new information regarding audio upgrades...

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Thread: new information regarding audio upgrades...

  1. #1

    new information regarding audio upgrades...

    Thought I'd share my latest exploits in trying to get a decent audio output from my AS-2 system.

    ok, lets start with the problem. I've got a stock AS-2 setup in my 2004 9-5. The main problem is that it's missing a big chunk of the audio range low/mid frequency, then has pretty crappy base response unless cranked right up. I've been trying to sort this out the hard way, which I can't recommend:

    1. Replaced the dash speakers with a pair of decent Pioneer units (TS-876).
    > Sound quality certainly improves, but still missing the low/mid-range.

    2. Replaced the door speakers with a pair of 4ohm JL Audio coaxials, 94dBm sensitivity
    > Volume substantially reduced (confirming these are directly driven from an amp circuit, not a crossover as I was hoping)
    > Speakers are still only kicking out very low frequency, no mid-range.

    3. It seems most of the audio problems are all coming back to the amp, so I pulled it out to play with (what a bitch that was).

    Firstly, I need to contradict Angry Kitchen: head unit to amp connection is NOT pro-audio differential line level, it's bog-standard speaker outputs (which are almost all differential in cars). This means replacing the head unit DOES NOT need any special circuitry to work with the amp. Just connect the speaker outputs into the amp (which is exactly the current wiring config on the DIN connector - no change needed).

    The amp itself is a pretty archaic design. The service manual dates it back to 1996 for the Saab 9000, but the circuitry looks much older than that (lots of through-hole, hand soldering and big 1206 SMDs). I've attached an extract of the service manual (full version too big to upload). The amp has got both low-pass and high-pass filters installed to decouple the front speakers. The door speakers have a lowpass cutoff at 140Hz, whereas the dash have highpass at 125Hz. I get the feeling Saab invested all the cash with Harmon Kardon here, leaving peanuts to 'throw something together' to fit. Theres no way 3" dash speakers are going to be able to pick up the entire range from 125Hz upwards, so no change of door speakers is going to make the slightest difference...

    This is now where I'm up to. It pretty much leaves the following options for sorting out the audio:
    1. Buy a new head unit, disconnect the amp in favour of some passive cross-overs (plus some minor rewiring)
    > A decent head unit can take over the work of the amp, just loosing centre speaker.
    2. Tweak the amp circuit to change the cross-over frequency
    > circuitry is all pretty simple and accessible, just need to find the right caps to change.
    > this also gives an opportunity to change the fixed gain on the door speakers, allowing 4ohm units to work properly.
    3. Find a new amp
    > not sure anything exists to do this job directly
    > going to involve lots of rewiring as theres no way I can mount one in the current location

    Will keep you updated as this progresses, thoughts/comments welcome.

    Mat
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  3. #2
    Super Moderator haloweenhamster's Avatar
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    Re: new information regarding audio upgrades...

    I seriously doubt that they would design the amp for low impedance bridge mode input that would make no sense where as a high level high impedance balanced input would make sense and alot of OEM amps use the same

    changing the xover points will be simple though and if its something your capable of doing its recommended but careful changing the gain as they are probably set so Max volume is JUST under clip which is probably supply rail limiting rather than current so the only thing you will achieve is heavily clipped audio as the amp has hit the supply rails causing the peaks to be chopped off making it pulsed DC output
    Currently
    9-3 2010 2T aero
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    900 1996


  4. #3

    Re: new information regarding audio upgrades...

    ok, starting with this blasted amp. I've attached the frequency response for dash (HPF) and door (LPF) filters. This does not include speaker response nor the equaliser section of the amp, but it gives you an indication and explains exactly whats going wrong with the sound. I ripped the circuit from the service manual and stuck it through Spice...

    Massaging the frequency response is reasonably straight forward: it's a few capacitor changes. I'm still calculating new figures, but it should be reasonably simple to not only extend the door speaker upwards, dash speaker downwards, and also rearrange the gain just through a couple of capacitors. The gain clipping won't be an issue because these filters are attenuators, so all we'll do is 'not reduce as much' rather than increase.


    in terms of the amp input, I agree that its a bit silly to take HU speaker outputs into the amp, but I'm about 95% sure this is exactly whats happening, based on the following criteria:
    1. the input circuitry on the amp certainly isn't line level. Firstly, the amp inputs are ~3:1 attenuated upon input, they are then put through fairly heavy isolators/levelers before feeding the rest of the circuit. This isn't typical of line level inputs. The input impedance is 45.6k ohm, which isn't any audio standard I know of (but would work fine for speaker output).

    2. The head unit outputs to the amp via the speaker pins on the DIN connector - given DIN is an international standard, outputting line level on these pins violates this standard and I doubt they'd have got through type approval doing this.

    3. Given the sheer amount of testing and type approval needed for all automotive modules nowadays, pioneer wouldn't have made a special HU for saab. Instead, all they ever do is respin the exterior/package, so the actual electronics will be a bog standard head unit already repackaged

    ok, truth is the only way to be 100% certain is to either pull my head unit apart or stick a scope on the output, but as I said, I'm now 95% sure from what I've seen so far.

    enjoy!

    Mat
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  5. #4

    Re: new information regarding audio upgrades...

    Hi Mat, I was wondering if you got ay further with the modificaton of the SAAB Pioneer amplfier. Did you manage to change the cross over frequencies? I'm also curious if you might have the complete schematics and not just the block diagram posted with your mail. I have had the same thougts as you concerning the missing mid-bas / low mid's and was really happy to find this posting since I have not been able to find any information on the Pioneer amp my self. I have had thoughts about changing to the HK amp with additional sub speaker outputs, but I have heard it's supposed to have more o less just treble to the rear door speakers, any thoughts on this?
    It really sounds stupid if they run high power bridged amp outputs from the main unit to the Pioneer amp, have you been eble to establish this yet? In tht case it would be possible to tap into these for drving full range dash speakers. Allthough it's a old posting I hope you get to see this.
    Thomas

  6. #5

    Re: new information regarding audio upgrades...

