What amp isn't reliable?

[The Golden Boy]

Every thing you are suggesting here are band-aid solutions that will never cure your overheating problem. Yes, in a perfect world you would not have had to go through any of this, however this is not a perfect world. You are stuck with a good unit that is crippled by a badly designed cooling system. Trying to get this system to work by doing what you are continuing to describe is never going to work in a million years. You have to redo said cooling system (surgery) to cure what is ailing it.

I have tried here to give you the benefit of heading on for fifty years of building, designing, modifying and repairing amplifiers both tube and solid state. I can SEE what your problem is, as can many others on this site, but I seem to be failing to pass that information on to you in such a way that would make an impression on you. For that I am truly sorry and it is exasperating me. If I could get my hands on your amplifier, this problem would be rectified to your satisfaction within about 30 minutes. You can try the cure that I have already suggested, it is very easy to do, and undo for that matter if I am talking through my rear end, or you can carry on drilling useless holes to your hearts content.

Good luck my friend...
Paul

Paul,

Seriously- thank you very much for sharing your insight, advice and input. I don't mean to exasperate, frustrate, or slight or insult you in any way. And I definitely do not wish to have my action or inaction convince you to not post the benefits of your experience and knowledge. If I don't heed your advice, there are other people that may be having similar problems reading what you have posted, and it may strike a chord with them.

 

[Jerrold Tiers]

That would help. The way you have it now doesn't help cool the amp much.

Keep in mind that the air flow on the high pressure side of a fan--that is, the air pushed by it--is directional. The air flow on the low-pressure side, though, is diffuse and non-directional; so unless it is ducted to the region of hot air you want to remove, it's much less effective at ventilating a specific space.

I disagree, if I understand the drift of the post, and have done a number of successful designs which prove the point.

The first part, about directionality, is reasonably true, although the fan actually creates a "cone" of airflow if the air is not confined in some sort of duct, such as the heatsinks in that unit.

Even then, the circular motion of the airflow (due to spinning fan) will cause some of the heatsink fins to get a lot of air, and others to get a bunch less, in a design such as the one shown.

However, the airflow before the fan, on the "suction" side is very controllable. In fact it is MORE controllable than the airflow on the outlet side aside from outlet ducting.

You simply put holes in the chassis wherever you want airflow. That creates the same sort of local directional airflow that would exist with a fan. You can let it into a duct, or you can have it blow over components that need cooling, etc. You have complete control over airflow.

The key fact here that is being missed is that airflow happens because of a pressure difference. There may be a pressure difference because a fan creates a high pressure area at it's outlet. OR there may be a pressure difference because a fan REMOVES air from an enclosed area. Either way there is flow induced from higher to lower pressure areas.

Getting out of the theoretical and to the practical, The SWR basic plan is a very good one. I have used the same plan in a number of products which have performed very well.

However, I ALWAYS made sure that air which exited the heatsinks ALSO exited the chassis. That is a basic point that is a fault with the SWR, due to the (edit to insert missing text) large gap to the chassis side at the end of the heatsink.

AND, I always made sure that the INCOMING air was directed to cool other items in the chassis such as transformer, power supply, etc. That is another point that was missed by the SWR designer. The incoming air through the large back vent bypasses all the other stuff in the chassis, except insofar as it may swirl around randomly inside.

It is the lack of attention to detail that is the problem, NOT the basic plan of blowing air out through the heatsinks.

An attempt to reverse the fan to pull air IN through the heatsinks might give an improvement of one sort, but at the cost of having hot air actually heating up other components that are now at least somewhat cooled.

Instead, I would add small baffles of insulating material to ensure that all the hot air leaves the chassis. That will make a significant improvement, especially if the rack is modified to allow some airflow away from the vent.

After that, it might not be necessary to add or move any holes in teh chassis, unless the transformer proves to be an issue with overheating and causing shutdowns. if it does, some holes in the back can be closed up and others added to provide airflow over the transformer.

Don't worry about pre-heating the air. If the fan is sufficient as to airflow now (we don't know that, BTW) it will not be a problem, the air won't be pre-heated enough to matter.

While a "screen" top, which is about what that "vegetable drainer" top is, may be better than teh original plan, if the airflow is improved, the "perforated top" will be worse than a properly designed airflow.

All the above is assuming the fan that is there will actually move enough air. It is possible that IT is poorly selected, and isn't doing the job. I would expect that a fan moving about 30 to 40 cubic feet per minute would be needed for good cooling, but that is based on some 'wild guesses" about the heatsink etc. It could be off by 30% or more.

