Hello,
I have a Rudistor RPX-33MK2 headphone amp which is producing noise in the left channel. The noise comes on a few minutes after the amp is turned on. The channel still works, but the static noise is just there along with whatever is playing. I've recorded a sample of that, which can be heard here - https://app.box.com/s/7htgpg3ieiuytt61qwhsd5ux05i3b0bf
I wanted to ask for some advice on how to go about resolving the issue. I can see the trimpots, maybe need to adjust those but have little idea where I would point my multimeter to..
Any tips are most appreciated, would like to put this dude back in use
.
Thanks,
-Art
I have a Rudistor RPX-33MK2 headphone amp which is producing noise in the left channel. The noise comes on a few minutes after the amp is turned on. The channel still works, but the static noise is just there along with whatever is playing. I've recorded a sample of that, which can be heard here - https://app.box.com/s/7htgpg3ieiuytt61qwhsd5ux05i3b0bf
I wanted to ask for some advice on how to go about resolving the issue. I can see the trimpots, maybe need to adjust those but have little idea where I would point my multimeter to..
Any tips are most appreciated, would like to put this dude back in use
. Thanks,
-Art
Attachments
Adjusting the trimpots would not help the noise, although pots can degrade and cause noise.
Avoid adjusting the pots, it seems to be a factory adjustment only, with no information available.
The transistors in sockets certainly could be a source of noise, due to lead or socket corrosion.
Try tapping them gently to see if that causes more noise.
Avoid adjusting the pots, it seems to be a factory adjustment only, with no information available.
The transistors in sockets certainly could be a source of noise, due to lead or socket corrosion.
Try tapping them gently to see if that causes more noise.
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Before replacing the transistors (shotgun approach is seldom a good idea),
remove the sockets and throw them away.
Then clean the transistor leads, and solder the transistors directly to the board.
Replace any that are still noisy. Transistors themselves seldom become noisy,
unless abused by hot swapping connections, etc. which causes degradation.
remove the sockets and throw them away.
Then clean the transistor leads, and solder the transistors directly to the board.
Replace any that are still noisy. Transistors themselves seldom become noisy,
unless abused by hot swapping connections, etc. which causes degradation.
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So what I did was I swapped the socketed transistors between the left and right channels to see if the problem would follow to the other channel, and indeed it did. So it does seem like it is one of the socketed transistors. Thanks everyone for chiming in about this.
They are marked F245C W 50. Would the 50 indicate 50V? The closest I'm finding online is BF245A, B, C. Though those are rated for 30V. Besides also being no longer in production. Any tips on a suitable replacement?
They are marked F245C W 50. Would the 50 indicate 50V? The closest I'm finding online is BF245A, B, C. Though those are rated for 30V. Besides also being no longer in production. Any tips on a suitable replacement?
I would also check for thermally fractured solder joints on the devices that get hot, like the gold power resistors and the semiconductors on the heat sinks near the fuses.
This looks like a class A circuit so some components will run hot when ever the power is on, no matter the listening level.
This looks like a class A circuit so some components will run hot when ever the power is on, no matter the listening level.
Will take a look, but I'm fairly confident the issue is with the socketed transistors. As the problem followed the transistors to the other channel when I swapped them.
Whatever the root cause is... have a look below.... the way that mains wiring runs in parallel with the yellow wiring is just bad.... you may or may not be able to hear it, but if you measure the noise, the penalty will be at least 10dB higher noise floor. The worst thing is.... the only way to prevent it (fix it) in this particular case, would be to relocate the mains switch to the back panel. Anyway, I thought it would be good to say something here... because I see this way too often on these forums.
Yes, that's a great test. And of course, go after the easier ones first, as pulling that board to get at the back side looks tedious.
Thank you, Hugo!Art, it is a BF245C nFET. Buy from a reputational source (no Amazon or Ali and the like) and make sure it is a 'C'. If you can find it...
Hugo
I've been looking for possible replacements but it ain't easy.
Some match but are also unavailable, unless you could go the SMD route.
Even the BF545C is obsolete.
But it might be worth looking at the proposed substitutes at Digikey:
https://www.digikey.com/en/products/detail/nxp-usa-inc/BF545C-215/807480
Hugo
Some match but are also unavailable, unless you could go the SMD route.
Even the BF545C is obsolete.
But it might be worth looking at the proposed substitutes at Digikey:
https://www.digikey.com/en/products/detail/nxp-usa-inc/BF545C-215/807480
Hugo
That definitely seems like one option, thanks for looking into it. I did find a seemingly legitimate vendor who has some NOS, but they only have 3 of them. The amp has 4 total between the two channels. If I swapped two, one on each side and kept two of the originals, would that be alright? https://www.silicon-ark.co.uk/bf245c-n-channel-silicon-field-effect-transistor
Looking at the MPF102 as a replacement for the BF245C. Is there any reason why it would not be a good match?
Here are the datasheets for the two
BF245C - https://www.mouser.com/datasheet/2/308/BF245C-1300109.pdf
MPF102 - https://www.jameco.com/Jameco/Products/ProdDS/26403.pdf
https://www.jameco.com/z/MPF102-Major-Brands-Transistor-MPF102-JFET-N-Channel-TO-92_26403.html
Here are the datasheets for the two
BF245C - https://www.mouser.com/datasheet/2/308/BF245C-1300109.pdf
MPF102 - https://www.jameco.com/Jameco/Products/ProdDS/26403.pdf
https://www.jameco.com/z/MPF102-Major-Brands-Transistor-MPF102-JFET-N-Channel-TO-92_26403.html