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EP1500/2500 HP Filter Mod

post #1 of 12
4/26/12 at 3:21pm
Thread Starter 
Has anyone attempted moding the internal selectable high pass filters in either of these amps? It seems an awful waste to buy this amp and then have to buy an additional filtering device for $50-$100+ more when there is already a HP filter inside.

I found a website with a blog post discussing the possiblity of modding this and he highlighted an area in the schematic that appears to be a passive 2 stage RC HP filter. I spent some time studying the schematic myself and have come to the same conclusion based on signal routing.

For the 50Hz filter it uses 2x 150 nF caps and 2x 20k resistors for a cutoff of fc=1/(2*pi*sqrt(R*R*C*C)) = 53.05 Hz

For the 30 Hz filter it adds in a 220 nF cap in parallel to the first 150 nF cap for a combined capacitance of 370 nF on the first stage. This gives an fc=33.7 Hz

I attached a sample from the schematic to illustrate. This is for channel 1; channel 2 has identical filtering. The input signal +/- is on pins 2&3 on the left labeled X10 respectively.

I plan on building a custom sub soon and will likely attempt this in a month or two from now unless someone has had a bad experience doing this. I do not own this amplifier yet.
LL
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post #2 of 12
4/26/12 at 5:40pm
Could you post a link to the blog you mention please?

Most pro power amps without switchable filters usually have one cap determining the LF -3dB point. From your schematic, that would be C13, the 10uF/50V unit. This is easily replaced in many amps to lower the LF -3dB point for those wanting an infra response and (without looking at the whole EP schematic) is also likely the LF limitation here too.

Make sure you choose caps that will fit, or make arrangements so that they can be made to do so, eg PCB pins as stand offs or vertically mounting an axial cap. For the smaller values MKP or MKT types are best and there are plenty out there. Sprague 716P are good, easy to find and inexpensive.

Make sure you can solder/desolder without destroying the tracks.

Make sure you can do it safely - even 110V can kill you.

You know you're voiding warranty too right?
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post #3 of 12
4/26/12 at 8:26pm
Thread Starter 
Original site that brought the idea to my head: http://mikescloset.blogspot.com/2012...er-ep2500.html

As far as C13 goes, I guess I didn't specify what my plan was. I don't intend to lower the overall system cutoff point. For the EP1500 the -3dB points are 5Hz and 50kHz which is plenty for my needs. I intend to change the actual switchable filter cutoff values. Perhaps something like 20 and 10 Hz. This would be changing C18, C22, C21, R111, and R110.

Soldering shouldn't be a problem, I have a full set of gear for doing that stuff. I'd probably let it sit for a while to let the caps bleed off first.

Warranty I'm not too worried about. Seems everyone and their mom does the fan mod on the EP2500 to void the warranty anyway.
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post #4 of 12
4/26/12 at 8:49pm
NEO Dan looked into this, alas, it's all SMT mount caps and resistors, and they are located on the bottom side of the board. Unless you are a solder ninja, and work on that stuff daily ( and have nice tools ), I would suggest passing on modding the high pass filters.
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post #5 of 12
4/26/12 at 9:01pm
Quote:
Originally Posted by Bushi View Post

Original site that brought the idea to my head: http://mikescloset.blogspot.com/2012...er-ep2500.html

Cheers. I don't have time right now to look at it in detail, but will over the w/e.

Quote:
Originally Posted by Bushi View Post

As far as C13 goes, I guess I didn't specify what my plan was. I don't intend to lower the overall system cutoff point. For the EP1500 the -3dB points are 5Hz and 50kHz which is plenty for my needs.

Mentioning C13 was meant as a more generic comment. Some of the poweramps people have complained about the LF response being too high (and don't have filters like the EP does) can easily be changed by swapping out one capacitor per channel.

More later.

Quote:
Originally Posted by michael hurd View Post

NEO Dan looked into this, alas, it's all SMT mount caps and resistors, and they are located on the bottom side of the board. Unless you are a solder ninja, and work on that stuff daily ( and have nice tools ), I would suggest passing on modding the high pass filters.

Good point. I don't own an EP, but SMD is a PITA even with good tools.
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post #6 of 12
4/26/12 at 9:01pm
Thread Starter 
I kind of expected SMT parts as it's before amplification. Hopefully they are 0805 parts. I saw the post where NEO Dan requested the schematic, was there another where he investigated further?

Anyone have a schematic for the newer EP amps? EP2000/4000? I was looking at prices and it seems a refurbished EP1500 is about the same price as a EP2000 delivered because they are charging like $80 shipping to Alaska on the EP1500. EP2000 comes from Amazon with good old free shipping. I've heard they are more or less rebadged but it would help to know if the schematic or silkscreen labels changed.

Also, what would be the best way to confirm the change after I completed it? Would a before and after chart of voltage vs. frequency across the sub terminals be enough to see the new corner or would the changing woofer impedance mask it?
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post #7 of 12
4/26/12 at 9:06pm
I just plan on ordering those fmods for$25 right now lol
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post #8 of 12
4/26/12 at 9:29pm
Thread Starter 
Quote:
Originally Posted by pokekevin View Post

I just plan on ordering those fmods for$25 right now lol

Those are certainly attractive. I just wish they made <20 Hz versions.
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post #9 of 12
4/26/12 at 9:42pm
Quote:
Originally Posted by Bushi View Post


Those are certainly attractive. I just wish they made <20 Hz versions.

Yeaa
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post #10 of 12
4/26/12 at 9:49pm
Quote:
Originally Posted by Bushi View Post

Those are certainly attractive. I just wish they made <20 Hz versions.

They are questionable in terms of their posted -3dB points as they don't specify the load they need to see to get the specified response.

As you're willing to solder, you can DIY this easily enough and add it inside the EP case. tap off from the board after C13 before the attenuator and use this to determine values. IIRC the attenuator was 10k but I'll confirm later - that's Ramp.

Design for 20Hz, then add the extra caps in parallel to get the 10Hz response and switch the extras so you always have a circuit. Build them onto a tagstrip or turret board like an old tube amp - no PCBs or SMD soldering required.
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post #11 of 12
4/26/12 at 9:58pm
Quote:
Originally Posted by A9X-308 View Post

They are questionable in terms of their posted -3dB points as they don't specify the load they need to see to get the specified response.

As you're willing to solder, you can DIY this easily enough and add it inside the EP case. tap off from the board after C13 before the attenuator and use this to determine values. IIRC the attenuator was 10k but I'll confirm later - that's Ramp.

Design for 20Hz, then add the extra caps in parallel to get the 10Hz response and switch the extras so you always have a circuit. Build them onto a tagstrip or turret board like an old tube amp - no PCBs or SMD soldering required.

Sooo they aren't worth it?
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post #12 of 12
4/27/12 at 12:17am
Quote:
Originally Posted by pokekevin View Post

Sooo they aren't worth it?

No
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