 

[Chazinroch]

I have a background in reliability engineering. Usually something that is defective will die out quite quickly (called infant mortality in RE parlance). There is something called a bathtub curve (think of an old steel bath tub cut in half an look at the profile). Failure rate on the vertical axis and time on the horizontal axis. Most failures (manufacturing defects or poorly made goods) occur in the beginning of its lifecycle, and if the amp survives, the failure rate drops with time. As it reaches its useful life, or in the case of computers e.g., planned obsolescence, the failure rate starts to increase. This is why I never buy extended warranties. They are a big rip . I would suggest that bass amps follow a similar life cycle. That said, amps take a lot of abuse, heat, ohm mismatch, transportation, and don't forget sitting on top of a vibrating speaker cabinet show after show, or the occasional beer bath etc.

I do believe you get what you pay for and pay close attention to the warranty if you are buying new. Check of the how and where to get it serviced. And treat it well. -Oh and play the heck out of it when you first get it to shake out any problems while it is still under warranty.

 

[BWB]

I do believe you get what you pay for and pay close attention to the warranty if you are buying new. Check of the how and where to get it serviced. And treat it well. -Oh and play the heck out of when you first get it to shake out any problems while it is still under warranty.

Amen to that -- and Carvin owners, beware. They don't release schematics for their gear, meaning you have to not only pay to have them look at it for exorbitant shop rates, you get to pay round trip shipping as well rather than having your well-qualified local amp tech look at it. That's a non-starter, living on the east coast.

I've got a good local amp tech -- and you can imagine my shock when I found out I couldn't have him repair a Carvin amplifier for me for lack of a schematic. I have bought my final piece of Carvin equipment -- and that decision is not based on reliability. I was not angry that the amp needed service. I was extremely ticked when told I would have to pay them $95/hr (double the going rate here) plus $75-$80 for round trip shipping to have them look at it.

All electronic equipment can potentially need repair, just like your car. But audio design is not exactly rocket science and not releasing schematics for repair purposes is ridiculous.

 

[The Golden Boy]

While a "screen" top, which is about what that "vegetable drainer" top is, may be better than teh original plan, if the airflow is improved, the "perforated top" will be worse than a properly designed airflow.

All the above is assuming the fan that is there will actually move enough air. It is possible that IT is poorly selected, and isn't doing the job. I would expect that a fan moving about 30 to 40 cubic feet per minute would be needed for good cooling, but that is based on some 'wild guesses" about the heatsink etc. It could be off by 30% or more.

I found this picture- I don't have one of the older heads, but note the grille on top, and the apparent lack of an exhaust grille on the left side.

The new-er amp does not have a grille on the top and I don't know how the interior of this amp is arranged.

The fan in my amp is on- after the first few overheating incidents the first tech I took it to did something to give the fan a 2 speed thing- low and full. Normally the fan does not engage until the amp reaches a given temp. Without the rack fan on, and after running the amp around stage volume with 4ohms bridged (at operating temperature)- you could feel the hot air 6" away from the holes drilled in the rack. BECAUSE OF THAT, I'm putting much more stock in the air not being able to clear the chassis because of the rack wall.

Although it's said the SKB racks fit snugly- they're not uncommon, and I'd imagine the MOST common of racks used for musician's gear. Any manufacturer not designing a rack mountable unit without keeping in mind the confines of an SKB rack isn't thinking properly.

Am I correct in my assumption that running a 4 ohm cab on each side of the "stereo" is less of a load on the amp as 1 4 ohm cab in bridged mode?

 

[nickelseye]

Amen to that -- and Carvin owners, beware. They don't release schematics for their gear, meaning you have to not only pay to have them look at it for exorbitant shop rates, you get to pay round trip shipping as well rather than having your well-qualified local amp tech look at it. That's a non-starter, living on the east coast.

I've got a good local amp tech -- and you can imagine my shock when I found out I couldn't have him repair a Carvin amplifier for me for lack of a schematic. I have bought my final piece of Carvin equipment -- and that decision is not based on reliability. I was not angry that the amp needed service. I was extremely ticked when told I would have to pay them $95/hr (double the going rate here) plus $75-$80 for round trip shipping to have them look at it.

All electronic equipment can potentially need repair, just like your car. But audio design is not exactly rocket science and not releasing schematics for repair purposes is ridiculous.

This isn't always the case. My brother has a Carvin Legacy head which needed repair. He called Carvin, was given the option to return it for repair or have a local tech service it. He chose the local tech and Carvin faxed the schematics.

 

[Bob Lee (QSC)]

I disagree, if I understand the drift of the post, and have done a number of successful designs which prove the point.

The first part, about directionality, is reasonably true, although the fan actually creates a "cone" of airflow if the air is not confined in some sort of duct, such as the heatsinks in that unit.

Even then, the circular motion of the airflow (due to spinning fan) will cause some of the heatsink fins to get a lot of air, and others to get a bunch less, in a design such as the one shown.

