Should I be worried about buying a used Class D amp?

[arbiterusa]

I'm curious if people are wary about buying class D amps, especially used ones, given that when they go they are often so difficult and expensive to fix?

Nope. I bought my MB500 used, liked it a lot and got another one, also used. They hadn't been used much, both look brand new.

Gig twice a week, plus a band practice every now and then. I don't worry about them, I frankly expect as least one of them to outlive me.

The ONLY difference is that when one these die, I'll probably just toss it. Old amps are like old TVs - every part can be worked on. Yeah, the screen is tiny, the power consumption is horrific, and they're heavy as granite and look like furniture, but you can fix 'em part by part.

New SMPS amps are like new TVs - far better screen, far larger, far lighter, but only two or three circuit boards (my GK has three) and when something goes you replace the appropriate board. Which is expensive as 1/3 of the parts are on it. Or toss it and get a newer one.

 

[sing-modulator]

All my Class D amps were bought used. Not a single issue so far. Oh and there is no such thing as a digital amp. Class D does not mean digital.

Many class D amps have digital signal processing built into the amplifier section, which makes them digital. In addition to this, the "switching" aspect of them makes them "digital" in the sense of "on/off" information, if not purely in the "computer" way of being digital. Class D amps sit at the intersection of delilcate components and high operational stress, which is not a crossroads I want to have powering my music.

 

[dave64o]

I've bought the following Class D heads used (except for the Genzler, all from fellow TBers):
G-K MB200
G-K MB500
G-K MB800
Mesa D800
Mesa D800+
Genzler Magellan 350

I still have the MB500, MB800, D800+, and 350. I've gigged the MB800 and D800+ heads and have taken the MB500 to basement jam sessions. I've had no problems with any of the heads I've bought.

Yugo built crappy, unreliable cars, but that doesn't mean all cars are crappy and unreliable.

 

[xroads64]

nope
I haven't bought a new amp since 1984

 

[bassdude51]

Should I be worried about buying a used Class D amp?

Yes! They give off radiation and cause cancer! Don't ever use a class D amp!

Joking of course.

They are excellent amps. They are cheap. Buy 2 and have one for a back up. Enough folks use them!

 

[tradernick]

I bought all 3 of these very gently used. No worries. Mesa has a 5 year warranty as well. Just make sure that you choose carefully.

Agreed, MB's 5 year transferable warranty is pretty cool, and I've bought a couple of MB amps from the classifieds here. Since the OP has the word 'Guelph' in his name, s/he may be from Canada. If so, I would suggest a call to MB in California to understand the procedure for Canadians who buy in-warranty stuff that was originally sold in the USA.

 

[KarateChris]

I bought a used Ampeg pf-350 on Reverb. I love it.

 

[agedhorse]

Nope. I bought my MB500 used, liked it a lot and got another one, also used. They hadn't been used much, both look brand new.

Gig twice a week, plus a band practice every now and then. I don't worry about them, I frankly expect as least one of them to outlive me.

The ONLY difference is that when one these die, I'll probably just toss it. Old amps are like old TVs - every part can be worked on. Yeah, the screen is tiny, the power consumption is horrific, and they're heavy as granite and look like furniture, but you can fix 'em part by part.

New SMPS amps are like new TVs - far better screen, far larger, far lighter, but only two or three circuit boards (my GK has three) and when something goes you replace the appropriate board. Which is expensive as 1/3 of the parts are on it. Or toss it and get a newer one.

Actually, many class D amps are repairable without replacing PCBs. Your MB-500 is a well laid out with a preamp board that's easily repairable by a qualified tech and many (not all) other amps are built similarly. Regarding the repair of the SMPS and class D portions (which are all on the same PCB), due to the level of complexity, compactness and relatively inexpensive replacement cost, it's usually less expensive to replace the power module as the labor required to repair is generally higher than the replacement cost. By replacing the power module with the factory replacement part, the safety and EMC performance remains intact because the level of testing during the manufacture of these modules he very comprehensive and highly automated.

Many class D amps have digital signal processing built into the amplifier section, which makes them digital. In addition to this, the "switching" aspect of them makes them "digital" in the sense of "on/off" information, if not purely in the "computer" way of being digital. Class D amps sit at the intersection of delilcate components and high operational stress, which is not a crossroads I want to have powering my music.

The class D amp portion is not digital because there may be DSP incorporated before the power amp, no different than a preamp tube incorporated before the amp making the class D amp a tube amp.

