While checking bias on my F-5, I noticed something I hadnt noticed before. On one channel, (the other does not have this toasty feature) I noticed some browning of the two resistors that are used to measure off of when setting bias.
These are Peter Daniels boards BTW.
This amp sounds fine, bias is steady and has been running since 2010 or 2011 with no problems. I never noticed this before, the other channel does not have this. Both are right at the .59 on the bias . I though I smelled something a little hot, dont know if that was it or this has been there. Seemed odd it was only 1 channel.
These are Peter Daniels boards BTW.
This amp sounds fine, bias is steady and has been running since 2010 or 2011 with no problems. I never noticed this before, the other channel does not have this. Both are right at the .59 on the bias . I though I smelled something a little hot, dont know if that was it or this has been there. Seemed odd it was only 1 channel.
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Any thing I should check? The mosfet closest to that end always ran a little hotter than the others.Something happened to run lots of current through them. They should not
be seeing more than a watt or so on the stock build with normal use.
Bias has been at normal amount for several years. Ideas as to maintainence for this age and sitiation?
Russellc
I can do that, it would just be a mstter of mounting the boards to the sink ( they are "dead bug" mounted right now) then running leads to the fets.I think I would put in new ones and leave the leads long so that you can
put some distance between them and the hot transistors.
I understand getting it away from the heat of the resistor (the little thermoiistors are REALLY hot but I cant get the fet away from them) and of course as creator of this amp I take your word for it, but could you explain to me how this aids the problem? Not doubting at all, just want to understand. I am a babe in the woods here and feared something about the amp or power supply had gone bad.
I recently installed neutrik connectors for the twin power cords (amp is dual mono including two cords)....I have.twin terminal blocks with the CL-60 attached to them like 6L6 does in his build thread. Yes Zen Mod, I also have twin CL-60s for the grounds!
When I reattached the red and black transformer leads could I have made a mistake that would cause this? It doest appear I did any mixing them up, verified which black went with which red, this the only recent change. For all I know, this browning could have happened a while back, just thought I should mention this....
I also have parts and DIYstore F-5 boards as well as more of the Peter Daniels tyoe. Perhaps the store boards are laid out better or at least larger?
I just want to fix this thing so I dont have to worry about it...for several years it was no problem, would like to get back there!
Thanks for the time, it is much appreciated!
Russellc
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One other thing just occurred to me. I have an original Roku box that was connected to the other input of the B-1 I have been using for the Pre with this amp. I use it for streaming various materials, and I streamed some spotify to see how it would play...just moved F-5 downstairs as BA-3 took its place upstairs. The Rokus out put to its RCA jacks must have shot craps, as it began humming...moving the cables seemed to alter this, but it was loud enough I just shut it down.
With new source connected, all seemed well until I decided to recheck bias and saw the toasty resistors. DC on the Roku was only a few milivolts, it works fine hooked up to my TV (with HDMI cable, not RCA outputs) but the RCA out must have cooked or lost its ground. The speaker that hummed loudly is the side this happened to. Coincidence?
Russellc
With new source connected, all seemed well until I decided to recheck bias and saw the toasty resistors. DC on the Roku was only a few milivolts, it works fine hooked up to my TV (with HDMI cable, not RCA outputs) but the RCA out must have cooked or lost its ground. The speaker that hummed loudly is the side this happened to. Coincidence?
Russellc
OK, I believe there is something to my last post. I do believe I have something miss wired after that last power cord in change and am going back through everything. I just brought out the trusty tube preamp and power amp and very begrudgingly hooked it up to the roku box and it streams fine. Not that this is some music source deluxe or anything, it just had a huge problem with the F-5 it hadnt had previously, so something is amiss there. I must have messed up a ground or something. Oddly, I tried steaming with lap top and that works fine with B-1 and F-5.
I dont know if this big hum thing caused my resistor to tan or not, but something is whacky with my rewire. Taking it apart now for a redo.
Russellc
I dont know if this big hum thing caused my resistor to tan or not, but something is whacky with my rewire. Taking it apart now for a redo.
Russellc
Sometimes when an amp is humming it is because there is system
oscillation that will often create high current draw.
That it improved with the cables moved might indicate that the output
of the amp is bleeding back to the input there.
Remember that there is quite high bandwidth in this amp, and that is a
potential issue.
oscillation that will often create high current draw.
