# Rockford Fosgate 200m



## blueatlanta (Feb 10, 2011)

I need to replace both 330uf 63v capacitors (right next to the B+), (2) 2200uf 35v capacitors, 1 buz103 fet, the gain pot, and (2) PK IN 4003 0205 diodes.

can anyone give me some recommendations on which parts to replace them with?

should i change out the other, smaller, 35v caps with 105 degree ones?

i would also like to upgrade this amp while im making these replacements to learn more about amp repair, as i have about 10 more amps that i would like to get working again.


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## Matt R (Aug 29, 2007)

I have an upcoming project with some of the dsm amps. Prolly very similar to your amp. I would paralell 2 of these Digi-Key - P10347-ND (Manufacturer - EEU-FC1J221S) to replace each 330uf cap. That will cut the resistance in half and they are already very good low esr caps.

I would do the same with the 2200uf caps two of these in paralell will have way lower resistance Digi-Key - P12406-ND (Manufacturer - EEU-FM1V122L). 

Digi-Key - 1N4003FSCT-ND (Manufacturer - 1N4003)

I couldnt find the mosfet but I did find the datasheet for it. Looks like this would be a suitable replacment. It is prolly a good idea to replace all the buz 103's so the devices match closer.Digi-Key - FQP50N06-ND (Manufacturer - FQP50N06) 

Find a pot with the same resistance, size, shape and pin configuration.


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## blueatlanta (Feb 10, 2011)

wow. thank you for the links matt. i just got in today a series 1 2030 as well that i will be tinkering with.

also, why would you choose those 1200uf caps over say, the 3900uf ones?
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P11249-ND


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## Matt R (Aug 29, 2007)

You can use those, that ups the capacitance which is fine. I would use multiples of the smaller ones because the resistance is cut in half if you use 2 instead of one. and cut in half again if you use four instaed of two. 

You could also add some resistors in series in between the caps to form an RC filter to further lower PS noise/ripple. Here is a good example http://www.passdiy.com/pdf/BA2 r1.pdf R1-R8 is what im talking about, that will considerably lower ripple. C3 and C5 would be the two 1200uf.

It would take a little work to do it, you might have to cut a trace or connect the big caps to the next component or something like that to get the resistors in series.


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## blueatlanta (Feb 10, 2011)

Matt R said:


> You can use those, that ups the capacitance which is fine. I would use multiples of the smaller ones because the resistance is cut in half if you use 2 instead of one. and cut in half again if you use four instaed of two.
> 
> You could also add some resistors in series in between the caps to form an RC filter to further lower PS noise/ripple. Here is a good example http://www.passdiy.com/pdf/BA2 r1.pdf R1-R8 is what im talking about, that will considerably lower ripple. C3 and C5 would be the two 1200uf.
> 
> It would take a little work to do it, you might have to cut a trace or connect the big caps to the next component or something like that to get the resistors in series.


would i be able to run the larger capacitance capacitors in parallel as well? it's not that i'm stuck on the idea of increasing the capacitance, i just want to know if it would be better/worse/no noticeable difference. i'm assuming there is no sonic difference, but is there one in operational reliability or efficiency?

could i do something like getting one of those blank boards from radio shack and implement the resistor bridge on that and run wires from that to the pcb? i assume the largest issue with that would be space requirements and mounting issues.

would running larger capacitance in parallel with the resistor bridge be worth the time and effort? how do i calculate what resistance to use?

as for the gain pot, would i use a log taper or linear type?

again, matt, thank you for your time and replies to my scrub questions. once im comfortable, id like to work on upgrading my other oldschool rf amps and eventually learn enough to mod the ms8 and p99 that i will buying in the next couple of months. this stuff is just too neat to not do. taking something like an old, beat up amp and having it perform on-par with new amps and maybe even having much cleaner sound than new amps.


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## Matt R (Aug 29, 2007)

Yeah, you could run the bigger caps in parallel. You may hear an audible difference in doing that. Its the PS ripple that your trying to get rid of. AC ripple is noise that is amplified along with the audio signal. The more noise you get rid of, the more quiet, blacker background, and potentially more micro detail that will be able to be heard.

The resistors in the Pass amp are 1ohm 3 watt and he uses 4 per polarity. That will work for your amp. You could add inductors in series with the power supply lines too. That will filter out even more PS noise. 

There are prolly some cheapo 7812 or 7815 regulators that power the front end of the amp. Those regs can be upgraded to lower noise substantially. 

I'm still not sure what pot it is your replacing but the ones in the amps ive looked at were 2k and one like this Digi-Key - 3386X-202LF-ND (Manufacturer - 3386X-1-202LF) would probobly do.


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## blueatlanta (Feb 10, 2011)

i dont think this thing has any regulators.. i see two rectifiers?

MUR1610CTR & MUR1610CT


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## Matt R (Aug 29, 2007)

There should be some lower voltage to power the opamps and the front end of the amp. There should be a 7815 or 7812's and a 7915 or 7912's. If I remember they are the TO220 package and are on the heatsink with the output mosfets.


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## blueatlanta (Feb 10, 2011)

Here's what I have on the MEHSA boards.

MEHSA board near power input:
LM337T
LM317T
MUR1610CT
MUR1610CTR
BUZ103
BUZ103

MEHSA board near the speaker-level inputs:
IRF540
IRF540
IRF9540
IRF9540


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## Matt R (Aug 29, 2007)

The 337's and 317's are the regs. Those are much better than the 7800 series if they bypassed the adjust pin with a 10uf cap. I'd put an elna silk there. Looks like they improved the supply from the dsm and IX series on that one.


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