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Old 4th January 2012, 04:12 AM   #1
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Default DH-101 with a noisy phono stage

I have a Hafler DH-101 with a noisy phono stage. The noise is a hiss that is very apparent at high volume and is not related to the cartridge itself. It is noisy with no phono input connected. All the other inputs do not exhibit this noise. Any suggestions regarding what to check?

Thanks!

Guy
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Old 4th January 2012, 04:18 AM   #2
kevinkr is offline kevinkr  United States
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This is probably normal, the high gain required for phono inputs comes with a price, provided that you cannot hear any pre-amplifier noise during normal playback there is no issue. The noise levels of the phono stage should be well below the surface noise level of the record..
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Old 4th January 2012, 01:40 PM   #3
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That is comforting. I was in the process of hunting down the cause of a hum from my Thorens TD-160 MkII + Grado MF-1 and wanted to figure out what I was hearing on the bare input first.
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Old 6th January 2012, 11:40 AM   #4
sreten is offline sreten  United Kingdom
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Hi, phono inputs always have hiss compared to line level inputs, rgds, sreten.

Grado's seem to be more susceptible to hum than other cartridges,
though I've never had the problem with the ones I've used.
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Last edited by sreten; 6th January 2012 at 11:58 AM.
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Old 10th January 2012, 09:14 PM   #5
pixpop is offline pixpop  United States
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I have a DH-110, and the phono inputs are noisy. I quit using them, and built a Pearl, with which I'm more than happy. I feed the Pearl into the Tuner input of the DH-110.
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Old 10th January 2012, 10:36 PM   #6
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i will keep the pearl phono stage as a future enhancement. Thanks!
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Old 11th January 2012, 12:55 AM   #7
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The phono stage shouldn't be "that" noisy, and I wouldn't replace it -- why not try replacing the MC7818/MC7918 voltage regulators with LM317/337 -- and place 100uF cap between the adjust pin and ground. I think you can get almost an order of magnitude reduction in noise with this simple change. I would also replace the RCA female jacks with new ones. Clean switch contacts with isopropyl acohol, the high test version if you can get it.
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Old 11th January 2012, 01:09 PM   #8
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Thanks for the tips jackinnj. I have replaced the rca sockets with gold plated and I have cleaned them recently. I just cleaned the switches and pots with Deoxit. I am trying to decide what mods to make first out of the following:

Power supply and line stage capacitor upgrade.
Full capacitor upgrade.
Active components upgrade.

Odd. My power supply has Motorola devices. 185 M2159 QQ7948 is on the right hand side.

--
Guy
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Old 11th January 2012, 01:21 PM   #9
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Also, I am not sure what you mean by the "adjust pin".
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Old 11th January 2012, 02:10 PM   #10
DF96 is offline DF96  England
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Have we established whether we are talking about a fault to be repaired or a design shortcoming to be upgraded from? A failing resistor can create noise, or a poor solder joint. Solder flux residue which has got damp can create a lot of noise in a high impedance circuit. I would look for simple repairs like that before doing the usual audiophile thing of 'upgrading' all the components.
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