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Old 18th April 2011, 12:44 AM   #1
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Default Hafler DH 110 preamp problem

Hi. I recently obtained a Hafler 110 preamp from a friend who had not used it in years. I am not getting any sound from the right channel. I also tried my headphones without the amplifier(DH 120)on, and I only had sound from the left side. Does this tell me it is definitely the preamp? What are the most likely causes? Thanks
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Old 18th April 2011, 03:33 AM   #2
djoffe is offline djoffe  United States
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Default Here's a good start

you may already have it, but here's a link to the manual, including schematics:

http://www.hafler.com/techsupport/pd...preamp_man.pdf
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Old 18th April 2011, 11:10 AM   #3
Tajzmaj is offline Tajzmaj  Slovenia
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Hi I have done some repair works on such preamp some years ago and there was heavily oxidated selector switch....if you can buy new,replace it if not try with some contact spray but it will solve problem just temporary....and there is also possible that some pot is breaking too. And more. It is also possible that there you have dry or defective cap. There is a lot of tantals in signal path and also some other electrolytics on tone control circuit and psu.... Regards and good luck
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Old 18th April 2011, 08:48 PM   #4
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Default Hafler DH110 preamp problem

Hi. Thanks for the advise. I will look into what you have suggested.
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Old 18th April 2011, 09:25 PM   #5
amp_guy is offline amp_guy  United States
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Most common cause of no or distorted output from a DH110 is bad muting FETs and oxidized switch contacts.
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Old 19th April 2011, 02:12 AM   #6
PB2 is offline PB2  United States
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There are no Tantalum caps in this preamp as far as I can remember, but there are many aluminum electrolytics that go bad. Mine had issues in the mute timing circuit, C39 and C40, and I do think one of the mute FETs went bad also. I just pulled the FETs and the output thump was not that bad, but most of my power amps mute on power up anyway so I'm not sure how bad the preamp is.
I changed all the caps in the line stage, and would do the phono section also if I used it. Note that many of the electros are non-polar types which are not so common.
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Old 19th April 2011, 03:29 AM   #7
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Default Hafler DH110 preamp problem

Thanks for your input Pete. I just wish I knew more about this stuff. I had a very knowledgeable friend who suddenly past away last year. This would be childsplay for him.OH well,onward.
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Old 19th April 2011, 11:09 PM   #8
PB2 is offline PB2  United States
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Quote:
Originally Posted by bluesbaby View Post
Thanks for your input Pete. I just wish I knew more about this stuff. I had a very knowledgeable friend who suddenly past away last year. This would be childsplay for him.OH well,onward.
Very sorry to hear about your friend. Just ask away here and we'll try to help.
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Old 19th April 2011, 11:51 PM   #9
Tajzmaj is offline Tajzmaj  Slovenia
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I'm sorry too....
Pete was probably right....I work on DH101 and there if I'm not wrong was some tantal caps...all dry.
If this helps.....
Best regards
Taj

Last edited by Tajzmaj; 20th April 2011 at 12:10 AM.
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Old 24th March 2012, 01:10 PM   #10
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I purchased this at an Audio Show on Long Island in 1980 (I believe). Since that time it was used by 2 of my sons -- and came back owing to bad RCA's --- found another problem at the same time:

Click the image to open in full size.

Fixed:
Click the image to open in full size.


New Input connectors:

Click the image to open in full size.

Will probably replace the floating LM317/337 regulators and install a ground loop breaker. The main input board ground is connected to the chassis at the phono inputs which will have to change as well.
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