# Audio Control Corporation - Nonsense and tomfoolery LC1-800



## icansolvetheproblem (Sep 7, 2013)

After a bunch of fooling around I came to the realization that the Audio Control LC1-800 has a subsonic filter set at 27hz. In their lit they call it a PFM Subsonic filter - and anyone who has experience with Audio Control products knows that PFM is their moniker for "Programmable Filter Match" and is 'programmable' by changing the resistor array plugged into a small socket. Evidently this has changed - and programmable means something that you cannot change.

This is not very helpful when one is using the amplifier to reproduce 20-40hz. I'm actually surprised at this tomfoolery given the amplifier was designed by Robert Zeff over at Nikola on the Olympic Peninsula in Washington State. 

Furthermore, I can't understand why Audio Control even has a support line - the people who man it know essentially nothing about their product line. They don't know what PFM stands for, and when directed to check out the Audio Control FAQ's to see, they tell me that programmable doesn't mean you can change the value: 



> Dec 13, 2021, 17:58 MST
> Hi Icansolvetheproblem,
> 
> Thank you for contacting AudioControl. The LC-1.800 does not have an
> ...





> _Subject:_
> Subsonic PFM Disable
> _Your Request:_
> The LC1-800 literature states that the subsonic high pass filter is via
> ...


My guess is the amplifier has such poor performance below 27hz that the non-adjustable non-defeatable subsonic filter was implemented. While they say the filter is at 24hz it actually begins rolling off at 27hz (Linkwitz -3db down at filter point.) 

Anyone have prints of this amplifier so I can defeat the subsonic filter?


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## bnae38 (Oct 3, 2015)

On crutchfield it's labeled as fixed 24hz subsonic.

Interesting it's 18db/Oct per audiocontrol. Usually the low end response is just set by the DC block cap at input.

Suppose it could be a combination of that and an active circuit they end up with about 18db/Oct..

How are you measuring response? Oscope?

Ps I would want flat to 10 or 20hz as a least an option.. that's a stupid design for a sub amp.


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## SQ_Bronco (Jul 31, 2005)

It’s the same on the processors (DM-608 and 810). If you figure out a way to easily disable it you would become an instant hero…

Not sure about the amps but inside the processors there are also a bunch of undocumented jumpers. I haven’t had the guts to mess with those yet but if the amp is similar there may be a way to do it with those.


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## cman (Aug 24, 2020)

icansolvetheproblem said:


> After a bunch of fooling around I came to the realization that the Audio Control LC1-800 has a subsonic filter set at 27hz. In their lit they call it a PFM Subsonic filter - and anyone who has experience with Audio Control products knows that PFM is their moniker for "Programmable Filter Match" and is 'programmable' by changing the resistor array plugged into a small socket. Evidently this has changed - and programmable means something that you cannot change.
> 
> This is not very helpful when one is using the amplifier to reproduce 20-40hz. I'm actually surprised at this tomfoolery given the amplifier was designed by Robert Zeff over at Nikola on the Olympic Peninsula in Washington State.
> 
> ...




Desinged by Nikola engineering? You know I thought they vaguely looked similar to some ARC class D models.. the terminals.. a few other features internally.. kind of ARC X2-ish if you will but not completely... and ive seen distortion numbers.. Audiocontrol is much higher, albeit still quite low I believe it was like 0.05-0.1% and the ARC was 0.02%

I thought it was just coincidence... where did you find out this info?


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## icansolvetheproblem (Sep 7, 2013)

SQ_Bronco said:


> It’s the same on the processors (DM-608 and 810). If you figure out a way to easily disable it you would become an instant hero…
> 
> Not sure about the amps but inside the processors there are also a bunch of undocumented jumpers. I haven’t had the guts to mess with those yet but if the amp is similar there may be a way to do it with those.


Have you seen the information on jumpers in that equipment on the FAQ at Audio Control? 









Where are the jumpers on my DM-608? - AudioControl


To access the jumpers, you will need to take the top cover off of the DM processor via the 4 top screws of the chassis: Close up of grounding jumpers: The GTO jumper enables or disables the signal sense feature on the main input (either High level or RCA level inputs). The output jumpers […]




www.audiocontrol.com





I think I can figure out how to bypass the subsonic filter by opening this amplifier up on the bench and run a 10hz sine wave into it and then follow the traces with my scope until I see an op-amp with an output that is seriously attenuated. Then I'd change the frequency of my generator to something like 50hz without altering the output gain and measuring the signal along the same path as the 10hz signal and seeing if the output becomes equally as attenuated as the previous signal. 

