Jump to content


Full Member
  • Content Count

  • Joined

  • Last visited

Everything posted by Suzyj

  1. Yup. No need to mess with compensation if you’re increasing gain.
  2. Apologies. Was looking at the AEM6000 schematic. Change R19 from 22K to 100K. That’ll give 12dB more gain.
  3. Change R48 from 47K to 220K. That’ll give you an additional 12dB gain from the power amp stage. Note that the noise level and harmonics will also go up by 12dB. If this is a problem, then don’t use a passive preamp.
  4. It’s very soluble in isopropyl alcohol, so cotton buds dipped in iso to mop the majority up straight after soldering. Once the board is assembled I do a thorough scrub in hot (like 80 degree) water with some safe wash detergent in it, then rinse with deionised water.
  5. Normally I clean my boards before I take photos, as showing my flux is a bit like going out in my PJs. This thread, however, is about flux.
  6. There’s nothing wrong with SMD! I quite like building surface mount boards. I like to do an unholy mix of surface mount and through-hole, with plenty of MELF resistors and diodes.
  7. Additional flux is needed when you’re reflowing solder. A typical SMD process is to tin a pad, then bring the component into contact with the pad and reflow. If you don’t use additional flux then this doesn’t work. The flux in the solder wire is (barely) enough for the initial wetting of the pad. There’s none left for the subsequent melting. I do piles of SMD, and use a lot of flux. It’s the secret sauce for perfect solder joins.
  8. We're in a no-clean, water-based, lead-free world, and that sucks. Decent rosin paste flux is getting harder to find every time I go looking, and with the secrecy around formulations who knows what's in that stuff. Here's a recipe for paste flux just like your grandma made when you were a kid. Nothing but the finest free-range organic ingredients, and made with love. Cook some up and gift it to that special engineer in your life, or just make a batch for your own use. Seriously, this doesn't just resemble paste flux. It's the actual thing. It's not activated, which mean
  9. A pleasure! I'm getting such great warm and fuzzies reading of people building these. I'm assembling a pair of more uber ones on the bench today with Class G (erroneously referred to as class H on my silkscreens) output stages, in a 100W and 200W flavour. In simulation they show great promise. I can't wait to test them.
  10. I’m not aware of any substitutes for the Exicon parts. I designed it originally around Hitachi lateral MOSFETs, but they haven’t been available for some years.
  11. There are two manufacturers that I know of: CA Logic, distributed by future electronics, and Linear systems, distributed by micross.com
  12. Okay then, I'll go along with this. Here's what I've done: 1. In simulation: Insert a 10mV 10KHz AC voltage source in series with the zener, and simulate the circuit. Measured AC on output is 450nV, giving me 87dB rejection of voltage noise at this point. Like I said, good CMRR. 2. In reality: Stick a 12V zener in series with a 1K resistor. put that across my lab supply and put 5mA through the zener. Measure the voltage noise density across the zener with my 3585B. I measure 79nV/√Hz, flat across the band. For reference my 3585B does 11nV/√Hz with it's input shorted. It's a re
  13. I look forward to seeing the results of your simulations and measurements of your proposed changes on a board.
  14. TE 63756-1 https://au.element14.com/amp-te-connectivity/63756-1/terminal-pcb-tab-1-4mm/dp/2841308
  15. Instruments (ie guitars) are generally very high impedance. Cable for guitars is usually designed to have low capacitance, as cable capacitance destroys the high end on guitars. Resistance wise it’s low, just like other cable.
  16. I suspect the whole diffamp thing is confusing you. Can you agree that the node at the junction of R4 and R5 is a virtual ground due to the symmetry of the differential amplifier? If you do that, then split the whole input diffamp down the middle and look at one side. Q1a source goes to virtual ground via a degeneration resistor. Q3's base is held at 12V wrt our virtual ground, due to the 12V zener. The node formed by the emitter of Q3 and the drain of Q1a is at 11.3V. Our load resistor (R6) hangs off Q3's collector. It's a straightforward, uncomplicated cas
  17. Yup, all the parts are available. See the parts list. Also, I'm not a sir.
  18. I did a write-up of some of the development process: http://www.suzyj.net/2017/01/measuring-mosfet-power-amplifier.html In testing, I used a 2x40VAC 300VA toroidal (MT2140 from Jaycar) for the supply, with a BY224 (4.8A) bridge rectifier, and 2 x 6800µF 63V electrolytics for the rails.
  19. Hi David, They're a connector I quite like, a Faston 110. They're a shrunk version of a Faston 250 (general purpose spade connector). The particular flavour I use is 2.8x0.81. Here's a link to the relevant Mouser page for terminals: https://au.mouser.com/Connectors/Terminals/110-FASTON-Series/_/N-5g5u?P=1ywwwf4Z1yphpxn The uninsulated ones generally have a U shaped part where the wire goes in. A Hero FRH-07 crimp tool is just the ticket for crimping them (or of course you can just solder to them). I got mine from Eastern Beaver (and still chuckle
  20. On the basis that more is always better, here’s a 100W version: 100 watt design files Same thing, but with twice as many MOSFETs. I’ve only built a few of these, as the little one makes more sense for my usual active crossover speakers, but they perform quite well.
  21. The idea is you send the Gerber files to a pcb manufacturer, and they send you pcbs.
  22. The build price is dominated by the MOSFETs, at around $15 each, and the JFET, at around $8. I’d guess something like $60-80 per amp.
  23. Way back, I wanted to build some amplifiers to drive a lovely old pair of Infinity RS-5B speakers that my PhD supervisor gave me. I found the original articles for the AEM6000, and set to updating that to use available (at the time) transistors. Since then I've done some other versions of this amp, mostly working to shrink the PCB somewhat, optimise the layout, and achieve respectable noise, THD, and slew rate specs while keeping the quiescent current under control. This latest version uses one pair of Exicon ECX10N20/10P20 lateral MOSFETs, for around 50W RMS into 8Ω. I
  24. I can put the CDs in either way. The top four rows rest on top of the lower back bar, and the rest of the rows have the CDs inserted so the bar is behind. This just makes it a bit easier to read the CD spines on the lower ones without bending over as much. I use this as well to flag CDs to make them easy to find - I just insert a CD so it opposes it's neighbours and then I can find it easily. I think when I outgrow this one I'll just make longer bars (from 12mm steel rod so they don't flex). I reckon I could easily do 1.2m wide (~1200 CDs).
  • Create New...