What amp isn't reliable?

[BassmanPaul]

Have you thought of this? Remove the existing fan and re-install it the other way round so that it is pulling air in through the heatsinks. Add another 120V AC fan mounted on the grille at the back of the chassis. This should be mounted so that it is pushing air out of the chassis. Re-install the original top plate (no holes). You need a constant path for the air to flow.

This will now suck cold air in through the heatsinks and into the chassis where it will in turn be blown out of the back of the amp, along with any heat from the tube and power transformer I bet your problems will disappear! Incidentaly there is at least an inch between the side panel and the rack case side in every SKB case I own.

 

[skidrawk]

it is a bit unfair to blame a manufacturer for the actions of a repair company which is not a part of the manufacturer, and whose 'relationship" to the manufacturer is a contractual agreement relative to repairs, only. I would be willing to bet that your disappearing SVT was accompanied by substantial unpaid bills owed to many manufacturers, and many other 'disappearing" units belonging to other customers.
I might add also, if the IRS closed the company down, you were NOT getting your unit back without the original bill of sale. The IRS siezes everything on the premises, and assumes it is all 'assets" of teh company unless you can prove it is yours. Another reason NOT to leave your gear at the gig......

I wasn't blaming Ampeg for the actions of the repair company. I'm blaming Ampeg for poor design and poor customer service regarding my broken amp that was supposed to be repaired under warranty through their authorized service company. I think I might actually have the sales receipt somewhere. I've already put this experience behind me but if anyone asks about customer service and reliability, I don't mind opening my chops. I put the blame of my loss of my amp on the repair company. I put the blame of not helping me find a solution with Ampeg. To be fair, when it came time to replace a horn in my SVT 410HE the Ampeg people were helpful getting me a replacement @ a fair price. I did the work myself. Would I buy Ampeg again? Maybe. Would I trust their warranty and their authorized services? Can you see why it would be hard for me to go through that again?

 

[The Golden Boy]

Have you thought of this? Remove the existing fan and re-install it the other way round so that it is pulling air in through the heatsinks. Add another 120V AC fan mounted on the grille at the back of the chassis. This should be mounted so that it is pushing air out of the chassis. Re-install the original top plate (no holes). You need a constant path for the air to flow.

This will now suck cold air in through the heatsinks and into the chassis where it will in turn be blown out of the back of the amp, along with any heat from the tube and power transformer I bet your problems will disappear! Incidentaly there is at least an inch between the side panel and the rack case side in every SKB case I own.

I've had two additional thoughts regarding auxilliary fans on the amp.

1. A fan at the rear to force cool air in.
   
2. A fan at the end of the heat sink to draw air through the heat sink in it's intended direction.

Forcing air in is going to introduce a lot of dust directly onto internal components. It also doesn't guarantee that air will go through the heat sinks.

The fan pulling air out of the amp is a much more viable option- the trick is finding a fan that fits, 24v DC and adding it to the existing fan circuit. The fan would be fighting the existing fan, so that might have to be removed. The advantage there is that all the air going through the heat sink will be pulled out of the chassis. I found the perfect sized fan, unfortunately it was a 12v fan.

I don't like the idea of reversing the existing fan, just from it's location inside the amp.

As far as the sides of the rack wall- check out the distance from the area where the handles are- it's intruding farther into the amp than the actual rack wall- and that's RIGHT where the exhaust grille is.

 

[Jazzman]

Excellent post! Thanks for that feedback. In your experience, what is the most reliable amp you have used?

Joe

Sorry for the delay...I missed your question. I had very good luck using an Ashdown ABM-RPM-1 preamp (the first version with blue paint) and a Carvin DCM-1500 power amp (the older 3-space version)...but from reading other posts, maybe I was just lucky. I also can't recall any catastrophic failures with an Ampeg SVT-CL (1996 model...TBD with my new 2007 model that has lead-free solder ).

 

[GreyBeard]

The only unreliable amp I ever owned was a Traynor yba3. It worked fine as long as I only worked on the weekend but started eating power tubes on the road.

 

[Jerrold Tiers]

I wasn't blaming Ampeg for the actions of the repair company. I'm blaming Ampeg for poor design and poor customer service regarding my broken amp that was supposed to be repaired under warranty through their authorized service company. I think I might actually have the sales receipt somewhere.

