Music Hall Dac 25.2 repair

[GytisB]

Hey! I bought a used Music Hall Dac 25.2 a few months ago. It was functioning fine, although I always heard strange noise on the headphones right channel when I was turning it off (headphones are 250ohm). Anyway, I was never paying attention to it, since it didn't damage headphone speakers. Recently I thought that it would be cool to try out different OPAMP's, since many are upgrading/trying other and tweeking the sound to their liking. It comes originally with 2xOPA2134PA and 1xOPA2604AP (also 1xNE5532 in the headphone volume pot meter section). Many choose to go for fairly expensive Burson V5i or V6. But I wanted to start small and went with a recent and loved by many OPA1656. TI (Texas Instruments) say that this OPAMP is "OPA1656: Next generation OPA2134 and OPA2604 replacement". So I thought that it would not hurt the amp dac in any way, and replaced all of them at once (including the NE5532). Turn on the unit, and it works just fine, no smoke, sound comes through. 2-3 minutes into using it with OPA1656, I lost sound in the right channel. Turned it off, opened it right away, no burning signs. Switched back to original OPAMP's. Turn it back on, and... right channel more or less dead. I get 50% less volume from the right channel. Thought that it was the headphone amp that died, but probably it is not the case. Running amplifier using RCA output, I hear also 50% less volume in the right channel. Changing from USB input to Optical input, I still get the same result. I can't seem to observe any critical burning signs or anything. I only own multimeter, so it can be quite challenging finding the problem, but... is there anything I could try to test myself/replace? or should I just bring it straight to the professional technician with proper testing tools? I still cannot believe it broke, especially when these OPAMPs are more or less interchangeable.

 

[Ray Gianelli]

Hey! I bought a used Music Hall Dac 25.2 a few months ago. It was functioning fine, although I always heard strange noise on the headphones right channel when I was turning it off (headphones are 250ohm). Anyway, I was never paying attention to it, since it didn't damage headphone speakers. Recently I thought that it would be cool to try out different OPAMP's, since many are upgrading/trying other and tweeking the sound to their liking. It comes originally with 2xOPA2134PA and 1xOPA2604AP (also 1xNE5532 in the headphone volume pot meter section). Many choose to go for fairly expensive Burson V5i or V6. But I wanted to start small and went with a recent and loved by many OPA1656. TI (Texas Instruments) say that this OPAMP is "OPA1656: Next generation OPA2134 and OPA2604 replacement". So I thought that it would not hurt the amp dac in any way, and replaced all of them at once (including the NE5532). Turn on the unit, and it works just fine, no smoke, sound comes through. 2-3 minutes into using it with OPA1656, I lost sound in the right channel. Turned it off, opened it right away, no burning signs. Switched back to original OPAMP's. Turn it back on, and... right channel more or less dead. I get 50% less volume from the right channel. Thought that it was the headphone amp that died, but probably it is not the case. Running amplifier using RCA output, I hear also 50% less volume in the right channel. Changing from USB input to Optical input, I still get the same result. I can't seem to observe any critical burning signs or anything. I only own multimeter, so it can be quite challenging finding the problem, but... is there anything I could try to test myself/replace? or should I just bring it straight to the professional technician with proper testing tools? I still cannot believe it broke, especially when these OPAMPs are more or less interchangeable.

You can signal trace with a DMM by injecting a sine wave into the inputs and tracing it with the DMM in AC volts mode. I'd use a signal less than 1 Khz since I don't know the limits of your DMM. OTOH, you're not looking for absolute levels, so as long as you can see the input level on your DMM you're good.

You can create high quality sine waves with Audacity for PC or Mac. Either output them directly from you computer or burn a CD and use a CD player for your signal source.

Here's one view on op amp rolling. You may agree or not, but I tend to, as the author backs up his statements with measurements:

https://nwavguy.blogspot.com/2011/08/op-amps-myths-facts.html

https://nwavguy.blogspot.com/2011/08/op-amp-measurements.html

 

[GytisB]

You can signal trace with a DMM by injecting a sine wave into the inputs and tracing it with the DMM in AC volts mode. I'd use a signal less than 1 Khz since I don't know the limits of your DMM. OTOH, you're not looking for absolute levels, so as long as you can see the input level on your DMM you're good.

You can create high quality sine waves with Audacity for PC or Mac. Either output them directly from you computer or burn a CD and use a CD player for your signal source.

Here's one view on op amp rolling. You may agree or not, but I tend to, as the author backs up his statements with measurements:

https://nwavguy.blogspot.com/2011/08/op-amps-myths-facts.html

https://nwavguy.blogspot.com/2011/08/op-amp-measurements.html

Sounds like a good idea! Will do some research and reading on how signal tracing is done using DMM. Hope I can spot something. I own a UNI-T UT61D DMM by the way, so I guess it should work good enough in this case. I did some diode testing (with components on the PCB), and if I am not wrong, 3 or 4 diodes are bad. When I reverse the leads on DMM, I do not get O.L., but mV and V readings. Only 1 out of all diodes pass the diode test using DMM.

Will read the provided thoughts on OPAMP rolling! Always great to hear other people thoughts. Although I had great results switching from NE5532P to OPA1656 in my FX502S Pro chinese amp.