Another method I could use is using my SA3050 RTA - the input can be converted to a probe (as I have done) and I can simply inject pink noise into the amplifier input and trace the signal until I see attenuation in the low frequencies. Oh, wait a moment, the SA3050 doesn't have this low of resolution....that's right...it's an Audio Control product. Okay, fine, I have an Ivie IE-30 I can attempt the same thing with and it goes to 1hz. 

Once I determine the op-amp that is being used as the subsonic filter it may be as easy as soldering a jumper, or, it may require my hot air rework station to replace some components. I'll keep you apprised of my finding.


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## icansolvetheproblem (Sep 7, 2013)

cman said:


> Desinged by Nikola engineering? You know I thought they vaguely looked similar to some ARC class D models.. the terminals.. a few other features internally.. kind of ARC X2-ish if you will but not completely... and ive seen distortion numbers.. Audiocontrol is much higher, albeit still quite low I believe it was like 0.05-0.1% and the ARC was 0.02%
> 
> I thought it was just coincidence... where did you find out this info?


The info can be seen in my photos perhaps or, I will attach a better photo here. The amplifier board says "Nikola Engineering" and when you go to the Nikola Engineering site, well, you go ahead and see. 




About Nikola | Nikola Engineering



*About Nikola*
Nikola Engineering has been doing bespoke electronics designs for more then 20 years. Started by Robert Zeff and Brent Waddell after leaving Zapco, Nikola has been a freelance design company, always open to new opportunities.


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## cman (Aug 24, 2020)

Wow! I never saw that before! What a shame it must have been built on a budget... Signal to noise is mehh and so is distortion.. 

Dont get me wrong.. its not bad, but relative to an ARC... its nothing to write home about. And they are built well.. just not perfomance wise on par with an ARC... Still great pieces and very reliable.. just a few odd things that throw me off.. and now this crossover is one more thing.


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## icansolvetheproblem (Sep 7, 2013)

I'm going to telephone Nikola tomorrow and see what they have to say.


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## cman (Aug 24, 2020)

icansolvetheproblem said:


> I'm going to telephone Nikola tomorrow and see what they have to say.



Great Idea! if they can or will tell you is nother question to be answered.. but i dont think it hurts to try.

Also, I will add this in addition to my last comment... distortion is not everything.. I've had a couple ARC KAR series that measured at 0.1% THD... and they sounded way better than another amp I had that was measuring lower.. Zeff amps always have great tonality to them IME.. I havent heard one of these in person but it definately gives me alot more confidence in the product knowing they are designed by one of the best if not the best amp designer of our time.. pretty cool actually.


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## SQ_Bronco (Jul 31, 2005)

icansolvetheproblem said:


> Have you seen the information on jumpers in that equipment on the FAQ at Audio Control?
> 
> 
> 
> ...


No but I think those were in the manual. Iirc there are 2 or 3 other sets of jumpers on the board.

I look forward to seeing your results!


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## icansolvetheproblem (Sep 7, 2013)

Got a call today from a management guy at Audio Control. He was incredibly cool. He agreed that the filter is not a Programmable Filter as advertised and he said he was having conversations with marketing about it and would be getting back to me soon. I'm fairly happy about that. I'll keep you posted as far as the results.


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## cman (Aug 24, 2020)

icansolvetheproblem said:


> Got a call today from a management guy at Audio Control. He was incredibly cool. He agreed that the filter is not a Programmable Filter as advertised and he said he was having conversations with marketing about it and would be getting back to me soon. I'm fairly happy about that. I'll keep you posted as far as the results.



If it makes you feel any better I always purposefully set a 20-25hz high pass on my sealed subwoofer anyways due to a high amount of cabin gain.. If not I end up making major EQ cuts down low.. alot of times these things are done on purpose because so many people use ported enclosures and they dont want idiots saying "bro this audiocontrol amp blows my subs" when in reality its just some idiot playing under tuning frequency of the ported enclosure  

- Kicker's CXA amps have a hard set subsonic.. the higher end Kicker KXA amps have a variable knob where you can adjust it.. In this instance it seems Audiocontrol took the cheap route since _most_ users want a subsonic filter to protect their sub in a ported enclosure. Anyways depending on your vehicle and cabin gain it might not change anything for you.. especially if you have a DSP.


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