Class D amp long term reliability

[DMill]

Based on what I’m hearing from experts I’d certainly consider Class D on my next purchase. I think most layman, like myself, pick one up and it just feels flimsy, so how could it be as solid as 90lb beast of an amp from the past? I think I’ve been conditioned to think heavy=better build quality and parts. That said, I would challenge higher end manufacturers to have the beautiful case work and aesthetics that many lack if they choose Class D designs.

 

[somebodyelse]

That said, I would challenge higher end manufacturers to have the beautiful case work and aesthetics that many lack if they choose Class D designs.

We've seen a number with custom extrusions or milled from solid. Naturally these live further up the price range.

 

[egellings]

Based on what I’m hearing from experts I’d certainly consider Class D on my next purchase. I think most layman, like myself, pick one up and it just feels flimsy, so how could it be as solid as 90lb beast of an amp from the past? I think I’ve been conditioned to think heavy=better build quality and parts. That said, I would challenge higher end manufacturers to have the beautiful case work and aesthetics that many lack if they choose Class D designs.

Class D gets away with using little walnuts for transformers with negligible inductance due to the high operating frequencies involved. At 50/60Hz, you need a good deal of iron in order to get a high enough primary inductance for operating at such low frequencies.

 

[tmtomh]

Based on what I’m hearing from experts I’d certainly consider Class D on my next purchase. I think most layman, like myself, pick one up and it just feels flimsy, so how could it be as solid as 90lb beast of an amp from the past? I think I’ve been conditioned to think heavy=better build quality and parts. That said, I would challenge higher end manufacturers to have the beautiful case work and aesthetics that many lack if they choose Class D designs.

I too was raised to value "big iron" - heavy amps with giant transformers and massive cases. I got a Purifi-based power amp in 2020 and I'd never go back after that. Light, runs cool, no self-noise, built-in speaker protection, adjustable gain, performs perfectly, drove a pair of Infinity Kappa 9s to about 100dB SPL at 1 meter and didn't break a sweat.

 

[DonH56]

Based on what I’m hearing from experts I’d certainly consider Class D on my next purchase. I think most layman, like myself, pick one up and it just feels flimsy, so how could it be as solid as 90lb beast of an amp from the past? I think I’ve been conditioned to think heavy=better build quality and parts. That said, I would challenge higher end manufacturers to have the beautiful case work and aesthetics that many lack if they choose Class D designs.

Weight and size is largely a function of power supply and heat capacity.

Power Supply

Your old amp recharged the power supply capacitors 50/60 times a second (Hz). Those capacitors store charge as voltage peaks at that rate, then provide the energy to produce power (watts, sound) between charging cycles. The transformer needs to be big to supply enough power to keep the power flowing at 50/60 Hz, and the capacitors need to be large (in value and thus physically) to supply enough power to the amp between recharging peaks.

A modern class D amplifier's power supply operates at several hundred thousand times a second, say 200~500 kHz, so recharges the power supply capacitors about 5,000 to 10,000 faster (more often) than older "linear" power supplies. That means the capacitors can be that much smaller and provide the same effective energy (power) output, and transformers (or small inductors) can be that much smaller operating at such high frequency (relative to your wall outlet's 50/60 Hz). The result is that the class D (switched-mode) power supply can be a tiny fraction of the size and weight of the old "llinear" supplies.

Thermal Management

Class A/AB amplifiers are at best around 50% to 70% efficient at maximum output, meaning 30 W to 50 W out of 100 W input is wasted as heat. That heat must be dissipated, and that requires large (heavy) heat sinks and perhaps active cooling (fan(s)). It is not coincidence that most A/AB amplifiers have a lot of open space inside, surrounded by great big heat sinks, to keep the amplifier operating at reasonable temperature.

Class D amplifiers can approach 90% or more efficiency at maximum output, so out of 100 W input only 10 W is wasted as heat. Heat sinks can be much smaller, to the point that many class D amps have small'ish internal heatsinks and the chassis provides the rest. That high efficiency also means that fewer active output devices can be used since they do not have to support high waste energy; they only dissipate significant power when switching state.

As an aside, there are a number of A/AB amplifiers that incorporate power supplies that can change their voltage on the fly in response to the signal. The power supply's voltage rails can switch among two or more voltages (class G) or actually track the input (class H), adjusting the voltage up and down with the audio signal. That way, waste power is reduced since the voltage is reduced when higher power is not needed, and similarly smaller heat sinks can be used since the average power dissipated is much less. Benchmark and other amplifiers do this.

