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427 Posts
Discussion Starter · #1 ·
Build Log: Bride of Zen

This is a log that will document the building of my "Bride of Zen" preamplifier. The BOZ is a preamplifier with a single JFET gain device. Why just one gain device? To preserve maximum detail and neutrality -- the more gain devices you add, the higher the distortion. The average op-amp has about 20 gain devices (transistors) on it's die. You can see why one might be inclined to build such a preamp.

The BOZ will go in between my DAC and Gainclone, and also serve as a volume control.

Parts list:
-Cigar box
-Ladder-type stepped attenuator
-Vishay/Dale 1% 50ppm metal film resistors (CMF60), hand matched
-Nichicon "Fine Gold" capacitors (No KZs in 2200uf)
-Solen 10uf/250vdc polypropylene film capacitors
-2SK170 JFETs, hand matched
-Vishay 100nf film caps
-Vishay 25k trimmers
-IRF610 FET w/ heatsink
-1n4004 zener diode, rectifier
-25v transformer
-Blue LED
-Terminal blocks
-Power switch

Today is my-parts-came-in-the-mail day! I populated most of the board today, I still need to match and solder on my JFETs though. Here are the pictures from today:

Boxes of parts! and the PCB with a few things that I already had.

All the parts laid out


Power supply side done Yes, I know the heatsink is upside down. The holes didn't line up.

Both sides done! minus the JFETs

Top view

Dale CMF60 resistors

Capacitor bank

Test fit. Final version will have shielding

Almost done!

My next update, I will have connected all the inputs and outputs, power plug, added the stepped attenuator, power switch, shielded everything, and connected the transformer.

Keep watching!

427 Posts
Discussion Starter · #2 ·

427 Posts
Discussion Starter · #4 ·
Update: Finished!

I just finished building the preamp. How does it sound?

Well, I had the DAC going straight into the amp, without an output stage at all, and thought that it could certainly not get any clearer, dynamic, or detailed. BOY, was I wrong. The BOZ retrieves an incredible amount of detail and seems to not degrade the sound at all, ever. What amazes me most about it, is that during complex and loud passages, it seems to have INFINITE dynamic range that never breaks up or gets painful to listen to. The detail during these passages is something I have never heard before. The BOZ has added so much to the listening experience, without any detrimental effect.

I even hooked it up to a tone generator and a oscilloscope. The waveform looks EXACTLY like the one that comes out of just the tone generator, only bigger. Perfect.

This design by Nelson Pass is simply genius. I even wrote him an email to thank him for the design.

J-FETs in!

Wired up

Rear panel

Preamp and DAC together


My next small project for today. It is a CMOY amplifier. It can be used as a decent headphone amp or as a preamp. Very small and easy to build. I highly recommend it for people wanting to learn how to assemble electronics. Here is the website: http://tangentsoft.net/audio/cmoy-tutorial/

Thanks for reading.

1 Posts

very nice build. what's the output on your DAC?
you have no issues with clipping on the input?

I read the stock build cannot handle very high input voltage.
just curious if you changed the values.
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