Ampeg SVT4-Pro Problems

[Enzo]

I still think getting lost here is that while the power amps may be capable of full output or close enough to it, the preamp signal needs to be able to drive it there. So a power amp test is not worth a lot out of context of the whole amp. This really doesn;t sound like a power amp issue to me. I could be wrong.

[doombilly]

yes

I have thought it was a pre-amp problem from the start. I have a date with someone who is going to let me bring the amp head and both cabs to check out the entire rig. The "authorized" person I brought this to some time back seemed dis-organized at best and flakey at the worst. The owner of the shop he does repairs for had to take him aside for fixing something that wasn't broke and ignoring what he was paid to repair on another customer's equipment. I am though talking to Loud or Ampeg. I think I have found someone that can give it a thorough going over. Hopefully this will all be resolved in early March.

Thanks all,
Eric

[doombilly]

just dropped her off at the shop.

This guy has fixed many of these. Claims it is fairly common that the ckt board soldering is just shite. Generally after he re-solders them they are bullet proof. And this seems highly likely as the damned thing will work fine for a while and then not work as well. If that's the case (poor soldering on ckt boards, jumpers etc...) then at least it will be fixed and it IS a great amp when it works. So that is good. On the other hand, I have to say I REALLY don't want to ever buy a Loud Technologies product again. I'd expect this from Behringer or some cost point product. This was a $1500 amp (new). It was under warranty and the manufacturer just made up excuses. They in no way stand behind their products and have to know they are just not hitting on a lot. I brought the entire rig to the shop to get him to check every component. This is the third shop I've brought it to. The 1st was an certified Ampeg repairman. I will let y'all know how it turns out. Stay tuned.

[Bassboy49]

Novice Input

Thought I'd put my 2 cents in. I owned an SVT 4 Pro for about 8 years, loved it, sold it, might have made a mistake there. Got a 5 Pro now, love it, keeping it. Now, with your cab resistance (ohms) mismatched, the amp is working twice as hard as it normally would with matched cabs. When I used the 4 Pro with cabs of different resistance, I would use the diagram for BiAmping a full range cab and a low range cab. Try setting it up that way...two patch cables, one for the Amp B to the high side and one for the Amp A to the low side. You may have to make adjustments to your frequency and level controls on the front right hand side to get the right mix on the cabs. Don't forget to take it out of Mono Bridged mode. Good luck, nice amp.

[doombilly]

actually...

we tried it bi-amped and did not get that good of a sound. I have to wonder if the differing impedance is not either a poor measure or a poor metering. The 1x15 is listed as 8 ohms as is the 4x10. We are currently running it dual mono, full range not bridged mono. I will let you know when this guy takes a look at all the components what he finds. Thanks.

[pacAir]

Check the configuration of the Speakon Connectors!

Since the amp channels develop power, I would check your Speakon cables for proper wiring. These things can be wired and connected in a variety of ways that can bite you in interesting ways if you are not careful.

The same connector can be wired Mono single channel, Stereo two channel or Mono Bridged and within each of the wiring schemes it is possible to get phase reversals if the connector is not wired properly.

Didn't the SVT Pro 4 come with a special Mono Bridge Speakon cable? Are you actually using this cable along with a standard cable? If so, this might be part of your problem.

You will only get proper output if the connections are correct. Can you bypass the Speakon connections and use 1/4" speaker cables to test the theory?

Steve

[MarkusBass]

Eric,

First of all - congratulations on your wife/bassist - you are a lucky guy .
It seems that you have problems with so called "authorized" service. I play bass guitar but since I know electronics, I also fix amps. Ampegs are my favorite (mainly due to very good sound). What you write below looks like poor marketing of this guy (and as excuses for not being professional):

This guy has fixed many of these. Claims it is fairly common that the ckt board soldering is just shite.

I'm not an authorized Ampeg service but I fixed many of them (not because they fail so frequently - in most cases the failures were caused by inproper use - shorted speaker cable, etc.), they are just very popular in the area where I live. And I cannot confirm the poor quality of soldering.

Generally after he re-solders them they are bullet proof. And this seems highly likely as the damned thing will work fine for a while and then not work as well.

