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Another noisy amp thread (Read 309 times)
Mannytheseacow
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Another noisy amp thread
04/08/23 at 19:29:49
 
Recently my zkit developed a buzz. Itís always had a low level hum that is tolerable, hardly audible from the listening seat with no music playing. But this new noise is a higher pitched buzzing that increases as I turn the volume up. I tried switching tubes, no difference. I took off the anniversary mods thinking maybe something got hot there with all those big caps packed in, but no change in the buzzing.  Preflight voltage checkpoints are fine.
Any ideas? I feel like since the buzzing started with no change by me that it is an early part failure? Before I repurchase the basic caps and resistors I would scan the group here in case anyone else has experienced this. Hopefully not a transformer issue.
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4krow
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Re: Another noisy amp thread
Reply #1 - 04/08/23 at 19:52:49
 
This kind of thing is always a shot in the dark. There could be a change in the AC line. This might be a new DC offset, or maybe some sort of recent purchase of a piece of equipment or appliance. I am hoping that this can be found outside of the amp. Now, the first question in case I missed it is whether the hum is in both speakers or just one. That leads us in a different direction.
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Mannytheseacow
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Re: Another noisy amp thread
Reply #2 - 04/08/23 at 20:04:10
 
Thanks 4krow. I tried a different outlet, different circuit, and different service and same buzzing, coming from both speakers. Nothing new, no new gear or anything, and still buzzed when no other components are plugged in to the circuit or the amp.  Iím guessing it is coming from the amp. I have triple checked all the solder points and did the chopstick test. I noticed one of the tube sockets is slightly loose and rattly (the socket itself, not the soldered connection) but I donít have another on hand to replace it today.

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4krow
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Re: Another noisy amp thread
Reply #3 - 04/08/23 at 20:46:16
 
You have been pretty thorough and the comment about the tube socket is of interest to me. It all depends about everything in the universe (or so it seems) about this stuff. If it is possible, it won't hurt to clean the pins and sockets of course. Tightness of the socket might be improved from slightly bending the pin connectors of the socket with a pair of needle nose pliers. IIRC there are sockets out there that have superior design for just such a reason. Similar to the RCA jack design that have six sided connectors for the RCA pin. The it becomes what the the damned connector is actually made of. These days, they can make something look great and yet be made out crap metal.
Meant to ask again if you are getting DC offset at the wall outlet. Pretty interested in finding a solution just so I know what works for future reference.
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Mannytheseacow
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Re: Another noisy amp thread
Reply #4 - 04/08/23 at 21:26:24
 
I used the parts express gold pin sockets Steve recommended in the instruction manual.  For better or worse I just ordered three new ones of the same. Reordered new sets of the original caps and a new volume pot too. The volume pot is suspect as the buzzing get wonky at about 70%. Seems like 40% is the sweet spot in my system- thatís where I usually run it. Iíll keep you posted.
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4krow
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Re: Another noisy amp thread
Reply #5 - 04/08/23 at 22:40:46
 
 Thanks man. I have yet another Phono pre that I am working with. It certainly is balance between gain/noise/grounding. Some of this applies to everything electronic.
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Mannytheseacow
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Re: Another noisy amp thread
Reply #6 - 04/14/23 at 02:57:57
 
Some of my parts arrived today. I replaced all the caps except the 3.3ufs in the preamp power (arriving on a different order) and replaced the volume pot. The hum is quieter and the buzz is quieter but both are still there. Much better though.
I first did the caps and plugged it back in and it was the same. Then did the volume pot and thatís where the improvement was made. I think what is happening is that the board flexes when I change tubes (i roll tubes often, especially preamp tube which is right there close) and that flex pushes the pot, which is fixed to the board, up against the hole in the chassis and is flexing the pot. I reamed out the hole for the pot while I was in there so it no longer makes contact with the chassis.
Mounting the pot off the board would be an easy solution, but more likely my next project will be just rebuilding the amp as a point-to-point.
When the other order arrives Iíll install those two last caps and replace the wonky tube socket too. Then maybe Iíll be good as new.  8-)
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4krow
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Re: Another noisy amp thread
Reply #7 - 04/14/23 at 16:35:31
 
It seems endless, doesn't it? I can relate. Even the highest quality builds have had confounding problems at certain stages. The only thing that I can say is that I have had to be patient with even my own designs, not anticipating unseen problems. The flexing of the board may be key here, and suggest a possible faulty solder joint caused the flexing in the first place. I have been known to extend the tube sockets beyond the board using wires, just for this reason! But of course, that can create new problems. Sigh.
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Mannytheseacow
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Re: Another noisy amp thread
Reply #8 - 04/15/23 at 04:58:50
 
