Having Fun with OEM Amplifier

Audiophyle · Dec 7, 2015

I have an OEM amp I tore apart a while back for a random PC/Home Theater project I wanted to experiment with, but it never happened.

Anyway, here is what I did to the OEM amp today out of boredom while babysitting my kiddos.

For starters I drilled new holes on the side for the ICs, dropped a thin plastic liner between the board & the chassis, and inverted the board mount so it mounts to the chassis & not the stamped steel bottom with wacky flanges.
The 4 tapped holes on the bottom of the chassis are almost exactly the same spacing as a 120mm PC fan, which could be utilized for some active cooling if necessary.

I soldered RCA cables onto the input section of the amp, color matched speaker wires on the output section, and installed 8ga power & ground cables. The 8ga wire is overkill, a 10ga or 12ga would have been perfectly fine and probably easier to work with too. Fired the amp up on the test bench & everything was working flawlessly. Had I put the chassis end caps on before soldering the power cables to the board I could have moved them over a little farther, but because the board is flipped & the plugs are on the opposite end now, the end panel has the plug holes backwards & misaligned. I may modify it to fit better, as well as fabricate an acrylic cover (with or without a fan).

Now to have a little fun with it because there are a lot of unknowns about this amp and I didnt care if I killed it so I thought Id put it through some testing & abuse.

SIGNAL RESPONSE
The front & rear channels are full range with no built in crossovers, & I did not see any integrated equalization either, which is good on both counts.

The sub channels did not have any equalization either, but it DID have an integrated low pass filter. With a full range input the subwoofer output was filtered to play everything below 800hz~1khz, which is very high for subwoofer duty but an acceptable range for a 6.5~6.75 subwoofer & less of an imaging issue because the sub is in the front of the vehicle. (this would sound awful if the sub was in the back)

POWER OUTPUT
Now for the fun part, how much juice is this thing belting out. Honda advertises it as being a 270w 7 speaker system, run by a 6 channel amplifier. Following conventional amplifier marketing (selling the peak power numbers) 270w/6ch=45w peak output / 2 = 22.5w RMS per channel (& the power rating that matters).

The actual output I measured from the front & rear channels was 18w RMS @ 4 ohm, and 33w RMS @ 2 ohm, and the output from the sub channels were measured to be 36w RMS @ 4 ohm & 66w RMS @ 2 ohm. All tests done at 13.8v & driven to the edge of clipping.

Interestingly enough the sub channels are exactly twice the output of the fronts, telling me this is an 8ch IC with stacked channels for the sub section to boost it's output.

(18x4)+(36x2)=144w RMS x2 = 288w peak output, or using the 2ohm values (33x4)+(66x2)=264w RMS.
I was pretty impressed to see the numbers on the sub channels, and they seemed to run at 2 ohm without fault. The two channels share a common input so they are a true mono output, but they are also distinct channels & cannot be bridged together. The fronts & rears ran fine at 2 ohm when testing, and the only thing I saw was the amp ran a bit hotter. I do not have the equipment to run all channels simultaneously at 2ohm, I could only test one channel at a time so there is a possibility that driving multiple channels at 2ohm could push the amp into thermal protection.

My element did not come with any of the original speakers, but has anyone confirmed what the impedance is of each OEM speaker?

Jive_q · Dec 21, 2015

Can you shed any light on the Balanced Inputs? I see you put RCAs in.. how did you deal with the extra wires of the Diff. Balanced input.. would it make any difference if you put the Plus with Neg vs. the Plus with the Ground?

Would input voltage change your output readings?

I read that the OEM head puts two 4v signal wires to the amp which results in an 8v combined signal - what Voltage were you feeding the inputs?

Any thoughts?

stickygreen · Dec 21, 2015

Great write up!

