# Do I really need a head unit?



## Spasticteapot (Mar 5, 2007)

I'm hoping to put an el-cheapo stereo setup in a Honda Civic, and was wondering as to the necessity of actually using a head unit. In this day and age, most folks just plug their iPod or F/M equipped Mp3 player into their headunit anyway, often turning a $200 lump of electronics into a glorified preamp with a spiffy LCD. Why not just build a simple op-amp based preamp (with a good-quality PSU to cut down on noise) and bypass the headunit entirely?


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## kulic (Sep 27, 2008)

I was thinking a high-quality headphone amp. Same idea.


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## kulic (Sep 27, 2008)

I have a Clarion hu, relatively high end. The LEDs are sure pretty, and the other thing about a hu is you can do the filtering, bypass, eqing, etc. the unit is crap though, noisy. and the cd player is broken already. 

I was going to try the aforementioned high-quality headphone amp into a TRU linedriver. But I'm not sure if the linedriver can do the filtering to the respective channels. What would be cool is if TRU or someone (hey put me on the design team) just went ahead and made a head-unit without a CD player, or with a CD player but without an onboard amp, just an integrated linedriver. 

I think there aren't really any good HU's at decent quality/cost ratios. But don't know. 

One thing I don't get is where the noise is coming from on my setup. it sounds like tape-hiss. The HU internally? Electrical noise leaking into unshielded cables (RCA and/or speaker lines)?


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## Knobby Digital (Aug 17, 2008)

My classic car buddies use a 1/2 din EQ mounted under the seat so the dash stays stock.

You'll still want some tone controls because the EQ on the iPod is garbage.


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## kulic (Sep 27, 2008)

I've read other people say the eq on the iPod is really good. knowledgeable sounding people, but I wouldn't begin to know how to verify what these people say. 

I have an iPod which is essentially bricked at 30gb (it's supposed to be 160 gb), I do not like it. 

My primary source player is a Cowon S9 (32 gb) which is an excellent player; also renowned for good sound quality. 

Talking to myself now, possibly my noise issues are not unrelated to having amp-gain all the way up; of course that's just begs the question of noise source (high gain is not a noise source, it's just high sensitivity to a noise source)

As far as EQ and bypass filtering. If using a line driver and maybe remote bass control (to the amp direct) and have enough wattage around maybe wouldn't even need to mess with bp filtering, just let the cones produce to the frequencies they feel like responding to/producing, a natural bypass filter. This assumes no need to conserve and allocate wattage sparingly. 

Emmeline SR-71 Headphone Amp - Ray Samuels Audio


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## Spasticteapot (Mar 5, 2007)

Making a simple high-pass/low-pass mixer/filter for separating the various speakers isn't that difficult - all you really need is a few op-amps. EQ is a bit more tricky, however - aside from either using an on-iPod EQ or using something big and complicated, I'm at a bit of a loss.


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## Knobby Digital (Aug 17, 2008)

kulic said:


> I've read other people say the eq on the iPod is really good. knowledgeable sounding people, but I wouldn't begin to know how to verify what these people say.
> 
> I have an iPod which is essentially bricked at 30gb (it's supposed to be 160 gb), I do not like it.


It's not the filters themselves, it's the boost-happy presets that Apple gives you, and that you can't make adjustments on the fly.

Have you tried replacing the HDD in your sick iPod?










Teapot,

Are you trying to get away without using a processor either?


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## kulic (Sep 27, 2008)

replacing HDD on iPod. I considered it, but the thing has been an epic pita forever, and it's an expensive process. I may at some point do that. For now it's got about 30gb of music on it and aside from that is a very pretty brick. 
Just annoyed with Apple generally. I'd like to avoid them in the future. I have an iPhone 3G too and while it's been a good product to me there are very good alternatives out there. I have a Nokia N900 which is so vastly superior to the iPhone in just about every way imaginable. Linux OS! (Maemo).

On amps and lp/hp: many amps (Billets) have crossover/lp/hp controls. Not mine. But not sure it would be an issue anyway. 

On EQ, I have no idea. I don't do much EQ on the fly, just set it up for the system and go. The exception is subwoofer volume. I'm adjusting that constantly depending on the track and where I am. Again though, that could be controlled by remote bass control from the amp. 

Dream signal path:
Cowon S9--> cardas miniplug cable --> SR71A amp --> cardass mini-to-RCA --> Tru-linedriver--> decent shielded RCAs --> Billet(s) --> dyns.
|-remote bass control

*Am I really a cable snob? No, actually. But I wonder. I've never heard comparisons so don't know how much a difference it would be. A car a potentially around/producing a lot of em noise, so it seems at least plausible that well insulated cables could preserve detail better. Don't know.


