Ashdown MAG300 EVO2 problem

[Enzo]

A lot of amps are made to be real loud by 1 or 2 on the volume control because they know a LOT of buyers will try the amp and say to themselves, "Well if it is this loud on only 2, just think how loud it will go." But really it doesn't get much louder from there. Some amps are made more reasonably so the volume control is more useful. If your 100 watt amp makes 100 watts at its loudest, does it really matter if it does it at 2 instead of 9? other than the convenience of adjusting the level?

[m1989jmp]

A lot of amps are made to be real loud by 1 or 2 on the volume control because they know a LOT of buyers will try the amp and say to themselves, "Well if it is this loud on only 2, just think how loud it will go." But really it doesn't get much louder from there. Some amps are made more reasonably so the volume control is more useful. If your 100 watt amp makes 100 watts at its loudest, does it really matter if it does it at 2 instead of 9? other than the convenience of adjusting the level?

I figured that since the pots are linear, it should roar on half, but I guess it does come down to the design, as you've said.

[J M Fahey]

Since the preamp was worked on way more than we originally thought, including burnt tracks, a couple added wires, etc. , they *might* have touched something which affects preamp output or gain.

To use some numbers instead of subjective perceptions of what does "loud" mean, inject 100mV 1kHz at the "Passive" input, set all eq controls halfway, master volume to 10, no frills, so no Compression/Sub octave/Deep/Bright/etc. load amp, scope output (or measure Vac with a multimeter) and slowly rise input gain/volume to check you can get some 30/40VAC at the speaker out (150/200 W RMS).

If you can, sensitivity/gain is fine for a regular Bass Guitar.

If not by far (you need 200/500 mV input even with volume and master flat out) you still have a problem.

One weird design trait (WTF class) is that input stage has unity gain and immediately feeds preamp volume pot, practically same as runnin amp full gain and controlling it from instrument, normal is a 10X/20X pre stage before volume control (and up to 50X/100X in Tube amps) to minimize internal hiss and noise.

We do not know later stages gain, since values are not shown in schematic.

[m1989jmp]

Since the preamp was worked on way more than we originally thought, including burnt tracks, a couple added wires, etc. , they *might* have touched something which affects preamp output or gain.

To use some numbers instead of subjective perceptions of what does "loud" mean, inject 100mV 1kHz at the "Passive" input, set all eq controls halfway, master volume to 10, no frills, so no Compression/Sub octave/Deep/Bright/etc. load amp, scope output (or measure Vac with a multimeter) and slowly rise input gain/volume to check you can get some 30/40VAC at the speaker out (150/200 W RMS).

If you can, sensitivity/gain is fine for a regular Bass Guitar.

If not by far (you need 200/500 mV input even with volume and master flat out) you still have a problem.

One weird design trait (WTF class) is that input stage has unity gain and immediately feeds preamp volume pot, practically same as runnin amp full gain and controlling it from instrument, normal is a 10X/20X pre stage before volume control (and up to 50X/100X in Tube amps) to minimize internal hiss and noise.

We do not know later stages gain, since values are not shown in schematic.

100mV peak to peak?

[J M Fahey]

Unless otherwise noticed, in general we talk RMS

Some useful tones.
Download and play them, any Phone/MP3 player headphone out will giv you at least 100mV RMS, most up to 200mV
Set player to Loop or Repeat, to have a continuous tone (with a small glitch every 30 seconds):
http://www.mediacollege.com/audio/to...6bit_30sec.mp3
http://www.mediacollege.com/audio/to...6bit_30sec.mp3

if you want to test how loud can cabinets get while specifically playing a Bass Guitar:
http://www.mediacollege.com/audio/to...6bit_30sec.mp3

[m1989jmp]

Unless otherwise noticed, in general we talk RMS

Some useful tones.
Download and play them, any Phone/MP3 player headphone out will giv you at least 100mV RMS, most up to 200mV
Set player to Loop or Repeat, to have a continuous tone (with a small glitch every 30 seconds):
http://www.mediacollege.com/audio/to...6bit_30sec.mp3
http://www.mediacollege.com/audio/to...6bit_30sec.mp3

if you want to test how loud can cabinets get while specifically playing a Bass Guitar:
http://www.mediacollege.com/audio/to...6bit_30sec.mp3

I set these samples to around 150mV peak and hooked the oscilloscope to a 1000W 4ohm cheapo Behringer bass cab as I don't have a dummy load. At 9o'clock input (output maxed, EQ flat and all switches off as you suggested) I get around 5V RMS; at that point the sound got too loud, so I didn't raise the input any further.

