Hello again DIY, Im back with another problem, 
Ive Just replaced one of my car amps, an old Phoenix Gold XS2500 with a tiny Kenwood X301-4 Class D. I hooked up the scope and was surprised to see a complete mess, has anyone seen a sine wave like this before? The funny thing is I cant here any distortion, I know my ears are old but wouldnt I hear such a bad signal? Obviously Ive tested the same RCA's before connection and Ive also tested them on another XS2500 and the signal is sweet. Oh and just a heads up, this amp has the worst potentiometers I have ever had the misfortune to come across, they have drove me mad, they seem ok upto about 15v then in the tiniest increment the amp is off doing 75-100v, Iv settled on a lower number than i wanted and the channels are 2.5v out, would love to here if anyone has had similar grief.
Alan
Ive Just replaced one of my car amps, an old Phoenix Gold XS2500 with a tiny Kenwood X301-4 Class D. I hooked up the scope and was surprised to see a complete mess, has anyone seen a sine wave like this before? The funny thing is I cant here any distortion, I know my ears are old but wouldnt I hear such a bad signal? Obviously Ive tested the same RCA's before connection and Ive also tested them on another XS2500 and the signal is sweet. Oh and just a heads up, this amp has the worst potentiometers I have ever had the misfortune to come across, they have drove me mad, they seem ok upto about 15v then in the tiniest increment the amp is off doing 75-100v, Iv settled on a lower number than i wanted and the channels are 2.5v out, would love to here if anyone has had similar grief.
Alan
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Thanks for the quick reply Perry!
No there is no DC offset pot, not externally anyway, I havnt actually tried to measured DC on its outputs, I didnt realise it was relevant, I kind of just get by with this stuff. The voltage in the picture is AC measured directly across the amp terminals, I am measuring the amp bridged so basically as it would be connected to my speakers and i tried both A and B amps, (the kenwood has 2x stereo amps they have named A and B.) I will measure again and let you know what settings I used on the scope, They will be different now as ive increased the input sense for about 18v output.
No there is no DC offset pot, not externally anyway, I havnt actually tried to measured DC on its outputs, I didnt realise it was relevant, I kind of just get by with this stuff.
The voltage in the picture is AC measured directly across the amp terminals, I am measuring the amp bridged so basically as it would be connected to my speakers and i tried both A and B amps, (the kenwood has 2x stereo amps they have named A and B.) I will measure again and let you know what settings I used on the scope, They will be different now as ive increased the input sense for about 18v output.Ah great! Your the first person to say this is normal for class d, I think all the other people responding on my other threads are just guessing, although one guy did say he measured a class d car amp and it didn't look like mine, I also measured a TPA 3116 stereo and a twin mono last night that I forgot I had in my projects room, both those hifi amps looked normal, well more normal than the Kenwood, my dual mono was a bit shaky at the top. . I'm just installing a new head unit so I will report back, the gains are set close to 20v at the mo anyway now. Thanks again.
. I'm just installing a new head unit so I will report back, the gains are set close to 20v at the mo anyway now. Thanks again.To clarify...
The scope will be set at 5-10v/div. Try both.
The timebase will be set to 2ms or whatever gives you about 3-4 cycles of the input waveform on the scope.
The amp will be driven with a sine wave of about 50-100Hz.
The input signal level (volume) will be great enough so that the amp produces about 20v AC at the speaker terminals.
The 20v has nothing to do with the gain control.
The scope will be set at 5-10v/div. Try both.
The timebase will be set to 2ms or whatever gives you about 3-4 cycles of the input waveform on the scope.
The amp will be driven with a sine wave of about 50-100Hz.
The input signal level (volume) will be great enough so that the amp produces about 20v AC at the speaker terminals.
The 20v has nothing to do with the gain control.
Thanks Perry, its pretty much the same, the only difference here is i have set the signal level to 16v using the head unit, close as i could get using the stepped control, it goes way over on the next notch which is strange because its not like i can here a massive change listening to music. I am setting the gain on the amp for roughly 100w at a specific setting on the head unit, tested to be clip free, so this is why im using the Input Sens (GAIN) on the amp. The end result is the same, 20v at the speakers for a setting of the number 30 on my head unit. I ran 100Hz.
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Thanks Nigel, I've sent my findings off to Kenwood, if they say the scope is normal then I may just send it back anyway, I've got another class d coming this week for the sub so will see how that reads too.
