j4cbo

Kevin: as it is now I've got a solder jumper to ground the middle feedback point (just before the diamond buffers). Under what circumstances is that necessary? Do you think it should be kept as a solder jumper, exposed as a 1x2 pin header, or just removed?

How many of those heatsinks designed for the JFETs are available? We could retrofit some of those

Here's what I'm thinking at the moment: I'll probably widen out the devices so they spread the full width of the board, and move the mounting brackets in a little bit, but it's using a fairly solid amount of width already.

I'm letting interested people get in on the purchase of my custom version of the board layout because there's no reason not to, but I am not designing it as a second group buy. The entire purpose of the custom work is to let me make whatever design decisions I need for my amps without worrying about compatibility; mounting bracket compatibility and identical features are explicit non-goals. If you just want to use surface mount parts in a Dynahi-compatible board, that's what the main design is for. At the moment it's looking like the custom board will be 3.7" x 3.4", with output devices right at the edge of the board for direct mounting to a heatsink, on 0.5" centers rather than 0.45". This will not be final until I send CAD files to HiFi2000 for custom chassis modification.

What's that heatsink you're using?

Good thing we went with the OPA447, then...

What's the output voltage of the servo sitting at?

And here's our display: Noritake GU140X32F-7003.

Marc: Should be doable; I'll just add some extra mounting holes and pins. Here's our display: Noritake GU140X32F-7003

OK, I've got most of the changes done on the board. I'll hold off on finishing it up until the final JFET layout and test results are ready. What do you mean by "PPAv2 type slip ups"?

That does look like a fab problem. I'm surprised; PCBFabExpress has done better with the other boards I've ordered from them. Might be worth contacting them to see what's up. Will do. Looking at it, yeah, that should be no problem to change. I've actually got a more compact TO-92 layout that I think I'll try to switch to (it's used in my custom layout for my own builds, here). Hopefully that will allow making all the devices face the same two directions. I'll see what I can do, but I'm not too worried about the positioning now... they're staggered, so heat shouldn't be too much of an issue, and the actual terminations are well-spaced. Will do. Whoops, that's R31. Not sure how it got unlabeled. Will do. I don't think there are any spots that immediately preclude enlarging the outer pads on the resistor footprint, actually. I'll see what I can do there. Adding silkscreen on the bottom will increase the cost a bit. Maybe just put a label in copper and then a little more explanation on top? That looks great. Will do. Let me know what else you find. Thanks! I want more photos once it's all stuffed

I've made some component name tweaks and fixed the 2SJ76 pinouts: EAGLE brd, EAGLE sch, Gerber files. And here is my BOM. It's based heavily on DigiPete's; I went through and checked all the footprints, tweaked the capacitor choices, and fixed up component names for my changes. This assumes we're using an OPA445 and jumpering over the regulators, which is probably the best choice for the first prototype run. To the best of my knowledge, those Gerbers are ready to be ordered.

Sorry for vanishing... my laptop decided to die a few days ago and I'm working on getting it replaced. Once I have EAGLE back I'll look into that pinout issue.

I've gone ahead and designed a constant-impedance logarithmic stepped attenuator. This relies on the fact that it is driving a fixed output impedance, as would happen within an amplifier or preamp, and in turn presents a fixed impedance to its source. I wrote a program to calculate out and verify all the stages, and simulate the actual impedance and attenuation for each stage. Here's the source code and sample output. It's set up for a 7-stage (128-step) attenuator, 0.5dB per step, with source and load impedances of 15k ohms, but that could easily be changed. The program takes into account available resistor values and selects the nearest E96 series (1%) value. Code, written in Standard ML: http://b.j4cbo.com/stuff/attenuator.sml Output: http://b.j4cbo.com/stuff/attenuator.txt

http://b.j4cbo.com/temp/gbf2.brd http://b.j4cbo.com/temp/gbf2.sch Here's the current layout; consider this Release Candidate 2. If nobody finds any show-stoppers, I'll work with Icarium to get prototype boards ordered this week. Changes since the previous layout: - Added 5mm spacing for the film caps on the rails - Fixed orientation of LED3

justin: Of all the possible part interactions to worry about, this doesn't seem like the most worrying one to me...

Depends on how you define "pretty easy" and "like this". I'm primarily doing the controller board design for the builds I'm doing. I'll release everything, yes, and it'd be straightforward for someone who's competent with AVR C programming to integrate pretty much anything in... but I don't really have time to add support for the kitchen sink if I won't be using it myself.

Haptic feedback, yes. (I could also add an RS232 connection from a Transporter to the amp, such that the amp could be controlled via a Transporter or Controller, but not everyone who will be using this thing has a Transporter )

Graheme: That's exactly what I'm thinking. I'm going to be using the same knob module as the Transporter. The UI won't be quite the same since they have a separate "back" button, which I'd like to do without, but overall the concept will be similar. And yes, coming up with a good way to manage the potential customizability of it all will be tough...

The left and right channels will have independent attenuators, yes. The UI for controlling two separate channels at once might be kinda awkward, though, since there will only be one knob.

