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Sub amp selection #4866421 09/11/18 06:58 PM
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Colt45ws Offline OP
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In my work van, I currently have a Blaupunkt THA1250. Its a [email protected] Class D amp. I purchased it about 6 years ago, and works great, except for one problem.
You see, I am a licensed HAM radio operator. What I have discovered is the Blaupunkt amp spews so much noise @145MHz that my VHF radio is basically unusable, because the RF noise floor is so high. I can take a handheld radio tuned to 145MHz, walk dozens of feet from the van and still hear the digital fluttering. Its comical that it ended up there because the 2 meter amateur band runs from 144-148MHz and being where it is manages to wipe out about 80% of the band, its so broad.
Right now I have two line filters in series on the power going into the amp, trying to knock the noise down. And that works, to a point, but Im still having issues and Im seriously ready to rip it out and go with something else.
What I would like is another Class D amp, because I only pulled wire suitable for running a 250-300w Class D amp. It may end up that because of the digital switching noise, none of them will have acceptable RF noise level and in that case I would have to pull thicker wire and go with a Class A/B.
So Im really grasping for straws here; I doubt any one would have knowledge of what exactly their amp is doing, but Im hoping maybe, just maybe someone might have experience with the same situation and found something that works.
Ill probably end up buying a A/B type amp but I'd like to avoid pulling a new wire run. Its only got 8ga running to the fuse panel.

Last edited by Colt45ws; 09/11/18 06:59 PM.

-Colton
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 86k
Pennzoil Conv HM 5W30, Fram XG2
Re: Sub amp selection [Re: Colt45ws] #4866432 09/11/18 07:07 PM
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SubieRubyRoo Offline
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JL Audio or Rockford Fosgate. The former because they deliver rated wattage without fail, the latter because they nearly always deliver 15% more and at half the cost of JL.

Re: Sub amp selection [Re: Colt45ws] #4866459 09/11/18 07:37 PM
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Cujet Online Content
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No surprise with a class D amp and it's switching power supply. Shield the entire thing, including the wires? It's generally accepted that class D is the right amp for a sub. Efficient, powerful, cheap. A good class D amp won't have sound quality issues.


People who count on their fingers should maintain a discreet silence.
Re: Sub amp selection [Re: Cujet] #4866527 09/11/18 09:41 PM
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Colt45ws Offline OP
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Originally Posted by Cujet
No surprise with a class D amp and it's switching power supply. Shield the entire thing, including the wires? It's generally accepted that class D is the right amp for a sub. Efficient, powerful, cheap. A good class D amp won't have sound quality issues.

I agree with you on the Class D being right for a sub. The problem is its broadcasting the noise back out the power wires, and turning the entire van into a antenna. Like I said Ive got two line filters in series on the input DC jack, and there is STILL noise coming out.
They must have put it at 145Mhz intentionally because if it was about 10MHz higher, it'd be in the middle of the VHF public safety band and every vehicle with one of these would be unintentionally jamming such communications. Any cop or fire unit that happened to drive by or be sitting next to a vehicle with one would suddenly find they had no communications. About the only way to get the FCC to do anything about anything is to broadcast on the PS freq. They would be all over this if it was doing that.
I may just buy another Class D and see how it fairs. Probably a Rockford, since I have a old 4 channel A/B from them that must be 20 years old and still running strong. I guess worst case Ill send it back.

Last edited by Colt45ws; 09/11/18 09:43 PM.

-Colton
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 86k
Pennzoil Conv HM 5W30, Fram XG2
Re: Sub amp selection [Re: Colt45ws] #4866535 09/11/18 09:53 PM
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Colt45ws Offline OP
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I ordered a RF P300X1 off Amazon....if its too noisy, its going right back. I can tolerate some noise, but this blaupunkt is just out of control.


-Colton
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 86k
Pennzoil Conv HM 5W30, Fram XG2
Re: Sub amp selection [Re: Colt45ws] #4866543 09/11/18 10:01 PM
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It’s more than just noise from the power supply. I believe the ps is running around 50khz, while the output section is possibly as low as 150khz since this is a low pass only amp. Unfortunately I’m 1000 miles from my scope and similar blaupunkt amp to test it for you. You will need a class d amp with a higher switching frequency on the output stage or a class a/b amp. Something old school like a punch 60ix will work on your 8awg and give you 240 watts if you can get a 4ohm bridged load out of the sub.


2008 F250 6.4 PowerStroke 52k
2005 Honda Pilot 260k
1963 Nova SS 84k
2008 GMC Yukon Denali 186k
2013 Mahindra 3016HST 128hrs
Re: Sub amp selection [Re: Jim_Truett] #4866551 09/11/18 10:22 PM
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Colt45ws Offline OP
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Originally Posted by Jim_Truett
It’s more than just noise from the power supply. I believe the ps is running around 50khz, while the output section is possibly as low as 150khz since this is a low pass only amp. Unfortunately I’m 1000 miles from my scope and similar blaupunkt amp to test it for you. You will need a class d amp with a higher switching frequency on the output stage or a class a/b amp. Something old school like a punch 60ix will work on your 8awg and give you 240 watts if you can get a 4ohm bridged load out of the sub.

