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Discussion Starter · #1 · (Edited)
Hi All
Its been a while since ive done anything car audio. This seemed like the best section for this post.

Short version:
Which affordable Class D amps are the best/arnt rubbish?
Ive been browsing at the various options and its difficult to know what to go for. I figured class D would be better for overly sensitive car electrical systems these days. plus i want to locate the amp(s) behind the boot side panel, so small and cool is also good.
I'm based in the UK, so not all brands that are available in the US can be had here for sensible money, if at all.

Shortish version:
Ive been looking at the specs, specifically the CEA signal to noise ratio (1w into 4ohm) of a bunch of different amps. In theory at least, the signal to noise ratio is a good indicator of the quality of an amp and the CEA spec should keep all things equal. I'm trying to avoid getting hiss through the tweeters. I doubt i can tell the difference between a THD of 0.05% or 0.01% or between 60W or 80W, but i will hear hiss. Particularly because the output of my MiniDSP is about 1v RMS max, so i'd have the input of the amp up quite high. In theory, this shouldnt cause an issue as the DSP will be close to the amp, and its not really a "Gain" control anyway, so noise shouldnt really increase with the sensitivity control significantly, though thats not to say it definitely wont.

Usually you have to look in the manuals for the CEA S/N but ive seen values from 75 up to about 88dB with a few in the 90s that were AB amps i think.

What sort of CEA S/N is considered good?
I cant really justify a big outlay, especially since warranty periods aren't often more that a year, also, i dont really know how much space i have to play with, but im trying to get the lay of the land on amps.

I'm thinking of a 4 channel amp for the fronts and then maybe another, hairier, 4 channel for the under seats and the sub. JL Audio seem like a safe bet, but they are pretty expensive, and most of the ranges seem largely the same, which is odd. i see Pioneer make something suitable, though i have heard comments about hiss. Rockford fosgate, and some of the other USA brands from back in the day also how some amps at various prices, but are they any good these days?

Longer version:
I'm in the planning stages of a new system, in a brand new car that isnt even built yet. Its a BMW 128ti (the closest in the US looks to be the 228 Gran Coupe) and due to the semiconductor shortages, i wasnt able to order the HK audio upgrade. Its not great anyway, but it would have been better than the standard system. Anyway, ive decided to look into putting a new system in. The car should have:

4" in the doors
4" in the rear doors
6 or 8" under the seats

the standard audio doesnt have the tweeters by the mirrors, the centre speaker in the dash, or the rear speakers in the roof that the HK system has.

My plan is currently:
Fit tweeters into the existing trims by the mirrors, run separate cables to these to run them active.
Fit some nicer 4" drivers into the doors.
Upgrade the speakers under the seats. There are a number of companies that make custom fit speakers that fit here.
Maybe run a slimline sub in the space under the boot floor.
leave the rears alone, and fade it to the front.

The "Receiver Audio module" is in the boot and seems to have 6 separate audio outputs. 2 for the front doors, 2 for the rear doors and 2 for the underseat woofers.

i have a Wavtech Link 4 that would take the fronts, and the underseat speaker outputs and sum them together into a single pair. this will then feed to 2x MiniDSP 2x4s that i already have one for left and one for right. I'll use the parametric EQs on the inputs to flatten the output from the car, then set the outputs for tweeter, mid, midbass, subwoofer (maybe) and tune from there. The advantage of doing it this way, is that i should be able to run a separate output from say a DAC from my phone into the other DSP input as an alternative source that is potentially better than what is coming out of the car. So i just need the amps to be amps. i dont need high level inputs on onboard DSP.

If youve got this far, thanks for sticking with me.

Cheers
 

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Sorry for replying without reading everything, but 0.1% THD+n is the threshold of inaudible. 75dB signal to noise is quite bad, listen to quiet music at 90dB (about what you’ll get using 1w into, give or take a couple dB) you’ll have 15dB of noise, that’s the minimum it’ll only get worse from there. So, higher the better but try to at LEAST stay in the mid to upper 80s.

You already have a DSP, correct? If you’re okay with 50w AudioControl makes a 50w x 4 channel amp that has very good signal to noise (I don’t recall exact number, about -115dB [-90dB is quite good, -115dB will be impossible to hear]) and THD+n is either 0.1% or 0.01%, either way that’s a lot better than even a $1,500 JL Audio amp (my VXi is <1%). In USD that AudioControl is $320USD (which is cheap for an amp of that quality). They also make a 75w x 2channel version for the same price if you need 6 channels (640usd for 6 channels with those stats is a good price, if that setup works. They are very small so fitting 2 shouldn’t be a problem). They also make a 125w x 4 channel with same stats for about 5-600usd, 125w x 6 channel for about 700USD ish. AudioControl isn’t CEA but the stats they give are solid.
Personally, if I was using a stand alone DSP I’d probably go with AudioControls 50w x 4ch and 75w x 2ch, or some other combination depending on speakers used. You can use a 125w amp with speakers rated at 75w, just need to make sure gains are set so speakers don’t receive enough power to damage them or create distortion.

