Monkeymatic Black Butte (univalve build)

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xtian
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Re: Monkeymatic univalve build

Post by xtian »

Colossal wrote: Thu Dec 07, 2017 6:45 pmAre you running that NFB/presence control on the fake PI? Maybe disconnect the feedback temporarily...

Yes, did that. Does reduce the amplitude of the "ping" but not its existence.
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xtian
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Re: Monkeymatic univalve build

Post by xtian »

tictac wrote: Thu Dec 07, 2017 6:43 pmYour grounding looks "daisy chained" to me; could the way you're using the volume control lug as a star ground point be an issue?
Thanks. The Vol pot is not a star point; the ultimate ground point is my input jack, which grounds to the chassis. The "daisy chain" is equivalent to a ground buss, at least to my eye. Do you agree?
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tictac
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Re: Monkeymatic univalve build

Post by tictac »

I maybe using the term "star Ground" a bit loosely but the point is you've got several ground points tied onto your ground lug while other ground leads are running in series. My point is your grounding scheme is non-standard and I've seen this type of grounding cause issues. It may not be your problem but it's worth looking into as a possible source of your problems...
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Re: Monkeymatic univalve build

Post by xtian »

Thanks, TT. Here's what I have now:

Screen Shot 2017-12-07 at 12.08.24 PM.png

and here's what you're suggesting:

Screen Shot 2017-12-07 at 12.10.03 PM.png

Perhaps this makes sense, because, for example, the Attitude control would be sourcing its electrons more directly from the chassis instead of through the same ground path as the preamp stages. Is that what you're thinking?
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Re: Monkeymatic univalve build

Post by Colossal »

I might also be concerned with the physical position of the Attitude cap with respect to the bridge rectifier (at least from the drawing's perspective).
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Re: Monkeymatic univalve build

Post by tictac »

that drawing looks much better layout wise. Each item having its own individual ground. Grounding grids, cathode, signal and filter on the same gain stage close together but keeping each gain stage separate would be the idea Merlin, O'Connor, etc... keep stressing

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Re: Monkeymatic univalve build

Post by xtian »

I redid the grounds, and it made no difference.

Let's revisit. Here's the noise I'm seeing:
IMG_8829.jpg

Isn't that weird? One pulse or "ring," 150 times per second. Could this be my DC heater rectifier?
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Re: Monkeymatic univalve build

Post by sluckey »

Could this be my DC heater rectifier?
Maybe. But the frequency would be 120Hz, or 8.3mS between pulses. And the signal would be synchronous with the line. Trigger the scope with line to see if the display is stable.

It should be easy to rule this out. Just disconnect the four diodes and use a 6 volt lantern battery to power the filaments. Or, disconnect the four diodes and big filter cap and power the filaments from the 6,3VAC, just like your power tube.
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Re: Monkeymatic univalve build

Post by xtian »

Things are working better now, though I can still see that sleeper "ping" (and I confirmed it's at 150Hz), and runaway oscillation still happens if I turn the volume up too high on the high input. But somehow I've lessened the noise to acceptable. A lot of the buzzy hash noise is gone, and I think that was improved by redoing the grounds.

As Steve suggested, I removed the DC heater rectifier and filter cap entirely. And...this did not change anything. Hardly even raised the hum, if at all.

At any rate, I'm running a KT88, plate 346v, cathode 27.4v (300R), which is making 12 watts clean.

The sounds is quite nice, very JTM45--articulate pick attack, and substantial thump in the low end.

Here is a demo recorded on iPhone, playing thru a Weber attenuator:


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Re: Monkeymatic univalve build

Post by pompeiisneaks »

Sounds great!

I don't notice any noise that you're referring to, but then again, due to being in the military and being in rock bands, I'm half deaf :P

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Re: Monkeymatic univalve build

Post by xtian »

Thanks, Phil. The "noise" is totally mitigated by the attenuator. :)
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Re: Monkeymatic Black Butte (univalve build)

Post by xtian »

Faceplate arrived!

IMG_8937.JPG
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Re: Monkeymatic Black Butte (univalve build)

Post by Colossal »

Looks great! Nicely done.
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Re: Monkeymatic Black Butte (univalve build)

Post by jjman »

Very cool and PTP rules. How is the ping thing? Did you try moving both the main filter grounds and the HV CT to a "star" via home runs? Those show "daisyed" too.
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Re: Monkeymatic Black Butte (univalve build)

Post by Phil_S »

Fabulous tone! Thick, meaty, articulate. Nice job, Aaron.
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