# DIY Line Level Converter



## llebcire (Nov 17, 2016)

Did a quick search and didn't find any discussions about making a line level converter. 

I realize I could spend $10 - $15 for one and minimize much of the risk to my factory HU and aftermarket amp but it feels like this would be so simple.

Needs:

Reducing factory sub woofer output to line level to drive a sub channel on my amp. Factory system is Honda "premium" 7 speaker with dedicated amp and sub output. I haven't tested it (could with multi-meter) but it "feels" like the IB 8" sub might be getting 50 - 75 watts. If so, I would need to use beefier resistors, such as 0.5 watt? If I remember 1/8 watt is common.

Not needing noise isolation as this will be for the sub and I'll be using built in converters for the other channels. For some reason Zapco has level converters built in for mids/highs but not sub? Interesting.

The amp has gain controls so I don't need a potentiometer.

I will need to parallel 2 RCAs off the converter as the sub output is mono and I would prefer to feed both amp inputs.

Found an old post referencing Car Stereo Review (loved that magazine) that discusses using a 10k (R1) resistor, based on amp input impedance, with a 1.2k (R2) to drop the voltage.

Thoughts?
-Eric


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## llebcire (Nov 17, 2016)

Forgot the article from Car Stereo Review









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## jijivs (Mar 26, 2016)

Most of the professional hlo input impedance ranges between 33 ohms to 47 ohms. The disadvantage of having high impedance is that the power amplifier may end up having poor frequency response. Search for active attenuation, IMHO.

Drive safe,
JVS


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## llebcire (Nov 17, 2016)

jijivs said:


> Most of the professional hlo input impedance ranges between 33 ohms to 47 ohms. The disadvantage of having high impedance is that the power amplifier may end up having poor frequency response. Search for active attenuation, IMHO.
> 
> Drive safe,
> JVS


Thanks for your reply!

If this doesn't work out, I've researched the Audio Control lc7i and lc6i which would do exactly what I'm attempting.

However, my wife doesn't see the need to upgrade the factory system at all so I need to limit spending another $130 - $150 until next Spring. 

-Eric


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## llebcire (Nov 17, 2016)

Just to circle back around: I created a DIY converter as pictured above using a 10K and 1.2K resistor (believe they were 1/2 watt) for the sub input and it sounds great! I did parallel 2 RCAs off the converter as I used a factory sub channel (mono) and fed both amp inputs. 

I don't know if there's any noise as the sub is electronically crossed over but this was easy and $2 with tax.

-Eric


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## Victor_inox (Apr 27, 2012)

quality converters has transformers in them.resistors is a hack job.


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## llebcire (Nov 17, 2016)

Victor_inox said:


> quality converters has transformers in them.resistors is a hack job.


I agree. Ideally I would want electronic conversion.

The role of the converter is to present a high impedance load to the outputs and drop the voltage down to a level the amp can handle. Resistors, in this fashion, accomplish this. Transformers are needed to isolate noise, which in this case either doesn't exist or is masked by the frequencies, as well as diminish any DC pulses from the source, which may be present as I'm dropping a factory sub amp and not typical speaker level outputs.

I don't know if I consider this a risk or not given the source for the design.

-Eric


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## Victor_inox (Apr 27, 2012)

$20 converters has transformers in it, what is the purpose of this exercise? clearly not to save money.....transformers convert higher voltage speaker levels to the voltage down to a level the amp can handle. actively diminishing ground loop noise in process. resistors does not do such thing. There is no need to invent a wheel, it`s already has been invented. What you do with your most valuable asset-time is of course up to you.
Factory sub out IS typical speaker output processed to only present sub frequencies.


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## What? (Jun 5, 2008)

Audio Control LC2i is a good option. If someone is being cheap, I'll use the Power Bass ALC-2 (I think it is sold under a number of different brand names).


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## Victor_inox (Apr 27, 2012)

What? said:


> Audio Control LC2i is a good option. If someone is being cheap, I'll use the Power Bass ALC-2 (I think it is sold under a number of different brand names).


For even cheaper someone this one works great https://www.amazon.com/PAC-SNI-35-V...81830215&sr=8-1&keywords=line+level+converter


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## What? (Jun 5, 2008)

Victor_inox said:


> For even cheaper someone this one works great https://www.amazon.com/PAC-SNI-35-V...81830215&sr=8-1&keywords=line+level+converter


Sure, but not electronic, will not handle the input power of an electronic LOC, and degrade input signal.


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## Victor_inox (Apr 27, 2012)

What? said:


> Sure, but not electronic, will not handle the input power of an electronic LOC, and degrade input signal.


 Have you used one? It will handle factory sub output just fine and it only 9 bucks. As of signal degradation.. everything in path degrade signal to a degree, even speaker cable.


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## What? (Jun 5, 2008)

Yes, I sold them for many years. Passive LOC is a "last resort" type of product IMO.


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## Victor_inox (Apr 27, 2012)

What? said:


> Yes, I sold them for many years. Passive LOC is a "last resort" type of product IMO.


Yes, they are least profitable things to sell...
You missing the point- cheapest solution acceptable.


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## llebcire (Nov 17, 2016)

Let me ask another question:

My goal is to use factory HU and the HU does have balanced differential outputs that aren't equalized. Currently I'm running the speaker level into a Zapco with high level inputs and the converter referenced here to the sub channel - for some reason the amp has high level on 4 of 5 channels.

Should I:

A. Leave everything alone and add a true converter to the sub channel 
B. Find a way to convert the HU balanced to unbalanced for the amp 
C. Use something like an Audio Control LC7i

I do care about sound quality and may add equalization in the future along with processing (after I learn more as time alignment is new to me) which may leave me with B or C. However I would like to try B if it's not outrageously expensive. It'd be great to find a half DIN parametric that accepts balanced differential and outputs unbalanced as I can hide that in a pocket in the console.

Thanks for your input.
-Eric

Sent from my SM-G930R4 using Tapatalk


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## llebcire (Nov 17, 2016)

Update:

The resistors "seemed" to work well and serve their purpose for several months.

This week I swapped everything over to an Audiocontrol LCQ-1 to electronically process the high-level input and add equalization. The low end sounds (feels) better and I don't have the AccuBass enabled so while the resistor was an inexpensive option electronic is certainly better, although several hundred dollars more (or $80 for an LC2i). No surprise.

Eric


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