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Old 19th November 2005, 04:22 AM   #1
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Default Ticking noise, need help.

Hi all.

Lots of questions....

I just made a line-stage with the low mu part of an 6EM7 as a simple grounded cathode amplifier. B+ is 345V, anode voltage 172V, running at ~30mA. Silicon rectifiers.
I can`t get rid of that ticking noise, sounds a bit like an old clock The ticking in the right channel is different from that in the left. There is also too much hiss, and some hum. I guess the hum comes from the AC powered heaters..
As I didn`t have high wattage resistors for the anode, I paralelled a bunch of 0,6W resistors, could this be a problem? I plan to change it to a CCS sometime later.
I tried bypassing the psu with a 4.7uf poly-cap--no change..
I tried with a larger value gridstopper- for some reason it got worse. Is the grid picking up some signal from the output??feedback??
The noise doesn`t change with different volume settings.
Very microphonic, but it is the same with several different tubes, changing tubes made no difference.
What am I doing wrong?

Please somebody, HELP!

Regards,
Peter
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Old 19th November 2005, 05:47 AM   #2
SY is offline SY  United States
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AC heaters, when wired properly, will probably not be a hum source. Examine lead dress, grounding, and placement of transformers.

As for the ticking, is it periodic? Does that period correspond to any of the circuit time constants? Does it go up and down with balance control changes? Have you put a scope on the output to see if you have oscillations?

If you've got a schematic, let's have a look.
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Old 19th November 2005, 06:42 AM   #3
Enzo is offline Enzo  United States
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Is there a cel phone near the amp? They make odd ticks and other noises that can be picked up by audio circuits when nearby.

Connect the amp in a totally differnt location to rule out environmental noises.
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Old 19th November 2005, 08:22 AM   #4
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Grid stoppers want to be as low as possable.
AC heaters should be fine on a low MU triode.
Maybe its a hissey tube.
Have you run ground straps from the valve bases and case near the valves, to the main star ground. There can be huge amounts of induced current between different parts of the case.
My headphone amp can pick up the flashing of my cookers digital clock !!!!!! Also if you live in the country electric fences put out a nice clicking sound which radios and some amps can pick up.

shoog
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Old 19th November 2005, 09:37 AM   #5
dhaen is offline dhaen  Europe
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Check that the heaters are refered to somewhere eg gnd, and not floating. Floating heaters cause hum, and can cause ticking as they discharge.

Unless we are talking pickup or mic levels, AC heaters should not hum.

Edit: Microphony is largely valve dependent. Try another make. There are also good and bad ways of mounting. Horizontally on a 90 deg chassis angle is about the dorst...
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Old 19th November 2005, 06:03 PM   #6
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Thank`s all!

The ticking noise is random. I have a scope but no probes,,, note to myself: /must buy probes/.
The heaterwire is very tightly twisted glued close to the chassie, maybe a little close to the HV caps. Heaters are ground referenced. The voltage is slightly high, 6,6V instead of 6,3V.

I`ve only got a hand-cad schematic, and no digital camera or scanner.

I got ac heaters in a guitar amp I made some time ago, cascaded high gm high mu triodes(6HA5), even at full throttle only minor hum. Didn`t expect to have heater induced hum with this low mu triode.

I tried some more tube swapping, the noises varies a little but is still there.

I`ll try out your suggestions, thank you all for your kind help

Best regards,
Peter
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Old 19th November 2005, 06:10 PM   #7
dhaen is offline dhaen  Europe
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Peter,

One last thing: The ticking really does make me think of a discharge somewhere, even though it's random.

Let us know what you find
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Old 25th November 2005, 10:37 AM   #8
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Now my linestage actually sounds very good, very detailed and a huge, wide and deep soundstage. I`ll never go back to my OPA627 pre!

Got rid of that ticking noise! -I reduced the heatervoltage with a couple of resistors, from ~6.6V to 6.3V. Strange...maybe I just had a bad solderjoint...

-Tried relocating transformers and chokes- made no difference.

-Added more resistance in the CLCRCRC psu- got less hum and a little less hiss.

- Tried shielding the tubes with som copper foil- no difference at all.

-Bypassed the rectifier with a small cap- no difference.

-Installed a zener string in the psu- got less noise overall.

-Tried CCS at the cathode(LM337 and a resistor) it sounded like I`d got the Niagra falls in my living room! Maybe I wired it wrong, but i don`t think so.

-Removed the CCS and the cathode bypass cap, and used only a resistor -hiss allmost gone Why is that? I know the gain goes down a little without the bypass cap, but the difference in noise was not small.

Thank`s again for your help


Best regards,
Peter
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