Crate V series and Class D amplifiers in guitar/bass amps

[Duffy]

As some of you may recall, I bought a deep discount Crate V50 from one of the big online places. I loved the tone of that amp and the overdrive was great. Crate had advertized it with one of the famous old timer blues dudes sporting it a a great V50, at the same time claiming that the new "switching power supply" in the V series, except the V5, was the greatest achievement in power supply technology yet. It provides great power reserves and instant power and is very very light, they claimed.

Well, a deal too good to be true probably is, and the V50 flashed out and could not be repaired. The switching power supply was apparently part of the problem, possibly blown out by a castatrophic tube failure.

Bottom line: the Crate switching power supply could not be rebuilt by the techs I took it to, professionals; and a new one could not be made from scratch. Furthermore, according the the techs, a conventional power supply could not be retrofitted.

The Crate engineer told me that the new V series was a bad compromise from the beginning, it was a bad design.

He also said that switching power supplys, digital power supplies also known as a type of class D amplifier have proven to be effective in solid state amps but have not been effective in tube amps.

Lately I'm looking at getting a new bass amp and I am seeing that the CLASS D AMPLIFIERS are quite common in the new designs; they are way cheaper to make than the old school analog power supplies and transformers. All of the bass amps that have the class D amps in them are either solid state or hybrid with preamp tubes.

I'm not sure how long Class D amplifiers, switching power supplies, have been being offered in bass amps. It might be a good thing, I don't know, but they are definitely promoting the Class D amplifiers in the bass amps fairly big time at present, even with the Peavey bass amps, in addition even the Ampeg B300 bass amp is "featuring" a "Class-D switching power supply". This is not a cheap amp.

I have looked into "switching power supplies" as a result of my personal experience, to some small extent, and I recently discovered this great semi technical article that the average person can actually read and understand.

I thought that some of you might want to read it for whatever reason; especially those owning or considering a tube amp with a switching power supply or even a solid state one like I'm considering. These Class D amps are definitely lighter than the comparable old school analog power supply amps.

The article is interesting and reveals why "switching power supplies" may have a long way to go in the real world of far Eastern manufacturing, even though they demonstrate audiophile potential.

Here is the article: http://www.irf.com/technical-info/appnotes/an-1071.pdf

I hope some of you find it useful or at least informative.

[Duffy]

Crate V series amp owners might want to read this because of the switching power supplies in the V series, except the V5 which has the traditional power supply.

[jim p]

I don’t think you can consider switching power supplies to be something that is new and unproven. The idea of switching power supplies existed before there were components available to make them. With the introduction of mosfets around the 70s switching power supplies became a reality. The computer you are using, the charger for your cell phone and almost every new electronic device uses them. That Crate did not take into account what would happen to the supply if it was subjected to a near short circuit is a design flaw on their part.
As far as the repair shop if you don’t know the theory of switching supplies and have not repaired many then they can be confusing and scary. A boost switching supply is almost the same as the ignition system on a car so if it goes unregulated the voltages can get very high.
On the class D amplifiers if you don’t mind doing to live music what an MP3 player does to recorded music I suppose they are fine. The amplifiers in MP3 players and smart phones are this type of amplifier because of their high output power and high efficiency.

[Eric]

Hi Jim,

I do have a Crate V50 out on loan to a friend right now, so I'm somewhat interested in all of this.


That Crate did not take into account what would happen to the supply if it was subjected to a near short circuit is a design flaw on their part.
Are you referring to the power tubes dying, as was the case with Duffy's amp?


On the class D amplifiers if you don’t mind doing to live music what an MP3 player does to recorded music I suppose they are fine. The amplifiers in MP3 players and smart phones are this type of amplifier because of their high output power and high efficiency.
I'm not sure what you intimating here. Does a class D amplifier compress or in some other way alter the sound? I would imagine it has some impact, but was wondering what the sub-text is here.

Also, I have heard of acoustic amps being class D before. Is the class D designation referring to the PS or the amplifier setup itself? Perhaps I should read that linked article...