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## bigguy (Apr 13, 2010)

Alpine makes a few CDless HU's, and i think eclipse has a player with no amp in it. My kenwood has the ability to defet the amp, i have it off now. there are options out there, but i dont think they are any cheaper then a standered HU


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## kulic (Sep 27, 2008)

my clarion has that amp defeat too. i use it. It has a lot of decent options and a decent EQ. But the cd player broke already and why have an onboard amp in the first place when could just use the money and space for better components. Eclipse is no more. People do make good HU's (by reputation) but they are boutique and of huge cost, much of which goes into making a reference quality CD player that can handle road abuse--which I don't really need.


Almost thinking linedriver would be moot in above "dream signalpath" It would be basically doing what the headphone amp (with 2 x 9volt batteries, in series or parallel don't know) would already be doing probably just as well. 
In that case:
Cowon S9--> cardas mini-to-mini --> SR71A --> my 15ft Grado headphone extension cable I have around (with the adapter here somewhere) --> some 1/4 to RCA adapter --> Billet --> etc.

Would like to avoid splitters but likely necessary at some point, definitely if have 2 amps.

I don't know what I'm talking about though. EE illiterate.


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## Knobby Digital (Aug 17, 2008)

kulic said:


> replacing HDD on iPod. I considered it, but the thing has been an epic pita forever, and it's an expensive process. I may at some point do that. For now it's got about 30gb of music on it and aside from that is a very pretty brick.
> Just annoyed with Apple generally. I'd like to avoid them in the future. I have an iPhone 3G too and while it's been a good product to me there are very good alternatives out there. I have a Nokia N900 which is so vastly superior to the iPhone in just about every way imaginable. Linux OS! (Maemo).
> 
> 
> ...


Yeah, it's cost prohibitive to replace HDDs in iPods. I just opened mine up to replace the battery. The work isn't hard, but those 1.8" drives are more costly than a used iPod.


Andy W, has been explaining for years why it's better to use EQ to control low end than the subwoofer level. -The XO point goes to ****. Hope this doesn't pull it too far off track, but here are some representative graphs:

Subwoofer fader:










Shelf filter:


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## kulic (Sep 27, 2008)

interesting point, about eq vs sub faders. I'll have to think about that more. I augment levels separately because I wanted more midbass and less high end. Today realized that I could control that from the passive crossovers by moving some wires around, and leave the EQ flat (any advantage to doing so I've no idea).


On the headphone amp as replacement for HUs, I spoke with someone literate about that today; he said the output impedance might be a problem, as on headphone amps tend about 16Ohms, with HUs maybe more in the k regions. 


Therefore the OPs idea of building from scratch seems indicated, if not asking one of these companies to custom one of their amps for a higher output impedance plus 12volt DC inputs. At that point it's pretty much an HU.


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## Spasticteapot (Mar 5, 2007)

kulic said:


> On the headphone amp as replacement for HUs, I spoke with someone literate about that today; he said the output impedance might be a problem, as on headphone amps tend about 16Ohms, with HUs maybe more in the k regions.
> 
> Therefore the OPs idea of building from scratch seems indicated, if not asking one of these companies to custom one of their amps for a higher output impedance plus 12volt DC inputs. At that point it's pretty much an HU.


Actually, many headphone amplifiers are based around buffers or op-amps that have an effectively infinite output impedance. Worst case scenario is that you wire a 40-ohm resistor in parallel with the input of your amplifier, which is usually on the order of ten thousand ohms.

Incidentally, getting a headphone amp to run off of 12V is really easy, thanks to an IC called the TLE2024, which splits 12V into +/-6V. Just connect it to a LME49720 op-amp (of which I have a few spares  ) and you have yourself a 12-volt preamp. The only bugaboos are the possibilities of ground loops and the massive electrical noise from the rest of the system; the former can be solved most easily with transformers and the latter by placing a linear regulator and a nice big filter cap in front of the TLE2024. 

Incidentally, I'm not sure how much voltage the average automotive power amplifier wants. Is 4V RMS enough? 




Knobby Digital said:


> Teapot,
> 
> Are you trying to get away without using a processor either?


Ideally, yes - I'm just going to use a passive xover. (I have a Hi-Vi 2-way component set that looks pretty spiffy.)


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## 240sxguy (May 28, 2009)

I know you are local to me. I have an eclipse 8445 with a dead cd drive that I would be interested in parting with. I think it has an aux. in 

PM me if your interested.


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