Thanks for the info.

cursh · Dec 21, 2015

Also - Thank you for all of the info. I'm also interested to hear about balanced inputs. I'm guessing it doesn't matter so much for the amp, but is more important for the HU? (this is what my reading and partial understanding concluded. I'm wrong as often as I'm right, though . . . )

I can test mine - Question. Can I just read with the OHM setting on my multimeter where the speaker attaches to the door? (that would be three philips and a quick pop of the grill with a bread knife) or do I need to test it at the amplifier (something I haven't done yet but was planning to get around to eventually.)

Audiophyle · Dec 22, 2015

I question the claims of the amp using balanced inputs.

Typically a balanced signal has 3 conductors; a high (+ volt) & a low (- volt) 180* out of phase for noise rejection, and a reference (zero volt) which is often used as a grounded shield. The OEM deck has a grounded shield for the sub signal and all four of the other outputs share a single ground shield. The reason I question the balanced signal claims is because the ground shields do not connect to the amp like they should, so the amp does not have a reference ground unless it uses the negative conductor for each speaker channel, which would make it an unbalanced signal.

Pushing test tones I could hear clipping with signals reaching 1.5v, and the power ratings in my first post were with input signals around 1.3v, so I doubt the OEM deck is pushing anywhere near 8v (or even 4v). The numbers I got were pretty spot on with Honda's 270w rating, so I believe the amp was working to full capacity with the unbalanced input signals.

Cursh, to test the speaker impedance it would be best to test them at the amplifier. Pop out the passenger lower kick panel, and unplug the large grey plug from the amp and you will have access to every single speaker. I am pretty sure the door speakers are 4 ohm, what I am interested to see is if the fronts are actually a 2ohm load at the amp (because the door speaker & tweeters are wired in parallel). You could also test the sub's coils from that plug & see if each one is 2 or 4 ohm.

BigAl205 · Jan 7, 2016

This is an awesome write-up...great job!

Audiophyle said:
I question the claims of the amp using balanced inputs.

Typically a balanced signal has 3 conductors; a high (+ volt) & a low (- volt) 180* out of phase for noise rejection, and a reference (zero volt) which is often used as a grounded shield. The OEM deck has a grounded shield for the sub signal and all four of the other outputs share a single ground shield. The reason I question the balanced signal claims is because the ground shields do not connect to the amp like they should, so the amp does not have a reference ground unless it uses the negative conductor for each speaker channel, which would make it an unbalanced signal.

Pushing test tones I could hear clipping with signals reaching 1.5v, and the power ratings in my first post were with input signals around 1.3v, so I doubt the OEM deck is pushing anywhere near 8v (or even 4v). The numbers I got were pretty spot on with Honda's 270w rating, so I believe the amp was working to full capacity with the unbalanced input signals.

I did my balanced audio thread after reading about it on other Honda forums, talking with a Honda tech/ audiophile buddy, and reading the troubleshooting instructions in the Honda Service Manual (although I should have used the phrasing 'differential balanced')

Page 23-33

11. Check audio unit connector A (20P) terminals No. 4,
5, 6, 7, 8, 15, 16, 17, and 18 individually for
continuity to body ground.

Is there continuity?

Yes- Repair short to body ground in the wire...

Connector A (20P) is the connector coming from the back of the radio, and pins 15, 16, 17, and 18 are all the negative audio outputs. If this was an unbalanced system, the negative audio outputs would be grounded.

cursh · Dec 22, 2015

Thanks. I'll report back front rear and sub channels as soon as I get a chance.

I wonder if that means I can use any old 5 channel amp . . . the alpine I was looking at was balanced anyway, and seemed like the best bet for the $$.

-Ben.

Audiophyle · Dec 22, 2015

I will say after dissecting and experimenting with the OEM amp I am fairly impressed with it and it's flexibility, which has me questioning the value in bypassing it unless you are installing a more powerful amplifier to replace it.

I am surprised by the sub channel output, because if it is running at 2 ohm the amp is pushing 132w which is impressive, and possible if the front channels are also running at 2 ohm (which is what I suspect).