[jim p]

With class D the amplifier just supplies pulses of voltage (current) to the speaker that is being driven and uses the inductance of the speaker, or an inductor in series or capacitor to ground to take the high frequency edges out. So it is like flipping a switch on and off to the speaker unlike a class A or AB amp where the amplifier is continuously supplying current to the speaker. Some class D amplifiers have a feedback loop to sense the output signal of the amplifier relative to the input signal to create a closer match. So as in MP3 compression the process of reproducing the output waveform in this manor can lead to distortion.
On the Crate V50 on the one I have I increased the value of the resistor connected to the screen grid of the power tube to reduce the inrush current and then reduced the value of the fuse on the plate supply. So if the tube fails and draws high current the fuse should blow at a much lower current.

[Duffy]

Eric,

Read the article.

Also, class D amps, while being used in tiny electronics for some time, are not, in most Far Eastern cases proven to be perfected to the point of traditional power supplies in guitar amps.

There are reasons for this and it is because the mfg's there make their own class D amps, don't outsource to places that know how to do it right: cost containment, competition, narrow profit margin, pressure to stay in business. These Far Eastern designers do not have the knowledge to produce audiophile quality class D amps for big amps like guitar amps.

At the high voltages and current types found in guitar amps class D amplifiers face challenges if they are going to produce the same quality as a traditional power supply.

We will probably be suffering from inferior class D amp designs from companies that make Far Eastern amps for a long time, because the in house designers are not knowledgeable of the limitations of the class D amps in powerful guitar amps.

Cell phones and things like that are a different story completely from big guitar amps where a lot of power is needed and needs to be regulated and controlled and produced to function over a wide volume and gain range and maintain a quality sound within specific parameters in order to avoid unwanted nonmusical distortion across the spectrum both of frequency and volume.

It is a good article that explains something that we should be informed about so we can make the best purchases.

Class D amps have not been proven to work right in tube guitar amps, at a reasonable production cost.

[jim p]

It is up to any amplifier company to set the specifications of their product and test to verify that these specifications are met. If they are going to allow the offshore source to do all the design and specifications and the end product falls short then it is their own fault. Many products are designed here and built there, so there is no reason that a switching power supply in a tube amplifier should be failure prone except for poor design or quality. There is no magic in a high voltage low current switching supply working properly versus a high current low voltage supply as in your desktop computer. The computer supply is probably a higher wattage supply then the one that would be in a tube amp.
In regards to failure if the offshore manufacture under specifies the line transformer or filter caps used in their design it would also make it prone to failure, so a linear supply could fail from poor design and quality just as well as a switching supply.
As far as class D amplification here is the Wikipedia page http://en.wikipedia.org/wiki/Switching_amplifier I am not a fan of reproducing sound with a string of modulated pulses. I would rather waste some watts and stick with class A or class AB myself.

But check this amp out http://crownaudio.com/pdf/legacy/belchfire_datasheet.pdf

[Duffy]

According to the article, designing a class D guitar amplifier requires education and expertise, including an ability to understand how to control it properly in a guitar amp application so that the sound is of high quality at volume.

Far Eastern designers do not, according to the article, possess that expertise or possibly even education, in order to produce a high quality class D guitar amp.

I have noticed that a LOT of the new bass amps are featuring Class D power supplies with, in some cases, tube preamps. These bass amps are lighter. It will be interesting to see how they pan out.

I also noticed a class H guitar amplifier, which sounds like a really good power supply. Probably real expensive.

Also, have you seen any all tube amps made here that use class D amps? The only ones I know of were the discontinued Crate V series that I had which had a major blow out, irrepairable, supposedly because of the switching class D power supply. The Crate engineer told me that it was a bad design from the get go and that switching power supplies, although successfully used in ss amps have not yet proven to be effective in all tube amps, at least at affordable levels.

Your idea that they can be used with no problem may be correct, theoretically, but, to my knowledge, they have not been produced efficiently and effectively in all tube amps, and are less than equal to traditional power supplies in ss amps as well.

Class D amps are a cost cutting decision. Amp mfg's are very competetitive, as you can see. It is a struggle to stay in business and you have to make inexpensive competitetive amps to market to the largest segments of the target population; look at the Vox chromie VT amps, which seem to be good amps by the way. Almost every amp company has a modelling amp that directly competes with it. A lot of these amps are really cheaply built and as expensive as a more old school designed amp. The driving motivation is apparently kids and their parents that want to achieve instant gratification with a very affordable amp that produces a million sounds, without the expense of separate pedals, etc.