Would I trust their warranty and their authorized services? Can you see why it would be hard for me to go through that again?

If you had your sales receipt, and the unit was under warranty, you could have gotten warranty service through the factory service center in St Louis.

Poor design? Because it stopped working? OK, whatever. But that model is not known for any excess failures.

The service center is an extension of the company? Maybe.....although they are an independent contractor......... BUT,THE LIMIT OF CONTROL THE COMPANY HAS OVER THE SERVICE CENTER IS TO DE-AUTHORIZE THEM IF THEY MESS UP. Since the offending company seems to have gone defunct, that would not have been a very effective penalty, I suspect.
.
.
.

As far as the SWR.........

With the added info, it seems that there may indeed be a problem with the SWR design. There should have been vents by the transformer, for sure, and the air exit with no 'forced guidance" is an issue. I assumed that the heatsinks and top form a tunnel that guides the air from the fan. In that case, the air could have been guided right out the side if the sinks were closer to the side. Added 'guide pieces" can fix that, and may make the unit work well.

But, as far as the "passive circulation", and theoretical "preheating" of air, I have designed a number of PA and other amplifiers with exactly that same design overall. NONE of them had any cooling problems in production or use, and I have seen units that were 15+ years old and still in daily use. But, you have to handle the details.

The location of inlet vents is chosen to pull air over any parts needing cooling. I know you say "passively", but I can assure you that when a proper fan blows air out of the chassis (directly or thru a heatsink), the vacuum inside pulls air in VERY "actively". It is a pressure difference, whether the fan adds an extra pressure, or whether the pressure inside the chassis is reduced by blowing air out of it. Pressure difference induces flow thru openings.

In fact, the suction method allows very good control of airflow, and exceptionally good cooling. Apparently the SWR designer didn't appreciate that, and failed to handle the details that make it work so well.

The key is the air volume and the fact that the heatsinks get hotter than other things, and dissipate far more heat. With a lot of airflow, the change in temperature of air passing over tubes or transformer is small. The MAJOR change in temp occurs going thru the heatsink.

Another good feature is to pull air FROM the rack and blow out the front. That is my favorite design, and I have done several units that way. it keeps the rack cool, and effectively gets rid of the heat. The reverse flow, in the front and out the back, tends to 'cook" the rack, although if flow is fast enough it may blow quite a bit of the hot air right out and not collect as much in the rack.

While you'd think that back to front flow would just get hot air from other things in the rack, in actual fact, it pulls in enough air that it always gets cool air unless you really have an exceptionally bad situation.

However, on many bass amps, including Ampeg units such as SVT4PRO (which has side venting) there isn't room on front and back for vents of adequate size. Too many knobs on front, and too many jacks on back. So, side venting is required.

But, any side vented unit needs space for the air to leave. Either a side vent in the rack, or an open space inside the rack about equal to the height of the amp. Many racks can supply the open space, fewer have any provision for side venting.

 

[VtypeV4]

My Trace V4 (V8 looker) is questionable as to terms of reliability. Half of my posts are probably "the V4 has packed up again, help" Its got a habit of muching fuses! Unstable biasing which causes valves to glow very shortly before munching its HT fuse. Its been that hot at a gig once that i had to keep turinhg it to standby between songs to keep it going. I think the fault lies in the bias circuit design but its inconsistant, it doesn't do it for months then will do it twice in a week. I love it though, missing it a little too at this time, i like the hiwatt (which continued to function on three valves for an afternoon after a vacuum failure with no dramas whatsoever!) i've borrowed but it'll be good to get the V4 back too...

 

[Jerrold Tiers]

Quoting Jerrold:
"The transformer is pretty good power line protection and isolation by itself.... not much gets through."

I have to disagree with this statement. If you apply 120V AC to a transfomer and get say 100V on the secondary normally, when you apply a spike of 240V you will get a 200V spike on the secondary. This will lead to failures virtally every time.

Ah, but you assume some things..... that are not true.

1) You apparently assume that the theoretical 240V spike has a lot of power behind it.

Spikes don't have much power behind them in general. If they did, the puny little protector would be blown out of the chassis if it tried to protect.