HTH - Don

p.s. Here is an article describing basic class D amplifier operation: https://www.audiosciencereview.com/forum/index.php?threads/class-d-amplifiers-101.7355/

 

[MCH]

Guys, question somehow related: I read that class D amps should not be operated unloaded, but there is always someone answering that they have been using only one channel for years with no issues.
Are there any risks or are you hurting longevity, or both, by leaving the output filter floating without load?

 

[DonH56]

Guys, question somehow related: I read that class D amps should not be operated unloaded, but there is always someone answering that they have been using only one channel for years with no issues.
Are there any risks or are you hurting longevity, or both, by leaving the output filter floating without load?

Tube amplifiers with transformer outputs should NEVER be operated without a load. Most SS amps are OK.

Check with the manufacturer to be sure. What amp? Most modern amps will be fine, though you will waste power. You may be able to disconnect the power supply from the unused channel. What I normally do is put a shorting plug on the input and drop a 100-ohm, 5 W resistor or something across the output just in case.

HTH - Don

 

[Fahzz]

I have an Audiophonics class D amplifier, that stopped working. $250 to ship from the States back to France for repair (lesson learned!), which is not justified given that I bought it for $400. I tried to find a local repair shop but no luck. Anyone fixing these here in the US?

 

[Davide]

I have an Audiophonics class D amplifier, that stopped working. $250 to ship from the States back to France for repair (lesson learned!), which is not justified given that I bought it for $400. I tried to find a local repair shop but no luck. Anyone fixing these here in the US?

Out of curiosity, which module does it have?

 

[tmtomh]

Out of curiosity, which module does it have?

Good question. If he bought it for $400, I’d guess it uses a Hypex NCore 122 or 252 module.

 

[Roland68]

I have an Audiophonics class D amplifier, that stopped working. $250 to ship from the States back to France for repair (lesson learned!), which is not justified given that I bought it for $400. I tried to find a local repair shop but no luck. Anyone fixing these here in the US?

A few thoughts from me.
- Contact Hypex.nl and ask them to help with a cost-effective solution.
- The shipping costs seem disproportionately high to me. The defective board can definitely be sent back and forth for under €100.
- Also ask Audiophonics to find a cost-effective solution, perhaps together with Hypex.

Once you have worked through the above points, you can create a friendly but firm thread on ASR and DIY and look for someone in the USA who can repair Hypex modules.
An honest and neutral description of the situation could help motivate Hypex to create a uniform warranty and repair solution for the USA and other continents.
The Hypex modules and amplifiers are also well known in the USA.

Maybe @Hypexsales is reading this....

 

[Fahzz]

Good question. If he bought it for $400, I’d guess it uses a Hypex NCore 122 or 252 module.

252

 

[Rick Sykora]

Would not discourage trying Hypex support, but even as an OEM, the shipping costs along with the price of a module have not been worth the expense. I can offer a decent deal on a used or new NC252MP and testing to ensure the repair is solid.

Since even domestic shipping can add up, would want to know a bit more before would have you ship to me.

PM if you are interested.

 

[pma]

There is a 6.3A fuse on the PCB. Is it OK?

 

[Rick Sykora]

As an aside, not sure why Hypex or Purifi or any part supplier should somehow be responsible for the OEM’s end product. If my display fails on my Dell monitor, even though the Samsung made the display, would not turn to Samsung and expect them to fix.

Whether you bought a Hypex-based amp from Audiophonics, Buckeye or NAD, they are responsible for repairs. It may be appropriate to pick on Hypex/Purifi for other reasons but fixing an OEM product is the responsibility of the OEM to support.

 

[Davide]

252

In all likelihood either a MOSFET or a capacitor has died.
If they have not done any other damage, an electronics repairer should solve with a few money.
From personal experience, I recommend that you review the thermal management of the Hypex modules in those fancy chassis. It is not adequate to me.

 

[Roland68]

As an aside, not sure why Hypex or Purifi or any part supplier is somehow responsible for the OEM’s end product. If my display fails on my Dell monitor, even though the Samsung made the display, would not turn to Samsung and expect them to fix.

Whether you bought a Hypex-based amp from Audiophonics, Buckeye or NAD, they are responsible for repairs. It may be appropriate to pick on Hypex/Purifi for other reasons but fixing an OEM product is the responsibility of the OEM to support.

If you mean my post, then you should read it again carefully.

