Try to use a dc filter for toroidal transformers :
http://www.diyaudio.com/forums/powe...t-buzzing-toroid-transformers-what-right.html
http://www.diyaudio.com/forums/soli...oidals-summary-most-interesting-comments.html
http://www.diyaudio.com/forums/powe...t-buzzing-toroid-transformers-what-right.html
http://www.diyaudio.com/forums/soli...oidals-summary-most-interesting-comments.html
I played with my F5 today. It sings beautifully, but 120 Hz hum/buzz is something annoying with high efficiency speakers.
Since it is 120 Hz (confirmed with scope), I think it's power supply ripple. It also reduces significantly when I disconnect one channel. Reducing the bias to 1A didn't help that much.
So I added total of 60,000 uF today, on top of 80,000 uF. It helped a little but not completely gone.
Those whose F5 doesn't have hum problem, how big PS capacitance are you using? Total of 140,000 uF not enough?
Can I show you the picture later? It's too shamefully ugly now. I am very lazy at cutting wires to the right length.
Wiring is very similar to 6L6's illustrated guide to F5 build. I basically followed his way.
One big difference is that I use common bridge diode, 600V 25A. Will it help if I replace them with MUR860s?
The transformer is 18V x 2, 600VA.
Wiring is very similar to 6L6's illustrated guide to F5 build. I basically followed his way.
One big difference is that I use common bridge diode, 600V 25A. Will it help if I replace them with MUR860s?
The transformer is 18V x 2, 600VA.
I have F5 with two series 19.5V laptop SMPS and 2000uF of capacitance per rail, and it has no hum.
I also have built one with 0.45F of capacitance and 2kVA transformer and that has no hum either.
Your power supply is probably not the culprit, that's my guess - not at that capacitance level. The bias reduction not helping, and only one channel connected helping, points to the certainty of a ground loop.
Do you get the hum with both channels shorted? With one channel shorted, is there hum in that channel? The other channel?
I also have built one with 0.45F of capacitance and 2kVA transformer and that has no hum either.
Your power supply is probably not the culprit, that's my guess - not at that capacitance level. The bias reduction not helping, and only one channel connected helping, points to the certainty of a ground loop.
Do you get the hum with both channels shorted? With one channel shorted, is there hum in that channel? The other channel?
I basically was thinking over what might be the reason while I was sleeping. I kind of feel like I was working on the amp in my dreams.
Anyway, first thing I tried this morning was to disconnect additional 60mF of capacitance I added later. I added them while only one channel was connected, and I thought it was helpful. Later I wired them somewhat in a mess.
Alas, that was the problem. Wire to the 60mF bank, or capacitors themselves, I don't know. I disconnected them, and F5 is dead quiet with 98dB speakers without source.
Assuming wiring and capacitors were OK, can adding excessive capacitors to the power supply cause hum/buzz?
Anyway, first thing I tried this morning was to disconnect additional 60mF of capacitance I added later. I added them while only one channel was connected, and I thought it was helpful. Later I wired them somewhat in a mess.
Alas, that was the problem. Wire to the 60mF bank, or capacitors themselves, I don't know. I disconnected them, and F5 is dead quiet with 98dB speakers without source.
Assuming wiring and capacitors were OK, can adding excessive capacitors to the power supply cause hum/buzz?
wrong assuming
cap bank , along with rectifiers , must be wired/routed in proper way , so that amp is connected in way to see least amount of ripple
What I did was to wire them to V+/G/V- terminals, instead of terminals of last caps directly. Does this matter that much? Or the wires were a bit too long at 4 inches or so.
By the way, I was wrong. The amp is not dead quiet without signal.
The noise was shifted upwards. 60Hz/120Hz hum/buzz is completely gone, but there's slightly higher frequency noise coming from tweeter crossed at 1kHz with 2nd order high pass filter. I didn't measure the frequency of this noise.
What can this be?
ZM, sorry still no pictures. I made the wiring look better, but not yet for the show.
Anyway, I found the problem. It was signal input cable from RCA to amp board. If I short them, amp is absolutely quiet. I relocated the input cables so that they now run along the heatsink rather than floating across the amp in the shortest way. The noise got much lower, but still it's not as low as when the input is shorted to the ground.
Anyway, I found the problem. It was signal input cable from RCA to amp board. If I short them, amp is absolutely quiet. I relocated the input cables so that they now run along the heatsink rather than floating across the amp in the shortest way. The noise got much lower, but still it's not as low as when the input is shorted to the ground.
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