The switching aspect is not digital, but a non-linear time based analog operation. There is no information that can be extracted from the pulses themselves, it's the variation of time and duty cycle within the pulses that contain the information. You can't take this pulse information and perform calculations on it, store it in memory, or manipulate it like a digital signal.

Now there are some interesting (mostly) theoretical applications where the PWM train is generated digitally, but I don't know of any amps in the bass guitar world that does this (yet).

As far as being at the intersection of delicate components and high operational stress, perhaps you are unaware that virtually ALL pro audio touring amps at the highest level are now SMPS and class D? These amps are operated under the most grueling conditions you could imagine, and their reliability has ended up being significantly higher than their old school counterparts.

 

[David Jayne]

Many class D amps have digital signal processing built into the amplifier section, which makes them digital. In addition to this, the "switching" aspect of them makes them "digital" in the sense of "on/off" information, if not purely in the "computer" way of being digital. Class D amps sit at the intersection of delilcate components and high operational stress, which is not a crossroads I want to have powering my music.

There's literally nothing true in this post. Zero. DSP can be found in every topology. The switching supply is not in any sense digital. Class D is not a reference to 'digital.' It's just a letter.

 

[GuelphBassie]

Lot's of great advice here, thanks everyone! I definitely feel better about buying a used Class D amp. Now my only frustration is getting a chance to try them. I'm about an hour outside of Toronto and none of the music stores around here seem to carry any of them. I know, just drive to Toronto...... I'm busy, I've got gigs to practice for!

 

[74hc]

My MarkBass is certainly not repairable for the most part, but board replaceable. There's too much hardened goop everywhere that removing it would risk too much damage. Plus the extra labor to remove it carefully would be too expensive in my neck of the woods.

One of the reasons for the increase use of goop is lead-free solder which is harder and more prone to cracking under thermal and vibration stress. There are Youtube videos on how to fix issues from lead-free solder ranging from Playstation BGA reflowing in your oven, same for Thinkpads, iPhones, and anti-lock brake controllers, etc.

I would not recommending reflowing in one's oven unless one is single, going to throw out the device anyway, and is willing to replace the oven if needed, and is careful enough not to burn the house down.

 

[Spirit of Ox]

I'm huge GK fanboy and have my eye on the Legacy series but if I were to go Class D, it would probably be Genzler. Genlzler seems to be a step above the rest in the Class D market. This is just my opinion and based on research and experimentation.
Plus there's a member on this forum who works with them as an engineer in testing and development.

 

[agedhorse]

My MarkBass is certainly not repairable for the most part, but board replaceable. There's too much hardened goop everywhere that removing it would risk too much damage. Plus the extra labor to remove it carefully would be too expensive in my neck of the woods.

One of the reasons for the increase use of goop is lead-free solder which is harder and more prone to cracking under thermal and vibration stress. There are Youtube videos on how to fix issues from lead-free solder ranging from Playstation BGA reflowing in your oven, same for Thinkpads, iPhones, and anti-lock brake controllers, etc.

I would not recommending reflowing in one's oven unless one is single, going to throw out the device anyway, and is willing to replace the oven if needed, and is careful enough not to burn the house down.

Lead-free solder is not much of an issue with proper layout and especially well controlled chemistry. I've been using it for almost 15 years, we were an early adopter at Genz Benz after years of studying the available processes, and looking back on the reliability data I see no difference between lead and lead-free solder. That said, you can't get sloppy with process control and chemistry using lead-free, which is less tolerant of out of spec parameters.

Usually, the goop is used to prevent larger parts from vibrating and making (mechanical) noises, as well to protect them when the amp takes a tumble. It's also sometimes used to make the circuit harder to reverse engineer, but not very often.

 

[sing-modulator]

There's literally nothing true in this post. Zero. DSP can be found in every topology. The switching supply is not in any sense digital. Class D is not a reference to 'digital.' It's just a letter.

I mean digital in that it's either on or off in the switching power supply. Just semantics. Many class D amps use DSP in the power supply itself, making it very difficult to repair.

 

[sing-modulator]

Actually, many class D amps are repairable without replacing PCBs. Your MB-500 is a well laid out with a preamp board that's easily repairable by a qualified tech and many (not all) other amps are built similarly. Regarding the repair of the SMPS and class D portions (which are all on the same PCB), due to the level of complexity, compactness and relatively inexpensive replacement cost, it's usually less expensive to replace the power module as the labor required to repair is generally higher than the replacement cost. By replacing the power module with the factory replacement part, the safety and EMC performance remains intact because the level of testing during the manufacture of these modules he very comprehensive and highly automated.