Lol, no doubt. My Pearl 2 has been flawless but then you have all the LP monkey business.
Point to point would solve most of my problems, but I would add tube rectification if/when I do it so that will create as many problems as it would solve. Most likely. Sigh is right.
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Mannytheseacow
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Re: Another noisy amp thread
Reply #9 - 04/28/23 at 04:38:27
 
Responding to goso64 I figured I should update here. Iíve replaced pretty much everything in the circuit now. New caps, new tube sockets, new pot, triple checked my solder joints (WBT silver solder) and still have a low residual hum. One I can live with but still there. The only thing that hasnít been replaced is the transformers. I can head a hum in the power tranny, no speaker cables attached. It didnít do that when new so I suspect the hum Iím hearing comes from there. Oh well. Unless it gets worse Iíll live with it.
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4krow
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Re: Another noisy amp thread
Reply #10 - 04/28/23 at 16:23:53
 
Manny,

Waaay back in the day, AC was set at 25hz! I had better qualify that by saying this was in the lab so to speak when AC was being developed. Interestingly, much lower voltages were suggested for industrial use. Don't know why. That didn't last of course for a number of reasons and the higher frequency of 60hz, and a higher voltage was chosen. We have lived with its downsides ever since. Who hasn't heard hum even in our childhood? That is NOT an acceptance of it on my part, but rather a wondering why it couldn't have been addressed more successfully in a lot of cases. No doubt, there are consequences of most any 'answer' to it. It is simply what the general public will put up with overall.
Now, since I had a career in the Bell System, I have had the opportunity to observe other things that are tolerated by people over the years. Way back when copper was king, most every phone line was dead silent. Being a field troubleshooter, I saw all of the exceptions. Usually a ground was causing a hum, but not always. My point here is that dead quiet was normal, and a hum wasn't, but Many people out there didn't care too much (unlike me). Now, let's fast forward to even 20-30 years ago when cell phones became a thing. Yes, I am well aware of the many crappy technologies in between. Dropped calls, inconsistent service, high or at least unacceptable amounts of spiking distortion, and I could go on. The people have 'spoken'. I guess that they are willing to accept this as normal. And so it isn't a big leap to see that they feel the same about audio and a lot of other stuff too.
Then there are the very few of us that don't want what is popular, hum included. Apparently, the price is high to get that box checked.
I will end by saying that in spite of my many efforts to reduce or eliminate it, the results vary. Good equipment, matched with anything from the AC power to the equipment that feeds it (and a hell of a lot more!), can just be a PITA.
As of yesterday, I am moving to an integrated amp design in hopes of a better outcome.
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Mannytheseacow
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Re: Another noisy amp thread
Reply #11 - 04/28/23 at 16:58:59
 
No doubt, 4K...  coming to hi-fi from the studio side I was always blown away at how noisy those great sounding old guitar rigs are.  They sound so good on albums and not many people appreciate how hard the engineers work to make the noise go away.  Usually it just involves turning the volume up really loud so the background is hidden by the low gain on the board.
Keep us posted on how your solid state experiences turn out.  I've been solid state for decades, eventually settling on Hegel integrated quite happily... until this zkit came along.  The zkit was just a hobby project and it just blew the Hegel out of the water.  Although, when it was first built it was dead silent.  My ears are too sensitive anymore and I'm preserving what I have left so cranking the volume isn't a solution anymore.   Grin
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jazz_fool
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Re: Another noisy amp thread
Reply #12 - 05/20/23 at 19:17:42
 
SmileyI may be able to help. Or at least offer a suggestion to save your amp Smiley I had a similar problem with my zkit and with 100+bd sensitive speakers, I agree, the slightest hum can be maddening. I tried every grounding scheme I could think of and had all but given up; †accepting that my amp would have a mild hum forever.

Digging through the depths of the hum threads one day, I came across a thread that suggested eliminating the ground trace from the RCAs to the potentiometer on the circuit board (which runs directly thru the entire board), by connecting each RCA jack shield directly to its corresponding ground lug †on the pot. The thread suggested solid core wire and I didnít have any on hand so just used fairly heavy gauge hook up wire to test the theory, and low n beholdÖ IT WORKED!! I can now run my amp wide open without a sound and adjust the volume with my pre Smiley

Hope this helps!
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