Hi,
The design is very simple and more or less a class A design. It moves into class AB, but not far into AB, so if you are looking for plenty of power this is not the way to go.
The local shunt feedback is ~9dB and will lower the output resistance of the EL84. Global NFB is approx 10dB set by a 1k2 feedback resistor (I have to check this out, I’m not at home now..)
I achieved a damping factor of 8 (Zo=1 ohm) with 10dB gNFB. The distortion figures are also quite low, 3rd harmonic <0.3% and higher order harmonic less than 0.1% at half power output.
The amplifier sounds very transparent and does not have any dominant sound signature.
After some experimenting I found the best sonic working point for the EL84s to be ~41mA cathode current: Rk=2k2/10W and Vk=90V. The cathode voltage (Vk) is adjusted by trimming the CCS.
(I will upload the updated schematic later today).
Jan E Veiset
NO-6600
The design is very simple and more or less a class A design. It moves into class AB, but not far into AB, so if you are looking for plenty of power this is not the way to go.
The local shunt feedback is ~9dB and will lower the output resistance of the EL84. Global NFB is approx 10dB set by a 1k2 feedback resistor (I have to check this out, I’m not at home now..)
I achieved a damping factor of 8 (Zo=1 ohm) with 10dB gNFB. The distortion figures are also quite low, 3rd harmonic <0.3% and higher order harmonic less than 0.1% at half power output.
The amplifier sounds very transparent and does not have any dominant sound signature.
After some experimenting I found the best sonic working point for the EL84s to be ~41mA cathode current: Rk=2k2/10W and Vk=90V. The cathode voltage (Vk) is adjusted by trimming the CCS.
(I will upload the updated schematic later today).
Jan E Veiset
NO-6600
Here is the current schematic for the miniPP:
Jan E Veiset
NO-6600
An externally hosted image should be here but it was not working when we last tested it.
Jan E Veiset
NO-6600
Key figures:
Max Po: 7V rms into 8 ohm. (40Hz - 25kHz)
Frequency response (1W, -3dB) 22Hz - 40kHz
DF: 8 (Zo = 1 ohm)
THD: Less then 0.3% (5V rms output)
Distortion pattern 400Hz input (5V rms output):
But if you are looking for power, take a walk to SY's red light district: EL84 in pentode mode with very stiff cathode bias is the way to go for some real good spanking.
Jan E Veiset
NO-6600
Max Po: 7V rms into 8 ohm. (40Hz - 25kHz)
Frequency response (1W, -3dB) 22Hz - 40kHz
DF: 8 (Zo = 1 ohm)
THD: Less then 0.3% (5V rms output)
Distortion pattern 400Hz input (5V rms output):
An externally hosted image should be here but it was not working when we last tested it.
But if you are looking for power, take a walk to SY's red light district: EL84 in pentode mode with very stiff cathode bias is the way to go for some real good spanking.
Jan E Veiset
NO-6600
Does anyone have this schematic to repost, or better yet upload to diyaudio. I shall really appreciate lt. It is not nice to discover all these dead old links.