    Hi Essi,

    I'm sorry to say that it's been so long I've lost most of the information for this, so what I write is now from memory...

    The full service manual was obtained via google, so you just need to find the amp part number (it's the same part as used in Saab 9000's) and google it.

    I'm still convinced the amp inputs are just speaker outputs from the head unit, nothing more complex. It's a standard head unit, re-badged for saab - theres nout special about it's outputs. Indeed, feeding the amp from pre-outs will sound terrible because of the attenuation on the amp input circuitry. So, in theory, just putting another OEM head unit in will work fine (in practice, I've never tried). Conversely, bypassing the amp will give you a world of pain, because it has the crossovers integrated into it, so you'll then need to provide separate cross-overs for the woofers and mid-dash speaker, which is not trivial.

    As for re-working the lowpass filter, I didn't do this in the end, as I found an easier solution!

    The simple solution was actually just to use the fader control on the head unit to put a 60:40 volume boost to the rear speakers. Bear in mind those front door woofers are NOT connected to the front fader, but are a combined signal (in the amp) between both front and rear. This means by mucking about with the fader, you can use the fader to separately control the tweeter gain without affecting the subwoofer. Need to be gentle doing this, because you'll just end up rattling your door. For me (bear in mind I have aftermarket dash tweeters), turning the fader just to 11am on the clockface re-balances the mids without causing excessive bass. Of course, all of this is at the expense of the rear passengers, but as the sound quality is already pretty poor back there, no-one notices anyway.

    Bingo bango: you've corrected the mid-range inbalance without any replacement parts (well, apart from my replacement dash tweeters which I had already).

    Mat

  7. #6

    Re: new information regarding audio upgrades...

    H
    Hi Mat, thanks for your quick reply!
    I managed to get the service manual after looking thoroughly and really digging.
    Looking through the schematics I'd have to say I doubt the amp is feed from a high level BTL output from the head unit.
    The balanced inputs has 16kohm in series with the +- inputs which is then voltage divided by 6.8kohms to ground.
    This gives an attenuation to about 1/3 of the input voltage. If feed by a BTL output stage the voltage at high volume
    would be 8-10V (top value) or more, then resulting in some 3V after attenuation.
    The ground isolator IC on the input (TA2050S) is a unity gain (1X amplification) buffer and does not handle above 1V output with reasonable distorsion.
    Above 1V the dist. just sky-rockets. This makes it hard to believe that the amp. unit is feed with high level signals.
    I would have expected more attenuation than to 1/3 if this was the case. I could be wrong though...

    The schematics say LPF is at 140Hz - 18dB/Oct, your spice simulation shows something else, more like 50 Hz. This is also what it sounds like in my ears.
    I have bought a spare amp from the junk yard to do some experiments on, I hope to measure the frequency responce with real signal to make sure.
    The indicated 140Hz sounds about right to get a reasobnable sound balance, so if I find something else from measurements I'll try to change it to that or perhaps even 200Hz.
    The schematics I found has really crappy resolution so comoponent values are difficult to read, hopefully I'll manage to figure it out...

    I have ordered but not installed a pair of JBL GX-302 3.5" speakers for the dash, should be a good step up from original speakers.
    The center dash speaker I'll replace by a 1" silk dome since it's 3kHz filtered before the amp.

    To be continued

    //Thomas

  8. #7

    Re: new information regarding audio upgrades...

    Hi again,
    Ran the GM-2416 Pioneer/SAAB amp filter components through some simulations. I come to the conclusion that LPF is 18dB oct. at 131Hz cut off. The HF section is 12 dB oct at 118Hz.
    This is not in agreement with Mat's simulated respons for the LPF section, but more in-line with what sounds reasonable. Still the sound stage seem to lack mid bas / low mid.
    Looking at the phase combining one 18dB LP and one 12dB Hp section they seem 180 deg. out of phase at cross over (~125Hz).
    This cold cause serious cancelation around this point if not considered when selectig polarity for the dash / door speaker properly.
    It's a bit tricy to follow this through the schematics of the amp since it's not always obvious if (the numerous) stages are inverting or non-inverting.
    I'l simply hav to make a test once all things are mounted in the car. The JBL GX302 3.5" dash speakers looks very good from a build and quality point of view, have not played music on them yet though.
    They have a proportionally large membrane for a 3.5" unit and should well be able to cover down to 118Hz.
    nortuately did not manage to upload the frequency and phase response plots for LPF and HPF sections.
    Tomas

  9. #8

    Re: new information regarding audio upgrades...

    The JBL GX302's (3.5") in the dash made a ton of difference over the original Pioneer speakers. The soundstage is now much more balanced in terms of mid bass. Surprisingly enough they sound good om most types of music, really good actually. I also replaced the center dash with a 1" silk dome since I found out this channel is HP filtered 12dB oct. from 3kHz. Contrary to what many say, I think this speaker contributes a lot to the sound stage, especially since the listening position (driver) is so off centered. Qiute a big difference in efficiency of this set up over the original speakers, hence more head room from the amp and balance towards the bass door speakers.
    Next plan is to mount 5.25" (probably JBL GTO 509C) in the rear doors in separate bass / treble set-up. Also plan to lower the cut off frequency for those from the amp to 60hz (original is about 118hz). This is a rather easy operation paralleling 4 smd capacitors in the active filter section. This should dramatically improve the rear seat passenger sound quality. This procedure comes a bit later on though, I hate working outside in cold weather and snow (Sweden).
    Tomas

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