I do not think the OEM deck has a balanced output, and I do not think the OEM amp has a balanced input, I think they are both unbalanced systems and the issues people have with varied output levels are a product of installation, not the mixing of balanced & unbalanced systems.

cursh · Dec 23, 2015

Impedance at the amp for each channel is 4ohms. I tested them all a few moments ago. Front and rear are the same.

lumenbeing · Dec 30, 2015

Would it be possible then to bridge the two coils of the sub driver so that it draws 66watts at 2 ohm? Would that make the stock sub hit harder?

Audiophyle · Jan 6, 2016

You cannot bridge the amp's sub channels, so the only way you could potentially do what you are thinking would be by installing a new sub with dual 2ohm coils (assuming oem sub is dual 4 ohm).

Jive_q said:
Audiophyle - thank you so much for your efforts at actually taking apart and testing the stock amp!

I have been wanting to use the stock amp as part of an active 3 way but have been obsessing over Balanced MiniDSPs and the like in an effort to compensate for the use of the balanced inputs. You just saved me from majorly overthinking this thing..

I have been running Infinities in the front and was a little worried with hooking up the 2ohm door speakers in parallel with the stock tweeters.. (which results in something like a 2.3ohm load at the amp) but it has been running great ever since.

Thanks again for putting some real numbers out there!

That's why I did it, & I too have been juggling with the idea of using a minidsp to make the amp run an active 3 way. Biggest hurdle I see is the sub channels being mono, not sure what kind of impact there would be on imaging with the woofers playing mono.

cursh said:
I should have been more specific on the resistance of the factory speakers as tested at the amp by my auto ranging multimeter:

rears were 4.1 ohms and the fronts (in combo - at the amp) were 3.6 ohms.

3.6, 4, close enough to me. Lol
What about the subwoofer coils, did those both test as 4 ohm too?

Jive_q · Jan 1, 2016

Audiophyle - thank you so much for your efforts at actually taking apart and testing the stock amp!

I have been wanting to use the stock amp as part of an active 3 way but have been obsessing over Balanced MiniDSPs and the like in an effort to compensate for the use of the balanced inputs. You just saved me from majorly overthinking this thing..

I have been running Infinities in the front and was a little worried with hooking up the 2ohm door speakers in parallel with the stock tweeters.. (which results in something like a 2.3ohm load at the amp) but it has been running great ever since.

Thanks again for putting some real numbers out there!

cursh · Jan 2, 2016

I should have been more specific on the resistance of the factory speakers as tested at the amp by my auto ranging multimeter:

rears were 4.1 ohms and the fronts (in combo - at the amp) were 3.6 ohms.

lumenbeing · Jan 2, 2016

Ohhhh. Okay that makes a little more sense. I was baffled how the front channels could be exactly 4 ohms when the door speakers are 4 ohms by themselves and they are wired in with the tweeters. I'm still confused as to what combination of impedances and wiring would yield something like 3.6 ohms.

cursh · Jan 6, 2016

3.6, 4, close enough to me. Lol
What about the subwoofer coils, did those both test as 4 ohm too?

The factory sub was running at 4 ohm on each channel. I would have noticed it if it were at 2. (I think it was also 4.1, but I can't recall at this exact moment.)

lumenbeing · Jan 7, 2016

Can anyone explain how the front channels are measuring 3.6 ohm or even 4 ohm when they also have tweeter tied in? As I understand it, those stock tweeters only have a bass blocker. There isn't an actual crossover. The stock woofer in the door has "4ohm" stamped right on it. So with that as a known variable, wouldn't the tweeter have to be something like 36ohm wired in parallel to yield a total load in the range Cursh measured. And there's no way to get a lower impedance by adding anything in series unless it has negative impedance (no such thing).
So what can explain this?

cursh · Jan 8, 2016

Audiophyle said:
I was pretty impressed to see the numbers on the sub channels, and they seemed to run at 2 ohm without fault. The two channels share a common input so they are a true mono output, but they are also distinct channels & cannot be bridged together. The fronts & rears ran fine at 2 ohm when testing, and the only thing I saw was the amp ran a bit hotter. I do not have the equipment to run all channels simultaneously at 2ohm, I could only test one channel at a time so there is a possibility that driving multiple channels at 2ohm could push the amp into thermal protection.

