Possible, but probably not. The 3 ways it usually happens are dead right out of the package (or shortly thereafter, manufacturing defect), old age, or burned by excessive current through the wiper.
I've run into at least two dead 9mm Alps dual pots right out of the package. One was scratchy in one channel like yours and the other had one channel just completely dead. Just last week I exchanged some PMs with a fellow who has a bad (scratchy) channel on his 9mm Alps pot (different project) after about a month of use. It happens!
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Hm, do you think The Wire could put out enough current to fry the pot when set to silent (=shorting the amp's output)? I was using the amp as a preamp before and had the pot wired between the Wire and the power amp... I couldn't find any max. current specs for the RK27, but if this could be what broke the pot I might have to think about a series resistor at the Wire output.
I think wiring the pot before the input rather than after the preamp stage might degrade performance slightly?
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Sounds like maybe you have the pot wired up incorrectly.
If you're using The Wire as a preamp (which is perfectly fine) then it should be driving the resistive element, and the output (the wiper) should be connected to the input of the amplifier you are driving.
Having the wiper at minimum volume will short the input of the amp, but the output of The Wire still sees the full resistance of the pot, which shouldn't be a problem if it's 10k or more.
If, for some reason, you have The Wire driving the wiper of the pot, then you've got things wire up incorrectly. In this case, The Wire most certainly can drive enough current into the wiper to damage it. Short circuit current from The Wire can be in excess of 400mA which would easily cook a 1/4W pot.
Can you draw out how you have it hooked up?
Regards,
Owen
If you're using The Wire as a preamp (which is perfectly fine) then it should be driving the resistive element, and the output (the wiper) should be connected to the input of the amplifier you are driving.
Having the wiper at minimum volume will short the input of the amp, but the output of The Wire still sees the full resistance of the pot, which shouldn't be a problem if it's 10k or more.
If, for some reason, you have The Wire driving the wiper of the pot, then you've got things wire up incorrectly. In this case, The Wire most certainly can drive enough current into the wiper to damage it. Short circuit current from The Wire can be in excess of 400mA which would easily cook a 1/4W pot.
Can you draw out how you have it hooked up?
Regards,
Owen
Attached is a diagram to illustrate what I mean.
Scenario 1:
A properly connected pot will never short the output of the previous stage. At minimum volume (wiper connected to GND) the stage driving the pot sees the resistance of the pot (eg. 10k) and it is the input of the following stage that is shorted to GND.
Scenario 2:
An incorrectly connected pot will short the previous stages input to GND at minimum volume, which is not acceptable. It could damage the wiper of the pot, and causes a very low input impedance at most volume settings. This is not good practice.
Scenario 1:
A properly connected pot will never short the output of the previous stage. At minimum volume (wiper connected to GND) the stage driving the pot sees the resistance of the pot (eg. 10k) and it is the input of the following stage that is shorted to GND.
Scenario 2:
An incorrectly connected pot will short the previous stages input to GND at minimum volume, which is not acceptable. It could damage the wiper of the pot, and causes a very low input impedance at most volume settings. This is not good practice.
Attachments
Turns out I didn't think it all the way through - I have it wired up like the "good" side in your picture, obviously hardly any current will be going through the wiper. I guess that means I got a dud from the factory - I think that shouldn't happen at $15 a piece, but nothing I can do about it now. Or maybe I managed to fry it with my soldering iron. Sorry for the brain fart.
volume control SE wire on output of DAC w/buffer
Owen,
I am putting a SE/SE wire on my 9023 dac with buffer. I would like to include a volume control for wire. I would prefer not to put a switch on the DAC output to select headphone use or normal output. I would think putting a volume pot in front of the wire would adversly effect the normal output to the preamp. If I put one on the output of the wire, what would you recommend?
