View Full Version : I think my amp has declared war on my speakers...
I could do with a bit of advice on a potential issue with my system. I think my amp might be killing the DM2's. I was listening to Elbow's, Seldom Seen Kid this afternoon when I noticed a crackling coming from the left speaker. Now, this has happened before just after Christmas and luckily Mark (Dingdong) had a spare bass unit knocking around which he kindly fitted for me, but now that unit is on its way out too. I was listening slightly above my usual position on the volume control (just past 9 o'clock) which was exactly the same scenario as before. This has got me wondering whether perhaps the power output of the Hafler is more than the DM2's can handle. The Hafler is rated at 110wpc and the DM2's can handle 60watts. I don't have the means to test the DM2's impedance but it got me thinking that if they are offering a 6ohm load to the amp that may be enough to push things over the edge. The Hafler has had all its caps replaced or upgraded recently.
Reid Malenfant
24-04-2012, 19:57
I don't see why they shouldn't be happy with clean power ;) I doubt you were clipping the amp so I fail to see why bass drivers are complaining.
I'd expect them to be doing some serious excursion before any problems show up.
As a for instance, the NS1000 is rated at 50W or 100W music power, but the bass drivers have often seen over 450W (of clean non clipped power) & they are still in one piece :)
Odd indeed :scratch:
It seems strange that it is the lefthand driver yet again. Marco has suggested that it might be a duff resistor. It is a nightmare to be honest because I can't afford to replace them. I am not well enough to be able to take them apart to fix 'em (they are huge and very heavy) so I have a choice. Use the broken Celestion's (the cabs are fooked) which work okay and are in the garage, or a pair of cheap and nasty KAB studio monitors (allegedly) which I picked up from fleabay for three quid :lol:
I wouldn't expect a failing driver to produce the fault you are describing - a buzzing at certain frequencies yes, but not a crackling.
Are you absolutely sure it isn't an amp related issue?
I have run CLEAN 300 watts into speakers rated at 30 watts or less. That does far less harm than a 30 watt amp into speakers rated in the hundreds of watts, because a clipping amp is feeding some nasty current through the voice coils.
Maybe the amp is biased badly so it is feeding a small DC current through the speakers, or the speakers are at that age where they are on their way to voice coil heaven anyway?
As far as memory serves there is no bias adjustment on the Hafler power amps, but a leaky cap somewhere could be passing some DC.
I wouldn't expect a failing driver to produce the fault you are describing - a buzzing at certain frequencies yes, but not a crackling.
Are you absolutely sure it isn't an amp related issue?
Yes Mark, I swapped the speakers around and the issue is definitely with that bass unit.
Frank, the amp was recapped just over three months ago so I'm almost certain it isn't a cap problem. It could be a biasing issue I suppose but I wouldn't have a clue how to deal with that, my knowledge of electronics is fairly meagre :eyebrows:
Yes Mark, I swapped the speakers around and the issue is definitely with that bass unit.
Frank, the amp was recapped just over three months ago so I'm almost certain it isn't a cap problem. It could be a biasing issue I suppose but I wouldn't have a clue how to deal with that, my knowledge of electronics is fairly meagre :eyebrows:
I have the original build and set up manual for the DH200 out in the shed somewhere, so I will dig it out and have a look tomorrow. As I said earlier, I don't ever recollect setting up the bias on these amps as they were designed to be module wired in the kit assembly.
Was that just the reservoirs and the smoothing caps replaced, or the whole lot Dave? My suspicions lie with the smaller value caps on the PCBs.
The MOSFET output drivers don't normally play up, they either work or they don't - lovely devices.
Just dug out the manual for the Hafler DH-220 and there is a bias adjustment which is normally set at the factory and according to the manual should not need adjusting during the kit build - but that is soon after manufacture and not to say it won't drift over time.
It also tells you how to check for DC offset at the speaker terminals which requires a voltmeter capable of reading down to 10 millivolts. If you don't have a meter, let alone one that can read that low, it would be advisable to get someone who can to take a look at it.
hifi_dave
25-04-2012, 10:04
Yes Mark, I swapped the speakers around and the issue is definitely with that bass unit.
Frank, the amp was recapped just over three months ago so I'm almost certain it isn't a cap problem. It could be a biasing issue I suppose but I wouldn't have a clue how to deal with that, my knowledge of electronics is fairly meagre :eyebrows:
If you have swapped the speakers from right to left and the fault moves with the speaker, then surely, it is the speaker.
The fault is with the speaker Dave, but I think what is being suggested is that a fault or incorrect bias setting in the amps LH channel might be responsible for the failure of that speakers bass driver. This is possibly supported by the fact the previous bass driver in that particular cab suffered the same fate. The two bass driver failures have occurred since the cap upgrades were implemented just over three months ago.
Ok, scrub everything. My partner Jo forgot to swap the speaker cables for me so we have just done that and guess what? It is not a faulty drive unit. Interestingly, it isn't the Hafler that's at fault either. Let me set the scene:
The track that induces the anomaly is track 9 on Elbow's, Seldom Seen Kid. I'll need to closely listen to other CD's in my collection to see if I can replicate the issue. Another interesting observation is that the anomaly only manifests when playing the CD. If I play the same album from Spotify there is no distortion at all. This narrows down the field somewhat. It is either the CD player, dirty cables or a faulty No1 input on the Caiman. I shall report back once I have done some further testing.