That it improved with the cables moved might indicate that the output
of the amp is bleeding back to the input there.
Remember that there is quite high bandwidth in this amp, and that is a
potential issue.
Sometimes when an amp is humming it is because there is system
oscillation that will often create high current draw.
That it improved with the cables moved might indicate that the output
of the amp is bleeding back to the input there.
Remember that there is quite high bandwidth in this amp, and that is a
potential issue.
I recall Zen Mod I believe, showing a small device easily put together with an led that would indicate the amp showing any oscillation. I am searching for that post. If anyone knows of it, I would appreciate a heads up. I am searching through the gigantic F-5 thread, I believe that was where it was.
In the mean time I have been experimenting. I hooked up the B-1 to my tube power amp, and all seemed fine, unless I brought the dreaded Roku device near it. If I got the interconnect in contact with the B-1's RCA, the noise began, just like the F-5 exhibited. I am hooking up my BA-3 pre to see if it also has this problem. My tube preamp with tube power amp played it fine...if the BA-3 pre plays it with streamer box, I will switch tube power amp with F-5. If that combo plays it, I suspect the B-1.
Even if all this proves out, it does not necessarily mean the this noise festival is connected to the tanned resistors, but this is the only odd behavior this amp (F-5) has ever shown. With inputs shorted, or which ever pre attached it is dead silent unless I try to attach the roku streamer box. If BA-3 plays it, tube pre plays it, then I will look hard at the B-1.
In the mean time, searching for the Oscillation detecting device schematic.
Thanks again for your personal attention!
Russellc
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That was quick, thank you Zen mod. Let's see if I have all the goodies. In mean time, hooked up the BA-3 pre to tube power amp, and it, like the Tube preamp (AVA Super Pass II) plays the dreaded streaming box fine...
Time to try F-5....If this works, I'll go to work on B-1.
Now let's look in box of goods and see If I can cobble together Zen Mod device. do resistors need to be of any certain wattage? I think I have tons of 1/4 watters. Digging for caps, I have plenty of LEDs, hope blue is good!
Russellc
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The first thing I see is the Panasonic "3W" resistor. Ha!
The resistor size is more appropriate for a 1W part, which then should be derated by 50%.
There are no miracles - if a resistor is small for its rating, it will run hot, as it will not have enough surface area to shed the power. If you are cool with the resistor running hot, fine - keep in mind, though, that the printed circuit board and adjacent parts may not be tolerant of the extra heat. Space the hot part off the board using kinks in the leads (common), teflon sleeving, or ceramic beads, and keep it away from other parts that won't appreciate the sauna bath (just about everything else, but including film caps, electrolytics, and semis. Or, use a larger part that will run cooler for the same dissipation.
The resistor size is more appropriate for a 1W part, which then should be derated by 50%.
There are no miracles - if a resistor is small for its rating, it will run hot, as it will not have enough surface area to shed the power. If you are cool with the resistor running hot, fine - keep in mind, though, that the printed circuit board and adjacent parts may not be tolerant of the extra heat. Space the hot part off the board using kinks in the leads (common), teflon sleeving, or ceramic beads, and keep it away from other parts that won't appreciate the sauna bath (just about everything else, but including film caps, electrolytics, and semis. Or, use a larger part that will run cooler for the same dissipation.
I put F-5 in with BA-3 Pre, hooked up streaming box and it hummed. Not as bad, no cracks like when pulling plug out on guitar amp, but noise. Re doing grounds where new power cords were installed, if it persists will post photos. really odd that problem with humming F-5 only occurs when roku streamer is put in system.
It used to work fine. With any other source, laptop, CD, Tuner, it is quiet as the grave.
Putting missing parts for Zen Mod's gizzmo in current mouser order.
Russellc
It used to work fine. With any other source, laptop, CD, Tuner, it is quiet as the grave.
Putting missing parts for Zen Mod's gizzmo in current mouser order.
Russellc
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Here's a 3W, 390 ohm Panasonic metal oxide resistor, running with 20V across it (~1W) dissipation. Temperature is close to 100C. It might have gotten hotter, but there was a very slight breeze in my lab area, and I only let the part toast for 5 minutes or so. It actually did a little better than I thought it would - I was expecting about 120C. It doesn't take much to get the small parts toasty..
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