Hi Guys,
I had purchased a 12G kit and put it together. Used a couple of the mods that were recommended including bridging the filament wires and bypassing the input caps and the thing sounded
BEAUTIFUL. Unbelievable sound/dollar value. Built some Open baffle speakers and all was good with the world.
Well, after a week or so it was time to built a box to make it look as good as it sounds and make things work a little more practically.
I extended the leads from the board to the OTLs and the power Trans, put bullet connectors on them so I could run them though holds in the case easily. I moved the volume pot off the board so I could mount it on the front panel. I used approx 3" wires and twisted each pair. Finally I added a 3 channel switch and wired it to 3 sets of inputs and to the board, all the wires were made of twisted pairs from some cat 5 and braided together.
Now the bad part. The amp now howls.
It got worse when you touched the volume control, or even when you put your fingers near it.
I removed the volume pot so I could try it with the pot mounted back on the board but found out that even with the pot and wires DISCONNECTED from the board, it still howls.
It gets worse when you put your fingers near the board in front of tubes 2 and 3.
I've checked all the ground wires and all my new solder joints..everything looks good
Anybody have any thoughts?
While my soldering skills are good my general electronics knowledge is deplorably weak.
Thanks in advance for any advice!!
I had purchased a 12G kit and put it together. Used a couple of the mods that were recommended including bridging the filament wires and bypassing the input caps and the thing sounded
BEAUTIFUL. Unbelievable sound/dollar value. Built some Open baffle speakers and all was good with the world.
Well, after a week or so it was time to built a box to make it look as good as it sounds and make things work a little more practically.
I extended the leads from the board to the OTLs and the power Trans, put bullet connectors on them so I could run them though holds in the case easily. I moved the volume pot off the board so I could mount it on the front panel. I used approx 3" wires and twisted each pair. Finally I added a 3 channel switch and wired it to 3 sets of inputs and to the board, all the wires were made of twisted pairs from some cat 5 and braided together.
Now the bad part. The amp now howls.
It got worse when you touched the volume control, or even when you put your fingers near it.I removed the volume pot so I could try it with the pot mounted back on the board but found out that even with the pot and wires DISCONNECTED from the board, it still howls.
It gets worse when you put your fingers near the board in front of tubes 2 and 3.
I've checked all the ground wires and all my new solder joints..everything looks good
Anybody have any thoughts?
While my soldering skills are good my general electronics knowledge is deplorably weak.
Thanks in advance for any advice!!
Make SURE that the metal case of the volume pot is connected to the circuit ground! This can cause horrible noise if not. Might also want to add some carbon comp grid stopper resistors of 1k or so as close to the input tube grids as possible, as in 1-2mm. On circuit boards with no grid stoppers fitted i have in the past left the grid pin leg of the socket unsoldered and bent it outward then soldered a 1/4 watt CC 1.5k resistor from the pad to the tab.
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I got nervous being an amateur when I got my K-12G - could've built it myself easily - but got jumpy and instead had S5electronics build and test it before sending it.
Anyhow mine howled too but only with some speakers. Usually hard to drive ones. Amp seems fine. Swapped to easily driven dome / woofer (89-90 dB sensitivity) 2 and 3 ways and all noise totally disappears.
Howl on mine (with some speakers) disappears if volume raised past a certain point - at about 2 to 4 out of 10 on the volume control. Had to turn it up further (4 at most) with harder to drive speakers and all howl goes away.
I'd consider what others say first but just a thought. Amp runs fine, have had it in use for a couple of years, no problems whatsoever.
Anyhow mine howled too but only with some speakers. Usually hard to drive ones. Amp seems fine. Swapped to easily driven dome / woofer (89-90 dB sensitivity) 2 and 3 ways and all noise totally disappears.
Howl on mine (with some speakers) disappears if volume raised past a certain point - at about 2 to 4 out of 10 on the volume control. Had to turn it up further (4 at most) with harder to drive speakers and all howl goes away.
I'd consider what others say first but just a thought. Amp runs fine, have had it in use for a couple of years, no problems whatsoever.
I think that is a pretty good indication that the amplifier is "conditionally" stable due to improper loop compensation or a design or layout related stability issue. I'm always surprised what people are willing to tolerate..
(hum, buzz, hiss, amps that oscillate at the drop of a hat.)
Hi Jeff,
Looks like your going to have to remove your mods one by one until you find which one (or more) has made your K12 unstable. Nobody wants to undo good work unnecessarily so the order in which you remove the mods might be worth some thought.
Could you list all the mods that you have done since buying the amp.
Perhaps some people on the forum might give good reasons why you should de-mod in a particular sequence and perhaps save you some unnecessary work
Brgs Bill
Looks like your going to have to remove your mods one by one until you find which one (or more) has made your K12 unstable. Nobody wants to undo good work unnecessarily so the order in which you remove the mods might be worth some thought.
Could you list all the mods that you have done since buying the amp.
Perhaps some people on the forum might give good reasons why you should de-mod in a particular sequence and perhaps save you some unnecessary work
Brgs Bill
kevinkr:
people's tolerations: True, good point, and had worried that over many a time in myself.
In my case I feel I just don't know enough to rework it safely myself yet. So I'm pretty limited unless I scrape up the cash and ask someone else to do it safely.
But actually I was wondering if that would turn up in this thread (howl) with the K-12; if it anyone noticed problems driving some speaker loads, even working 'properly' (well, stock for example).
Anyway very clearly I don't know with the K-12; but I meant I'm interested too to see what turns up in this thread, to help address the original poster's problem.
(hope that made sense)
people's tolerations: True, good point, and had worried that over many a time in myself.
In my case I feel I just don't know enough to rework it safely myself yet. So I'm pretty limited unless I scrape up the cash and ask someone else to do it safely.
But actually I was wondering if that would turn up in this thread (howl) with the K-12; if it anyone noticed problems driving some speaker loads, even working 'properly' (well, stock for example).
Anyway very clearly I don't know with the K-12; but I meant I'm interested too to see what turns up in this thread, to help address the original poster's problem.
(hope that made sense)
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