JBL DSP 4086 Review

[bobsled]

This is for a non-B&O install in my GT350. As a recovering audiophile, my goal is to put together a nice system that looks stock for around $1,000. I am very pleased so far.

1) The short story: The JBL DSP 4086 is 40W x 8 at 4 ohms/60W x 8 at 2 ohms. I was concerned that it wouldn’t be loud enough. Could it be louder? Sure. But it’s louder than any stock system and CLEAN! For comparison, I measured stock amplifier voltage output at 7.95 volts with a 100hz tone at max volume, which is equivalent to about 16 watts per channel at 4 ohms. My unscientific guess is that the JBL DSP volume at about 2/3 is the same as full volume with the stock amp.

• Pros: Clean sound, customizable DSP, fits in the factory amp location, and can use the factory speaker wiring. 8 channels. Shockingly clean sound with gains up and volume maxed.
• Cons: It can always be louder, but unlike high school, I don’t need to hear it across the street. I have to turn it down when I want to listen to the exhaust. The software was intuitive to me, but opinions vary. No preamp output – so my sub amp will have to accept high-level inputs. It is a tight fit in the factory amp location - tighter than I expected, but no cutting needed.

2)Use the DSP to set the crossovers for the door 6.5’s lowpass at around 3.5khz and high-pass the 2.5’s + tweeters (they are wired in parallel) to over 3.0khz, or somewhere in that range that is to your liking. I had to dial back the gain on the tweeters a little to make the hiss go away.

The rear speakers are very brassy that no DSP can correct. I replaced those immediately, and now the system sounds really good. I’m in the process of replacing the front speakers and a 10” JL Audio sub for the trunk (stay tuned for my box build).

3) Install: Follow these directions (thanks to @StangTime for the writeup).
https://www.mustang6g.com/forums/th...premium-audio-systems-no-loc-required.159271/

It’s taller than the stock amp. I took two 2-inch strips of aluminum and bolted those to the stock amp bracket to hold the amp. I didn’t take a pic: See @Jaymar ’s solution that will give you an idea: https://www.mustang6g.com/forums/th...o-systems-no-loc-required.159271/post-3449202

There is a small gap at the top after install, and very little room at the bottom, but you don’t need to cut the kick panel. It fits, but it will take some patience.

For remote turn on, I used the stock remote turn with a PAC-TR4 to convert it to 12v. The wiring is all there, and I am also using it to power my Valentine One (which means my V1 cycles on when I open the door). I ran the power cable from the battery through the fender, as most folks do, and you wouldn't know its there unless you pulled off the battery cover.

There is not a lot of room for the wires under the kick panel. I made the mistake of cutting the slack out of the wiring harness before install. That made the kick panel difficult to install. You will want to get the amp in place, then figure out how to route the wires behind the kick panel before trimming and bundling wires.

Feel free to PM me if you have any questions.

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[Jaymar]

I have a feeling that there is actually a little bit more to the amp than we're getting right now. The amp can max the gain out and still not clip so I believe we are leaving a bit more headroom than needed using the factory low level direct in. I haven't tried yet but I have a pair of line drivers I'm going to add in so I don't have to use so much gain at the amp. I ran against the noise shelf as well trying to maximize it. I'm not complaining, it's a great little amp but I've gone further with 40W per channel than this before. This is my first full range switching rail amp though so I could be wrong.

 

[Jaymar]

Oh, and if you want a sub out you can get it with this setup and still get DSP control. Wire both rear speakers in parallel and run them off of one channel. Use the other channel that used to be rear speakers as a signal to the preout for the sub. Within the DSP software, back off the gain on the sub channel and change your setup accordingly then run both rear inputs into the now single channel rear. You won't miss having stereo rears at all, rear channel is highly overrated by most. I usually low pass rears with a high crossover point too just to take them out of the stereo image even more. Try -6 db/oct at 1K or more to see what you think, your mileage may vary.

 

[StangTime]

Oh, and if you want a sub out you can get it with this setup and still get DSP control. Wire both rear speakers in parallel and run them off of one channel. Use the other channel that used to be rear speakers as a signal to the preout for the sub. Within the DSP software, back off the gain on the sub channel and change your setup accordingly then run both rear inputs into the now single channel rear. You won't miss having stereo rears at all, rear channel is highly overrated by most. I usually low pass rears with a high crossover point too just to take them out of the stereo image even more. Try -6 db/oct at 1K or more to see what you think, your mileage may vary.

Are you using the entire head unit volume control range? The volume can be turned all the way to max on the dial without clipping the signal. It puts out 2.7V
So try turning the gain on the amp down, the head unit all the way to max and then bring up the amp gain until you hear it clip or you hear distortion from the drivers.

 

[Jaymar]

Are you using the entire head unit volume control range? The volume can be turned all the way to max on the dial without clipping the signal. It puts out 2.7V
So try turning the gain on the amp down, the head unit all the way to max and then bring up the amp gain until you hear it clip or you hear distortion from the drivers.

Fairly certain of it. I turned up to max volume and used a 0 db pink noise track in .wav from the USB source. USB seems the strongest source signal but I didn't try CD, I couldn't find a CDR to use and really couldn't be bothered since I never use the source anyway. At max volume, 0db signal on the strongest source I could max the gain and still not clip according to the indicators in the DSP software. I didn't do much dynamic testing with real music to confirm but given the low volumes that I was working with versus other 40W sources I've dealt with I could tell I was leaving some on the table with excessive headroom. That, and maxing the gain brought on far too much noise to be anywhere near tolerable so I backed it off to pursue the signal route I mentioned before. The results are livable but I know the system isn't properly adjusted for what the equipment can do. Until I replace the speakers it's just temporary anyway and since the customer is me I can delay the project all I want.

