Sales update 2015 Sep

September 11th, 2015

Please note that I am still selling Toshiba 2SK170 and 2SJ74 jfets in match pair or quad.  Please write to ask.

For the other items, I only can sell F5T, FDA-1B and FDA-2A bare pcbs as kit is no more time to pack.



Update in Aug 2015

July 19th, 2015


Audio Lab is up !

After spending some time for few weeks, the Tek Curve Tracer has been repaired due to a capacitor short circuit on the main board.  It is replaced and the set works again!  See the Tek 577 on the left side of the table.


After that I am thinking of a way to sort the Long Wait Toshiba power mosfets – 2SK1530 and 2SJ201.


F5T Pre-amp + FDA-2A AD1955 DAC in one box

May 11th, 2014

This is a pre-amp plus a FDA-2A in one box.  It was built in year 2012.  I use a old Yamaha DA8X box to house eveythings insides.  See the pdf files at bottom for details.


FDA-2A with USB, Optical and AES digital input.  Push button for digital input selection at the front panel.

DAC direct output is available in RCA sockets.

F5T Pre-amp:

Alps volume control from DAC output and note that there is no other analogy input for the preamp.

The pre-amp is based on Nelson Pass F5T power amp design and striped down to only one pair mosfet and lower bias current at about 200mA.  Supplier voltage is at about +/-23V with a small transformer.  Power mosfet is using Toshiba J200 / K1529 pair and casing is acted as the heatsink of power mosfet.

A headphone jack is connected in parallel with the pre-amp RCA sockets.  It can drive most headphones due to sufficient high bias of the power mosfets.


Details refer to this pdf file: F5T-Pre_DAC



Toshiba 2SJ74BL measurement

January 3rd, 2013

Many diyers have been buying some fake 2SJ74 from China sources or even from US source and thus some of them ask me for the measurement curve of this genuine Toshiba part.  Here is the file which you can enlarge to see the curve and estimated Yfs (gain) of the part.  The jfet selected is at about 10.8mA Idss (top curve).  The setting of Tek 577 is highlighted for easy reference but you can zoom in the pdf to see actual setting of equipment.


Note that the part is laser marked as it is new part production in 2008, probably the last production batch in Japan.  For ink mark, those are very old part that I have sold before – 2SJ74V.


You may notice that I have increased the price from 2013 because there are not too many stock left for sales.

J74 measurement

F5T Turbo Power Amplifier kit for sales

November 23rd, 2012

Those who had brought my F4 kits few years ago can purchase this kit or boards for a quick conversion from F4 into F5T because all the holes and mosfet locations will be same as the F4 pcb.  The optional MUR3020W can be obmitted if not use.   If F4 buyer has the original IRF9240/240 power mosfet, it can be re-used.

The To-92D transistor are Toshiba 2SC2705Y/2SA1145Y rated at 800mW and thus it is very safe to use at 60 deg C environment for less than 200mW dissipation.  It would survive safely under a maximum supply voltage of +/-32V.  The Panasonic capacitor is rated at 35V and thus a supply voltage of no more than +/-32V is recommended for this kit.

I build a version using Toshiba Mosfet 2SK1530/2SJ201.  The supply voltage is +/-22V and thus I do not use the cascade transistors (2SC2705Y and 2SA1145Y).  I also change 3 resistors and details refer to the “F5T-BOM-cost” document.  The change on R11/R12 is to increase the thermal stability and R27/R28 is for increasing the supply voltage to jfets to be minimum 10V or above for a supply voltage of 22V.  49.9R to replace 47R do to stock issue.

Sound wise, it is more powerful than the F5 original due to higher current output and more pairs of mosfet is used.  Overall the sound is smoother and warmer than F5. Nelson said this amp sound more relax!

Please look at the F5T-BOM-cost documents for the detail kits offer – Price & BOM options.

Details: F5T-BOM-Cost2 (updated shipping cost)

Manual: F5 Turbo Assembly Instruction v3 (NEW)

Power supply ripple comparison CLC vs CRC: It can be seen that an inductor of 0.47mH air-coil has improved the ripple peak to peak level to 20 times smaller.  See attached: F5T ripple

After building another set with Cascade transistors, the noise level with grounded input is about half of that without cascade transistors.  The reason is that the filtering of the transistors at the base is much better and thus the jfets is supplied with a more stable supply with lower noise level.  Here is the measurement comparison.

Notes for F4 up-graders:  For the MUR3020W, I have no pre-tap holes for them and thus I use a L-Bar to fix the 3 power mosfet and MUR3020W as shown.

I have built the third set with 32V supply as suggested by Nelson Pass.  Here is the measurement of distortion vs Power Output at 8.2 ohm load.  With higher supply voltage, the distortion is lower at 0.004% 1W.  The non-cliped output is about 50W.  For this measurement, the bias is about 1.6A to 1.7A  for each channel.  The conclusion is that the distortion is lower at 32V and higher at 22V supply.  With no surprise, this set sound the best after adding the Solen 1mH coil in  the power supply (CLC) filter.