Of course, as a manufacturer of OEM products, you can see it that way and act accordingly, as you describe.

But I see an opportunity for a manufacturer like Hypex to support both the manufacturer and the customer in such a situation. The effort would not be very great, the customer's trust in the products and brand would be improved and would be priceless in terms of marketing in this day and age.

It's all a matter of perspective.

 

[Rick Sykora]

If you mean my post, then you should read it again carefully.

Of course, as a manufacturer of OEM products, you can see it that way and act accordingly, as you describe.

But I see an opportunity for a manufacturer like Hypex to support both the manufacturer and the customer in such a situation. The effort would not be very great, the customer's trust in the products and brand would be improved and would be priceless in terms of marketing in this day and age.

It's all a matter of perspective.

No, did not just mean your post (although admittedly was a reminder)…

Open to other perspectives if they make good business sense or supports some regional requirement. As a Hypex OEM, have had conversations with them about many of these scenarios. Never have they suggested they want to take on general repair of their OEM’s products. If the OEM was no longer in business, could see that they might be willing to supply parts but otherwise suspect they are busy enough supporting their OEMs. As for end users, they set up diyclassd.com to handle and, while there is some overlap, the modules are mainly unique to that channel.

In @Fahzz case, still do not know what exactly is wrong with his amp. Am big proponent of understanding the target problem before suggesting a fix.

 

[Roland68]

No, did not just mean your post (although admittedly was a reminder)…

Open to other perspectives if they make good business sense or supports some regional requirement. As a Hypex OEM, have had conversations with them about many of these scenarios. Never have they suggested they want to take on general repair of their OEM’s products. If the OEM was no longer in business, could see that they might be willing to supply parts but otherwise suspect they are busy enough supporting their OEMs. As for end users, they set up diyclassd.com to handle and, while there is some overlap, the modules are mainly unique to that channel.

In @Fahzz case, still do not know what exactly is wrong with his amp. Am big proponent of understanding the target problem before suggesting a fix.

Every manufacturer has to know how to deal with such situations.
But there are two things I don't understand about such manufacturers.
Every customer who publicly reports a defective device/module prevents a certain number of interested parties who read it from buying. Simply sending a customer a module as a replacement would definitely not be expensive. A direct response to such a post would reach hundreds or thousands of interested parties in a positive way, and that for an investment of €50 - €200.
I call that a missed opportunity, because you can't invest money in marketing better, and in such a targeted way. This thread has had over 90,000 views so far.

I think the second point is just as important. We try to get back every one of our products that fails prematurely in order to analyze the failure and improve the products.

I think it's a shame when manufacturers only think about numbers and lose sight of such essential things.
But as I said, every manufacturer can decide for themselves how to deal with something like that.

 

[Rick Sykora]

Every manufacturer has to know how to deal with such situations.
But there are two things I don't understand about such manufacturers.
Every customer who publicly reports a defective device/module prevents a certain number of interested parties who read it from buying. Simply sending a customer a module as a replacement would definitely not be expensive. A direct response to such a post would reach hundreds or thousands of interested parties in a positive way, and that for an investment of €50 - €200.
I call that a missed opportunity, because you can't invest money in marketing better, and in such a targeted way. This thread has had over 90,000 views so far.

I think the second point is just as important. We try to get back every one of our products that fails prematurely in order to analyze the failure and improve the products.

I think it's a shame when manufacturers only think about numbers and lose sight of such essential things.
But as I said, every manufacturer can decide for themselves how to deal with something like that.

Your post assumes anyone is qualified to replace an amp module. Many are not and even if they are, how would a manufacturer know they did it correctly. I suggest you are oversimplying electronic repair for many who are not technically skilled. In any case as I already mentioned, it is also essential to properly diagnose the problem.

As it turns out, @Fahzz is having an issue with trigger input operation and so is likely NOT a Hypex module failure. So while they may have opportunities to improve, from my dealings, they seem like a decent company. While I agree about avoiding negative perceptions, if a company simply conceded a replacement for everyone that complained about their product, unlikely they would remain in business.

As a matter of full transparency, despite being a Hypex OEM, am not making any major profit. So, I have my opinion but am hardly biased by my ongoing relationship with Hypex. While this thread may have accumulated 90,000 views, would hope they consider the overall picture and not just the few negatives. I do work with Buckeye and know he has had a very low rate of Hypex module failures. So suggest we should be careful not to focus on one or two trees and miss the healthy, abundant forest all around us.