2) You assume that the protector can actually be set for 240V....

For a unit accepting 120/240, that isn't true, the protector muust be set substantially ABOVE 240V.

3) Even if the spike were 240V, and the protector was set for 180V, that would still provide 150V out, by your assumptions, which is STILL going to cause a failure most of the time.

4) You completely neglect the filtering provided by the transformer. Fast spikes simply do not get through a 50Hz or 60Hz power transformer worth a dang. It filters them out.

5) Even if the spike DID get thru the transformer, it would have to charge the filter capacitors up. Since they store an amount of energy proportional to voltage squared, raising the voltage takes a lot of energy. The line spikes don't have that sort of energy.


So, the type of fast transient that a protector CAN handle is mostly filtered out by the transformer.

The part that gets through is filtered out by the rectifier and filter capacitors.

A 'spike" or "surge" that has sufficient power to get past the transformer and filter capacitors will have enough power to blow the "protector" to smithereens.

NO protector can protect against plugging into a wrong outlet, or a fault in the wiring which allows straight 240V onto a 120 line. The power line can supply at least around 3000 watts, enough to melt the protector in short order.

So I stand 100% behind my statement that the transformer is pretty good protection, and will protect against essentially anything the protector could protect against.

An SMPS might be another matter.... SOME of them are quite sensitive to spikes. Other types are very non-sensitive, and the required line filter does a good job of attenuating spikes as well.

 

[BassmanPaul]

I've had two additional thoughts regarding auxilliary fans on the amp.

1. A fan at the rear to force cool air in.
   
2. A fan at the end of the heat sink to draw air through the heat sink in it's intended direction.

Forcing air in is going to introduce a lot of dust directly onto internal components. It also doesn't guarantee that air will go through the heat sinks.

The fan pulling air out of the amp is a much more viable option- the trick is finding a fan that fits, 24v DC and adding it to the existing fan circuit. The fan would be fighting the existing fan, so that might have to be removed. The advantage there is that all the air going through the heat sink will be pulled out of the chassis. I found the perfect sized fan, unfortunately it was a 12v fan.

I don't like the idea of reversing the existing fan, just from it's location inside the amp.

As far as the sides of the rack wall- check out the distance from the area where the handles are- it's intruding farther into the amp than the actual rack wall- and that's RIGHT where the exhaust grille is.

Thing is that you can only force a certain amount of air into what is essentially a closed box. What we need here is air flow. Cool air in and hot air out. If the air inside the box (chassis) is already hot then it isn't going to cool the heat sinks all that much. You need cool air to allow for more cooling. Bringing cool air across the heatsinks and then venting it, via an auxilliary fan, out the back of the chassis is a much better idea than the opposite. Do not attach the fan to the existing circuitry, you just don't know how much extra power you can safely tap off. A lot of amp have variable speed fans and you don't want this if you are trying to cool the tube and the transformer. If you cannot find a 120V fan of the right size (they do exist) simply add a small transformer of the right capacity to operate the fan. Simple and you do have room.

 

[BassmanPaul]

Ah, but you assume some things..... that are not true.

1) You apparently assume that the theoretical 240V spike has a lot of power behind it.

Spikes don't have much power behind them in general. If they did, the puny little protector would be blown out of the chassis if it tried to protect.

2) You assume that the protector can actually be set for 240V....

For a unit accepting 120/240, that isn't true, the protector muust be set substantially ABOVE 240V.

3) Even if the spike were 240V, and the protector was set for 180V, that would still provide 150V out, by your assumptions, which is STILL going to cause a failure most of the time.

4) You completely neglect the filtering provided by the transformer. Fast spikes simply do not get through a 50Hz or 60Hz power transformer worth a dang. It filters them out.

5) Even if the spike DID get thru the transformer, it would have to charge the filter capacitors up. Since they store an amount of energy proportional to voltage squared, raising the voltage takes a lot of energy. The line spikes don't have that sort of energy.


So, the type of fast transient that a protector CAN handle is mostly filtered out by the transformer.

The part that gets through is filtered out by the rectifier and filter capacitors.

A 'spike" or "surge" that has sufficient power to get past the transformer and filter capacitors will have enough power to blow the "protector" to smithereens.

