High Plate Classic? Should We build it.

[rootz]

Curious: what is the effect of the 500pF cap on the 220k at the grid of v1b? Does it make for a much brighter amp?

[talbany]

Curious: what is the effect of the 500pF cap on the 220k at the grid of v1b? Does it make for a much brighter amp?

Dumble likes to use the 220k/500pF combo to shape the frequency response in quite a few spots..Grid V1b/Effects loop jacks/ and in his Dumbleator.

That cap creates a treble boost shelf that begins around the corner frequency of RC (1.4 kHz), but it interacts with the surrounding components too. You could say it counteracts the roll-off due to the Miller capacitance.

https://ampgarage.com/forum/viewtopic.p ... 58#p394258

Tony

[rootz]

I agree that must be the point of using that combo Tony. Sometimes the combo is part of the feedback loop (v1b in the preamp), sometimes not (dumbleator iirc). I guess to be sure what the actual effect of the cap is, I need to run some comparative tests. I think in the preamp the cap makes it marginally brighter. We’ll see...