1. Sign-up to become a member, and most of the ads you see will disappear. It only takes 30 seconds to sign up, so join the discussion today!
    Dismiss Notice

DIY Amplifiers: Penultimate Zen

Discussion in 'Archived Threads 2001-2004' started by Michael R Price, Dec 23, 2002.

  1. Michael R Price

    Michael R Price Screenwriter

    Joined:
    Jul 22, 2001
    Messages:
    1,591
    Likes Received:
    0
    Trophy Points:
    0
    I haven't seen much in the way of DIY amps here so I decided to post my own experiences.
    Today I finished the first of two amplifiers I am building, the Pass DIY Penultimate Zen. It is a single-ended, single-stage Class A Mosfet amplifier with (in the configuration I am using) about 30 watts into 8 ohms and 15 watts into 4 ohms. It's been a lot of work so far, with more to come. From some music I've listened to so far, I can tell this amplifier is going to be well worth it.
    Design and construction
    In 1994 Nelson Pass (head honcho of Pass Labs) published a design for a very simple single-stage amplifier (most amps have at least three stages) in an audio magazine. In the last year he has published articles on his web site, www.passdiy.com, showing improvements on this circuit, including a variable current source (similar to his Aleph amplifiers), power supply regulator, and input buffer. The sum of all these improvements, the Zen V4 or Penultimate Zen, is offered in the form of PCBs that can be used to build the amplifier. Pass himself is a member of the diyaudio.com forums and is really helpful, making this a desirable project even for beginners like me.
    I purchased a pair of the PCB's ($55) and the needed components ($80), which Pass has graciously compiled into a Digi-key ordering list. I also purchased a big honking heat sink ($30) from MECI surplus. The powersupply at the moment is based on a big Plitron toroid ($70) transformer and 23,400 uf capacitor, which is much larger than a soda can. It's funny how this amplifier is so huge (heatsink is a bit over 2 feet long; transformer weighs almost as much as my previous amplifier) yet only produces 15 watts. I like it.
    Soldering the PCBs was quite easy - there is a lot of space to work with, and there are solderpads on both sides. My little Radioshack soldering iron had some trouble staying warm on the large components like the output capacitor, but it went smoothly. I then wired up a simple unregulated power supply with the toroid, bridge rectifier, and capacitor. It provides about 50V DC to the amplifier board, and an on-board regulator provides a very stable 42V to the amplifier circuit. The PCB's three large transistors were bolted down to the heatsink with silicone insulators (pink pads) between the devices and the aluminum.
    Chassis? Ah, who needs that anyway. [​IMG] At the moment there is no chassis, and all connections (input, speaker wires, power) are soldered directly to the PCB. This is just because I'm lazy - and if I get better sound, cool. I connected the power supply with a 3 amp slow blow fuse and a CL-60 thermistor (which could probably be used to ignite a small fire) to prevent damage.
    Setting up the Zen is simple - just plug it in and hope nothing blows up. (Actually, the first time I unplugged it I accidentally shorted the power supply capacitor, which gave me a nice spark and pop. Lesson learned - I now discharge the capacitor with a big resistor whenever I turn it off.) The bound manual included with the PCBs shows the correct voltage drops across certain parts of the circuit, which for me happened to all be right the first time. Then you have to adjust the potentiometer on board to set the bias voltage correctly, and readjust after the amplifier reaches its normal temperature. Piece of cake, although "normal temperature" could probably bake a cake if you wanted to.
    The sound
    So I hook the thing up to my system (not before double checking nothing was shorted or otherwise mis-wired) and start playing music at low volume. It plays for about 1 minute then quickly fades away. Oops, I forgot to replace the 1.5 amp fuse I was using for testing - a 3 amp fuse works fine. No problems yet.
    [​IMG]
    The first thing I thought was, wow, this sounds the same as before (cheap 80 watt Audiosource amp). And it does - the tone of the speakers (Kit281s) is exactly the same, with the exception of slightly weaker bass. Then I realized that every little sound was coming from its own place - the smaller elements of the music weren't all blended together anymore. This is the biggest improvement I've noticed so far: the sound is absurdly clear. And I mean absurdly.
    The other major difference in sound was the lack of harshness. I can now hear more clearly the distortion in electric guitars - in your face, yet not harsh at all. With my previous amplifier it was sort of a distorted (and less than pleasing) sounding mess. And it doesn't sound really "loud" anymore: once I had it at what I thought was a quiet level, and the bass made the windows rattle.
    Of course all the other elements of the sound have improved - it's harder to tell instruments are coming from a speaker; your ears seem to be sure where every little sound is coming from (even well outside the plane of the speakers); there's more of the "floating in your room" effect with voices and such. All the usual stuff you hear people brag about when they get an expensive amplifier.
    In short, the sound has more depth and detail; it's just more real than before. This amplifier was a lot of fun to build and (duh) its sound quality improvement is well worth the cost. If you're considering building a Zen or any other sort of amplifier, head to www.diyaudio.com - the people there really know what they're doing and are willing to tolerate silly questions from people like me.
    I had said I was building two amplifiers. This is the first, the second one is something a little bigger (okay, a lot bigger). With 87db efficiency the Kit281s produce a decent amount of sound with the Zen, but I can't help but want the ability to really rock the house. 400 watts should do the trick. [​IMG] I'll eventually be bi-amping using the big amp for the woofers and the Zen for the tweeters.
    Anyway, thanks for listening. I just want to raise interest in other speaker builders here - if I can do this, anyone can do this. And this is really, really cool stuff. Have a nice holiday!
     
