Frustrated as hell with my Aguilar (amp help)

[GeneralElectric]

So I traded my GK2001RB for an Aguilar AG500 (dual channel) and its been nothing but problems since I've gotten it. When I got it in the mail, I had to shell out to get it fixed. The channel switch was broken among other things.

Now whenever I play a note I get distortion. Its low level but definitely there. When I don't have an instrument plugged in I don't get anything. If I just fret a note, even at low volume, you'll hear it. It sounds like I have a distortion pedal put in. No amount of different basses, cables, or cabs, seems to fix this issue. No twiddling with the EQ or anything seems to fix it.


When my tech fixed it the first time, he said it was a poorly designed amp (internally) that was extremely fragile and if anything broke on the amp again to just junk it as things would just keep breaking. I was also told never to push this amp as it couldn't even stand the abuse. I trust my tech a lot. He ghost builds point to point tube amps for a couple of companies and will rewire every Marshall that comes through his doors as their circuit board is flawed from the getgo. He treats everything like it was his own.


Any help on isolating this issue? I contacted Aguilar and all they offered was to fix it for $90 an hour instead of helping me isolate the problem. I already knew it wasn't under warranty.

[braydensharrar]

I hate to hear of your bad Aggie experience. I got my AG500 a couple months ago and it is by far my favorite amp I have ever owned; over a Epifani 502, Demeter/Stewart rack, Fender 300 pro, etc.

It really sounds to me like you got a lemon, it happens in all forms of production despite quality control. My parents had a $60,000 BWM that was a lemon, there was just no helping it.

Have you tried contacting Aguilar directly? I see you are in NY anyways, I would talk to Dave B. and see what they can do.

The only things about your post that strikes me as odd are the comments you're tech made about the head. I am in no way a tech of any sorts, therefore I am definitely not calling out his expertise. In my opinion, I don't think guys like Patitucci, JMJ, Tony Grey, etc. would use a poorly designed amplifier. And I know from my personal experience, I have pushed this thing hard at times and it kept up wonderfully. YMMV of course.

Good luck!

~B

[craig.p]

I haven't worked on that brand, but how hard can it be to introduce a sine wave at the input and check each stage's output with a scope, right down the line, for the first evidence of waveform distortion? If it's really that audible, it should show up visually.

That or a distortion analyzer, but this sounds bad enough not to warrant one, at least to start with.

Is the distortion less at high volumes? Or is the percentage of distortion relatively constant regardless of volume?

[GeneralElectric]

It seems to be at the same level regardless of volume. Its definitely more apparent at lower volumes since I've got less output coming through.

As for famous people endorsing a lackluster piece of equipment, I've spoken to a few people that have been approached by Aguilar to be endorsed. They were told they had to pick this amp. I'm sure I'd endorse something I didn't like if I got something out of it.

[johnk_10]

Originally Posted by GeneralElectric

I trust my tech a lot. He ghost builds point to point tube amps for a couple of companies and will rewire every Marshall that comes through his doors as their circuit board is flawed from the getgo. He treats everything like it was his own.

as a tech and a custom built amp builder for 30 years, IMO, as far as Marshall amps go, i have no ploblem with their circuit board designs on the mid '70's early 80's JMP and JCM 800 lines of amps. IMO, it's one of the best PCB designs ever offered, as they are extremely reliable and sound great. on the other hand, IME, the JCM 2000 and onwards are horrible designs with PCB mounted tube sockets, wimpy power and output trannys and way more SS circuit that necessary.

i've restored rebuilt lots of Marshalls, everything from very early plexi's (w/aluminum chassis and white panels), to mid year plexi's, JMP's, JCM 800's, 2000's and the 2000's onwards circuits are the only ones that i despise, both tone-wise and build-wise.

[craig.p]

If the distortion is constant as the volume is varied, i.e. the volume eventually masks the distortion or the distortion lessens as the volume is increased (versus being a constant percentage of the volume as the volume is increased), then it could be something as simple as too-low output transistor biasing (crossover distortion), or maybe even a bad output transistor.

I assume the fans are working in this thing.....

[craig.p]

Ah. Just noticed "channel switch broken" and "among other things." So maybe this amp was dropped? Wonder if there's a component or two that physically broke, or a cracked PCB etch (trace)? You could remove it from the case and play it while you press LIGHTLY down in various places with something WOODEN or PLASTIC, to see if you can make the problem better or worse. I don't know how complicated the fans would make this test, i.e. where they mount etc.

EDIT: When I say "remove it," I don't mean remove the PCB, I mean pull the entire amp guts from the case as a unit so you have access to the PCB & other components.

[js1]

Frustrating, I know - the risks of buying/trading used.