Yes. I haven't looked at what the base frequency is. Going backwards if it was running 142khz my interference would be the 10th harmonic.
Thanks for the tip on the 60ix. Ill look for that or something similar. My sub is a 4ohm so thats no problem. I do see its only rated 30wRMS x2. So its capable of more than that?


-Colton
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 86k
Pennzoil Conv HM 5W30, Fram XG2
Re: Sub amp selection [Re: Colt45ws] #4866608 09/12/18 04:26 AM
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A 4 ohm bridged load will generally net you 230 to 240 watts prior to clipping. It would run hotter than any class d amp, so that could be a concern depending on your listening habits.


2008 F250 6.4 PowerStroke 52k
2005 Honda Pilot 260k
1963 Nova SS 84k
2008 GMC Yukon Denali 186k
2013 Mahindra 3016HST 128hrs
Re: Sub amp selection [Re: Colt45ws] #4866652 09/12/18 05:47 AM
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danez_yoda Offline
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what kind of filter do you have. Most "filters" are for alternator noise not RF. You need small high frequency (ceramic) caps directly across the input therminals. Don't overlook the output terminals as well. An LC on the outputs would also keel the RF inside the amp.

regardless of the Class D or class AB there is a switching power supply inside the amp. It need to boost the 12VDC to +/- 50DC or so create a 32Vrms sign wave across a 4 ohm load to make 250 W. The class D is noisy because it the speaker wires have PWM signals on them and they are generally unshielded. as well as the speaker coil.

Try a high frequency filter on the speaker outputs.

Re: Sub amp selection [Re: Colt45ws] #4866774 09/12/18 08:33 AM
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Colt45ws Offline OP
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Uhhh, I'd have to look, but you make a good point. I had considered making my own filters that was targeted at the output of this thing. I guess what Im hoping for with the new one is that it has better filtering built in.


-Colton
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 86k
Pennzoil Conv HM 5W30, Fram XG2
Re: Sub amp selection [Re: Colt45ws] #4867223 09/12/18 05:52 PM
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sleddriver Offline
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As a fellow HRO, I understand. Class-D in a vehicle with unshielded power & spkr lines is asking for frustration as putting the whole amp in a copper cage still is not enough. You need to stop both emitted and radiated noise. An o'scope would be a useful diagnostic tool. Have you tried ferritte cores?

Have you checked the ARRL handbook?


1998 Volvo V70 T5 228,880 mi. Original Owner.
M1 10W-30 HM
"It's never a mistake to buy tools, defined broadly. They're not a cost, they're an investment." - J.B. Peterson
Re: Sub amp selection [Re: Colt45ws] #4867247 09/12/18 06:39 PM
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Colt45ws Offline OP
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I havent tried ferrites, but did consider it. I looked on amazon and found a few where people were like "I puit them on, I guess it works!" Okay. Well, that doesn't tell me if its a good ferrite.
I can get a scope, along with a lot of other gear, its just finding time to do it.


-Colton
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 86k
Pennzoil Conv HM 5W30, Fram XG2
Re: Sub amp selection [Re: Colt45ws] #4867309 09/12/18 07:41 PM
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Look up who sells ferrites on Digi-key or Mouser, then call the manufacturer, inform them of your HRO status and ask for engineering assistance. Also ask Q's on a ham forum. There is lots of good info in the ARRL Handbook. You don't need to buy it either; you can borrow/ILS from a library. Depending upon both the age and construction of the amp, it may need additional bypassing, recaped, or replaced.

Also remember: A DC and a HF AC ground are not at all the same. What looks like a short to one, still looks like an impedance as freq increases to the others. Complicated even more so in a vehicle.

The Sled's sound system is the premium version though not sure if any of the amps are Class-D. I experienced no interference problems with the Kenwood dual-band (2M/70cm) I installed. The wagon's roof makes for a great ground plane.


1998 Volvo V70 T5 228,880 mi. Original Owner.
M1 10W-30 HM
"It's never a mistake to buy tools, defined broadly. They're not a cost, they're an investment." - J.B. Peterson
Re: Sub amp selection [Re: Colt45ws] #4869797 09/15/18 10:32 PM
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Originally Posted by Colt45ws
I ordered a RF P300X1 off Amazon....if its too noisy, its going right back. I can tolerate some noise, but this blaupunkt is just out of control.


Got this in Friday...says on the front of the box its A/B...interesting, I thought I had ready differently. Oh well! Guess Im pulling wire sometime.


-Colton
2002 Ford Crown Vic PI 207k, Ex-Kootenai County, ID Unit #42
Down for engine swap
2003 Ford Crown Vic PI 86k
Pennzoil Conv HM 5W30, Fram XG2
Re: Sub amp selection [Re: Colt45ws] #4870607 09/16/18 09:31 PM
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SubieRubyRoo Offline
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If this is your amp:
[Linked Image]

Then yes, Crutchfield and RF's website agree it is a class A/B amp. These things usually have pretty stout birth sheets, what did yours look like?

rockford.PNG
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