My Crate V50 sounded great, really great; but it had a switching power supply that proved to be the end of it, irrepairable and no spare switching power supplies. Also the poor design may have allowed the current surge to take out other components.

The entire V series was a problem. The pro's that worked on mine refused to work on my friend's V 100 head because it's design was extremely dangerous, no shielding or isolation of dangerous components, even a fire hazard and a high risk to the purchasing consumer.

I'm not sure how widely this info is known by V series owners.

A visit to a knowledgeable amp tech might relieve some apprehension or help you make an informed decision as to whether to keep the amp or not.

Apparently the V 50 was not as much of a threat to the user as the V 100 head.

The Class D power supply was only one bad idea in the amp's design. Or rather, I should say that the switching power supply was not designed appropriately for the application to which they put it. Probably because of the lack of expertise and education of the designers in the Far East as mentioned in the article I posted.

[jim p]

As I stated above there design can be done here so no reason for it to be wrong as far as any product sold. If Crate did not take due diligence and just bought something at a China trade show and sold it that is there lack of involvement that was responsible for problems.
As far as design the IC manufacture gives all the necessary information in there data sheets as here http://focus.ti.com/lit/ds/symlink/tas5630.pdf and I am sure they have application engineers world wide to help. Relative to audio reproduction Crown sells high watt amplifiers used in cinema sound reproduction systems that are all class D with switching power supplies http://www.crownaudio.com/gen_htm/press/pr230.htm

I don’t think I would use a class D amp for a guitar amp but it may work well for a bass amp. And there is no reason that a well designed switching supply could not be used as the power supply in a tube amplifier. As far as repair for someone used to linear supplies it would be like going from an old CRT TV to a flat screen the basic guts are very different.

Just to note that IRF application note is five years old and electronic design changes fast.

On replacing the power supply in a Crate V50 you could use a Hammond 372JX transformer. You would just need to use the 6.3 volt heater supply and positive and negative voltage doubler circuits to replace the +/- 17 volt supplies that came from the switching supply. Better yet maybe the EDCOR XPWR023 it has two 6.3 secondarys one could be used for the +/-17 volts the other the heater supply http://www.edcorusa.com/Products/ShowProduct.aspx?ID=597

[Duffy]

I agree with you Jim.

It is a design challenge and a knowledge/education problem.

Companies have done it using the right people, properly educated, designing the amps to audiophile standards.

The potential is there, but I would be cautious if buying an amp today with a switching power supply. Possibly I woundn't worry buying a bass amp, as you mentioned, but as far as guitar amps: once burned twice shy.

I just want to make sure everybody knows that these Class D amps are showing up and some guys already have V series Crates; and that they have switching power supplies that may be far from the best designs.

Class H amplifiers sound even more exciting and definitely show a lot of promise, but I believe they are very expensive and not found in many amps.

[jim p]

I have the schematic for the Crate V 50 power supply and by the drawing it was designed here signed by Denny (Drawn in title block). One problem with a supply like this is it has five output voltages and only one the +17 volt is regulated. What I think the failure mode may be is if there is a short or near short on the plate supply this would just cause the +17 volt supply to drop and the and the switcher would increase the pulse width to the primary dumping more watts into the transformer. So the transformer may fail or the mosfet driving it may overheat and fail. They should have found this out in bench testing of there prototypes or they did not test for it. Possibly if the transformer was properly designed it could maintain the failure mode until the fuse would blow. Then the offshore manufacture underspecified the transformer and it then will fail during an overload, but they should have tested what was being made there over here. Another solution would be an over current circuit in the plate supply using the same shunt regulator IC used to regulate the +17 volts a TL431 a high voltage PNP transistor a couple of 8 ohm resistors, one or two more resistors and maybe a diode and you could accurately limit the current out of the plate supply. The overcurent circuit would be connected to the reference pin of the TL431 shunt regulator controlling the +17 volts. So if high current is drawn the +17 volts would go into over voltage and shut down the switching supply.
The cost of the added parts would be less then a buck and you could advertise that your amplifier has a specially designed over current circuit unique in the industry. I may add the over current circuit to the Crate V50 I have as well as the Crate V33 head I have which is close to the same power supply.
They should have tested for a high current condition on the plate supply, power tubes often go soft or have a grid short causing high current if they did not it was there lack of foresight. A good chance with a bit more thought or some support circuitry there is nothing wrong with the basic design of the supply Crate used. Also if power factor correction will have to be met by tube amplifier manufactures in the future due to government regulation then a switching supply like this would be the solution.

