Are Class D's Disposable?

[mike buzzetti]

That's just sad IMO.



It runs the gamut from power supply to class D switching, timing and everything in between. The problem is that I see so few module failures that I haven't been able to define a clear pattern. I replaced a total of 4 power modules in 2021, 2 legitimate failures, plus one that had 230V applied when set for 115V and the other was from a "tech" who was convinced that a ribbon cable was bad, removed the header from the module and soldered the wires to the PCB without realizing that he ruined the 4 layer PCB by damaging the plated holes. Turns out the problem with that amp was completely unrelated to the power module and was simply a tube pin bond that had failed intermittently inside the tube! 30 seconds of simple, basic troubleshooting could have eliminated the module as the cause. So 2 legit. failures and 2 caused by abuse to the amps.

Dont mess with multilayer PCB's ! ( used to work on 7 layer hard drive PCB's ) I figured most would be output sections as they do all the heavy lifting and or PS's , what are the timing issues ?? it seems that that would be a fixed clock that is mixed with the input signal to PWM correct ? I guess a freq. source could go to craP ?

 

[crazyBassClown]

it looks like class D power section seems to be way more reliable than class A/B amps or any other topology.

Reliability has far more to do with design and manufacturing decisions than topology. Peavey came into existence with a mission to build fender amps, but reliable.

 

[JakobT]

That's just sad IMO.

Sad, but true.

 

[GeorgesEric]

No there are not disposable. Pampers, Kleenex, syringes, pencils, and other one shot deals, those are disposable items.

It is true that nowadays parts are more often replaced than repaired by technicians however that does not make a device a disposable one.

 

[agedhorse]

Dont mess with multilayer PCB's ! ( used to work on 7 layer hard drive PCB's ) I figured most would be output sections as they do all the heavy lifting and or PS's , what are the timing issues ?? it seems that that would be a fixed clock that is mixed with the input signal to PWM correct ? I guess a freq. source could go to craP ?

There are very tight timing requirements within the gate drive circuits on both the SMPS and the power amp. With the power supply, this affects efficiency and radiated noise. With the power amp, this affects distortion and radiated noise. If the timing gets too close (each half of the bridge must turn off before the other half turns on) you get cross-conduction which is a quick way to lose all that expensive magic smoke.

Remember that the higher quality class D amps are switching at between 300kHz and 500kHz, so we are talking about very, very short time intervals between the pulses.

 

[JW56789]

I'm going to step up and do the Right Thing:

Anybody that's just not buying all this mumbo-jumbo, please PM me, and I will gladly dispose of those nasty Class D amps for you.

Thanks !

JW

(. . . .he grinned like a fool and gleefully rubbed his hands together . . . . )

 

[S-Bigbottom]

I don't know the failure rate of Class D amps, but it sure seems higher than the older amps still out there and working.

What everyone forgets is that for every old Sunn, Peavey, Eden or whatever old amp still out there, there were many more thrown in the trash.

I know I have tossed a couple Eden's "Made In USA" in the trash.
Yup, they were Class A/B, them in between Tube and Class D amps.

Repair shops and trash yards were full of broken amps long before Class D amps.

 

[mike buzzetti]

There are very tight timing requirements within the gate drive circuits on both the SMPS and the power amp. With the power supply, this affects efficiency and radiated noise. With the power amp, this affects distortion and radiated noise. If the timing gets too close (each half of the bridge must turn off before the other half turns on) you get cross-conduction which is a quick way to lose all that expensive magic smoke.

Remember that the higher quality class D amps are switching at between 300kHz and 500kHz, so we are talking about very, very short time intervals between the pulses.

Ya I can see timing being very important in these cases , dont short ur PS ! lol , I figured they were up in those Freq. thanks for the info ! long time sense I talked to someone about electronics that know what they are doing. again THanks !

 

[Gizmot]

Design is just as important in reliability. Many of the robust amps these days seem to take Andy’s approach and use the off the shelf power amps.

How many people dealt with major failures in their Ampeg PF/7 pro, original series orange terror bass, carvin bx (I think that’s the series?), etc., amps? How many people come here complaining about being sent through multiple layers of hoops to get their markbass, darkglass, etc, amps repaired through their strict warranty requirements. I’m sure that soured more than one person on those brands at the very least. The major issues these products had weren’t really attributable to people not caring for their amps.

It’s good there are companies who stand by their legacy product, even after the company is gone. I hope should I ever have an issue with my EA that I’ll have some recourse for repair, though given their reputation around here for legacy product support I doubt it.

i’ve been playing an EA amp for over a decade and it still sounds and looks brand new. it may even sound better than when it was new because i understand and know how to dial in the 4 band EQ. I’m confident i have a lot of years of useful life

 

[Guitalia]

Reliability has far more to do with design and manufacturing decisions than topology. Peavey came into existence with a mission to build fender amps, but reliable.

I once met one of the two brothers who ran Unicord Inc. in Rhode Island, back when they were the importers and authorized repair center for Marshall amps. I mentioned that I had one of the blue 60-watt Univox tube heads and two of the matching 2x12 cabinets from the early '70s, and he was clearly pleased to hear that. He said that he had designed that line of amps because he was sick of repairing Marshall amps, which were being cranked out so fast back then that the quality control was appallingly bad, and saw an opportunity to import reliable Japanese tube amps.

According to him, my 60-watt amp was essentially a Marshall circuit, but with upgraded components and stellar quality control. Given that it had been at least 8 years since the Univox amps had been discontinued when we had that conversation, and that I've had the amp now for over 40 years with zero issues, I believe he wasn't just blowing smoke.