Thanks
Bill
Owen,
I am putting a SE/SE wire on my 9023 dac with buffer. I would like to include a volume control for wire. I would prefer not to put a switch on the DAC output to select headphone use or normal output. I would think putting a volume pot in front of the wire would adversly effect the normal output to the preamp. If I put one on the output of the wire, what would you recommend?
Thanks
Bill
Hi Bill,
The output is definitely not a good place for a volume pot. Are you using this to drive headphones? If so, then the output definitely isn't an option.
Adding a pot between the output of the DAC and the The Wire shouldn't cause any problem at all, as long as the combined input impedance of the pot, The Wire, and whatever else you have hooked up isn't too low for the DAC to drive.
Aim for a combined total of 10k-20k and you should be fine.
Regards,
Owen
The output is definitely not a good place for a volume pot. Are you using this to drive headphones? If so, then the output definitely isn't an option.
Adding a pot between the output of the DAC and the The Wire shouldn't cause any problem at all, as long as the combined input impedance of the pot, The Wire, and whatever else you have hooked up isn't too low for the DAC to drive.
Aim for a combined total of 10k-20k and you should be fine.
Regards,
Owen
Bill,
More discussion on similar subject back at post #1603 might be a good reference http://www.diyaudio.com/forums/head...headphone-amplifier-pcbs-161.html#post3163183
Chris
More discussion on similar subject back at post #1603 might be a good reference http://www.diyaudio.com/forums/head...headphone-amplifier-pcbs-161.html#post3163183
Chris
Well, another one of my V2 PSUs has just kicked the bucket... It worked great for a while, then I used it for a few hours to supply a 12V relay from the positive rail (nothing big, certainly no more than 50mA coil draw) and when I moved it back to the amp it was supplying before, the negative rail had died. I might have accidentally touched the regulator, but should that really break the PSU?
Also, I then replaced the regulator and it first put out -11.5 on the negative rail, then it started to go up towards -20 and I unplugged it, now it's at 1V (not -1V!). I touched earth ground and everything before soldering in the new reg, but couldn't avoid touching it a few times after that. I'm really curious whether Mouser just has a bunch of bad regulators or what's going on here...
Also, I then replaced the regulator and it first put out -11.5 on the negative rail, then it started to go up towards -20 and I unplugged it, now it's at 1V (not -1V!). I touched earth ground and everything before soldering in the new reg, but couldn't avoid touching it a few times after that. I'm really curious whether Mouser just has a bunch of bad regulators or what's going on here...
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Well the output has now changed again to -0.024V. I proceeded to reflow all the resistor joints and it stayed like that.
These PSUs sure don't like me very much!
A gain of 1 only makes sense if you intend to only use low-z headphones. Some people have invested a lot of money and time in high-z headphones. There is more than one kind of "hard to drive".
.:Sent by pneumatic tubes
Isn't it also a function of the output level of your source?
Care to give an example including source and headphones that would require higher gain?
Chris
Isn't it also a function of the output level of your source?
Care to give an example including source and headphones that would require higher gain?
Chris
Sure. My Gamma2 dac has a somewhat generous output of 1.4Vrms at 0dBFS:
The γ2 Compact High Performance DAC
My RFT HOK 80 2 headphones were originally specified at "94db at 5mw" (18.8 db/mw?) but they require some mechanical damping to smooth out the frequency response and this necessarily reduces their sensitivity. They have a nominal impedance of 60 ohms:
RFT HOK 80-2 - Wikiphonia
94dB/5mW is closer to 87dB/mW without getting calculator out ... So that's just off the top of my head and knowing that power /2 is 3dB (or have I made a mistake here ... Should it be 6dB ... Its 1am here now :/ someone correct me if I'm wrong, please!).
1.4Vrms is not what I'd call generous but still should be enough for surprising output levels if you do the math and don't attenuate in the DAC unnecessarily.
Owen uses HE-6 or something with unity gain from memory and they're hardly a high sensitivity set of headphones ... He has a higher output level from his DAC though.