My element did not come with any of the original speakers, but has anyone confirmed what the impedance is of each OEM speaker?

Dumb question, but I figure yours is still on a bench. What are the overall dimensions on this thing? I've found a super small amp that I think will fit there, but I'm being lazy and don't want to pull mine out of the car.

lumenbeing · Jan 8, 2016

I have mine out. It's dimensions are:
5.5"x4.5"x1.75"
If you found a 5 channel that small let me know which one!

Marv · Jan 8, 2016

Not to step into a holy war, but it's an interesting one. COULD honda have used the power ground as reference, thus allowing true differential signals from the deck to the amp. Bad bad bad design but... Why not put a scope or a good dvm set on AC from ground to one of the signal negative pins on connector B at the amp (pins 12,13,14,or15) and crank up the radio? Nominal output from the radio is enough so that should answer it once and for all. I never ever grounded shields on both ends on my microvolt/nanovolt runs for noise reasons rather used a wire or wires within the bundle for reference but...

Audiophyle · Jan 9, 2016

Marv said:
Not to step into a holy war, but it's an interesting one....

Whoa no holy wars here man, this is a forum for people to find information and discussion is the path to discovery. Nothing would make me happier than if someone came in here with definitive proof of either, because I think we all just want to know. lol

Unfortunately my Element never came with the OEM radio, so I am unable to do any testing around it & the bulk of my familiarity with Honda radios is removing them & casting them aside to make space for something new.

lumenbeing · Jan 10, 2016

That's another cool amp that wasn't aware of. It's got more oomph than the Alpine or the Clarion models of similar size. THD specs better but the signal to noise is not as good. I guess the st5.1600d isn't available yet.

There are several extra inches of clearance both above and below the factory amp. I myself was hoping to fit the Soundstream Picasso Nano (5 channel) in there. Crutchfield specs say it's 12" long but Amazon says it's shorter. I think anything under 10" could fit.

Where did you get your posted dimensions for the Stealth? Crutchfield says it's 7.5" long. I think maybe they are taking into account the harness or the mounts.

cursh · Jan 10, 2016

lumenbeing said:
Where did you get your posted dimensions for the Stealth? Crutchfield says it's 7.5" long. I think maybe they are taking into account the harness or the mounts.

There is also room for the Picasso Nano models. You can get what looks to be a more honestly rated 520Watt 4 channel that is only .25" wider (just checked, there seems to be room on the sides) for about the same as the Stealths. (two 30A fuses)

You can also roll the dice on the PN5.640 which is 10.3" long . . . you think you can find another half inch? The protrusion seems to be the speaker outs and power/ground which are a lot less than 5" wide and the RCA inputs are on 3-4" leads which should help the squeeze as well.

Lastly, there is room for a second 2 channel Picasso Nano under the front seat in front of the vent bump. I just measured and you could put it in the front most area under the seat and you'd never see it with the seat as far back as it goes or if you slide it all the way up to the dash.

cursh · Jan 10, 2016

The manufacturer's site lists it as the dimensions I mentioned. I believe them based on the overall proportion. They would have had to botch every single dimension to botch those numbers because it's very clearly 4(x) by 2(x) by 1(x)...

-ben

lumenbeing · Jan 10, 2016

Just so I don't further hijack the OPs thread, we were also discussing putting an aftermarket amp in the stock location in this thread.

BigAl205 · Jan 12, 2016

Well, I thought that if it did show continuity it would answer the question once and for all...but it's still up in the air.

