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06/19/18 at 05:31:46 


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HUM vs. DYNAMICS (Read 1499 times)
Steve Deckert

If the 1st watt
sucks why continue?

Posts: 3362
03/03/09 at 16:43:11
Subject: Just built Zkit1


I  completed the amp last weekend, all parts present, easy build.
It worked well I thought, went into distortion at about 75% volume.
The test points "A & B" were low A=332vdc, B=295vdc (other points ok).
Mains are at 119-121vac. Speaker impedance is 4ohm.

Yesterday I tried playing with the 1K-6w value. With 913ohms I got the points "A=336vdc" and "B=300vdc" with C=10.47 and DL=2.58, DR=2.63.
The amp now has the same clarity and tone but has much more muscle and headroom, just a hint of distortion at 100%.
Points A&B seem to be very critical.

Would I gain anything by trying to get closer to A=346vdc and B=309vdc values?
Also should I try to get the the DL & DR equal and closer to 2.60vdc?

I am using a Triplet DVM, it is not a lab instrument but is very repeatable with good specs.



The 1K resistor was chosen to keep the ripple down and consequently the hum.  As you lower the value, dynamics and power continue to increase as does the noise floor.  If you can take a bit of background hum, you can lower the value all the way to 500 ohms.

The cathode resistors on the input tube can be raised or lowered to fit within the window of 1.3 VDC and 4.7 VDC.  The lower voltages will increase dynamics and lower listening levels.  The higher voltages will decrease dynamics in exchange for more headroom.

- Steve Deckert

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