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Old 27th February 2021, 03:07 AM
Audionorth Audionorth is offline
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Join Date: Dec 2006
Location: Anchorage, Alaska
Posts: 81
Default Basic question regarding noise and grid leak resistor

Hello

I have a "second" preamp that I've been using for a few years made up of Audio Note kit parts (from years ago) just in a different chassis. I also have an Audio Note kit preamp and DAC with AG recommended txs and different output stages that I've been running happily for years in another system with similar changes described below. So I've done this output stage change with a very similarly configured preamp using 1 x e80cc and 1 x 6350 tubes . . . (just not the grid leak resistor change - see below)

Sooooo, I decided to implement a similar output stage that changes to 1 x 12au7 and 1 x 6463 instead of the 5687/7119 configuration. Easier to find single tubes than matched pairs of 7119s etc. . .

So I have successfully done this (change opt stage) twice (preamp above and DAC) but this time I'm having issues. . .

My voltages check out.
The preamp plays music.

But, their is an loud noise that doesn't sound to me like typical 60 or 120hz hum but more like a 120hz static of sorts . . . after changes the preamp was put back in the system it was used in successfully for years (including a nice recently recapped pair of WAD 300B PSE monoblocks).

Questions:
1-could significantly reducing the grid leak (with the desire to create a voltage divider to reduce gain) lead to the noise issue? 1M to 2K2 with a 1K grid stopper

2-what other issues are likely at fault? music plays, voltages are good, noise not affected by volume change . . . just loads of static type noise (I've replaced the tubes; disconnected the source)??

Thanks in advance for any assistance!

Mike
Anchorage, Alaska
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  #2  
Old 27th February 2021, 08:20 AM
Audionorth Audionorth is offline
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Join Date: Dec 2006
Location: Anchorage, Alaska
Posts: 81
Red face Re: Basic question regarding noise and grid leak resistor

Well, I seem to have discovered what a noisy power supply sounds like . . .

I altered the AN power supply years ago adding a 0B2 which required removing the likely quieter zener and a cap. I added a second choke and cap "external" to the PS board. Thinking it was over kill, I removed it when I switched out the output stages today. . .anyway, I realized the possible issue and re-installed the additional choke and cap and the "noisy static" disappeared. . .mostly, a bit more work to do but at least it will be sorted. . . while in retrospect it seems obvious, clearly it wasn't to me; I've apparently not heard a load of ripple in a PS . . .

If anybody has followed along and I've made this little adventure clear enough to understand . . .I am still interested in the grid leak value change question and any implications . . . maybe without the schematic it's hard to answer. . . I thought the voltage divider (grid leak/grid stopper) would increase the usability of the attenuator but it doesn't seem to be noticeable . . .

Thanks,

m-
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