GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Melquiades Amplifier
In the Thread: Single-stage Melquiades vs. DHT amps

Post Subject: Looks good, but....Posted by floobydust on: 2/23/2009

Romy,

That gets you where you want.. good transfer curve, low distortion and about 2.7-watts output. 2A3 should last a long time. One question and one comment:

Question: the 0.75 ohm resistors in the filament lines on the 2A3. Is it your intent to drive them from a 2.5VAC transformer or a 5.0VAC transformer. Voltage drop considering the 2.5amp filament requirement would result in insufficient voltage to light it up.

Comment: On the balancing scheme. Using a 100-ohm balance pot is quite common. Effectively this results in a 25-ohm resistance in series with the bypass cap. I also use a 100-ohm balance pot but pad it with a pair of 12-ohm resistors (end to wiper) which widens the adjustment range and drops the effective resistance down to ~4.8 ohms.

Secondly, you might want to try a split balance approach. This has worked well for me with the 45 and 2A3 (dual-section types). I use a center-tapped filament transformer and connect the cathode resistor from the center-tap to ground. The balance pot has the padding resistors and the bypass cap only from the wiper to ground, i.e., you have a fixed DC balance and an adjustable AC balance.

Regards, KM

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