Hafler DH 110 preamp problem

[bluesbaby]

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

[djoffe]

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

http://www.hafler.com/techsupport/pd...preamp_man.pdf

[Tajzmaj]

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

[bluesbaby]

Hi. Thanks for the advise. I will look into what you have suggested.

[amp-guy]

Most common cause of no or distorted output from a DH110 is bad muting FETs and oxidized switch contacts.

[PB2]

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.

[bluesbaby]

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.

[PB2]

Originally Posted by bluesbaby

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.

[Tajzmaj]

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

[jackinnj]

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:



Fixed:



New Input connectors:



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.