I never start fixing an amp from re-soldering it. First you need to know the reason for the failure and only then you can start resoldering. But you do not resolder everything because in this case you actually do not know the reason for the failure (and it can happen again at any time in the future). And if you read carefully the statements above, you will find them not logical. Either the amp is bullet proof, or they do not work. From my experience the amps are bullet proof and they sound great.
You say that you do not have any equipment to test the amp. But I think that you can still test it in order to find out the reasons for the problem you have. First, you can plug an external preamp into Power Amp Input jack and check whether the problem is related to the preamp or to the power amp. You could also ask some other bassist who plays differently (e.g. slap) about his opinion about the amp.

...
I have to say I REALLY don't want to ever buy a Loud Technologies product again. I'd expect this from Behringer or some cost point product. This was a $1500 amp (new). It was under warranty and the manufacturer just made up excuses.
...
This is the third shop I've brought it to. The 1st was an certified Ampeg repairman.

This again looks like a business problem related to poor quality of service. It shows how important is high level of service for the image of a company.
It looks like the problem is not that difficult to be solved. The real problem is to find someone who can do it. I wish I could help you but I'm to far to do it.
Maybe you could ask Enzo for help - I don't know how far from you he lives.

Mark

[Euthymia]

On the other hand, I have to say I REALLY don't want to ever buy a Loud Technologies product again. I'd expect this from Behringer or some cost point product. This was a $1500 amp (new). It was under warranty and the manufacturer just made up excuses. They in no way stand behind their products and have to know they are just not hitting on a lot. I brought the entire rig to the shop to get him to check every component. This is the third shop I've brought it to. The 1st was an certified Ampeg repairman. I will let y'all know how it turns out. Stay tuned.

Although I will take in and repair just about any amp, tube or solid state, that is made to amplify a musical instrument, solid state Ampegs and Crates over 100W shall not pass my door.

SLM were a pain in the ass to deal with when they owned the brands, and things only seemed to get worse when Loud took over (I say "seemed" because by that time I had banished them from my bench).

I wish MarkusBass were in my area so I could send them to him!

Eric's wife's amp's problem does sound to me like a cracked solder joint, possibly on one of the 12AX7 sockets. The act of pushing new tubes down into the sockets flexes the board enough to "fix" the bad joint for a while.

What I do in such a situation is pull the PCB in question, put it under my big magnifier lamp, and look for popped joints. Judicious chopsticking with the lid off can find the problem joint as well.

[Enzo]

Probably about 800 miles. And in kilometers it is even farther.

[MarkusBass]

Although I will take in and repair just about any amp, tube or solid state, that is made to amplify a musical instrument, solid state Ampegs and Crates over 100W shall not pass my door.

You didn't tell what is the reason. Is it the complexity of DC coupled high power amps? I had the same problem when I started fixing AMPEGs. If you are not careful enough, you will see a "magical smoke" as some manufacturer writes in their manuals. So first I simulated some AMPEG power amp in SPICE (to understand how it works), and then some good soul from the States told me how to power up the amp without output MOSFETs and verify that each stage of the amp works correctly. So the first step is very difficult. But if you pass this step, the amps are like any other amp. The only problem that I sometime have is how to get a part (e.g. potentiometer) that is specific to a given amp and it is hard to purchase in a shop. But luckily I never had a situation that I couldn't repair an amp.

I wish MarkusBass were in my area so I could send them to him!

Me too, thanks. Since I also play bass I always test (on stage) the equipment I fix. And I can tell you that AMPEGs are among the best sounding amps (especially SVT 3 and 4Pro but we also cannot forget CL).

Mark

[doombilly]

illicitizen still frowning at Loud Technologies

all of the cables, speakers and amp head have all been checked.
Our guy who has fixed many of these could not find anything. He did not pull all of the ckt boards to check all of the solder joints. One other thing I've noticed is from the very beginning with the amp is no sound guy or me could ever get a decent direct sound from the transformer balanced line/or xlr outputs on the back either live or trying to record. It is always the same thing. Bzzzzzzzzzzzzzzzzzzzzzzzzzzt. The buzz isn't just the normal 80hz thing. This is a higher pitched noise that really cannot be gotten around for recording or running her direct into the board live. It makes me wonder if there is not some kind of failure in the transformer or something else not quite right. It has been fine since we brought it home except now when the song she's playing is shaking the basement walls so bad it is picking up on the mic's. Tried the dir outs again. No dice. Yes I followed instructs re: Pre/Post. We don't use the EQ or Efx outs. I tried patching all the amp pres and efx loops with patch cords. $1500 for bzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz.
It'll be easier to try moving the rig upstairs than to try to EQ that out. I've put her on notice, if she buys another ampeg product I will not move it. It sounds great when it works. But I would settle for reliable and "sounds good."

