction? Is it worth $10?
Its the only power supply I've used on the fp so I have no baseline.
Old 27th September 2011 | Show parent
  #28
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🎧 10 years
Do you hear any 60hz hum or other noise when you plug an sm57 and apply enough gain?
Old 27th September 2011 | Show parent
  #29
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🎧 5 years
Quote:
Originally Posted by tenkas View Post
Do you hear any 60hz hum or other noise when you plug an sm57 and apply enough gain?

I'm sorry I'm a noob when it comes to recording. I dont have have any shure mics. I have a couple AKGs ones a emotion D880 and an older D320b and have not really used either one yet for recording. I am still in the process of building my setup.
Old 3rd October 2011 | Show parent
  #30
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🎧 10 years
I just ordered the Amazon link adapter posted above a few posts. I'm hoping it works. I just moved and my speakers have the hum when plugged into the FP. I bought a hum eliminator, which didn't help. I'm also going to try the mod suggested above.

Has anyone who has tried the Amazon power adapter seen a big difference? Is it working well with the unit?
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