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What’s the life of a class D power amp?


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Posted (edited)

I have an early GB Streamliner 900 - it has been to the tech for preamp replacements a couple of time in the past year (I’m not too bothered by that as they’re still the original valves). The message I got from the tech was that the power amp may become unreliable or lose volume due to its age (can’t say I’ve noticed a problem).


I asked what he would buy his bass player (ignoring tonal considerations) -     something with transformers or valves in the power stage rather than class D.

 

Any of our resident boffins have a view? (Paging Dr @agedhorse).


Should I be worried about the fact that my only amp is a 10ish year old class D? (I have never had a problem with it before other than the noisy pre-amp valves.)

 

I’m looking at this purely from a reliability / fix ability point of view - this isn’t a question about the tone.

 

Thanks!

 

Edited by Nickthebass
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Well I guess anything can go wrong. I suggest taking a small backup amp or a di pedal with some to e shaping capabilities to use through pA as a backup. I always take a small spare amp.

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Posted (edited)
11 minutes ago, King Tut said:

Well I guess anything can go wrong. I suggest taking a small backup amp or a di pedal with some to e shaping capabilities to use through pA as a backup. I always take a small spare amp.

I have a Radial Bassbone Mk1 and a SansAmp on my pedal board so I can run to the PA or into the head’s power amp if needs be (assuming the power stage hasn’t gone pop).

 

I’m trying to get a sense of the chance of me needing my back up option as that would change what I want as my primary back up vs 3rd string options. 

Edited by Nickthebass
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In my experience, D class and SS amps are more reliable than valve amps. Since I started playing bass I've had 3 valve amps fail, one in the studio and 2 on stage. My SS amps (since the late 80's) and D class amps (since the early 2000's) have 100% reliability.

 

I take 2 D class amps to every gig. While one is nominally a "backup" I check them both out on the sound check and use the one I prefer.

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15 minutes ago, chris_b said:

In my experience, D class and SS amps are more reliable than valve amps. Since I started playing bass I've had 3 valve amps fail, one in the studio and 2 on stage. My SS amps (since the late 80's) and D class amps (since the early 2000's) have 100% reliability.

 

I take 2 D class amps to every gig. While one is nominally a "backup" I check them both out on the sound check and use the one I prefer.

How old are the class Ds? Like you I have never had a hiccup but the STM900 is now ~10 years old. 

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Here in N. America, the Streamliners are still covered under the factory flat rate service program. I so rarely see a bad power module that it's almost the last thing on the list of potential issues and the replacement modules are in stock and still a current part.

 

All the other things are generally simple and straight forward for a QUALIFIED tech, but what's becoming far more of a challenge is finding a truly qualified tech... that's FAR more concerning than a class D amp (or any other amp for that matter).

 

As far as cost of repair of tube/valve amps being cheaper, has anybody priced out a set of tubes or a replacement transformer lately? Replacing a power module (as rare as it might be) is less costly (by quite a bit) than replacing a set of tubes/valves. Tube/valve amps (in my experience) are much less reliable than a quality solid state amp of any type.

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Ive had Trace Heads fail a couple of times and a Hartke HA5500 puff out the magic smoke once. Only prob I've had with a class D was a dodgy di socket on a GKMb 500 but that was repaired under warranty.

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5 hours ago, Nickthebass said:

How old are the class Ds? Like you I have never had a hiccup but the STM900 is now ~10 years old. 

 

My TH500 is nearly 10 years old and the AG700 about 6 years old.

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10 hours ago, agedhorse said:

Here in N. America, the Streamliners are still covered under the factory flat rate service program. I so rarely see a bad power module that it's almost the last thing on the list of potential issues and the replacement modules are in stock and still a current part.

 

All the other things are generally simple and straight forward for a QUALIFIED tech, but what's becoming far more of a challenge is finding a truly qualified tech... that's FAR more concerning than a class D amp (or any other amp for that matter).

 

As far as cost of repair of tube/valve amps being cheaper, has anybody priced out a set of tubes or a replacement transformer lately? Replacing a power module (as rare as it might be) is less costly (by quite a bit) than replacing a set of tubes/valves. Tube/valve amps (in my experience) are much less reliable than a quality solid state amp of any type.

