Please NOTE: This section on the MOSFET option for the Millett MAX diamond buffers has been superceded. Please refer to the MOSFET-MAX website for details on the new, JFET-mod MOSFET-MAX. This section will remain here for posterity, or in case the market's supply of JFETs runs out for the JFET-mod version.
photo by Neil Rothschild
NOTE - Differences from the BJT Diamond Buffer (DB) version and updates from prototypes:
RB12L/R trimmers are 1K ohm
RB1L/R is jumpered out
QB1L/R JFETs are 2N5486
RB4L/R, RB5L/R are 100 ohm
(same as DB version, but updated from protos)
RB8L/R, RB9L/R are populated
(these are jumpered out on the BJTs)
Heat sinks must be 1-1/2" tall minimum
220pF caps on QB8L/R
NOTE: You must decide which output stage to use - either BJT Diamond Buffer or MOSFET Diamond Buffer.
You cannot build both.
The MOSFET output stage option for the MAX uses the same MOSFETS that are used in Amb's M3 headphone amplifier. Due to the
relative high currents and the potential difficulties in trimming the bias at the high levels needed,
it is recommended that the MOSFETs are tested. Amb's Audio Shop is probably the
most convenient source and is referenced in the MAXBill of Materials.
Manufacturer specification sheets for the MOSFETs, the complementary small transistor pairs, and the input JFET are here:
Image by user "Ferrari".
User Ferrari was also the first MAX builder to point out the proper use of these compensaion caps - thanks!
From Ti Kan (Amb) on the MOSFETs: "For each channel, if you use 100Ω resistors for RB8 and RB9, then you should also install the 220pF capacitor CB8. The N-channel MOSFET's gate capacitance is less than that of the P-channel, and this capacitor equalizes them. An alternative to this approach would be to omit CB8, but change the values of RB8 and RB9 to 121Ω and 75Ω, respectively. This will assure symmetrical slew rates for positive going and negative going square wave pulses."
(referenced from Amb's M3 amplifier, but part labels - in bold - have been altered to agree with the MAX's MOSFETs)
file last changed:Sunday, September 7, 2008 7:00:00 AM
Please contact the MAX webmaster for questions about these web pages.