However, the airflow before the fan, on the "suction" side is very controllable. In fact it is MORE controllable than the airflow on the outlet side aside from outlet ducting.

You simply put holes in the chassis wherever you want airflow. That creates the same sort of local directional airflow that would exist with a fan. You can let it into a duct, or you can have it blow over components that need cooling, etc. You have complete control over airflow.

The key fact here that is being missed is that airflow happens because of a pressure difference. There may be a pressure difference because a fan creates a high pressure area at it's outlet. OR there may be a pressure difference because a fan REMOVES air from an enclosed area. Either way there is flow induced from higher to lower pressure areas.

Getting out of the theoretical and to the practical, The SWR basic plan is a very good one. I have used the same plan in a number of products which have performed very well.

However, I ALWAYS made sure that air which exited the heatsinks ALSO exited the chassis. That is a basic point that is a fault with the SWR, due to the (edit to insert missing text) large gap to the chassis side at the end of the heatsink.

AND, I always made sure that the INCOMING air was directed to cool other items in the chassis such as transformer, power supply, etc. That is another point that was missed by the SWR designer. The incoming air through the large back vent bypasses all the other stuff in the chassis, except insofar as it may swirl around randomly inside.

It is the lack of attention to detail that is the problem, NOT the basic plan of blowing air out through the heatsinks.

An attempt to reverse the fan to pull air IN through the heatsinks might give an improvement of one sort, but at the cost of having hot air actually heating up other components that are now at least somewhat cooled.

Instead, I would add small baffles of insulating material to ensure that all the hot air leaves the chassis. That will make a significant improvement, especially if the rack is modified to allow some airflow away from the vent.

After that, it might not be necessary to add or move any holes in teh chassis, unless the transformer proves to be an issue with overheating and causing shutdowns. if it does, some holes in the back can be closed up and others added to provide airflow over the transformer.

Don't worry about pre-heating the air. If the fan is sufficient as to airflow now (we don't know that, BTW) it will not be a problem, the air won't be pre-heated enough to matter.

While a "screen" top, which is about what that "vegetable drainer" top is, may be better than teh original plan, if the airflow is improved, the "perforated top" will be worse than a properly designed airflow.

All the above is assuming the fan that is there will actually move enough air. It is possible that IT is poorly selected, and isn't doing the job. I would expect that a fan moving about 30 to 40 cubic feet per minute would be needed for good cooling, but that is based on some 'wild guesses" about the heatsink etc. It could be off by 30% or more.

Sure, you can direct air flow in the manner you have described, but it requires that the high and low pressure sides of the fan be baffled from each other, as with a duct. The fan mounted in the rack has no baffling between the high and low pressure sides. Such a fan is effective on the high pressure side, but much less so on the low pressure side. Picture a standing floor fan in the middle of a room. You can stand in the air flow on the high pressure side well away from the fan and still feel its cooling effect, but you have to stand very close to it on the low pressure side to feel anything. The quantity of air flow is the same on both sides, but the pattern isn't. If you wanted to displace hot air in a particular location in the room with this fan, pushing air into that space would be much more effective than sucking air from it. That's the benefit of positive pressure; because it's directional, it's more easily controllable and focusable, more so than low pressure.

There are suitable applications for negative pressure, too. Imagine an attic fan in a house, which sucks air through the ceiling into the attic, where it exits through vents. This draws air into the house through open windows and doors. This is diffuse, non-directional air flow that will cool much of the house, but because the air flow is not directional it wouldn't necessarily, for example, cool the floor directly under and on axis with the fan more effectively than some other parts of the house. The air flow is controllable if you control the air intake points; opening a screen door in one part of the house may decrease the cooling in a room in another part (similar to adding random openings in a chassis). The air coming in a window or other opening does not necessarily travel in a straight line after entering, but flows toward the point of low pressure. Thus, being in line with a window does not ensure that one will be in the air flow, unlike the situation of having a fan actually in the window blowing in--i.e., positive pressure.

Like the fan mounted on the rack, the fan inside the amp also suffers from a lack of baffling between high and low pressure sides, but to a lesser extent. The fan is effective for the heat sinks themselves, as it is tightly coupled to the tunnel and pushes air through it. However, since the fan's intake and the heat sink exhaust are essentially in the same chamber, the only pressure differential between the inside of the amp and the outside comes from the air pushed out of the heat sinks that is directional enough to continue through to the vent slots in the chassis. I agree that if that space were closed or ducted, there would be better control of the pressure (and therefore, the air flow). That could be used to better induce air flow over the transformer, reservoir caps, and other components that need cooling but aren't mounted to the heat sink.

 

[The Golden Boy]

BTW- I did reverse the fan on the rack- however I haven't had a chance to really run the rig. I placed tape over the unused jacks and plugs on the power supply and tuner to cut down on dust in the units directly in the fan's path.