The class D amp portion is not digital because there may be DSP incorporated before the power amp, no different than a preamp tube incorporated before the amp making the class D amp a tube amp.

The switching aspect is not digital, but a non-linear time based analog operation. There is no information that can be extracted from the pulses themselves, it's the variation of time and duty cycle within the pulses that contain the information. You can't take this pulse information and perform calculations on it, store it in memory, or manipulate it like a digital signal.

Now there are some interesting (mostly) theoretical applications where the PWM train is generated digitally, but I don't know of any amps in the bass guitar world that does this (yet).

As far as being at the intersection of delicate components and high operational stress, perhaps you are unaware that virtually ALL pro audio touring amps at the highest level are now SMPS and class D? These amps are operated under the most grueling conditions you could imagine, and their reliability has ended up being significantly higher than their old school counterparts.

The preamp isn't the issue, the power supplies on class d amps go bad, and are often significantly more difficult and expensive to repair, in my experience. What happens when those power modules are no longer made?

 

[agedhorse]

I mean digital in that it's either on or off in the switching power supply. Just semantics. Many class D amps use DSP in the power supply itself, making it very difficult to repair.

Actually, it's not semantics. I don't know of any power supply in a class D amp that uses DSP in the popwer supply. Not a single one.

The preamp isn't the issue, the power supplies on class d amps go bad, and are often significantly more difficult and expensive to repair, in my experience. What happens when those power modules are no longer made?

Well, if you choose amps that have a history of long term support, this is generally not going to be a problem. As an example that I have experience with (I'm not making claims for any other manufacturers), I still have plenty of class D modules in stock for 15 year old Genz Benz amps and in fact I just looked and all of the module models are still currently being manufactured.

 

[sing-modulator]

Actually, it's not semantics. I don't know of any power supply in a class D amp that uses DSP in the popwer supply. Not a single one.



Well, if you choose amps that have a history of long term support, this is generally not going to be a problem. As an example that I have experience with (I'm not making claims for any other manufacturers), I still have plenty of class D modules in stock for 15 year old Genz Benz amps and in fact I just looked and all of the module models are still currently being manufactured.

I've seen DSP stuff with powered speakers a lot (JBL, QSC, etc). I guess my issue is that I know I'll be able to repair my solid state amps for pretty much forever, whereas there is a time limit on how long those power modules for class d stuff will be manufactured. Again, it's also much cheaper to repair solid state AB stuff, which is relevant to OP's question.

 

[agedhorse]

I've seen DSP stuff with powered speakers a lot (JBL, QSC, etc). I guess my issue is that I know I'll be able to repair my solid state amps for pretty much forever, whereas there is a time limit on how long those power modules for class d stuff will be manufactured. Again, it's also much cheaper to repair solid state AB stuff, which is relevant to OP's question.

Again, this is factually incorrect.

The DSP used in all of the examples you listed are signal processing BEFORE the power amp and have nothing to do with the SMPS.

Sometimes it's cheaper to repair class AB, but often it's not when labor is factored into the equation. For example, the 300 watt module used in one legacy product is only $99 to replace, plus $85 flat labor (including power amp and supply) but in general it's going to cost more in parts and labor to repair a linear amp of that size... especially if there's any PCB damage from catastrophic failure.

There is certainly the possibility that a module won't be available, but this scenario is also true for linear amps. Things like power transformers, and semiconductors. For example, all those linear amps built with lateral MOSFETs in the 2SC1058/2SJ162 family are pretty much SOL, as virtually every one I have seen in the last few years are counterfeits/fakes. There are a few cross-parts that are marketed as being exact, but they are not the same and may oscillate (catastrophically) in some circuits. Same goes for the old gull wing parts. How about the LM391 driver IC's?

 

[okcrum]

Knew I could count on being corrected.

Had you been able to count on being correct, you wouldn't have had to.

 

[S-Bigbottom]

Class D amps sit at the intersection of delilcate components and high operational stress, which is not a crossroads I want to have powering my music.

That is funny, as every event you go to or play at will be powered by Class D for the show.
Better tell The Rolling Stones, The Who, Primus, Rihanna, Jay-Z, Carrie Underwood and many other major acts and Event Centers to have their PA changed out.

PS, Your car stereo is also Class D, and they have been for a looong time.
They take the zub-zero temps in the winter to well over 100 degrees in the summer time. When it is freezing you get into the car, turn on the heater full and you are near 60 degrees by the time your ride is over, then it goes down to freezing again while you are at your destination, repeat on the drive home. Plus all that bouncing and bumping from driving on different surfaces at all speeds.