As they say in the  press, never  let the truth get in the way of a good story. I have investigated and  you can make up your own minds.

As an example, the ICEPower 250ASX2 power module is £299.88 from Profusion in the UK. That is the power module in the Aguilar TH500 among many others.

 

To replace the Mains transformer and power valves in an Ampeg SVT is £456 from Surrey Amps.  An SVT output transformer is £297.46 from the Tube Amp Doctor in the USA (I could not find UK stock). To replace the 6 output vales/tubes (SOVTEK) alone on an SVT is £240 from Watford Valves. 

 

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I don’t think any of us end users are qualified to assess the reliability and failure modes of different amp types as we have so few examples (i.e. amps owned) to work from. Amp repair people are much better placed to comment on this simply because they see so many on their work benches.

 

So here’s a question for them - are the caps in the SMPS sections of Class D amps their weak point?

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Posted (edited)
41 minutes ago, JapanAxe said:

I don’t think any of us end users are qualified to assess the reliability and failure modes of different amp types as we have so few examples (i.e. amps owned) to work from. Amp repair people are much better placed to comment on this simply because they see so many on their work benches.

 

So here’s a question for them - are the caps in the SMPS sections of Class D amps their weak point?

It depends on whether they are properly specified. Many Chinese clones or copies of evaluation boards cut costs by using component brands that "overspecify". Companies like ICEPower do not scrimp on the components and that is why the  DIY Audio forums are full of people whose module has blown shortly after powering up, 

 

There is no reason why a properly designed and manufactured Class D amp should be unreliable. TVs have been running with SMPS for around 20 years and with Class D amps (albeit lower powered) for almost as long. For example 65" plasma displays/TVs had 700-800W switch mode power supplies and were/are extremely reliable. Mine was 15 years old and working fine but I left it on the wall when I moved as it was too big for my new place. Incidentally I was Technical Manager for large screen displays at Panasonic Europe before I retired so I had access to reliability data.

Edited by Chienmortbb
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23 minutes ago, Chienmortbb said:

It depends on whether they are properly specified. Many Chinese clones or copies of evaluation boards cut costs by using component brands that "overspecify". Companies like ICEPower do not scrimp on the components and that is why the  DIY Audio forums are full of people whose module has blown shortly after powering up, 

 

There is no reason why a properly designed and manufactured Class D amp should be unreliable. TVs have been running with SMPS for around 20 years and with Class D amps (albeit lower powered) for almost as long. For example 65" plasma displays/TVs had 700-800W switch mode power supplies and were/are extremely reliable. Mine was 15 years old and working fine but I left it on the wall when I moved as it was too big for my new place. Incidentally I was Technical Manager for large screen displays at Panasonic Europe before I retired so I had access to reliability data.

 

Cheers, that's good to know! I think my Demeter head has an ICEPower unit (700W?) in it. I've been gigging that on and off for about 7 years now. Ironically that amp did go flakey on a gig but it turned out to be the bridge rectifier used to create a DC supply for the valve heaters. Fortunately I was able to fix that myself!

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Both my Streamliner heads (600 and 900) have zero volume/power problems, and both coming up on 10 years old. They both have crackling volume pots, but as AgedHorse said, the problem is finding a qualified tech to service/repair them. A well established local guy here won’t touch mine because of the Class D/transistor side of it.

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3 hours ago, Gareth Hughes said:

Both my Streamliner heads (600 and 900) have zero volume/power problems, and both coming up on 10 years old. They both have crackling volume pots, but as AgedHorse said, the problem is finding a qualified tech to service/repair them. A well established local guy here won’t touch mine because of the Class D/transistor side of it.

That is crazy, pots can be replaced easily. They can be cleaned but sometimes this is a temporary measure. 

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5 hours ago, Gareth Hughes said:

Both my Streamliner heads (600 and 900) have zero volume/power problems, and both coming up on 10 years old. They both have crackling volume pots, but as AgedHorse said, the problem is finding a qualified tech to service/repair them. A well established local guy here won’t touch mine because of the Class D/transistor side of it.