 

[KJung]

Am I correct in my assumption that running a 4 ohm cab on each side of the "stereo" is less of a load on the amp as 1 4 ohm cab in bridged mode?

Correct... bridge mode into a 4ohm cab is the equivalent of running each side of the amp at 2ohms. With the 900, this is also equivalent to turning a gas BBQ grill on full and closing the lid

 

[FortunaBass]

I'd never buy Eden. The moderator Catphish on Harmony Central had a huge run in with Eden and it was a huge pain in the ass stretching a long period of time.

Yo.

I've heard great things about eden amps. A friend of mine has had his serviced a few times in three years and they did a great job in good time and threw in some extras like extra tubes and fuses that he didn't pay for.

 

[JerryNovak]

The problem with any amp failure is that it is a sample of one. You might be the one failure in 100,000 for a great piece of equipment. To really see the reliablility of any piece of gear, you need a large sample size. You need to look at many to tell how robust they are overall. I had a very well built amp fail within a week of purchase. I also know of two Behringer units that have never had a problem. It is all statistics.

 

[KJung]

The problem with any amp failure is that it is a sample of one. You might be the one failure in 100,000 for a great piece of equipment. To really see the reliablility of any piece of gear, you need a large sample size. You need to look at many to tell how robust they are overall. I had a very well built amp fail within a week of purchase. I also know of two Behringer units that have never had a problem. It is all statistics.

This is a topic near and dear to my heart, since I am an applied statistician dealing with new product development and customer satisfaction in my 'day job'.

While you are correct about the only way to get an accurate read on the absolute level of a product's failure rate is with a relatively large sample of users of that product, sites like this are VERY predictive of higher than typical failure rates of specific products.

This site, made up of players highly involved in the bass gear category, serves as a very good 'early warning system' in uncovering products with failure rates higher than normal. This is similar to product consumer complaint call in 800 phone numbers. When a company starts getting a lot of calls, that is an indication of a problem. It's impossible to say that 'x%' of the products are failing based on these data, but it's a pretty widely used and relatively accurate 'warning signal'.

On this site, multiple problem threads with a moderate number of posters indicating similar problems, and/or a large number of threads/posts about either good or bad customer repair service (products that don't fail don't need customer service!) are a good indication of products you might want to avoid.

The 5 or 6 products that exhibited the above 'symptoms' on this site since I've been a member were later found to really have some problems.

 

[Jerrold Tiers]

1)

Bob, it looks like we agree...... I thought you referred to the INSIDE fan and turnignit around,, NOT the outside fan. The OUTSIDE one could benefit from being turned around.

2)

Amp failures, samples, etc.... The history of EVERY problem with a unit that I can recall started with ONE customer or tester having a problem. Sometimes a hazy and ill-defined problem, but something that wasn't right.

it is ALL TOO EASY to assume that the simple-sounding problem is really a user error, or something related to some specific condition that you think is rare and unlikely to repeat.

Only later do you realize what the real problem is, and can clearly see that it is NOT rare, NOT unlikely to repeat, and in fact is a 'real issue" that needs to be dealt with.

Don't dismiss reports of problems from "unconfirmed internet sources"...................... And don't ask me how I know this ("damhikt")......

 

[BassmanPaul]

Amen to that -- and Carvin owners, beware. They don't release schematics for their gear, meaning you have to not only pay to have them look at it for exorbitant shop rates, you get to pay round trip shipping as well rather than having your well-qualified local amp tech look at it. That's a non-starter, living on the east coast.

Well that statement is a load of bull for a start. Every time I have asked Carvin for the schematic for a piece of my gear it has arrived in short order. Either by email or snailmail. Perhaps you didn't ask them nicely enough.
Paul

 

[The Golden Boy]

Just wanted to say I used this head bridged into my 4x10 at an outdoor gig for 4 hours on Saturday. It worked awesomely.

I drilled the 4 rows of holes into the rack and reversed the rack mounted fan, so the air is being blown directly into the rack. I kept the "vegetable drainer" top on as well.

As ususal, I had to run the volume a little louder than ususal, being on an outdoor stage. We did 2 hours and a break and 2 hours, the handles were barely warm at halftime. After the second set I checked again, even the top and the chassis were vaguely warm- nothing like last 2 hour gig where the amp must've been right on the verge of thermal- it was really hot. But this time- twice as long- and probably a little louder, the amp was not just noticably it was at what I would consider a completely normal operating temperature.

 

[Bob Lee (QSC)]

1)

Bob, it looks like we agree...... I thought you referred to the INSIDE fan and turnignit around,, NOT the outside fan. The OUTSIDE one could benefit from being turned around.

Right, I can see that would confuse what I was saying! Sorry I wasn't clearer.