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In Reply to: RE: So the phon pre dies again, right before holiday listening. posted by jupiterboy on December 19, 2014 at 07:06:45
of mods did you do to the Phonomena. IIRC it has a lot of SMD devices, although it is a discrete amplifier section...
Stu
Follow Ups:
Mike changed out dip resistors to give me more loading options for my MM cart (62K, 50K, 38K). The caps were reduced to 68pF, and most recently, the caps were changed to WIMAs, including the caps in the RIAA circuit. And, we added a mono switch and upped the resistors on the output.
All good stuff. Sounds amazing. This unit is his own development unit, and it does blow resistors. IDK
hmmmmm...Mike is a very talented engineer. Have you spoke to hm about this. He's really busy now, but I'm sure he can solve the issue. He just designed an AMG phono section, IIRC.
I'm sure the resistors on the DIP switch have nothing to do with the failure, but most likely the change inthe output.
I would fix it as I am a great admirer of MY's designs
It’s great, and I am as well. Not to mention his service. Still, if I keep it in use I will need a backup unit. However, there may be some issue with this particular unit that is unique. It does use some different parts that were not available/discontinued in the first production. In other words, my issues should not be taken as characteristic of the model specifically because it is not typical of the model.
In some respects, Mike has been so generous with his time that I hesitate to send it back because I just got it back from him, it is not under warranty, and if I send it back to him again it will be the fourth time in a few years that he has repaired the unit at no cost to me. If I were to send it back and get the issue fixed, experience tells me I would be sending it back again in short order.
If so, is that the current problem, a blown resistor? If this is happening repeatedly, and if it's happening in the same part of the circuit, then an upgrade in the wattage rating of the resistor(s) that blow is warranted. Did he do something to increase voltage or current? You might take a voltmeter and measure VDC across the resistor(s) that blow, once the unit has been repaired. Then you can calculate the current; it is equal to the measured VDC divided by the value of the resistor. Then you can calculate wattage, equal to the same VDC measurement multiplied by the current. If the Watts are near to or above the wattage rating of the resistor in question, you need to replace that resistor with one of higher wattage rating. Some resistors are very sensitive to high voltages, even when their wattage rating is not exceeded; that's another possible issue. But you should not have to put up with that kind of recurring problem; it's curable.
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