  2. Fred Seger

    Fred Seger Stunt Coordinator

    Joined:
    Aug 13, 2000
    Messages:
    136
    Likes Received:
    0
    Trophy Points:
    0
    Thanks for sharing you experience Micheal. I've been wanting to build an ASKA amp for some time, maybe this spring I will get time.

    Where are you going to get the chassis from? transformer?
     
  3. Saurav

    Saurav Cinematographer

    Joined:
    Feb 15, 2001
    Messages:
    2,174
    Likes Received:
    0
    Trophy Points:
    0
    What 400W amp will you be building next? [​IMG]
    This is really cool... thanks for sharing. I've built Nelson Pass's DIY phono stage, and I'm pretty happy with it. I agree, the level of support on diyaudio.com is very good.
     
  4. Michael R Price

    Michael R Price Screenwriter

    Joined:
    Jul 22, 2001
    Messages:
    1,591
    Likes Received:
    0
    Trophy Points:
    0
    Fred, go for the AKSA, it'll be a lot of fun and the sound will be a good excuse for going to the trouble. If anything you'll have something to start conversations with: "Say, what is that homebuilt-looking thing there?"
    I don't know if I intend to build a chassis at all, but I may have to experiment with damping materials because this heatsink has a little metallic resonance. The transformer was a standard Plitron 750VA 35V (secondaries wired in parallel), model #107018201. I bought a larger than necessary one because it was only $20 more, and allows me to play with higher bias (more power/better sound) if I get more heatsinking or fan cooling.
    Saurav, my 400W amp is the Symmetrical Mosfet amplifier by Anthony Holton (www.aussieamplifiers.com).
    [​IMG]
    I'm ordering bleeder resistors for the large amplifier so I'll get a couple more for this one. I think 5K ohms at 5W should be alright. Thanks for the tip. For now, I just leave the amp on and be careful not to touch anything.
    Speaking of touching things, the heatsink is so hot that you can touch it for a second and then it gets to you - yow! I'm guessing it's somewhere between 55 and 60 C given this and the heatsink simulations (this is 0.28 C/W and 130-140W dissipation), but it was enough to make my mom say "If you don't put up a warning sign, we could get sued." And so I did. [​IMG]
    I haven't simulated the power supply. My multimeter says 50V DC going in, and I know the board has an onboard discrete regulator that according to Pass reduces output noise to 35 uV (!). I'll increase the capacitance to 42,000uf in a week or two, and I don't believe there will be any voltage drop (loss of dynamics perhaps) caused by the transformer given at the moment it is way overrated.
    And oh heck no, I'm not modifying anything. I used decent quality parts (what Pass specified). Who knows, maybe I'll try some better capacitors or something but definitely not change the circuit design.
    I still think it's funny I have a 24 by 7 by 3 inch block of aluminum here that's almost too hot to touch, yet the amplifier is only 15 watts [​IMG] And yes, I am definitly having fun.
     
  5. Saurav

    Saurav Cinematographer

    Joined:
    Feb 15, 2001
    Messages:
    2,174
    Likes Received:
    0
    Trophy Points:
    0
     
  6. Michael R Price

    Michael R Price Screenwriter

    Joined:
    Jul 22, 2001
    Messages:
    1,591
    Likes Received:
    0
    Trophy Points:
    0
    Saurav,
    I have a question I'm not sure belongs here, but anyway: The Zen doesn't have much gain (2.5V or so input sensitivity, I believe), and while the variable out of my CD player can drive it almost to its limit (90-95db) I imagine I may have a gain problem when I try to bi-amp using a 400 watt woofer amp with 1.2V sensitivity. I recall you saying you had a DIY passive line stage - how much voltage does this provide and how much does it degrade sound? Could I perhaps use one of those on the high frequencies only?
    I may have to put some more thought into the DAC and crossover I am planning to get it to work with the different levels of the amps and the drivers they will be used with. This is further complicated if I choose to upgrade my speakers, which is not unrealistic in the next year. Gee, I completely ignored gain matching figuring this stuff out. [​IMG]
     

Share This Page