[MarkusBass]

Eric,

First you complained about the power of the amp and now you are talking about the DI output. I played several SVT 4Pro and none of them had such symptoms. I think that still the biggest problem is with low quality of service. The users expect the lowest possible price for service but on the other hand the highest quality. These two: lowest price and highest quality do not go togehter . The guy that was trying to fix the amp should start with an attempt to identify whether the problem is with the power amp, or with the preamp. It should be done on a top-down basis. Otherwise you end up with random tests, which do not clarify anything.
The simplest test that I can advise is to plug an external preamp into the power amp input of this amp and see whether the amp has enough power. If not, you have to fix the power amp first. Only then you may start checking the problem with DI. I assume that you tried the Ground Lift button. If this didn't helped, the little board may need some attention. Just a week ago I had a SVT 3Pro in which someone was trying to plugin a cable into DI socket that it was disconnected from the board. I fixed it in 1 minute and the problem with your amp may be also so simple. But you (or the guy who wants to fix it) need to test it in a logical way and not by doing random test ("lets try cables today").
Also he should have equipment like generator and oscilloscope to perform such tests. I wish I lived closer to you - I would be able to help directly then.

Mark

[doombilly]

ok

Well let me start by saying the tests have been less random than my communications. I have a pretty distracted speaking, typing pattern. The amp HAS been connected to an oscilloscope at the 2nd place I took it to. They could not find a problem. I had forgotten about the DI's on the thing until I needed them. Otherwise I would have had him look those over.
But let me respectfully get one thing perfectly CLEAR.
We were not bargain shopping for an amplifier. I actually went to an ampeg because cost was not so much of an issue as reliability. We even spend over $100+ over the retail price for an extended warranty. I just did not know that would be an extended period in which we would be condescended to and ignored by Loud and Ampeg. I wrote that money off a while ago. Frankly I don't care if 99.99997% of their amps come off the line with no defects. If I got the one that is problematic and their customer service folks are belligerent, then it scarcely matters how good their engineering, design, and manufacturing is. They ALL deserve to be painted with the same brush. Albatrosses for everyone. We would have spent $2000 for it if it worked properly. And we are not wealthy people. But we've spent a huge portion of our meager income on gear, and gigging. At this point I don't care where the weak link is in the chain.

I don't know if I mentioned this above, we noticed the power drop again and I patched one pre to power amp (A) first and it was improved enough that I could see the 1x15 move farther (not to mention louder). She played that way for a while then I patched pre to power amp B and got similar results. I went ahead an patched the FX loop too at this point because 1) she doesn't use bass fx and 2) I wanted to eliminate all of the fixable defects.

I know how it is when you have a product you like and some random guy is whining about it online. I make no apologies. I did not buy a Yugo. Cheers.

[MarkusBass]

I have a pretty distracted speaking, typing pattern. The amp HAS been connected to an oscilloscope at the 2nd place I took it to. They could not find a problem.

Eric,

Connecting an amp to an oscilloscope does not mean a thing. There has to performed a series of activities: pluging-in a signal generator, adding high power resistor on the output, connecting an oscilloscope, connecting multimeter to the resistor on the output, measuring the output power. All of these activities have to be performed. And the word "All" is very important here. Did they do it? I don't think so.

But let me respectfully get one thing perfectly CLEAR.

For me it is still not clear. You bought an amp, the amp has some technical problems, the service cannot fix the amp and you say: "Ampeg is bad". I'm not defending Ampeg but I do fix them and in my opinion you can only say: "The service is bad". And this is not the same because in my opinion the amp can be easily fixed. You just haven't found people that can do it. And I'm sorry for this.

I don't know if I mentioned this above, we noticed the power drop again and I patched one pre to power amp (A) first and it was improved enough that I could see the 1x15 move farther (not to mention louder). She played that way for a while then I patched pre to power amp B and got similar results.

You see? If this true, the problem is as simple as dirty jacks on the back panel. How on earth the service was not able to notice this?

BTW: I suggested to plug an external preamp into one of the power amps. This would tell you whether the problem is with the preamp or with the power amp. And again, the word "external" is important here. And you used internal preamp. If you want us the help you, you need first to help yourself (e.g. by checking the amp with external preamp).

I know how it is when you have a product you like and some random guy is whining about it online. I make no apologies.