Not mine, but same amp:

 

[crazyBassClown]

was essentially a Marshall circuit, but with upgraded components and stellar quality control.

And I have no doubt that it was far more reliable but at least some of the tone of a cranked marshall is those components being pushed to or past their limits.
Hence people still using them today despite needing repairs semi regularly when used hard.

 

[baxter_x]

Reliability has far more to do with design and manufacturing decisions than topology. Peavey came into existence with a mission to build fender amps, but reliable.

I have heard Peavey was actually a very reliable brand, yes.

 

[Guitalia]

And I have no doubt that it was far more reliable but at least some of the tone of a cranked marshall is those components being pushed to or past their limits.
Hence people still using them today despite needing repairs semi regularly when used hard.

Yes, my Univox 1226 head doesn't do Marshall tone as such. It's a clean 6L6GC machine unless I crank it up to a painfully high volume, so I mostly use pedals for distortion. Still, it does have the Marshall Plexi configuration of four inputs (bright [guitar] and normal [bass] channels, high and low sensitivity), which can be jumpered for greater versatility of tone.

 

[coreyfyfe]

i’ve been playing an EA amp for over a decade and it still sounds and looks brand new. it may even sound better than when it was new because i understand and know how to dial in the 4 band EQ. I’m confident i have a lot of years of useful life

Yeah no complaints with mine so far, doesn’t change the fact that the company has closed and future product support will not exist.

Zooming back out to the point I was making - a manufacturer who stands behind their product is as important as one who designs it well from the start.

 

[shoot-r]

Considering what it costs to get a replacement board for some amps and what you can get them for used are they essentially throwaways like everything else now? We had this discussion in the a local shop and I am not talking caps and simple things, but when problems are more digital it was mentioned that it often takes longer to chase those down than they are worth and sometimes can't be solved without replacing whole boards and what not. Is there anything to this thinking? I am not a tech , but it does seem worth pondering.

I only have one Class D and I keep it as a backup for tube and hybrid amps. I do consider it my most reliable, but at least I know for a fact the other ones are repairable. What about straight non hybrid class D's? Are we now into the land of disposable amps?

Few years back, during my class "D" bass head search, I had a BAD run with "two" of Amp*g's PF500 "D" amps.

Both heads burnt out.

Loud/Amp*g replaced the first one, second one I had to take to a certified Amp*g service center.
Service techs actually told me to toss it!!!!!

I've now (somehow) 4 class D amps.
A Mesa 800+, a G.K. MB Fusion 800, a G.K.MB2-500, and a G.K. MB500.

They've all proven to be real work horses in the gigging band I'm with.

 

[Gizmot]

Yeah no complaints with mine so far, doesn’t change the fact that the company has closed and future product support will not exist.

Zooming back out to the point I was making - a manufacturer who stands behind their product is as important as one who designs it well from the start.

What I was trying to convey in my remarks is that I'm not too concerned about my iAmp lasting for decades to come. One thing about mine is that I use it exclusively for a weekly gig I play at a church - - so it isn't moved and it has more than enough output to cover my application, so it isn't pushed hard. Since the build and parts quality is so high, it should be rock solid for a long time. I've already gotten my money's worth from this excellent product, so if I have to replace it, I won't have many regrets.

 

[paskisti]

Many components are integrated into 1-2 PCBs and if one of them fails there is high assumption that it is not worth repair when warranty expired. Spare part cost is often high and no components will be replaced separately. I know we are reminded often of qualified techs that can do a lot of things, but they are not always available depending the country, or importers/distributors are not willing to repair PCBs, just replacing them.

Example:

My old Sansamp RBI failed and new PCB (one of the two) would have cost 230€ + shipping while new unit 350€, and importer's workshop did not want to make PCB level repair. Luckily I knew that problem were somewhere in Sansamp circuit (dry side of blend worked fine but Sansamp side only when bending the PCB) and my colleague in R&D lab found single faulty SMD resistor and replaced it. Cost 5 snt + beer.

Yes, it was not class D amp. But if it were, let's say 10 years old 500€ Quilter or Markbass, would I invest 200€ into new PCB + labor cost + shipping. No. Is there qualified tech repairing PCB cheaper? No.

Intended service work in theory and practice often separates.

P.S. This post concerns many of modern electronics designs, costs structure and business, not just class D or A/B amps.

 

[baxter_x]

My old Sansamp RBI failed

How old was it? I never heard any issues with those devices. But I never owned one.

 

[Jefenator]

I just Googled "durable goods" and the criteria is an item expected to last over 3 years. I would hope for more like 15-20 years from any brand new purchase I have to save up for or finance.
It usually is. But sometimes it winds up being more like 3 years and a month.
And it's definitely not just amps; I just helped a buddy swap out his busted washer & dryer that looked to be one day out of warranty. (Meanwhile his mom's washer & dryer from the 1980s are still going strong.)
There's luck of the draw, but I also think there's the corporate culture; some designs & service departments are worse than others. And sometimes a once-solid brand can really go down the flusher under new ownership. (DAMHIK...)

 

[paskisti]

How old was it? I never heard any issues with those devices. But I never owned one.

10 years old, but it didn't break by itself, there were serious damage happened to my ATA rack because someone dropped it from 1-2m height. Unfortunately I didn't secure my QSC power amp at rear and landing to concrete was too much for front rail. QSC ear (aluminium) cracked, and RBI ear was bent but both units worked fine. RBI started make troubles one year later and we found out that SMD resistor's one end was not anymore attached to its body and there were no visual damage.

Lesson learned: fasten the deep heavier amps at rear too.