The carrier frequency looks to be very low but it could be just how your scope is displaying it. Many of the less expensive scopes can't capture the high frequency waveforms as they are. That may also explain why the carrier residual is so irregular.
In many of the full range class D amps that I've worked on, the amplitude of the residual is similar but at a timebase of 2ms, the frequency is so high that it simply makes the trace look wide/blurry, not jagged.
In many of the full range class D amps that I've worked on, the amplitude of the residual is similar but at a timebase of 2ms, the frequency is so high that it simply makes the trace look wide/blurry, not jagged.
My class d amps have always had a little residual carrier too.
I would be inclined to measure the frequency of the carrier to make sure it is correct.
The OP says he cant hear the carrier so its probably OK.
The specs are fudged a bit on most of the less expensive digital scopes. I was trying to find a cheap way to check the drive signals in class D amps. It requires a floating ground (or a differential input to the scope, which most people won't use). The DSO138 was supposed to be good to 200k... not even close. It wasn't even good enough to read the relatively low frequency of a power supply drive signal. The owon VDS1022i (<<< the 'I' is very important) was the cheapest option I could find. It would be awful as an 'only' scope for repair work but it has its uses.
Wow, yeah I'm a long way from that, im just setting the gains on a car audio system! What makes me doubt this new amp is that I've tried my scope on 2 very cheap hifi class d amps, and I mean cheap, we are talking £5 per mono PCB, my power supply is a cheap laptop job, I've had my new car amp apart and it looks really well built for the money.
how you finding the Kenwood X301-4? I see there now £80 on amazon while other places are £130! Tempted to get one as a ready made amp. Would you mind posting a photo of the insides? i would be interested in knowing what brand of caps there using, to get a idea of its life span. Even better would be knowing what amp IC there using but i guess thats hard to get access too?
I guess you dont know but might it be comparable to jl audio jx400/4d or pioneer class d amps? thd and noise floor?
Yea, whats the noise floor like? with sensitive speakers will i hear a hiss if i am sitting next to them?
I guess you dont know but might it be comparable to jl audio jx400/4d or pioneer class d amps? thd and noise floor?
Yea, whats the noise floor like? with sensitive speakers will i hear a hiss if i am sitting next to them?
Forgive me I missed this post, I sent the kenwood back to amazon, I didnt like the scope results, maybe thats mine for £80, lol. I can recommend what I purchased as a replacement, https://www.amazon.co.uk/gp/product/B00EJHCWG0/ref=ox_sc_act_title_1?smid=A1YW084KD8JNL6&psc=1
I paid £199, they are still on there for that price, here is a quick review. Test Car-HiFi Endstufe 4-Kanal - Audio System R 105.4 - sehr gut I can tell you its a bargain.
And no you shouldnt here hiss, if you do then its likely you have the sensitivity set too high on the amp, a lot of these new amps dont have a gain control, I asked pioneer and they said no, its not gain, its input sensitivity, so you want a HU with 4V outputs minimum really, having more sensitive drivers means you wont need to dial it up so far anyway, thats when it starts to get noisy.
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£80 is the brand new price. even less for 2rd hand price.
thanks for the german car amp review link. just the sort of car amp reviews i have been looking for!
Disappointing to see most amps do not get low thd near 0.01%. tpa325* amp boards are a lot better! Most of these are amps are more like old TI TAS53** amps level of thd. TAS53** amp boards cost a lot less money!. assuming you using 4 or 8ohm speakers and not 2ohm.
Well thanks for the reply. Been struggling with temptation of getting the kenwood amp on assumption your scope was problem, but after seeing typical not so low thd of most of these car amps. i think i will stick to the effort of boxing up tpa325* boards... hmm...
Shame really liked the thought of a ready made amp for £80.... hmm arr
thanks for the german car amp review link. just the sort of car amp reviews i have been looking for!
Disappointing to see most amps do not get low thd near 0.01%
. tpa325* amp boards are a lot better! Most of these are amps are more like old TI TAS53** amps level of thd. TAS53** amp boards cost a lot less money!. assuming you using 4 or 8ohm speakers and not 2ohm.Well thanks for the reply. Been struggling with temptation of getting the kenwood amp on assumption your scope was problem, but after seeing typical not so low thd of most of these car amps. i think i will stick to the effort of boxing up tpa325* boards... hmm...