NO protector can protect against plugging into a wrong outlet, or a fault in the wiring which allows straight 240V onto a 120 line. The power line can supply at least around 3000 watts, enough to melt the protector in short order.

So I stand 100% behind my statement that the transformer is pretty good protection, and will protect against essentially anything the protector could protect against.

An SMPS might be another matter.... SOME of them are quite sensitive to spikes. Other types are very non-sensitive, and the required line filter does a good job of attenuating spikes as well.

Last thing I want to do is to start a slanging match with anyone but I assume nothing. I gave a simily to try to explain to people, who may not have my technical background, a complex subject. If what you say is true, then no amplifier could possibly be damaged by a lightning strike to a nearby power line. I have repaired far too many amps damaged in this way. A surge protector is capable of passing incredable currents untill the fuse or breaker pops. I have experimented by popping a 240V 15A line with one of these little marvels and it didn't look any different physically from when I started.
I am going to agree to disagree, you go forth protected by your transformer and I will stay happily protected and filtered by my Carvin AC120!

 

[The Golden Boy]

Thank you for discussing this with me Jerrold.

As far as the SWR.........

With the added info, it seems that there may indeed be a problem with the SWR design.

I don't think so- I think it was designed to work with the components it had been designed with. If you talk to older SM-900 owners- if they're cool with the "SWR sound," they're generally happy with the reliability of the amps- it's the newer ones. I've "heard" that there were two changes made with the amp since 1997. One involved a change in the transformer, and another just prior to the Fender buyout. Just what I've heard...

There should have been vents by the transformer, for sure, and the air exit with no 'forced guidance" is an issue. I assumed that the heatsinks and top form a tunnel that guides the air from the fan. In that case, the air could have been guided right out the side if the sinks were closer to the side. Added 'guide pieces" can fix that, and may make the unit work well.

I agree, and although I've played with the idea of another fan, "guide baffles" might be pretty handy.

But, as far as the "passive circulation", and theoretical "preheating" of air, I have designed a number of PA and other amplifiers with exactly that same design overall. NONE of them had any cooling problems in production or use, and I have seen units that were 15+ years old and still in daily use. But, you have to handle the details.

The location of inlet vents is chosen to pull air over any parts needing cooling. I know you say "passively", but I can assure you that when a proper fan blows air out of the chassis (directly or thru a heatsink), the vacuum inside pulls air in VERY "actively". It is a pressure difference, whether the fan adds an extra pressure, or whether the pressure inside the chassis is reduced by blowing air out of it. Pressure difference induces flow thru openings.

Here's another pic of the amp:

The air intake is just to the right of the blue cap mounted to the right side of the board on the right heat sink. It may be a matter of semantics with the use of the word "passively" but nothing is forcing air in or drawing air out of the amp. The fan only pushes air through the heat sink towards a grate on the side, not in or out of the amp.

In fact, the suction method allows very good control of airflow, and exceptionally good cooling. Apparently the SWR designer didn't appreciate that, and failed to handle the details that make it work so well.

Again, I've always heard that the SM-900 runs hot, but I don't hear of older ones having "thermal" issues.

The key is the air volume and the fact that the heatsinks get hotter than other things, and dissipate far more heat. With a lot of airflow, the change in temperature of air passing over tubes or transformer is small. The MAJOR change in temp occurs going thru the heatsink.

I completely agree with you- I don't know if the caps generate heat, I don't know if any other components generate any appreciable heat- however the glowing filaments in the tube do, the transformer does, but the overwhelming majority of the heat in the amp is produced from the heat sinks.

Another good feature is to pull air FROM the rack and blow out the front. That is my favorite design, and I have done several units that way. it keeps the rack cool, and effectively gets rid of the heat. The reverse flow, in the front and out the back, tends to 'cook" the rack, although if flow is fast enough it may blow quite a bit of the hot air right out and not collect as much in the rack.

While you'd think that back to front flow would just get hot air from other things in the rack, in actual fact, it pulls in enough air that it always gets cool air unless you really have an exceptionally bad situation.

It makes the most sense to cool from back to front. Hot air from the unit(s) being moved far from where the amp will get it again.