I don’t know much about Helixes non-DSP amps but they are worth looking into. The stats for their DSP amps are quite good.
 

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Hi All
Its been a while since ive done anything car audio. This seemed like the best section for this post.

Short version:
Which affordable Class D amps are the best/arnt rubbish?
Ive been browsing at the various options and its difficult to know what to go for. I figured class D would be better for overly sensitive car electrical systems these days. plus i want to locate the amp(s) behind the boot side panel, so small and cool is also good.
I'm based in the UK, so not all brands that are available in the US can be had here for sensible money, if at all.

Shortish version:
Ive been looking at the specs, specifically the CEA signal to noise ratio (1w into 4ohm) of a bunch of different amps. In theory at least, the signal to noise ratio is a good indicator of the quality of an amp and the CEA spec should keep all things equal. I'm trying to avoid getting hiss through the tweeters. I doubt i can tell the difference between a THD of 0.05% or 0.01% or between 60W or 80W, but i will hear hiss. Particularly because the output of my MiniDSP is about 1v RMS max, so i'd have the input of the amp up quite high. In theory, this shouldnt cause an issue as the DSP will be close to the amp, and its not really a "Gain" control anyway, so noise shouldnt really increase with the sensitivity control significantly, though thats not to say it definitely wont.

Usually you have to look in the manuals for the CEA S/N but ive seen values from 75 up to about 88dB with a few in the 90s that were AB amps i think.

What sort of CEA S/N is considered good?
I cant really justify a big outlay, especially since warranty periods aren't often more that a year, also, i dont really know how much space i have to play with, but im trying to get the lay of the land on amps.

I'm thinking of a 4 channel amp for the fronts and then maybe another, hairier, 4 channel for the under seats and the sub. JL Audio seem like a safe bet, but they are pretty expensive, and most of the ranges seem largely the same, which is odd. i see Pioneer make something suitable, though i have heard comments about hiss. Rockford fosgate, and some of the other USA brands from back in the day also how some amps at various prices, but are they any good these days?

Longer version:
I'm in the planning stages of a new system, in a brand new car that isnt even built yet. Its a BMW 128ti (the closest in the US looks to be the 228 Gran Coupe) and due to the semiconductor shortages, i wasnt able to order the HK audio upgrade. Its not great anyway, but it would have been better than the standard system. Anyway, ive decided to look into putting a new system in. The car should have:

4" in the doors
4" in the rear doors
6 or 8" under the seats

the standard audio doesnt have the tweeters by the mirrors, the centre speaker in the dash, or the rear speakers in the roof that the HK system has.

My plan is currently:
Fit tweeters into the existing trims by the mirrors, run separate cables to these to run them active.
Fit some nicer 4" drivers into the doors.
Upgrade the speakers under the seats. There are a number of companies that make custom fit speakers that fit here.
Maybe run a slimline sub in the space under the boot floor.
leave the rears alone, and fade it to the front.

The "Receiver Audio module" is in the boot and seems to have 6 separate audio outputs. 2 for the front doors, 2 for the rear doors and 2 for the underseat woofers.

i have a Wavtech Link 4 that would take the fronts, and the underseat speaker outputs and sum them together into a single pair. this will then feed to 2x MiniDSP 2x4s that i already have one for left and one for right. I'll use the parametric EQs on the inputs to flatten the output from the car, then set the outputs for tweeter, mid, midbass, subwoofer (maybe) and tune from there. The advantage of doing it this way, is that i should be able to run a separate output from say a DAC from my phone into the other DSP input as an alternative source that is potentially better than what is coming out of the car. So i just need the amps to be amps. i dont need high level inputs on onboard DSP.

If youve got this far, thanks for sticking with me.

Cheers
you hit the nail right on the head. Your MiniDSP and it’s low output voltage limit you to a couple choices

- very high signal to noise ratio, make sure it’s rated at 1 watt into 4 ohms (cea standard) if it’s not listed you can assume it was measured at full power and discard it as the useless marketing gimmick it is. No s/n reference, means no real value.

- Input sensitivity needs to be very low, this is probably more important than the signal to noise… a lot of amps input sensitivity goes up to 8v (gain turned all the way down) so to reach 1v your gain will be really high….

it doesn’t matter how close your amp is to your dsp, your RCAS can be disconnected from the amp and if you turn the gain all the way up you will have humm or hiss on your tweeters.

JL Audio amps have low level input sensitivity that maxes out at 2v RMS plus alot have good signal to noise referenced at 1 watt… I would recommend JL HD, JL XD


Alpine PDX have signal to noise at 1 watt over 90db but input sensitivity goes up to 4v - I couldn’t say what would be better the JL or alpine but if I had to guess I would say JL

The real solution is buy an old helix dsp, literally any helix dsp or an arc ps8 and then buy any amp you want since they have high output voltage
 

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Discussion Starter · #7 ·
Thanks. The JLs do look like a good option. I could probably build a simple preamp or line driver if i need to up the output from the dsp. Ive always understood amps to have a fixed voltage gain with an input attenuator for you to match the signal. So they dont have "gain" controls, though everyone calls it that, they have an attenuation at the input. I cant imagine why anyone would design an amp any other way. So in theory, it shouldn't matter is the signal is 1v or 6v on the input to the amp, as long as it didnt pick up any interference along the way, which is the advantage of higher voltage outputs from headunits, and the marketing obviously.