It's not so much "design by committee" as "design by kitchen sink"...

Here we go, better late than never: Prototype Candidate 1 Let me know what still looks wrong... http://b.j4cbo.com/temp/gbf2.0rc1-all.png http://b.j4cbo.com/temp/gbf2.0rc1-no-gnd.png http://b.j4cbo.com/temp/gbf2.0rc1-sch.png luvdunhill: I'll look at adding those TO-3P footprints as well...

The board is 4.95" wide by 4.2" (same size as the Dynahi, maybe a little longer), with all the output devices in the exact same place as the Dynahi as well. I'm going through and updating the board with extra holes for the output resistors and a rearranged input filter now.

It really isn't tied to the DynaFET in concept at all. I will be designing in pads for sense resistors on the DynaFET boards, but the current sensing could be easily built off-board as well for a B22 or some such; that's about it as dependencies go. And, yeah, I have a Transporter and Controller too; controlling the amp power and volume from SC is definitely in the cards. Looks like all the spots in this build are full now.

I've been lending a hand with board layouts for a few projects, notably for a build of Kevin Gilmore's DynaFET design, and doing so made me realize two things: (a) there aren't any DIY projects for amps with a truly high-end feature set, and ( I want one, but I can't really afford it. The DIY crowd has some amazing analog designers and has produced some really astounding designs, but the supporting and surrounding circuitry often isn't much more than a pot and maybe a selector switch, and sometimes a power LED or relay control circuit. There's so much more that could be done to make amps more convenient, self-monitoring, and just plain nifty. So I decided that this was an opportunity to take matters into my own hands. To that end, I'm designing an input, attenuation, and control board which I'll be using in some amps for myself and Icarium. We're doing this as a a collaborative, long-term project, such that I'm contributing much of the design and construction effort in return for having parts for my own build subsidized; I could likely complete four or so of these by the end of the year, and so we're looking for other people who are interested in financing the build and getting a completed amp in return. The final cost will probably be somewhere in the $1500-$2500 range for a finished amp, depending on what parts, design, and case decisions we wind up making. Send one of us a PM (soon!) if you're interested. I also plan to release all the designs, code, and whatnot for the controllers as I develop them. This isn't a commercial, money-making endeavor; I'm in it to get myself the coolest amplifier I possibly can, whatever that involves. Without further ado, here's the feature set: - Four selectable inputs; each can be configured as either single-ended or balanced. - Two Sowter input transformers will be switched in as needed, to convert single-ended inputs to balanced, or vice versa. If the source and headphones are of the same configuration, the transformer can be switched out of the signal path entirely; otherwise, it is used to convert the signal as necessary. If all the inputs and outputs will be balanced, the transformers can be left out entirely to save on build cost. - A four-channel (true balanced stereo), 7-stage, 128-step relay attenuator (similar to the Twisted Pear Joshua Tree) for level control. The output of each channel of the attenuator is connected directly to the corresponding amp board. - Four DynaFET boards. The controller board could also be used for other amplifier designs, though, such as the Beta22 or Dynahi, but this build will be based on the DynaFET. - Both unbalanced and balanced output jacks; the full configuration would include 4-pin XLR (balanced), 2x 3-pin XLR (balanced), and one or more standard unbalanced TRS jacks. - A monitoring board to sense current on each amplifier's power rails, rail voltages, output offset voltage (differential voltage in balanced mode), and supporting remote temperature sensors on the heatsinks and other parts of the amplifier's case. This can be used to immediately shut down the amplifier in case of a fault, and also to aid in manual adjustment of bias and offset pots. - External power relays to switch the AC input power. - A front-panel UI based on a dot-matrix VFD display module and an Immersion PR-1000 haptic rotary encoder. This will work something like: normally, the display shows volume and some temperature/current statistics. Press the button for input selection. Press again for an advanced menu, with full voltage/current/temperature readouts, input configuration, and so on. The selected input and volume will be stored even if the power is unplugged. If you've used a Slim Devices Transporter, the interface will be similar. - An RS-232 port, to allow the whole thing to be controlled externally, by a Transporter or other such device. Other things I'm considering designing in are: - Level detection, to enable automatic volume matching for A/B testing of two different sources. This would make the amp essentially a source or headphone shootout-in-a-box. - Input detection to automatically switch to an active input. - A reduced configuration for single-ended amplifiers, leaving out the balanced inputs and conversion transformers, but still including the other features. There are a few electronics design issues to be figured out. The main question at the moment is how to arrange the attenuator and transformer. The style of attenuator I'm using has a variable input impedance, but transformers work best driving a fixed input impedance, so that's very much less than ideal. We could also put the attenuator before the transformer, since the attenuator does have a fixed output impedance, but that means that the transformer will be dealing with much lower levels most of the time, or develop an additional shunt circuit to make the input impedance of the attenuator constant. I'll be working on that issue in the coming weeks. I've started doing the schematics and board layouts for the input selector, and am playing around with sensing circuits for the power rails. No pretty pictures yet, but I figured I should post this now to gather interest and input. This thread will be the central discussion point for the project. Here goes nothing... Here's a big ugly block diagram: