Wednesday, December 17, 2025
Tuesday, December 16, 2025
Sunday, December 14, 2025
Riccardo Cocciante (con Cecilia Gasdia) – Due, Modulation from C minor to E minor to A minor to C# minor
1:24 modulation to the key of E minor
1:59 modulation to the key of A minor
2:45 modulation to the key of C#minor
Vicky showed me the importance of key change within a musical composition.
Is high gm, high current desirable for low noise?
At your risk.
Experience from Pleiades amplifier designs brings out that very small currents of the order of 50 to 100 microamperes give very low noise on electron tubes or JFETs.
An explanation seems to be that at low voltage, (hence low current), secondary electron emission is minimum on electron tubes, see much earlier posts.
For example the Pleiades V6 battery powered electron tube microphone booster. The Pleiades DC90 RIAA preamplifier. The Pleiades 3 K117 RIAA, no hiss can be heard even with volume control at maximum. The Pleiades K117, 1.3V microphone pre preamplifier.
No wander this approach is also used on classic condenser microphones.
Having said this most of the devices chosen for these Pleiades low noise preamplifier experiments are high gm such as EF183 or K117. But they are used at low current hence low gm.
Wednesday, December 10, 2025
2nd Pleiades 3 K117 RIAA MM Preamplifier Prototype continued
At your risk. protect your ears from high SPL.
A 10K load resistor was added at the 3rd stage which is a K170 JFET. The output transformer used is about 10 to 1. Quiescent current is 1mA at Vb=24V, Vd=14V. It sounds nice and loud driving the Sennheiser HD580 in mono i.e. (150ohms).
A source resistor bypass capacitor of 100uF was added to the 1st K177 stage otherwise overall gain is too low (an input transformer has not been tried yet on this preamplifier).
The potentiometer separating 2nd and 3rd stage is at the time being 470K log.
The preamp driven at the time being by a Lipshitz RIAA inverse network sounds very nice (one channel tested only in mono).
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