I would have totally given up on this amp years ago if it didn't sound so doggone good. I had a chance to trade this amp, problems and all, even up with a Mesa/Boogie Bass 400+ and it didn't do anything what this amp does- sound wise. I could have traded it even up with a Hartke 7000. Again, it was no contest. Both of those heads sound great, but the SM-900 sounds so good. I love my old Seymour heads, they're great sounding, the "stock" one is reliable, but neither sound as good as the SWR. While it makes all the sense in the world to sell the SWR and get something different, I'm hesitant to sell the amp and be stuck with an inferior amp. I hope that makes sense. I'm currently gigging with 3 different bands, reliability is a necessity.


Jerrold- thank you again for discussing this.

I have a 2 1.5 hour set outdoor gig on Saturday. Chances are those guys are going to want me to run 2 cabs- which is fine, and probably less of a load than 1 cab bridged.

Why would having the holes drilled in the top panel be bad? If hot air is exiting the chassis and cooler air is being blown through the heat sink, how is that bad?

I'm also playing around with the idea of covering the unused outlets and ports on the tuner and blowing the rack fan into the rack. Bad idea or not? I realize that it's going to introduce more dust into the rack and into the amp chassis, but it'll cool the unit, and allow cool air to be run through the heat sinks.

I'll try to post pics of the top cover and holes in the rack handle panel tomorrow.

 

[Jerrold Tiers]

Why would having the holes drilled in the top panel be bad? If hot air is exiting the chassis and cooler air is being blown through the heat sink, how is that bad?

It isn't necessarily bad. The issue is if the airflow is "designed" correctly to begin with, which it appears it is not, then extra holes may 'short circuit" the flow and leave part of the unit uncooled, such as the transformer.

As far as design, The major features that appear to be weak are the spacing from the exit vent in the chassis, which looks even larger than I thought in the last picture, and the lack of cooling for the transformer. The spacing from the exit certainly has the potential to have "internal re-circulation" which is a definite problem.

If you had transformer cutout, you'd know it, since it might take anywhere from 10 to 30 minutes for it to come back on. Transformers take a while to cool down, and while cut out, power to fans is usually off (except for AC fans).

Overheating of heatsinks usually takes from a few seconds to maybe a minute or possibly two, for recovery. The fan is generally still working, and acting to cool the heatsink down. In both types, the "recovery" temperature is from 5 to 10 degrees C lower than the 'cutout" temperature, to prevent "dithering".

Small changes have sometimes large unforseen effects. You mentioned a change to the transformer, and another unknown change. If the transformer voltage was slightly increased for more power, heating would be greater, and might be enough to make an "on the edge" design into a problem.

If the heatsink were moved back slightly to allow easier assembly, that could increase recirculation and heating.

Or, and this is possible, your unit could be biased too hot. That might make it start out hotter, and thus heat more. You would essentially be carrying around your own "instant hot day, just add power".

 

[Jerrold Tiers]

If what you say is true, then no amplifier could possibly be damaged by a lightning strike to a nearby power line. I have repaired far too many amps damaged in this way. A surge protector is capable of passing incredable currents untill the fuse or breaker pops. I have experimented by popping a 240V 15A line with one of these little marvels and it didn't look any different physically from when I started.
I am going to agree to disagree, you go forth protected by your transformer and I will stay happily protected and filtered by my Carvin AC120!

Lightning is another issue altogether. it can actually damage a unit that is not plugged in, although that is more rare. Lightning-damaged units, when really zapped, have weird problems, sections of wire vaporized, and the adjacent ones OK, parts literally exploded, etc.

I agree that the protectors can be good. With a proper fuse, they can be effective.

However, they are not a cure-all, largely due to the fact that they typically will let through a spike of hundreds of volts over the mains voltage. It is inherent in their ratings, which are VERY sloppy as to suppression voltage.

A proper application of transient suppressors is more than soldering in a couple of parts. At least half the "protected" outlet strips sold today will let through transients of over 500V. So much for "protection".

Aside from lightning, for which all bets are off, the transformer etc, DOES hold up against the vast majority of "normal" transients.

I would NOT think of a unit less positively if it did not have a "suppressor", nor would I consider a unit "better" if it DOES have one.