Went through your same pain with a Mesa MPulse 600 I bought used. Took 4 trips before it got fixed. Fortunately for me, the Mesa warranty was transferable, so it was free of charge.

The reason it came back the first 3 times was that it made sound at a reasonable volume after you replaced a tube. How "good" it sounded wasn't discernible to the tech. It wasn't until I had them compare it to a new one that it got fixed.

My recommendation would be to suck it up and send it to Aguilar, or to a tech that Aguilar recommends. They know the dirty secrets of their designs, and they can compare it to a properly working model. They'll also likely have a cap on what the charge will be.

Techs each have their areas of expertise, and a lot of tube amp guys aren't so good with transistor amps. The old school guys have a heavy bias (no pun intended) against modern construction techniques. The new amps can be harder to troubleshoot, and if they use surface mount parts, you'll need to have special tools to replace parts. But, the fact that old school techs don't have the ability to fix them doesn't mean that they're "junk".

js

[EricF]

Originally Posted by GeneralElectric

When my tech fixed it the first time, he said it was a poorly designed amp (internally) that was extremely fragile and if anything broke on the amp again to just junk it as things would just keep breaking. I was also told never to push this amp as it couldn't even stand the abuse.

I know you trust your guy, but everything I know about how Aguilar designs, engineers, and builds their products doesn't follow his conclusion. Like others have recommended, you're probably going to be a LOT better off with someone who has experience working with that specific amp. Unfortunately, it sounds like your amp may have been previously badly abused. Show it a little love and tenderness now, and I expect that thing will be roaring with lovely tones for a long time.

[GeneralElectric]

Originally Posted by craig.p

If the distortion is constant as the volume is varied, i.e. the volume eventually masks the distortion or the distortion lessens as the volume is increased (versus being a constant percentage of the volume as the volume is increased), then it could be something as simple as too-low output transistor biasing (crossover distortion), or maybe even a bad output transistor.

I assume the fans are working in this thing.....

There are no fans in this amp. One of the reasons why he said this was poorly designed. If I were to push this amp, I'd run a good chance of everything overheating and melting down.

I've also had this guy fix and maintain all my SS amps for a long time and never once had an issue. A lot of the studios around here send their stuff to him to get repaired because he really is one of the best in this neck of the wood.

[GeneralElectric]

Originally Posted by EricF

I know you trust your guy, but everything I know about how Aguilar designs, engineers, and builds their products doesn't follow his conclusion. Like others have recommended, you're probably going to be a LOT better off with someone who has experience working with that specific amp. Unfortunately, it sounds like your amp may have been previously badly abused. Show it a little love and tenderness now, and I expect that thing will be roaring with lovely tones for a long time.

He's worked on this type of amp before and even made me a custom footswitch to go with it since the original wasn't included. He said to me, after I bought it and was having it repaired, that I should've avoided having this amp unless I planned on keeping it in a rehearsal space or a home studio.

I'm not really one to trash talk my own gear, especially when I'll probably be selling this a few months later. But if its not good, its not good.

[B-string]

You did leave a top of the line G-K, at least give it a fair chance with proper repairs? As far as not having a fan on the heat sinks, if the sinks are large enough there is no need. Your trouble does have the character of improper bias or bad connection in the effects return jack.

[Limeman]

Originally Posted by GeneralElectric

There are no fans in this amp. One of the reasons why he said this was poorly designed. If I were to push this amp, I'd run a good chance of everything overheating and melting down.

I don't want to come across harsh, but that statement alone from your tech shows me he doesn't have a clue as to the workings or design of the AG500 amp. It runs extremely cool due to the modified Class-D design of the amplifier.

Taken direct from a Bass Player review "The AG 500 is like a Class D amp, but it utilizes switching technology developed by the Tripath Corporation. The Tripath power amp topology, named Class T, modulates the output using a proprietary module that purports to eliminate some of the weaknesses of Class D amps while maintaining the efficiency that’s a hallmark of the technology. Aguilar’s AG 500 uses a Class T output stage and a conventional linear power transformer."

I believe what this means is the AG500 runs extremely cool due to the efficiency of the amplifier, thus no need for a fan. This is opposed to a typical SS amp which often utilize a Class A/B design which require high-speed fans and large heat sinks to deal with the inefficiency of the amplifier design.

If I were you, I would call up Dave B. at Aguilar and talk about the issues you are having. I'm certain they can get you up and running.

[JEDBass]

The existence (or lack) of fans really doesn't give a good indication as to the quality of the amp design. I'd go so far as to say I'd rather have an amp that didn't have to rely on fans, since fans will eventually wear out over time, and as a result the circuitry will not be cooled properly. Unfortunately many amplifier designs nowadays rely on a relatively cheap fan since a proper heat sink design adds more cost and weight.