I'll lug it down to my rehearsal space soon and crank it harder.

Let's for a second presume the amp can't put out these numbers you suggested, and considering the output wave is undistorted, on which area should I focus?

[m1989jmp]

I've tried it out with a drummer today with both volumes at around 11 o'clock. Loudness is really influenced by compressor knob and EQ setting.

Since it sounds good and powerful set like this, I think I'll wrap it up. It took enough of my time as it is.

I do wonder if there is some kind of hypothetical fault that would sap, let's say 2/3 of total power while leaving sound quality intact?

Thanks again guys for your effort and time.

[Mick Bailey]

There are plenty of faults that would reduce power, but first you have to measure what the amp is producing. A couple of checks I do is firstly to scope the output with a sine test signal and see how close to the power rails it swings and whether it's symmetrical. Then run the amp into a dummy load - I use the lowest the amp manufacturer recommends as that's where the greatest power output will be. I then get the best output I can at the onset of clipping. You need to be fairly prompt as amps are not made to run at this level continuously. A constant sine wave is very different to an instrument input. Bear in mind that often manufacturers figures can be overstated.

[m1989jmp]

There are plenty of faults that would reduce power, but first you have to measure what the amp is producing. A couple of checks I do is firstly to scope the output with a sine test signal and see how close to the power rails it swings and whether it's symmetrical. Then run the amp into a dummy load - I use the lowest the amp manufacturer recommends as that's where the greatest power output will be. I then get the best output I can at the onset of clipping. You need to be fairly prompt as amps are not made to run at this level continuously. A constant sine wave is very different to an instrument input. Bear in mind that often manufacturers figures can be overstated.

The first test is done without a load, right? I will do the second test as soon as I get a dummy load with that kind of power dissipation.

Out of curiosity, could you name a few faults that would reduce power, except obvious ones (pair of blown output transistors or related resistors etc.) ?

[J M Fahey]

Let's for a second presume the amp can't put out these numbers you suggested, and considering the output wave is undistorted, on which area should I focus?

at that point the sound got too loud, so I didn't raise the input any further.

I do wonder if there is some kind of hypothetical fault that would

Out of curiosity, could you name a few faults that would reduce power, except obvious ones (pair of blown output transistors or related resistors etc.) ?

Just-DO-the-fucking-test , will you?

[Mick Bailey]

The first test is done without a load, right?

Yes.

[m1989jmp]

Just-DO-the-fucking-test , will you?

That's completely uncalled for.

If you re-read my posts, you'll see I've mentioned I don't have a suitable dummy load at the moment and don't feel like blasting my ears with 100W+ sine wave.

I'm here to learn from people willing to share their knowledge and experience, not just to repair this amp.

[J M Fahey]

Ok, then wait until you can do the test and then post results, just donīt send us on a wild goose chase for problems you do NOT have.

Once might have been ignored and in fact it was, but FOUR times in a row is annoying.

You want to worry about what **might** go bad?
Ok, think about this: thereīs some 150 components in that amp (maybe more) , some 300 or 400 soldered joints, 30 to 50 wires, a power transformer, 10 pots, 5 or 6 switches, etc. ANY OF THEM CAN GO WRONG. So what?
Should we go nuts thinking about bad possibilities?

[nickb]

Dummy load 50W/100W Shell Power Aluminum Housed Case Wirewound Resistor 1/2/4/6/8/10 Ohm | eBay

$1.58 Free ship.

[m1989jmp]

Dummy load 50W/100W Shell Power Aluminum Housed Case Wirewound Resistor 1/2/4/6/8/10 Ohm | eBay

$1.58 Free ship.

Have you used these?

I've ordered 10 just to make sure I can go way over the power ratings with all possible resistance values.