[NWBasser]

My Genz Benz Shuttle 6.0 is a class D hybrid bass amp and sounds great. I'm completely thrilled with it. Apparently Genz spent a great deal of time on the engineering to make sure everything was worked out and they have an awesome reliability record with their SMPS bass amps.

However, this technology hasn't really caught on for guitar amps and I suspect there may be some good reasons for that. I may check with the Genz engineers for an explanation on this. They a super-cool guys and are always ready to share their extensive knowledge.

FWIW though, I do use my bass amp with my acoustic/electric and it sounds quite good. Similarly, I put my Les Paul into it and it sounded far better than I expected.

[Duffy]

Jim P. I wish I would have known you when I had the catastrophic power tube blow out that supposedly took out the switching power supply or visa versa.

The Pro techs I took it to in Harrisburg are the best around here. All they do is fix amps and guitars for all the major players around here for quite a hinterland and they have a good reputation from everyone I have talked to.

They had my V50 for about six months and tried various things including contacting Crate for solutions. Crate did not have a solution and replacement power supply boards were not stockpiled as replacement parts and they had no idea who made them, etc. Blamed the Chinesse. Blammed Ruby Tubes for a bad run. Blamed a bad bunch of capacitors. Never narrowed the problem down to a specific cause; but apparently there were plenty of failures according to the engineer I talked to in the tech depatrment of Loud Technologies, a real good guy. I got a V32 212 old style with Celestion Seventy/80's in it free as a good faith gesture for an amp I paid 164 dollars for with the discount coupon at MF.

The Crate engineer was excited when the guys at Full Custom Music, no afln., in Leymoyne, Pa., told me that they could build a switching powers supply and fix the problem. I told the engineer and he told me to tell the guys at FCM that he could make it very worth their while to fix a bunch of these amps for Crate.

Unfortunately, a month later the tech at Full Custom Music called me and said the amp was not repairable and that I would have to try to see what I could do with Crate customer service that had been so cooperative with me earlier but wanted to give the tech a chance to find a "fix".

If you have a fix for the Crate V 50 switching power supply failure, common I believe to the rest of the V series except the V5 which has a traditional power supply. I could call the tech svc engineer I talked to and tell him I know of someone who can fix the V series power supply failures. Or you can call him. They probably still are junking the amps and crediting back the sales price to the customers if they are even still under warranty.

Nonetheless, the Crate guy might want to know who he could refer customers to that are having the same problems I had.

That V50 had an awesome overdrive and great clean and I really loved that amp until that one day it went pop, flash and came to it's functional end. I should have gotten the amp from FCM and used it as a cabinet.

I doubt if you are interested in contacting Crate, but if you think you can fix these things he might have a bunch of customers he can send your way.

[jim p]

Looking at the schematic I can see what may be problem areas for the supply, but the designer should have the best idea of where things are going wrong. Having a supply with multiple output voltages and only one regulated always has drawbacks. From the sound of it Crate may have farmed out the design of the power supply so they would have no one in house that would be familiar with its possible faults. They may not have specified the design well enough so it may not be all the fault of the designer of the supply. Also it could just be poor quality from China they tend to substitute parts with what looks close and costs less. You see this with Aqua Dots where they used a different chemical so it turned into the date rape drug or the dog food, cat food and baby formula problems.
As far as myself I have a full time 9 to 5 job and do this for a hobby so really would not want to handle a large volume of repairs. I would figure Crate could have had a run of replacement supplies built to repair amps with maybe some modifications to prevent future problems. All the V series amps except the V5 used the same supply with just some options on the plate supply configuration.
So far the V50 I have has no problem and as one precaution I increased the screen grid resistor and lowered the fuse on the plate supply. I have a V33 head also that is OK but it hasn’t been used I awhile.