Shame really liked the thought of a ready made amp for £80.... hmm arr
£80 is the brand new price. even less for 2rd hand price.
thanks for the german car amp review link. just the sort of car amp reviews i have been looking for!
Disappointing to see most amps do not get low thd near 0.01%
Well thanks for the reply. Been struggling with temptation of getting the kenwood amp on assumption your scope was problem, but after seeing typical not so low thd of most of these car amps. i think i will stick to the effort of boxing up tpa325* boards... hmm...
Shame really liked the thought of a ready made amp for £80.... hmm arr
I really wouldnt get hung up on THD in the car, unless your driving around in a bentley or something extremely quiet, from my experience what you need in a typical car is power. The Kenwood replaced an audison and some old school Phoenix Gold amps, XS2500's, about £700 back in the day, when I was listening to the Kenwood I was very underwelmed, I was hoping for more, when I switched to the German amps I sat in my car with a massive grin on my face, Its a very modest setup, £120 Hertz coax's (the old ones) in the front and a very old JL 12W6 in the back wired for 3ohm, I bought a Audio System Class D sub amp and the amp above for the fronts, bridging the fronts has given me nearly 300wpc into 4ohms but even though I will never be able to run at that,everything is better, dont forget high damping factor is very good for driver control and I now have more bass impact, better mid punch and what has surprised me is ive constantly noticed the fronts disappear, theres now a soundstage! i havnt chosen the car system for SQ, i just want it to rock for not too much money, I was thinking of buying some high end ish components but now Im happy. Maybe the Damping Factor is more important than I thought, I dont think ive ever seen it on the specs of any of my home hifi amps. Good luck with the boards, I always have more satisfaction from DIY but ive drawn a line for the car...
Oh bugger, after everything ive said I just remembered I got sent the wrong amp when I purchased the 105.4 from amazon, they sent me the 110.4, I didnt complain, I can honestly say I trust the german review site, they have this amp in the same class as a 1200 euro amp, there are a wide variation of prices in this class so its ideal to find a bargain and I think thats what the 110.4 is. Bestenliste Car-HiFi Endstufe 4-Kanal
Good luck with the build cacao ambiance, I wouldnd have the kenwood even if it was £20, stick with the boards then buy something from amazon to compare, try something on that list. I even damaged the mounting lugs on the Kenwood installing it but they said nothing when I sent it back, almost like you can demo it and get your money back if you dont like it!
thanks for the reply. annoying its now £108! For last one on amazon, says more are on the way :/ . not rushing now.
I’m making portable setups. for outdoor or indoor use. Quality is important for me, As is loudness. I have i different setups for different times. cheap and loud, smaller, bigger, hifi, ok-fi.
. not rushing now.I’m making portable setups. for outdoor or indoor use. Quality is important for me, As is loudness. I have i different setups for different times. cheap and loud, smaller, bigger, hifi, ok-fi.
Been looking at http://store3.sure-electronics.com/...e-control-mw-160w-36v-switch-power-adapter-vi
Uses https://www.st.com/resource/en/datasheet/tda7498l.pdf
THD around 0.1% or higher. so not the best, concerned by the SNR 82dB listed on the sure a2100 specs. itsa a ready made amp with lowpass for sub and handy digital inputs. great for spdif wireless setups. snag is a Sure 300w DC-DC to power it means it ends up being same sort of total cost as kenwood 301-4 and i guess THD is around the same for both amps.
so a tpa3251 diy build should be better with a phonix gold eq and kicker sub amp. just a lost more £££ but i have the bits already . Using nice sonance mariner 51 speakers so i suspect it will sound better with nicer amp setup. idk. i need to try it out
Uses https://www.st.com/resource/en/datasheet/tda7498l.pdf
THD around 0.1% or higher. so not the best, concerned by the SNR 82dB listed on the sure a2100 specs. itsa a ready made amp with lowpass for sub and handy digital inputs. great for spdif wireless setups
. snag is a Sure 300w DC-DC to power it means it ends up being same sort of total cost as kenwood 301-4 and i guess THD is around the same for both amps. so a tpa3251 diy build should be better with a phonix gold eq and kicker sub amp
. just a lost more £££ but i have the bits already . Using nice sonance mariner 51 speakers so i suspect it will sound better with nicer amp setup. idk. i need to try it out - Status
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