Amping you Head unit using line outs

[GaryM]

WARNING....
What you are about to see is not for the squeamish of feint hearted. Please look away now!

In my quest to keep my standard single CD slot Boost head unit, for reasons of styling and to keep the theives away. I'm striving to try and get the best sound from it. I'm finding this more difficult and as you will see I have decieded the modify the unit to get the much wanted line-outs to drive my external amp.

I chose to amp the HU unit but was only able to use the speaker outputs to drive the amp. Since doing this I was never pleased with the sound of the system. I knew it should sound better and rather than upgrade all the externals, amp, speakers, sub etc. I decieded to follow my hunch and modify the HU. The result...





The immediate effect of doing this has been better bass responce, imaging and trebble. So I'm pleased with my efforts and it endorses what I have said in many other threads that line-outs are the better way to go. From my results and what I have heard in other posts, I'm supprised that the HK system sounds so good even with it's DSPs if it really is driven from the speaker outputs of the HU.

Just to let you know what is involved in this mod



The amp is down the side to the right of the picture and that is it's heatsink. You need to strip the HU down and then tap into the signals that go to the onboard amp.



The pick up points are the tiny little pcb via's marked with the arrows and the Black pen. Intrestingly enough there is a little RC network for each signal just before the amp which I'm bypassing here. This would explain why the frequency responce has become better. I guess it is there just to prevent the amp from overdriving on signals that the standard speakers can not resolve.

[Dom]

WELL DONE!!!

How pleased were you when you put it back together and it actually still worked?

Dom

[GaryM]

Very, no actualy it is not that bad. It is a well built unit and now I know my way in it doesn't take long to gut it. The worst bit was soldering the wires on to the tiny vias.

Anyway what was the worst that could happen? It might of blown up and then I would have had the excuse to by a new head unit.

[chiph]

Where did you find a return/earth/ground for the shield conductor on the RCA cables?

Chip H.

BTW: nice bit of work!

[GaryM]

Whoops minor detail. Take a look at this pic...



It shows the clearly shows the grounds. As I said the hardest thing here was soldering to the little via's. The trick I used in the end was to insert little peices of wire into the vias and solder these in place and then soldered the coax to that. I used the tape to hold things in place while I was soldering. I then superglued the cables down when complete.

[AntH]

Nice one! Have done similar thing myself in the past - added line-outs to an integrated amp. But that was quite a bit easier - loads of room, nicely labeled PCB & big wire links to solder to! Doddle compared to your little mod. Think I will be swapping the head unit (mine arrives without the BOOST!) rather than modding it. The original can then go back in unused if I ever decide to part with my MINI.

[snoopy]

Good work Gary.

Do you have any pics with the laser unit in place and also the front panel. Do you only use the Front channel with your set up?

Did you measure what level signal was coming out of your new RCA outputs at all.

[FLiPSiDE]

VERY nice work!

I've gone the softer method and just got a line level adaptor with adjustable gains from david navone engineering



http://www.davidnavone.com/detail.asp?PRODUCT_ID=N-774V

not the cheapest option at $59US but i've been told they're one of the best around.. so im giving it a go.. i REALLY wanna keep the stock deck if possible

again congrats on this.. i love a bit of hacking.. just rarely daring enough to give it a go myself

[GaryM]

FLiPSiDE

Keeping the stock deck has been my aim but I'm afraid that the speaker outputs just don't cut it. So it doen't really matter what converter you use. I used the one integral to my external amp. I like the one you have shown though as I guess the pots are for level balacing?

Snoopy
Here is the cd deck. It is just held in by 4 screws and then just lifts out as the connectors are integral.


At the moment I only amp the front speakers and run a sub so I only need the front outputs for my RF500X 4 channel amp. While I was there I wired the rears but did not have enough RCA connectors so I'll add those another day.

Did'n measure the outputs but did have to crank the amp gain up when switching it from speaker inputs to line-in.

[MINI4PLAY]

That will most likely work, but you blew your radios warrantee. You would have been best suited with a high to low level converter.

[GaryM]

Quote:

Originally posted by MINI4PLAY
That will most likely work, but you blew your radios warrantee. You would have been best suited with a high to low level converter.

Obviously the warrantee has long gone but for the cost of a replacement it was a risk I was happy to take. After all the next step is to purchase an aftermarket HU anyway.

The main reason for this was as an experiment to see where the loss in sound quality is coming from. Sure the level converter probably would not trash the signal too much but how good is the internal amp that you are boosting using a level converter and an external amp? From this mod I can confidently say that if you are after quality sound then you ain't going to get it just by amping the HU using level convertors.

At the end of the day you like what you like. We all have different expectations and interpretations of what constitutes a good ICE system.

In this situation it realistic to say that a lot of time has been spent here proving this point but by sharing this information, in this thread, people are better informed to help make their own decisions.

I would very much doubt that anyone else would take this route but if you do let me know how you get on.

[Dom]

Quote:

Originally posted by GaryM

Is that when you got annoyed and stabbed it with a screwdriver?

Can't wait to hear what this sounds like, I too am interested in just how good the CD player could really have been

Dom

[chiph]

Quote:

Originally posted by GaryM
<snip> In this situation it realistic to say that a lot of time has been spent here proving this point but by sharing this information, in this thread, people are better informed to help make their own decisions.

I would very much doubt that anyone else would take this route but if you do let me know how you get on.

I'm very interested in doing this (I've ordered the cassette unit w/CD changer for my MCS), as I like the look of the factory radio, and I want to keep the MFSW controls.

Just need to borrrow an oscilloscope from a friend, and buy a new soldering station...

Chip H.

[GaryM]

Quote:

Originally posted by chiph
Just need to borrrow an oscilloscope from a friend, and buy a new soldering station...

Chip H.

Should get away without the silliy scope as there is no way to power the thing up unless it is in the car, security coding. Just make sure you have a soldering iron with a small tip, ideally temperature controlled and take your time.



Dom,

Don't build your hopes up, but is an improvement. I've still got the speaker level inputs wired so I can switch the inputs. Ideal for you to be a independent witness when we meet.

[snoopy]

Garym when you do you A to B testing can you see if you can make it a blind test. E.g. Dom does not know what source he is listening to. He just listens to them both and then chooses the best one.

So you did not remove the signal from the internal amp then? So how are you protecting it from any noise that you Rca leads might pick up and then feeding back into the internal amp?

I will be interested in you results from your test as I think the protection/limiting circuit (the caps and resistor network that you by passed) will be how you got a better signal. Did you try the Rca the other side of the network?

Must say you have done well with your little test (saves me doing it). Also I am looking for a pick up point to measure the speaker output to see at what level the signal starts to distort, have you got any suggestions for a easy pick up point?

How have you found the radio reception on the boost?