A perfect example of this is the GK 800RB. I don't see anyone claiming that the lack of a fan is causing those amps to fail or that they're a bad design. Quite the opposite in fact.

You might have a good tech, but his statement there is VERY misleading and uninformed.

Just my $0.02 of course.

[GeneralElectric]

Originally Posted by Limeman

I believe what this means is the AG500 runs extremely cool due to the efficiency of the amplifier, thus no need for a fan. This is opposed to a typical SS amp which often utilize a Class A/B design which require high-speed fans and large heat sinks to deal with the inefficiency of the amplifier design.

If I were you, I would call up Dave B. at Aguilar and talk about the issues you are having. I'm certain they can get you up and running.

Do you have a way I can get his number? I'd like to call him and let him know whats up. I don't really want to pay $90 an hour for a repair. It seems excessive to me, but this is a business and I don't begrudge them. I had gotten the amp fixed last time for $120 and that included the replaced switches and everything. Somehow paying at least $90 to get it fixed doesn't appeal to me. I'll most likely be bringing this back out to my tech to fix it.

The amp functioned flawlessly until I used it a two gigs. I'm not sure if it happened at either the first or the second as I didn't plug in the amp otherwise until recently at home. And yes this amp does run hot, although it takes awhile to get there. By the end of the night (so maybe 3 and a half hours of operation) the amp is hot.

[GeneralElectric]

Originally Posted by JEDBass

The existence (or lack) of fans really doesn't give a good indication as to the quality of the amp design. I'd go so far as to say I'd rather have an amp that didn't have to rely on fans, since fans will eventually wear out over time, and as a result the circuitry will not be cooled properly. Unfortunately many amplifier designs nowadays rely on a relatively cheap fan since a proper heat sink design adds more cost and weight.

Most of my amps in the past haven't had fans either. They were air cooled.

[craig.p]

Oops. Didn't realize that thing had no fans. Sorry.

There'll always be a debate about fan vs no fan. The acid test is whether the amp holds up long term while it's in service in its intended application, i.e. with a bass running through it on stage putting out max watts on the peaks, in this case. It's the non-peak periods that can eliminate the need for fans.

Is that really a TDA2500 in there? On pages 22-23 of the datasheet they discuss shoot-through, distortion, and MOSFET temperature. Is it possible the amp was overloaded (run at too high a temperature for any number of reasons) which caused one or more of the outputs to change its characteristics permanently, so the original shoot-through delay is no longer valid? In this scenario, your tech's objection to there being no fan would be valid. Eh. Who knows. I'm just guessing. It's all academic anyway. Looking at the manufacturer pics, that stuff's all surface-mount. Nightmare. Mfr. board swap would probably be cheapest in the long run, unless you can find something obviously wrong/physically broken/loose by poking around. I would do that first so you don't send it back just for a loose wire or ribbon cable or something.

[GeneralElectric]

It could've been. I'm not sure. I don't think I pushed this amp. I always set the amp so the clip light never comes on. After both gigs it was pretty warm to the touch. I don't play excessively loud either, my other main gig amp is an Ampeg B25 which is a mighty 55 watts.

[rodneyat]

I will PM you his contact info.

That said, I am somewhat confused as to why you are upset about paying $90 an hour to get the amp fixed when you paid $120 to get it fixed before. I would guess the tech did not spend more than an hour or so fixing it the first time and the parts were probably not that expensive...So, it equates to probably about the same rate. Which is about right for a good electronics tech.

I am sure if you send an email to Dave and explain the situation. They will be more than happy to help you out. I have had nothing but exceptional experience with Aguilar customer service and have owned and still own a number of their products. Including an AG500 that I still own. Since Aguilar is right there in NYC...I would recommend you take it to them before you even think about taking it to anyone else.

Originally Posted by GeneralElectric

Do you have a way I can get his number? I'd like to call him and let him know whats up. I don't really want to pay $90 an hour for a repair. It seems excessive to me, but this is a business and I don't begrudge them. I had gotten the amp fixed last time for $120 and that included the replaced switches and everything. Somehow paying at least $90 to get it fixed doesn't appeal to me. I'll most likely be bringing this back out to my tech to fix it.

The amp functioned flawlessly until I used it a two gigs. I'm not sure if it happened at either the first or the second as I didn't plug in the amp otherwise until recently at home. And yes this amp does run hot, although it takes awhile to get there. By the end of the night (so maybe 3 and a half hours of operation) the amp is hot.

[craig.p]

Ok, but the manual suggests that the clip light indicates more of an "input trim" problem than the power amp section overloading. There may be no visible clue to the power amp overloading.

Also is the amp getting the cool air it needs? Are the bottom vents under the power transistors free & clear?