A while ago I bought a pair of new Tango M705 and wanted to find a good use for it. I also had a small wood case made of oak and accent stained with chestnut. This was the beginning…
I always wanted to build a compact 4P1L amp and here it is my new “Shiny Eyes” Mini SE 4P1L amplifier.
This is a very nice sounding 1.7W amplifier that sounds way bigger that one might think. The secret is to match it with high sensitivity and easy to drive full range drivers., use it in small rooms or be fine with lower sound levels. It can also be used in multi system speakers when driving upper mids or highs when the level of power is sufficient when using high sensitivity drivers.
The amp is using top components and iron. The output transformers are Tango M705 and the power transformer and choke are Lundahl. The amplifier has only two stages which is my most preferred setup.
The power tube is the 4P1L in triode mode and the driver/gain stage is the 6SN7 loaded on a mosfet CCS ( cascode DN2540). Both stages are worry free, self biased. The overall gain allowed a very small GNFB of -3dB that improved the THD and the bass frequency response. The 4P1L filaments are powered by voltage regulators, a solution required by the compact size.
The B+ power supply is full wave tube rectified and using a 6BY5GA rectifier and a CLC filter: 50uF PP, LL1673/20H common mode and 220uF Mlytic Mundorf. A really nice 150mA sealed Marion meter is showing the total current. This meter will show about 85mA. The frequency response is 30-40kHz at -0.5dB and THD of 0.7% at 1W with 2nd harmonic dominant.
The amp sounding very detailed, transparent and quite dynamic for its small size. I am very pleased with the sound of a small power compact amp. The amp weights 22 lbs and the size is 13x11x10″.