Audiophyle · Jan 13, 2016

I really dont think it is a balanced setup, but it has me wondering if the OEM radio is not quite a typical low level output either.

cursh said:
I've got all of my OE equipment. I'd be happy to hook up a multimeter and report back, just tell me where/what I'm testing for. (I'm an eager amateur, so I'm not 100% clear based on what was previously posted in this thread).

If you can get a 60hz test tone to play from your deck you could test the output signal voltage, that could be a very good thing to know.
What I would do is unhook the small plug from the amplifier, then throw a CD in with a 60hz test tone track and crank the volume to 75%-80% (amp unplugged, so there will be no sound), and with a DMM set to read AC voltage I would measure the voltage of each channel in the plug you unhooked. (should be somewhere between 1.5v to 4v)

You could also test the ground shield wires (pink/black & light-green/black in diagram) and see how much resistance there is between the wire itself & the chassis of the radio. (harness needs to be plugged into the radio)

cursh said:
I'll see if it's possible for a mod to pull those posts and put them in Lumenbeing's original thread.

Dont worry about it, threads get confusing with too much overlapping conversation but we caught it in time.

cursh · Jan 12, 2016

I've got all of my OE equipment. I'd be happy to hook up a multimeter and report back, just tell me where/what I'm testing for. (I'm an eager amateur, so I'm not 100% clear based on what was previously posted in this thread).

Also, sorry for the cross talk. I'll see if it's possible for a mod to pull those posts and put them in Lumenbeing's original thread.

BigAl205 · Jan 14, 2016

Like he said, play a test tone or pink noise and use AC (not DC) on the meter to check voltage on the radio's output. I would choose a channel, left front for example, and use the positive (white wire) and negative (orange wire) to see what it's outputting. Here's how I would do it:

1. put the meter's red lead to the white wire, and the meter's black lead to ground, and write down the voltage.
2. leaving the black lead on ground, move the red lead to the orange wire and check that voltage.
3. put the red lead on the white wire and black lead on the orange wire, and write down that voltage.

If steps 1 and 2 show similar voltage, and step 3 shows double the voltage, it's a balanced system.
If steps 1 and 3 show voltage, step 2 shows little or no voltage, it's likely an unbalanced (RCA-style) system.

cursh · Jan 14, 2016

Second dumb question and results from the test mentioned above. Does it matter that I'm testing door speakers who's crossover probably limits the 50hz range?

Results:

*dmm in AC V
*50hz test sound playing via youtube and AUX cable
*Volume 11 clicks down from max (one click away from 8 out of 10 bars displayed on factory radio)

White(+dmm lead) to Black(-dmm lead) = 0.007V
Orange(+dmm lead) to Black (-dmm lead) = 0.077V
White(+ dmm lead) to Orange (-dmm lead) = 0.068V
Orange(+ dmm lead) to White (-dmm lead) = 0.068V

With AC voltage, I was pretty sure it wasn't going to make a difference which lead was where, but I checked both to be sure.

I'm using the Innova 3320 which is cheap, but has enough features for my tinkering.

Audiophyle · Jan 15, 2016

You need to run a 60hz test tone to measure AC voltage, not 50hz.
I dont know if the OEM radio has built in crossovers or not, but you could always meter the sub signal wires because 60hz is right where it plays the loudest. (red/blue & red/white wires)

Using your phone via the AUX connector is okay, but you need to have the volume cranked to max on the phone & the volume cranked to max on the youtube vid to get the strongest signal to the auxiliary input.

cursh · Jan 15, 2016

Cool - I'll repeat today. Thanks for walking me through this process. life long learning and all that jazz.

cursh · Jan 15, 2016

Ok. 60hz signal, bass wires.

Red blue to Blk(ground): .44 V
Red white to Blk: .36 V
Red/blue to red/wht: 7.6 V

Balanced it seems.

lumenbeing · Jan 22, 2016

How do you reckon that? Big Al suggested that the voltage should show double, not 7x. Your measurements are way outside of an expected value. Right? No offense, but do you trust those readings?

Having Fun with OEM Amplifier

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