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Old 31st July 2003, 07:27 AM   #1
wrl is offline wrl  United States
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Default Distortion in Hafler DH-200

Ok, so I recently purchased a used Hafler DH-200 off of e-bay. It usually works great but occasionally the channels become very distorted. After fiddling with the input jacks for a few minutes the music usually kicks back in nice an clear.

Where should I start to look to fix this. I was thinking of cleaning or replacing the input jacks since they look very oxidized. Could this be the culprit? What else might it be. It happens on both channels, but on one a little worse than the other.


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Wes
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Old 31st July 2003, 08:06 AM   #2
wrl is offline wrl  United States
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BTW, it seems that the distortion is worse in the bass than elsewhere. I don't know if the means anything useful though.

Just a thought.


Wes
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Old 31st July 2003, 11:49 AM   #3
SY is offline SY  United States
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Your instincts sound good to me- replace the input jacks, then see if it goes away. If that doesn't fix it, well, at least you've got new input jacks, they didn't cost much, you know one thing it isn't, and you can move on to the more complex possibilities.
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Old 6th August 2003, 07:32 AM   #4
wrl is offline wrl  United States
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Hmm, ok inputs are changed. Originally they had a resistor going from input ground to the main amp ground. Does anyone know the purpose of this??

Anyway, I removed these resistors because they didn't really fit well into the new input jacks, and things seem to be working fine, however, one channel still periodically alternates from working fine to really bad distortion. It will work fine for some time (like 30mins - 1 hr) and then go to distortion for a few minutes and then back...

Could this be a bad transistor maybe? It does it without any mechanical josteling, so I doubt that it is a faulty mechanical connection somewhere. Does anyone have any experience or suggestions about this??



Thanks,

Wes
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Old 6th August 2003, 12:05 PM   #5
SY is offline SY  United States
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It could be a bad part, a bad connection, or a bad trace. While music is playing, tap around the wiring and circuit board of the dodgy channel using an insulated probe. See if you can induce the distortion.

If that yields no results, try isolated shots of freeze spray to see if you can thermally induce it.

The input resistors may be important- I don't have a schematic at hand, but I would definitely put them back. You can use smaller ones if you have a mechanical problem with the originals, since there's miniscule power to dissipate.
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Old 6th August 2003, 12:24 PM   #6
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this amplifier was "POOGED" a couple of times in Audio Amateur -- there are a number of mods -- I purchased one as a kit when they first came out, now one of the kids uses it -- must be indestructible.
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Old 7th August 2003, 04:59 AM   #7
VictorG is offline VictorG  United States
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Default Insulated

I'm just going to second the need for an Insulated Probe, emphasis on the Insulated, many stores probobly have it in your area.

While it may seem like a steep investment, it's well worth it, and you or your friends will probobly find use for it in the future again. Suck it up, buy it.
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Old 7th December 2003, 03:22 PM   #8
lucpes is offline lucpes  Europe
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Do not fiddle with the inputs too much while the amp is on, you may damage your speakers.
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Old 8th December 2003, 10:59 AM   #9
djk is offline djk
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The input grounding scheme is critical, it must not be changed.

Looking at the amplifier from the back, the left jack is insulated from ground and a 2R2 1/2W resistor goes to ground.

http://www.hafler.com/techsupport/pd...00_amp_man.pdf

Read the instructions and assembley manual.
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Old 3rd April 2004, 07:03 AM   #10
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Default Help fixing dh-200

I've got an old DH-200 that was given to me from a friend. It has severe distortion in both channels.

The inputs are all oxidized, and the fuse caps are missing on the back (as well as the fuses, obviously).

I'd like to try replacing the inputs like wrl suggested. Does anyone know if I'll be able to find caps for the fuse holders? Would the lack of fuses cause distortion?

Here's the thing: I know how to solder, but beyond that I'm completely inexperienced at this type of thing. Frankly, most of the posts on this site fly well over my head.

I figure I can't electrocute myself as long as I don't open the thing up while its plugged in, but what about the capacitors? Do they hold a charge that needs to be released somehow (like when you work on a TV set)?

When people on this site talk about 'easy mods' do you mean easy for an experienced electronics hobbyist, or for anybody with a little patience and attention to detail?

What are the chances that this amp's problems are something a total beginner can fix fairly inexpensively, or would I be better off just picking up something cheap on ebay like an NAD 2100?

I'm thrilled to have an amp with such a venerable history, but I don't really need much (its just going to power a pair of Bose 901s in a second room), and I don't want to fool myself that I'm some audio expert, as fascninating as all this stuff is.

Sorry for the bonehead post, but I wanted to get a little advice before diving into this thing.
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