As I said I'm not defending Ampeg. I can see that the technical knowledge of the service is much below acceptable level. I've seen also many Ampegs with factory assembled MOSFETs, which should be closely matched but they were not. But I still say that this is an amp with a great sound and if I had to buy a bass amp, I would consider Ampeg (currently I play MarkBass F-1 but mainly due to its weight < 2 kg).

Mark

[Enzo]

We need to find someone who can actually diagnose the problem. It sounds like the local tech is not up to it. He may be a great guy, and may get 99.9% of the stuff that comes his way, but this is not falling to his skills. I think I myself am a pretty good troubleshooter, but sometimes I just can't get my head around some odd problem or other. And if they take it to someone else, he may find it right away. SO there is no shame in striking out now and then. But it doesn;t get your amp fixed.

I don;t know who sold the extended service contract, the manufacturer or the dealer. As far as my experioence, that has been something dealers sell, so it would fall on whoever takes care of those problems for that dealer. Calling the manufacturer usually doesn't solve technical problems. Problem with the manufaturer is he doesn't have the amp in front of him, so all they can do is offer generic suggestions: check the cords, try different guitars, plug into a different wall outlet. The only thing the factory is good for - and this is any brand, not just Loud Tech - is intervening. They can authorize an amp exchange, they can have the amp shipped to THEIR tech. Not their local representative tech, I mean their guy at the factory. They can refer you to someone they think is particularly qualified. But they will rarely have a technical insight beyond what any reasonably qualified tech can come up with, because over the phone they have no way to do so much as a voltage reading. The only issues they can really shine light on is a situation that involves a SYSTEMATIC failure of the product design. If tons of them are doing the same thing, then we might have something, and we might find it out before the bulletins are issued.

But that all brings it back to having a real guy put his real hands on it.

We can test the parts - does each power amp work? Check. Does the preamp work? Check. and so on, but the amp works as a system, all the parts must work together. And that is where we have to step in.

If we are losing power at times and it works OK other times, well we learn little or nothing by taking readings while it is working right. We have to use the symptom as a diagnostic tool. We only learn about the problem while it occurs.

SO with a test signal applied, we want to try to initiate the problem. We need to isolate the problem. We have two power amps, and two preamp signals that feed them. APparently only one power amp channel is affected, is that correct?

As soon as it happens, we ned to do several tests. We need to have another amp handy so we can run a cord from either preamp out to its input. So we can listen to what is coming out of the preamp. DO both channel preamp outs sound the same? And does probing those jacks affect the symptom?

And we need to have a couple short cords handy so we can quickly plug a cord from preamp out to power amp in on the affected channel. Does that restore the sound?

We need to flip the stereo/mon-bridge switch back and forth. If it has flaky contacts inside, they could cause this.

And we need to beat on the amp. I have a couple rubber mallets for the purpose officially, but really my fist is usually more... handy, pun intended. Whacking the chassis on top, on the ends, front and back, helps reveal intermittant connections.

And we need to explore the interconnects more closely. Things like switches and cutouts on jacks usually work, but when they get iffy, the performance suffers. One thing I have learned is to MEASURE the resistance of things like jacks and switches, and relays.

Jack cutout contacts, switch contacts, relay contacts SHOULD have almost zero ohms resistance. If you measure the contact resistance and it shows 2 ohms, there is trouble. A cutout with only 2 ohms across it will work fine. 2 ohms will not get in the way. But it should measure less than half an ohm. SO testing by function is not enough. That 2 ohms won;t get in the way, but the very fact that is measures a couple ohms instead of a dead short tells us the contacts are compromised. They may sit at 2 ohms right now, but they could just as easily go to 1500 ohms tomorrow. Clean contacts won't do that. So we can inpit a signal and hear it come out the opther end and ASSUME the jack cutoputs or switches are working, but we won;t discover the problem until we measure those seemingly OK contacts.

And CLiff style jacks are famous for this.

At the output of each power amp is a relay. It is there to disconnect your speakers during power up and down to protect them from thump. But if the relkay contacts getr oxidized or funky, they can reduce your power. We need to have the amp on and runnign and measure resistance through the relays.

At each output stage there is an inductor with a 1 ohm resistor in parallel. We ned to check that inductor to see if one end is broken free or has come unsoldered. If the coil leaves the circuit, then that 1 ohm resistor goes in series with your speaker.

These are just some of the tests to isolate the problem.


Buzzing DIs are probably not related to the power issue, we can solve them separately.

What we are doing here is trying to determine if the problem lies in the preamp or the power amp or the connection between them.