CDP + ASL MG-HeadDT + A900 = :(
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v_1matst

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I just received an A.S.L. MG-HeadDT amp today and couldn't wait to try it out. I plugged my IC into my sound card (office PC headphone jack) and the other end into the amp. I plugged in my A900s and let the amp warm up for an hour. After a quick listen I was upset with the sound quality. The detail was all but gone and there was a distinct fuzz sound in the background.

Thinking this was a result of an already amped headphone jack going to a tube amp, I ran home a grabbed my single CDP to try as the source. To my unfortunate surprise, the results were the same.


Any ideas on what the problem could be? My original setup (cheapo sound card headphone jack -> A900) sounds much better than my new one (sound card or CDP -> MG-HeadDT -> A900).

Also, the tubes on the amp are glowing very dim and are not getting very hot at all (they are warm and faintly orange). Is this normal? This is my first tube amp so I apologize for my ignorance.

Any help would be greatly appreciated. Thanks.
 
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SouthPaW1227

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That's a bummer man. I have an MGHead OTL MkI and it made a massive improvement in sound. My first instinct is to say it's malfunctioning. The tubes in my MGHead get HOT! I mean if you can hold you finger on a tube for more than 10 seconds you've got hands of steel. My tubes glow really bright too...any electrically inclinded members have any thoughts?
 
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acs236

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Does the fuzz sound increase get louder as you increase the volume or does it stay the same?
 
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v_1matst

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Quote:

Originally Posted by acs236
Does the fuzz sound increase get louder as you increase the volume or does it stay the same?


It increases/gets louder. It's almost like the volume is too loud (which it really isn't; it just gets the distortion like it is). I do have the gain switch set to low.
 
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go_vtec

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You amp may not be really suitable to run a low impedance can like A900. Can you try high impedance cans like Sennheiser HD580/HD600/HD650 with your amp? If buzz or noise goes away with it, then it may be just the way amp is designed. I'm not sure if your amp can handle low impedance cans (it needs lots of current)?
 
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v_1matst

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Quote:

Originally Posted by go_vtec
You amp may not be really suitable to run a low impedance can like A900. Can you try high impedance cans like Sennheiser HD580/HD600/HD650 with your amp? If buzz or noise goes away with it, then it may be just the way amp is designed. I'm not sure if your amp can handle low impedance cans (it needs lots of current)?



I had a pair of HD590 but I sold them before I received the amp so I couldn't do any testing with higher impedance cans


If I can't figure out the problem I will go to my local hi-fi store and bring the amp with me to try out different cans. The next step after that would be to try different tubes I guess.
 
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v_1matst

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So after getting frustrated with this, I did what any other self respecting head-fier would do... I took the amp apart to see if there was anything obviously wrong with the insides...

There was a fuse that seemed to be loose so I popped it out and reseated it. Other than that everything looked OK and there were no bad smells when I opened the case (like burnt electrionics).

Well, nothing has changed. It's like the amp isn't getting enough power. I swapped out a couple of power cords to see if that would make any difference and I also tried a couple of other sources that I have. No change at all with any different configuration I have tried.

Do I have a broken/malfunctioning amp? I have left the amp on for a few hours now and there is no change (the tubes are still not glowing that bright at all and I can hold my hand on them as long as I like). Anyone out there fix these things? Will A.S.L. service one of these purchased used?
 
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v_1matst

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Anyone have any advice? I'm going to look for a new set of tubes this afternoon and see if they make any difference. If they don't, at least I'll have an extra set of tubes laying around.
 
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v_1matst

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Quote:

Originally Posted by go_vtec
You amp may not be really suitable to run a low impedance can like A900. Can you try high impedance cans like Sennheiser HD580/HD600/HD650 with your amp? If buzz or noise goes away with it, then it may be just the way amp is designed. I'm not sure if your amp can handle low impedance cans (it needs lots of current)?


I don't think this is the case. According to the spec sheet for the amp, the output impedance (depending on the level selected; high/low) is 10 Ohm - 600 Ohm. The A900 shouldn't be a problem here. Again, I am inexperienced with tube amplifiers but I believe this is correct.
 
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go_vtec

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Specs means nothing when it comes to most of audio equipment. It is sort of guideline, not the absolute indication of how hardware will perform. Spec may indicate amp may be capable of delievering such range of frequency, but whether you will like such sound reproduction or not is whole different story. Manufacturers rarely (actually never) list hums and noises can be produced using low impedance cans. They haven't lie to you though. After all, you are hearing sound from your low impedance cans, right?
Frankly, most of tube amps have hardtime driving low impedance cans without creating audible noise, hiss or hum. Even some solid-state amps do produce audible noise with low impedance cans. I own OTL32 which was design to handle low impedance cans, but I can still hear faint amount of operational noise. Only PPX3 and Supra was immune from producing noise in my recent review.
 
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Can you go back to the seller and say WTH is going on here? I personally do not think it is in the tubes though.
 
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Quote:

Originally Posted by Mikey01
Can you go back to the seller and say WTH is going on here? I personally do not think it is in the tubes though.



I am in the process of doing just that (through email). I'm pretty sure the tubes aren't the problem, but I'm just trying to rule out all potential factors (besides, if the thing ends up working it's not a bad thing to have spare tubes around).
 
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Quote:

Originally Posted by go_vtec
Specs means nothing when it comes to most of audio equipment. It is sort of guideline, not the absolute indication of how hardware will perform. Spec may indicate amp may be capable of delievering such range of frequency, but whether you will like such sound reproduction or not is whole different story. Manufacturers rarely (actually never) list hums and noises can be produced using low impedance cans. They haven't lie to you though. After all, you are hearing sound from your low impedance cans, right?
Frankly, most of tube amps have hardtime driving low impedance cans without creating audible noise, hiss or hum. Even some solid-state amps do produce audible noise with low impedance cans. I own OTL32 which was design to handle low impedance cans, but I can still hear faint amount of operational noise. Only PPX3 and Supra was immune from producing noise in my recent review.




I totally agree with you on the specs not meaning all that much, however the noise being created is -very- noticable and not just me being picky. It's not a low hum (I know the noise you are talking about) but rather an overbearing distortion.

Imagine if you cranked up an amplifier (lets say a very good one) with crappy speakers attached with mediocre cable. You would get that scratchy, distorted, godawful sound. Now imagine that at a much lower volume and you would end up with what I am hearing.

I can accept that my cans are not matched with this amp, however I cannot accept that what I am getting is a reasonable result of the combination.
 
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v_1matst

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soooo....

call me crazy but swapping out the tubes for a new matched pair of EL84's and a new 12AX7R made this amp about 1000% better than it was before.

The original tubes don't look blown (any of them), however these new tubes (which aren't anything special... just some I got from Guitar Center - Groove Tubes with a distortion rating of 6 which is apparently normal) sound like I got a different amp.

So I guess this little experience wasn't all bad. I did learn what the amp sounds like when it's time to change out the tubes


Thanks to everyone for their help.
 
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