Ok here we go. Listening to the same track through headphones or speakers from the CDP through the Caiman reveals the anomaly, doing the same from the PC via Caiman & Spotify and the anomaly is not present. I have uninstalled and reinstalled the digital cable running between the CDP & Caiman and the problem is still apparent. I have yet to try the CDP connected straight to the pre-amp thus bypassing the Caiman, however I feel this is unnecessary as the fault is clearly in the CDP. Does anyone have a spare CDP they don't need? :eyebrows:
Reid Malenfant
25-04-2012, 16:04
It's likely to be the CD ;) Spotify is MP3 & thus compressed so it's likely to lose a small bit of distortion that might be present on the CD. I seriously doubt it's the CD player.
I have a few CDs that actually clip even if it's for a very short period of time, the Yamaha drivers show it up like turning on a light unfortunately :eyebrows:
At least the driver is ok thankfully :D
You could be right Mark. I wonder if anyone else who owns this CD has noticed the issue? I've yet to try the CD directly through the amp, I shall get on and do that in a few mins... ;)
Interesting! Bypassing the Caiman and running the CDP straight into the Classe and the distortion has now disappeared completely, what's more it sounds absolutely fabulous. Everything is less compressed and bass heft is phenomenal, It's looking like a Caiman problem now. Time to have a word with Stan methinks. Confused.com... :lol:
Have you got an early version of the Gator board, Dave? I believe there can be an issue with excessive gain that can drive some amps into distortion on some tracks. As you say, I think you need to have a word with Stan.
Have you got an early version of the Gator board, Dave? I believe there can be an issue with excessive gain that can drive some amps into distortion on some tracks. As you say, I think you need to have a word with Stan.
Yes Keith, I believe my Gator was from the first batch Stan produced. Just had a thought though, it could also be an issue with the digital output from the Arcam CDP but unfortunately I have no way of testing that. Digital output from the PC into the Caiman is unaffected by the way, that still sounds great. I'll try ripping Seldom Seen Kid to the 'puter later in .wav format to test out this theory.
Wow, I've never heard this album sound so good. There is richness and detail I've not heard before, the DAC in this Arcam is pretty darn good. I might just stick with this configuration... ;)
bobbasrah
25-04-2012, 17:04
An ironic thread title given today's Leveson Inquiry Brown/Murdoch spat....
Clipping digital files do sound rather as you describe.
I didn't think it was the drive unit - it probably wasn't the previous time you changed it either.
It is possible that the output of your CD player is causing the input of your DAC to clip. The output of many CD players is above the 2V nominal suggested.
If you record the track in Audacity directly from your CD player, and then from your DAC, it should be easy enough to see if clipping is being either introduced, or present in the first place,
Cheers Mark, I'll give Audacity a try a little later, got a few things to do first ;)
Thinking about it, it is most likely that the CD (player) is causing the input of the DAC to clip. You only need to record the particular section with an issue -if you compare the CD player direct into your computer and CD player via DAC into your computer, you should see the clipping happening.
http://i62.photobucket.com/albums/h90/markemark_2006/clipping.jpg
Will there be a trimpot somewhere inside the CDP to adjust the output? This makes a lot of sense because there is a huge discrepancy between the position I set the volume control for comfortable listening for the CDP and my TT, about the 9 o'clock position for the CDP is pretty loud compared with 11 to 12 oclock for the TT.
I very much doubt there Will be a trim-pot in the CDP (have never encountered one). If it has a digital volume control perhaps - but the level of most digital outputs is fixed.
If you are using a coax cable connection you can buy in-line atenuators intended for just this issue with satelite dishes and their boxes (they are only a couple of quid).
That is probably the solution I will have to go for, cheers for your input Mark ;)
Reid Malenfant
29-04-2012, 15:59
Putting an attenuator on the digital output will have no effect on anything at all, though it might stop it working. The volume level is goverened by the bit depth as is nothing at all to do with the level of output voltage ;)
A whole lot of digital outputs work at logic level, which is 5V. A digital output with 2V output will be exactly the same volume once the DAC has a handle on the bits themselves.
I'm sorry but I am really having trouble getting my head around the technicalities of this problem. I just don't understand why there is distortion when I play this particular track on the CD through my CDP and Caiman and yet when I bypass the Caiman or play it on my PC through the Caiman it sounds absolutely fine... :scratch:
Reid Malenfant
29-04-2012, 16:08
Well that makes two of us then :) At least you aren't alone with the problem :eyebrows:
I'm listening to Simon & Garfunkel via Spotify just now via the Caiman with the Mini T in circuit and it sounds bloody amazing. Perhaps the CD73 just isn't a fan of Elbow, eh? :lol:
May I suggest you do the audacity recording I suggested and post the results.
____________
If you are using Spotify then you aren't using your CD player.....
I'm getting to it Mark, I'm currently attempting to figure out how to do that ;)
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