Pictures of your diy Pass amplifier

Member
Joined 2008
Paid Member
Thanks for the compliments - I'm pleased to hear that :).
Yes, some more colors would surely be helpful, but currently I've only got 20 gauge in black and yellow. I was looking for some heavier gauge at work but only found green-yellow-striped and, well, black...

I tested the amp this morning and was very (VERY) satisfied with the results. Everything went as expected, nothing went up in smoke and the shrinking tubes on the transistor leads shrinked themselves after a couple of minutes :D.
First thing I measured was power supply ripple. On the big caps I have 90mV peak-peak and after the coils only 10mVpp left - 3,5mVrms, quite nice! On the output was nothing left, neither on the 'scope nor in the speakers. I'll hook it up to a soundcard to look at the spectrum this evening. That way I'll be able to adjust for lowest THD too, since it is not possible anymore to measure anything on the PCB - that's the drawback of my compact design :eek:.

Here are two things which really surprised me: First off, there is absolutely no turn-on thump, in fact it's more like a soft-start of 500ms or so. And second, the caps are powerful enough to keep the machine up for a whole second! Quite like a tube amp :rolleyes:.

The circuit is the simple Zen Redux, with a bit of feedback and, obviously, the C-L-C supply. I had it running for about an hour, the heatsink was getting quite warm but not really hot with the fan running at 10V. Maybe I'll settle for something like 8V fixed to keep it simple and quiet. Will have to test that while listening to the sound of this neat little hand-dryer ;).
 
I posted a quick video on youtube... with my bias readings...

YouTube - f5 amp

I've also got an initial sound demo (connected to my ipod & optimus speakers)
(ok, they're my computer desktop speakers :) )

http://www.youtube.com/watch?v=VW7MWNZsZUs

(this is private if you want to see this, send me an IM with your youtube id, or email address)

Looks great. Congratulations and double congrats on the wonderful readings you are getting.
Which box are you using?
 
Member
Joined 2008
Paid Member
I am trying to find the 'Zen Redux' , and not having any success. Is it published on PassDIY or is it a DIYaudio circuit?

Uuh, where did I got that Redux from? Can't remember... Actually it is called Zen Amplifier Revisited or Return Of Zen, here's the link: http://passdiy.com/pdf/retofzen.pdf.
Sorry for that inconvenience :eek:.

I'm not able to do any testing today anymore, since I blew the fuses. Didn't check what types were in that salvaged mains filter, but had to discover it was 1A fast blow, not exactly what's needed here :rolleyes:. Obviously the variac helped them to survive this morning.
 
Member
Joined 2008
Paid Member
If it's interesting for anybody, here's a plot that ARTA gave me. The blue plot is from the Zen, the pale red one from a Pioneer SX-339, for comparison. The Pioneer's volume was set to equal that of the Zen, as it obviously has a bit more gain. Both amps were tested with the inputs connected to the soundcard and the output loaded with a real speaker.
As you can see, the Zen has even lower hum than a commercial Class-AB amp (well, it's not that high-endish, but still) and is a lot less noisy! I'm using Spendor S6 with 88dB efficiency, where I can hear the noise of the Pioneer with the ear directly in front of the speaker. The Zen is totally inaudible.

I'm quite happy with my scrapzen, although I have to admit that the air flow through the heatsink is a bit more noisy than I'd like it to be. Guess I'll put a thermocouple on it, close the case and see how hot it'll run with only minimal air flow.
Anyhow I found some use for my collected parts, learned a lot about Class A and have a nice heat radiator now for next winter, wich also plays some warm tunes if I like it to ;).
 

Attachments

  • overlay.gif
    overlay.gif
    24.6 KB · Views: 2,422
My F5

Finally got the front panel end plates powder coated, so here's the final project:

-- F5 two channel, common PSU
-- Speaker protection
-- Weston "projection" VU meters, modified for LED light sources
-- Heatsink temp sensors/alarms (currently set for 55 degrees C)
-- Clipping monitors
-- African hardwood side panels (to match my other equipment)
-- All chassis plates 3/16" aluminum; Conrad heatsinks
-- Plexiglass top cover with internal blue LED highlighting
-- Two low-speed AC muffin fans to circulate air to the heatsink fins

Construction details and more details are at this thread:

http://www.diyaudio.com/forums/pass...-build-beautiful-music-different-drummer.html

Heatsinks running cool, the fans are silent, and the amp sound great! Thank you, Papa Pass.....!!
 

Attachments

  • 4204.JPG
    4204.JPG
    66.3 KB · Views: 2,445
  • 2202.JPG
    2202.JPG
    41.8 KB · Views: 2,417
  • 1201.JPG
    1201.JPG
    67.1 KB · Views: 2,414
  • 104.JPG
    104.JPG
    45.7 KB · Views: 2,386
  • 114.JPG
    114.JPG
    52.9 KB · Views: 1,258
  • 124.JPG
    124.JPG
    44.1 KB · Views: 1,030
Yeah, same here with K-Mart. Wal-Mart built a Superstore adjacent to a K-Mart here. The K-Mart parking lot is a ghost town; the Wal-Mart lot overflows on weekends. (And they say there aren't many "fun things to do" in Colorado Springs!)

While we're on the subject of blue LEDs, these two Weston VU meters are the only ones I've found in the last 45 years; they employ a light source (originally a 5W incandescent pilot bulb, but now a .5W blue LED) to project on the VU meter face, using the internal VU meter movement to deflect the beam. As a result, the VU reading is actually a "beam of light" from the LED that moves across the meter face.
 
Jacco,

Yep....the old-school "retro look" with a simple Pass Class A internal was what I was shooting for. Thanks for picking up on that.

I probably have mixed emotions, too, on the LEDs. I figure I'll tire of the internal LEDs about the same time I get tired of polishing the plexiglass. When that happens, I'll probalby swap out the plexi for a powder-coated top cover.

Same goes for the clipping (yellow) and heatsink temp (red) LEDs. If I rarely get any "alarms", I'll probably clean up the front panel (and the vectorboard) and remove them.