I didnt get any hiss last time, but i was using Genesis class ab amps in those days, just a bit over cautious about the class D amps i guess.

Thanks
 

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Thanks. The JLs do look like a good option. I could probably build a simple preamp or line driver if i need to up the output from the dsp. Ive always understood amps to have a fixed voltage gain with an input attenuator for you to match the signal. So they dont have "gain" controls, though everyone calls it that, they have an attenuation at the input. I cant imagine why anyone would design an amp any other way. So in theory, it shouldn't matter is the signal is 1v or 6v on the input to the amp, as long as it didnt pick up any interference along the way, which is the advantage of higher voltage outputs from headunits, and the marketing obviously.

I didnt get any hiss last time, but i was using Genesis class ab amps in those days, just a bit over cautious about the class D amps i guess.

Thanks

that is partially correct and partially incorrect. The output section of the amp is a multiplier, it just makes the signal larger.

the problem is RCAs are a single ended signal. Plus there are different voltages across different sources that sometimes need boosted, and sometimes need attenuated.

All car audio amplifiers use op amps in the pre amp section to prepare the signal for amplification. They will convert the signal from a ground referenced signal (single ended) to a differential signal (what comes out of your speakers) and now the amplification stage is ready to receive the signal.

the problem with line drivers is almost all of them are built like $hit. I’ve been through this exact problem. There is one and only line driver that is good on the market. It is the TRU technology ones… and buying one of those is spendy to where I couldn’t see the reason to not just get a DSP with higher output voltage….

DSP Chips output 2v RMS normally max. This is because this is the voltage they operate at. Maybe yours is only 1v but most are like 2v…

in order for a DSP to have output voltage higher than this the manufacturer needs to put an output section of op amps inside the DSP. MiniDSP only did this on the 8x12v2 - poorly implemented they can create noise like any gain stage.. so poorly designed DSPs will have to limit their max output voltage…

MIiniDSP used to have 6vRMS max on their 8x12v1 - their v2 version they lowered it to 4.5vrms and added a filtered/isolated power supply due to noise problems (might want to check into one of those minidsp sells them for their cheaper units that do not have filtered power supplies..)

Helix DSPs all have 6v RMS output, the promk2 and ultra have 8v RMS output

anyways I hope the JLs work out for you.. but like I mentioned if you get a helix or arc dsp you can literally use whatever amp you want signal to noise will more or less not matter because your gains will be on zero.. it’s really nice
 

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Discussion Starter · #9 ·
Thanks for that.

Minidsp do a car specific one now called a c6x8 or something along those lines. It has much higher output signals, so must have an output stage as you say. I was tempted to sell the ones i have and order one of those, but i figured id try what i have already first.
 

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I just installed a 100 dollar Jenson 4 channel from Walmart a mini dsp a id Como set and an old id sub.
The Jenson has no controls on the amp at all. So you mount it and that's it. You don't need to access it again. P
It's all done with a pretty nice app. Has worked everytime I have used it and has worked th3 same way. Not one glitch. It has a 5 band eq on channels 1/2 and another 5 bands that are the same on channel 3/4.
The app has a gain on a 1/10 scale in 10 steps. It then has a master control on the home screen. For both channels at once.
Oh and rgb leds. Can't forget those.
All that's cool or whatever. The thing that has stood out the most to me is how dead silent the thing is.
Gains and master volume maxed out and there is nothing.
Using Walmart rcas and a 80 dollar best buy kenwood.
The eq is also very nice. It works. The xovers have selectable slopes. 6 - 24 dB. And you can just type the frequency in. Like a real dsp you know.
All for 100 bucks.
 

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Discussion Starter · #13 ·
Any update on your build?
Not really no, i still dont have the car. Ive trawled through all the amps available at sensible prices, and the Kenwood X302-4 seems to have good CEA S/N of 85db, which is up there with most of the JL Audio stuff. 4x50W is plenty for my front end. i'll use another bridged to run the underseat "subwoofers" and if i feel i need a proper sub too, i'll add a third amp. If i'm short on space, they do a 5 channel amp, so i can use that to do the underseats, and ive got a sub channel if i need it.

People seem pretty happy with them, and with the lack of any proper reviews for any Amps, its a good a choice as any. I would have initially overlooked Kenwood, but theyve been making amps for as long as anyone these days, since a lot of the brands from the 90s arent the same company anymore anyway.

I got a Wavtech Link 4, which looks like a nice piece of kit as it came up for a good price. I've got a few plans for speakers, but cant really commit until i know they will actually fit. I know how i'm going to do the wiring now, without cutting any cables, so i'm getting things straight in my head.
 
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