I have a Hafler DH-110. it works great with two exceptions. When turning on, the unit make a very short pop through the speakers. It is not loud, it is very short. The unit does not have a capacitor across the switch like the Hafler power amps have. I have attached the power switch schematic portion. I checked Ic31 and it is okay. I tried a .01 MFD across the swtiched hot and neutral switched outlets and that did nothing. The second thing is that when pushing the tone control defeat on and off it makes a small noise. The manual even says this is normal. I do not know why. It even says how to press the button. Any help would be appreciated
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Try an X rated capacitor of around 0.05uF across the power switch.
The tone button probably has some DC voltage on it, in which case the noise would be normal.
The tone button probably has some DC voltage on it, in which case the noise would be normal.
Rayma, Thanks again for responding. I'll order one from Mouser or some place. If i remember from a previous thread you mentioned that there will be some voltage across this capacitor when not turned on...Correct? And that does not hurt anything?
Yes, that's why it must be an X capacitor, rated for across the AC line use.
Only buy such a part. If that does not fix the noise, try it connected across
the transformer primary.
Only buy such a part. If that does not fix the noise, try it connected across
the transformer primary.
Rayma, Thanks. I have a new problem and this just started when i turned the unit on today. I have attached the full schematic. I have my music source connected to the AUX input. when the selector switch is set to this input the ouput is perfect no buzzing or anything. It is clear in both channels. when I set the selector switch to any other position, tune, phone, tape 1, tape 2, there is source material playing very raspy and reduced volume. If i increase the volume pot it does increase in volume more on the left channel than the right channel. When I press the EPL switch in the raspy reduce volume continues. My limted trouble shooting skills think this is a leaky coupling capacitor, may one of the 22UF NP ones or the FET muting transistor. If you have the time I am open to ideas. I can also tell you the if you touch the top of C106 and C6 there is hum injected into the whole preamp. These are the phono section input cpacitors. It is gard to beleive both would go bad at the same time. Any advice would be great. Thanks Mark
You hear the noise on open inputs? Such noise pickup and crosstalk are often normal in preamps.
Try inserting shorting plugs into a pair of unused inputs, and see if the noise is still present.
These days enough RF noise is present in the environment that such pickup is common.
Also removing the cover will cause additional noise pickup, as will touching parts of the circuitry,
especially in high gain stages such as the phono stage. Nothing to worry about.
That said, replacing NP electrolytic capacitors in the signal path in such an old preamp would be reasonable.
Just not the film capacitors.
Try inserting shorting plugs into a pair of unused inputs, and see if the noise is still present.
These days enough RF noise is present in the environment that such pickup is common.
Also removing the cover will cause additional noise pickup, as will touching parts of the circuitry,
especially in high gain stages such as the phono stage. Nothing to worry about.
That said, replacing NP electrolytic capacitors in the signal path in such an old preamp would be reasonable.
Just not the film capacitors.
I tried the shorting plugs, no go. I have my turntable on the phone input and the aux streaming. the phone plays and the aux plays in the raspyness. I will order some new caps, jftes just in case and new electrolytics. thanks.
Rayma, Here is what I discovered. The selector switch is grounding the other inputs as designed. When I played material from the ipod, those leads also act as a FM receiver built into the ipod. When I moved these to the tape inputs all is okay as these inouts appear to bypass the other inputs. It is as if the back plane becomes a transmission line with the ipod for the material playing at a very reduced level. When I remove the ipod and connect the phono, CD player and tuner, there is no crosstalk or issues, absolutely dead quiet. Second, I found two leaky input capacitors on the left and right phono input. Bottom line problem is solved and I am happy with the sound. Thanks again.