The place I have been going to was recommended by a former Streamliner owner that I contacted from here. 
 

Turns out my issue this time was two preamp valves needing replaced. 

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6 hours ago, Chienmortbb said:

There is no reason why a properly designed and manufactured Class D amp should be unreliable. TVs have been running with SMPS for around 20 years and with Class D amps (albeit lower powered) for almost as long. For example 65" plasma displays/TVs had 700-800W switch mode power supplies and were/are extremely reliable.

I think most of the issues in the "other-than-instruments" SMPS' that I have seen has been poorly designed units without decent ventilation, or cheapo caps. Some of those could be repaired with good components. On the other hand a blown unit tends to blow severely.

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I bought an Ashdown MiBass 550, secondhand from Basschat, about 10 years ago. I gave it to the son of a friend of mine, about a year ago, who'd started to play bass and it's still going strong.

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Posted (edited)
18 hours ago, JapanAxe said:

I don’t think any of us end users are qualified to assess the reliability and failure modes of different amp types as we have so few examples (i.e. amps owned) to work from. Amp repair people are much better placed to comment on this simply because they see so many on their work benches.

 

So here’s a question for them - are the caps in the SMPS sections of Class D amps their weak point?

No, the ONLY cap failures I have seen in (quality) class D amps are in the SMPS when the user connected the amp to 230V while configured for 115V. This is not a cap issue, and generally there’s a lot more damage from this kind of accident.

Edited by agedhorse
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5 hours ago, agedhorse said:

No, the ONLY cap failures I have seen in (quality) class D amps are in the SMPS when the user connected the amp to 230V while configured for 115V. This is not a cap issue, and generally there’s a lot more damage from this kind of accident.

 

Thank you so much for that. I may be confusing this with SMPS cap failures in TVs, having watched a couple of YouTube videos where people have repaired these.

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Different industries source their products differently. Also, there were some earlier suppliers for both the computer and TV/monitor industry that sourced caps from vendors using counterfeit (and defective) materials. This is a much different situation, and not something that i have seen in the audio world that I live in. As long as the design respects the appropriate limitations of the caps being used, i almost never see an issue with caps.

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1 hour ago, agedhorse said:

Different industries source their products differently. Also, there were some earlier suppliers for both the computer and TV/monitor industry that sourced caps from vendors using counterfeit (and defective) materials. This is a much different situation, and not something that i have seen in the audio world that I live in. As long as the design respects the appropriate limitations of the caps being used, i almost never see an issue with caps.

Of course working for Panasonic. te capacitors all had the  big old M on them that meant they came from Matsushita Factories. For those that don't know Matsushita (pronounce Mat-Sush-Ta) was the Japanese name for National and Panasonic. Our only unreliable SMPSPSU on plasma displays was caused by an out of spec batch of semiconductors from another supplier.

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On 15/05/2022 at 22:11, agedhorse said:

Here in N. America, the Streamliners are still covered under the factory flat rate service program. I so rarely see a bad power module that it's almost the last thing on the list of potential issues and the replacement modules are in stock and still a current part.

 

All the other things are generally simple and straight forward for a QUALIFIED tech, but what's becoming far more of a challenge is finding a truly qualified tech... that's FAR more concerning than a class D amp (or any other amp for that matter).

 

As far as cost of repair of tube/valve amps being cheaper, has anybody priced out a set of tubes or a replacement transformer lately? Replacing a power module (as rare as it might be) is less costly (by quite a bit) than replacing a set of tubes/valves. Tube/valve amps (in my experience) are much less reliable than a quality solid state amp of any type.

Thanks very much for this. 

 

I may look into buying a spare power module to stick in the drawer in case of disaster! I'm still a massive fan of the Streamliner and in particular the pre-amp. If the worst ever came to the worst and the power amp did explode and was un-fixable I would still keep it as a DI box / pre-amp. In fact ... is someone happened to make a Streamliner style DI box I could be persuaded to be in the market for one!

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