My Exicon amp project....

[reiver]

I posted this in the Photos section, but several people on this forum had asked for an update. This is the final version of my Hafler clone monoblock. With specs of 145 watts/8ohms continuous, mosfet outputs and I decided to try this for a robust center channel amp.

The chassis is a gutted Dayton APA150, the only thing I kept were the binding posts and shell. I cut down the stock heat sink for space reasons and drilled holes for the mosfets. The design is actually half of a XL280: transformer is a 110v/63vdc, the board is a Musical Concepts PA3D. Caps are Mallory 12,000mf/75v with a 600v 25a Vishay bridge rectifier. Three Exicon EC10N20 and three EC10P20 mosfets were used.

It powered up perfectly, no smoke or hum, sound is pure, dynamic and articulate. The only problem is the heatsink is too small to run the Exicions at 100ma each which is the stock setting (330ma). The stock Dayton had a 12vdc 80mm case fan on the rear (behind the heatsink) so I put a new ultra-quiet fan in that spot. This let me turn the bias up to about 80% of optimum and the heat is ok now.


Thanks everyone for your Exicon tips on my earlier thread.

A larger image is HERE

-Bryan

[lineup]

Three pairs of Exicon EC10N20 + EC10P20 MOSFET per channel were used
---------


Cool Amplifier, reiver!

Exicon EC10N20 + EC10P20 MOSFET are some fantastic FET-s
I have setup some great Class A Amplifier using them in my Spice.

HAFLER XL-280 looks like original use SK134 / 2SJ49 Hitachi Lateral MOS.
The input stage of HAFLER XL-280 is a symmetrical dual differential
Complementary NJFET + P-JFET: 2SK147 + 2SJ72.

This is an amplfier with Symmetrical JFET input and Push-Pull Symmetrical MOSFET output.
A great amplifier design and should be one amplifier to LOVE.
I understand why you can be very happy with your amplifier, reiver

Lineup
http://www.hafler.com/techsupport/pd...80_amp_man.pdf

[krmaudio]

What a great amp, casework is brilliant.

I have been getting some heatsinks (hh s500d) together to build a small fan cooled amplifier with 3 x hitachi j50 and k135 mosfets......

still at that stage! due to other work like paying bills.......

cool design !

[lineup]

good luck with your Hitachis, krmaudio
they are old but very nice mosfets

[krmaudio]

thank you, i have never had much luck with the exicons or sml mosfets, and i have a few hitachis saved up here..........

just trying to attach heatsink pic for you...see what you think of it.....

[mlloyd1]

bryan:
pretty cool ...


you mentioned it was based on the hafler xl-280 but uses a musical concepts board. i thought the musical concepts hafler modification boards were actually a very different circuit from the hafler topology; for example, changed from the complementary diff amp input to the single ended input stage. also, no longer the cascoded jfet input of the xl-280.

can you say anything about the musical concepts board?
no need to give away any of their secrets ...

mlloyd1

[lineup]

great power module, krmaudio

here is some manual for Musical Concepts modicfications
for Hafler Amplifiers
http://www.musicalconcepts.com/myweb/PA3C_1B.pdf

I do not know if this pdf covers all. But there are many details.

[krmaudio]

Thank you,

just getting boards together, input driver one side, output protect other side......

what sort of rails are you running?

thank you

[Eva]

The two small yellow capacitors attached to the electrolytics do more harm than good. They may even make an amplifier oscillate.

[reiver]

A bit late responding on the above postings... my apologies.

The Musical Concepts boards are proprietary designs, but are designed as perfect substitutes for the original Hafler ones. I designed the amp above using the 6 mosfet design from the XL-280, but it could as easily have been Hafler 220 or 500 design as the boards are universal. A single resistor is changed depending on the voltage you need (63 volts, DH-200/220/XL-280, 91 volts DH-500/XL600)

John Hillig describes them as "...Single-Ended, Class-A front-end, the input stage is a Current Sourced Differential Amplifier exhibiting the advantages of symmetry and high input impedance to the driving device. The following LED biased, Single-Ended Cascoded Stage(SECS) voltage amplifier is operated at high current for linearity. This stage is collector coupled to the MOSFET output stage."

Bypassing the big electrolytic bypass caps is a decades old practice, I've never heard bypassing them could cause oscillation.