While there are many schools of thought regarding gain and signal level practices, I generally subscribe to the theory that a -5 db or average music track should start audibly clipping around 75%-80% volume on your strong source. That generally leaves adequate headroom for weak sources or low source material etc. The use case here can change that up or down, I find that the phone streaming as a source is rather weak and could justify moving that setpoint down the scale a bit but your mileage may vary. The volume adjustment on the source unit has a coarse scale so an argument can be made the other way too just to avoid the touchy throttle syndrome.

 

[StangTime]

That doesn't sound right. What position is your INPUT LEVEL switch on the amp set to? It should be set to "LO".

 

[bobsled]

I have 2 channels for the door 6.5's, 2 channels for the mids/tweets, and two channels for the rear. I'll use the 7th channel for the sub. I'll use the high input on my 300w sub amp. I use the LO input from the head unit into the DSP.

Regarding clipping, the DSP software shows a clipping indicator. I have the master volume max at +6db, the 6.5s and rears at +1db and the mids and tweets at -1db. I'm sure that will change some when I replace the front speakers. The noise comes from the tweets and mids when setting the gains. I'll report back if replacing them helps. I suspect it's the capacitors for the tweeters.

If I max out the gains, and push the lower frequencies on the EQ, I definitely get clipping. Where I have it set, I can max volume without clipping. Same process @StangTime mentioned in post #4.

I'd be careful running speakers in parallel to make sure you don't go below two ohms, which may overheat the amp. There is no need to run parallel to a sub amp, just use one channel; just run one paired wire to the sub amp. But reducing the gains to reduce the signal to a low-level input for a sub would make me nervous.

@Jaymar If you replace your rear speakers, it makes a world of difference. The rear stock speakers are worthless.

I recommend the source, such as iPhone to be at one click less than max volume, with bass boost off. Bass boost is bad for clipping - let the DSP do the work.

 

[Jaymar]

@StangTime yes the input is set for low. Don't get me wrong, the input is usable but I think there is some excessive headroom left on the table. The input is designed to accept a wide range of inputs and provide accommodating loads to each so some sacrifices had to be made. The accommodation on the low end, I believe, requires pushing the limits of the input stage too far to use the very low voltage 2.7V inputs hence the extreme noise found when pushed all the way up. @bobsled if I understand you correctly, that noise you're getting is like a hiss or white noise sound? That's from excessive gain, it's the introduction of normal background noise into the amplification stage because it is being pushed too far. My solution is a couple of line drivers. You would use these for the same reason you have a dedicated phono preamp before your actual preamp, the amplification of the signal is too much for a single stage to cleanly handle. I have them I just haven't had the ambition to work out in the rain and snow to try them out. Once I do get them put in I'll report back. I could be wrong, that could be all this little amp has to offer and even then it's fine for what it is. Like I said, this is my first switching rail full range amplifier. The last time I actually got paid to do this kind of work those were in their infancy and were generally limited to sub amps.

The factory speakers need to go for various reasons. Most importantly, if you've flattened the factory EQ from the source the EQ required to get a decent system response out of them is embarrassing and I'd hesitate to call what I got even decent. With the factory EQ applied they were OK as a factory system at that power but when all of their flaws are exposed with full range power they simply can't keep up to what one would expect once the system is modified. I have replacements from Morel to install when the weather doesn't suck. I've always wanted to try Morel as I've gone most of my career attempting to tame other people's idea of "high end" tweeters to get what I call good sound. To each their own I suppose, I hope to post a review somewhere once done because they are reasonably priced for the quality level and it looks like a fairly drama free fit that one could recommend even to a novice.

 

[bobsled]

@StangTime yes the input is set for low. Don't get me wrong, the input is usable but I think there is some excessive headroom left on the table. The input is designed to accept a wide range of inputs and provide accommodating loads to each so some sacrifices had to be made. The accommodation on the low end, I believe, requires pushing the limits of the input stage too far to use the very low voltage 2.7V inputs hence the extreme noise found when pushed all the way up. @bobsled if I understand you correctly, that noise you're getting is like a hiss or white noise sound? That's from excessive gain, it's the introduction of normal background noise into the amplification stage because it is being pushed too far. My solution is a couple of line drivers. You would use these for the same reason you have a dedicated phono preamp before your actual preamp, the amplification of the signal is too much for a single stage to cleanly handle. I have them I just haven't had the ambition to work out in the rain and snow to try them out. Once I do get them put in I'll report back. I could be wrong, that could be all this little amp has to offer and even then it's fine for what it is. Like I said, this is my first switching rail full range amplifier. The last time I actually got paid to do this kind of work those were in their infancy and were generally limited to sub amps.

The factory speakers need to go for various reasons. Most importantly, if you've flattened the factory EQ from the source the EQ required to get a decent system response out of them is embarrassing and I'd hesitate to call what I got even decent. With the factory EQ applied they were OK as a factory system at that power but when all of their flaws are exposed with full range power they simply can't keep up to what one would expect once the system is modified. I have replacements from Morel to install when the weather doesn't suck. I've always wanted to try Morel as I've gone most of my career attempting to tame other people's idea of "high end" tweeters to get what I call good sound. To each their own I suppose, I hope to post a review somewhere once done because they are reasonably priced for the quality level and it looks like a fairly drama free fit that one could recommend even to a novice.

Sorry to confuse. I had the hiss before I reduced the gains. But the hiss does not come from the new rear speakers or the door's 6.5s, only the front - either the 2.5s or tweeters or both. With my settings, I have no issues. I hear what you are saying about the 2.7v input, but it has plenty of volume for me, especially since I am going with 3-ohm speakers (Hertz).

Like yourself, while I don't do it seriously anymore, I've been doing it for 35 years. Please continue to post any updates in this thread. I'm always interested to hear what others are doing.

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