You can always buy a GOOD plug-in protector if you feel the need.

 

[el_Kabong]

I need to not sound like a broken record about SWR stuff... But it still chaps my bottom.

.... The amp has regularly overheated and gone into thermal shutdown. ....

TGB those pictures remind me of a trace elliot head I had. It also had one fan that removed hot air. I lived in the tropics and it would shut down all the time. I installed a second fan to push cool air in and never had a problem after that. If I owned your swr I would take that fan you have in the back of the rack and install it onto the back of the amp. I'd just zip tie it to the outside of the amp, onto the rear vents, making sure it pushed cool air in. Easy to try and I'll bet you a kipper it does the trick.

 

[X Wolf]

Old Vox Superbeatles, the one I had back in the Sixties broke weekly. This was the most un-reliable amp I've ever owned.

By the way, I have owned Ampeg amps since 1970 and my SVT with 2- V4B cabs and my B15-S Portaflex were the most reliable amps I've ever owned. Also my current V4-BH has been just fine, however my Ampeg SBT solid state amp was not reliable. Just my 2 cents.

George

 

[waffle puzzle]

I tend to agree with most, that many problems of average or great equipment is user oriented, while also agreeing with others that sometimes you get a dud, or a bad production run. Maybe the workers got inferior parts that particular week, therefore creating 100 inferior amps. Maybe Joe- assembly-line worker had a hangover....etc.....

BUT....how many times have you seen a band and either the bassist's clipping light was solid-on or blinking a whole lot, AND/OR the bassist was using an INSTRUMENT CABLE to hook up his speaker cabinet ?

ALSO....how many times have you seen a band loading/unloading equipment at a show where the gear was "being slung around". Gear has to be treated with care, even if it's rack mounted.

I'm sure the above mentioned has at least something to do with gear working/not working properly.

 

[DMX]

My Trace V4 (V8 looker) is questionable as to terms of reliability. Half of my posts are probably "the V4 has packed up again, help" Its got a habit of muching fuses! Unstable biasing which causes valves to glow very shortly before munching its HT fuse. Its been that hot at a gig once that i had to keep turinhg it to standby between songs to keep it going. I think the fault lies in the bias circuit design but its inconsistant, it doesn't do it for months then will do it twice in a week. I love it though, missing it a little too at this time, i like the hiwatt (which continued to function on three valves for an afternoon after a vacuum failure with no dramas whatsoever!) i've borrowed but it'll be good to get the V4 back too...

Never had a problem with mine, and it's been bumped around in the back of a van a fair bit on tour. Blew on output valve fuse once but it finished the gig on 2 valves and I didn't even notice. Currently has a bit of tranformer hum but is operating fine. I love mine too, but wouldn't say no to a Hiwatt!

 

[el_Kabong]

I had problems with the compressor chip in a marshall dynamic bass amp causing the volume to drop erratically. A trace elliot head that would shut down due to heat. An svt3 pro that had the bias/distortion issue that no one in my neck of the woods seemed to be able to fix properly. An svt-cl that had recurring issues with the output stage (burned screen resistors etc). My epifani quest II preamp apparently has a design fault in the effects loop which causes it to tick. Oh and if my wt800b put out the claimed 1100w bridged then I'm a wombat. I'm afraid that as a general rule I don't have a high regard for the design/quality of musical instrument amps. My pro sound gear, even behringer stuff, has been much more reliable.

 

[greenboy]

Search will bring up at least a couple more detailed posts by amp engineers why the typical rack-mount surge protector/power conditioner is not needed for amps (though it's useful for many effects and DSP-driven units) - and in some cases may actually be a bad thing.

I use a non-rack surge protector screwed into the back of the rack that's got just as good of specs, for dimes on the dollar. My power amp doesn't plug into it, but everything else I use does.

 

[Jerrold Tiers]

Search will bring up at least a couple more detailed posts by amp engineers why the typical rack-mount surge protector/power conditioner is not needed for amps (though it's useful for many effects and DSP-driven units) - and in some cases may actually be a bad thing.

And I may have written one of those posts.... I'm not against them, I am against considering them an essential item, something which dramatically enhances reliability. That's just baloney.