As for the perf-board block at the back, that is a great idea. If you expose V+, gnd, V-, possibly some switch pads, you allow for a great choice in power supply options (for those that don't use your preferred case).

Another idea is to provide a spot to do a small trickle charger. Say a LM317LZ,the required resistor and the required diodes.

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[Quoting cobaltmute]

I'd vote no for both the bass boost and the crossfeed on the board. I'm a purist - I want my amps to amplify, not modify the signal. I haven't used tone controls for over 20 years.

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The PPA bass boost is a particularly neat circuit, in that it uses the op-amp that already had to be there to create a shelving filter, which is fully bypassable. I, too, am not wild about full-on tone controls, but this simple little thing...only reason not to offer it is lack of space.

As for the crossfeed, I did some more thinking on it after posting the above, and I think I might try to put it where the C1s are, and move the four resistors down there somewhere else. Add a second set of input pads in the lower right that send the signal through the crossfeed, with an option to jump over the crossfeed with big caps. Then you have three options: rear input set with AC coupling caps, rear input set with crossfeed, forward input set direct to pot.

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[Quote]

As for the perf-board block at the back, that is a great idea.

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[Quote]

Another idea is to provide a spot to do a small trickle charger.

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[Edited by tangent on 02-11-2009 at 05:54 AM.]

in case it wasn't clear what I was asking for

I wanted to have a 3pin molex for controlling my relays but the pcb routing was messier than I wanted for my iron-on board at least having the pads there (and holes, on a real pcb) let me have a physical anchor to secure the molex and from there I can deal with where those landing pads go to, on a per-app basis if need be.

you mentioned a perf board area. like a 'scratchpad' area, but for electronics? I like that! example: if I wanted to add 1 more opamp (for my bass channel, say) and if there were some pads and holes and 'work area' on a section of board - that would be a neat little prototyping feature to have.

"/usr/local/circuit"

lol

some people go on and on about 'tube sound' when they are adding extra harmonics and such to the sound. this bass boost adds 'something to the sound' and its essentially free, its fully defeatable (with no ill effects) and its a very nice differentiating feature on this kind of amp.

again, its defeatable. so no one should be having a cow about it being in the design, okay?

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[Quoting linux-works]

some people go on and on about 'tube sound' when they are adding extra harmonics and such to the sound.

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Sigh ... this old canard? This is simply not true. To prove to yourself that it isn't true, use your computer as a sound processor to inject the "extra harmonics" you think necessary to reproduce a "tube sound"* and play it through your solid state device. It will sound like a solid state device with injected harmonics, not like a "tube amp".

Sorry to interrupt your thread, Tangent.

* as if there is such a thing.

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[Quote]

On this note, what about adding a second 3-pin Molex in the pot footprint area? You can already put one in the front RK097 pads, but that blocks the second gang.

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That would be unnecessarily redundant IMO.
(digikey # 609-2423-ND is just one example of an off the shelf, dual row, friction lock header that is already a "plug in fit" for the RK097 footprint)

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[Quote]

The PPA bass boost is a particularly neat circuit, in that it uses the op-amp that already had to be there to create a shelving filter, which is fully bypassable. I, too, am not wild about full-on tone controls, but this simple little thing...only reason not to offer it is lack of space.

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Plus it doubles as an easy way to add a gain switch.

FWIW If space is that much of an issue you could always reduce the resistor pitch to 5mm.

[Edited by Mister X on 02-11-2009 at 05:33 PM.]

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[Quoting tangent]

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[Quote]

Another idea is to provide a spot to do a small trickle charger.

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Now how did I forget that? Thanks for the reminder. That definitely needs to go in.

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[Quoting tomb]

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[Quoting tangent]

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[Quote]

Another idea is to provide a spot to do a small trickle charger.

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Now how did I forget that? Thanks for the reminder. That definitely needs to go in.

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That's great news. I was sort of afraid to ask, being so biased toward having one.

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I ended up with a fabulous fast charger board somehow, that lives in my PIMETAs case... 140 minute charge time for 10 AAs is hard to beat

IMHO, any un-perfected circuit should have a scratchpad.

Here's one. The left half is a pre-wired microcontroller. The right half is a few signal and power connections, and a whole lot of holes, which may be stuffed with whatever parts and wired (and re-wired) in whatever way.

This sample would probably get lights, switches, temperature controller chips; obviously you could have a near-perfect audio amp on one side and the other side is space for bass-bump or X-feed or whatever frills your particular heart wants to add.

From Tangent's point of view, it probably makes sense to have little or no scratchpad. It takes space/cost, most users won't use it, and experimenters can easily buy a proto-board. It would be nice to have the power and signal leads already run, but not essential.

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[Quoting PRR]

>IMHO, any un-perfected circuit should have a scratchpad.

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Neat idea that would be a welcome addition to many projects.

I am currently working on a small signal pentode board to play with lots of different circuits, take some measurements, listen to some options, etc. You use jumpers to change the various options. Below is what the board looks like, and a link to some of the circuits that can be breadboarded.

http://www.ecp.c...rd_circuits.gif

[Edited by dsavitsk on 02-12-2009 at 11:55 PM.]

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[Quoting PRR]

>
I'm quite sure battery life will be better with LARGE caps, either in/out or if you must pretend "capacitorless", then swamping the rail-splitter. With the pure active rail-splitter, most actual signal power is dissipated in the splitter. With ample caps, this power is re-cycled to the next half-wave.

I preached that before and got no takers. The experiment seems too simple to avoid. Devise a consistent source, such as a CD on Repeat. Buy a 10-pack of 9V batts and select four of equal voltage. Load an amp, play until batteries sag to say 8.0V. Note time. Then build-out the rail-splitter with 100R, add two 1,000uFd rail-caps, change batteries, repeat the run. I predict the splitter will run cooler and the batts will last longer.

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I may take you up on that idea

I did that sort of thing to test li-ion battery run-time for a camera test. it was quite fun setting this up, and very educational too:

http://www.nets...battery/graphs/

if I can reproduce my test setup again (the old rs232 and software driver that I had to hack at the time), I might be able to get some actual data (imagine that!)

speaking of batteries: I have thought about using those cheap camera li-ion batts (7.2v) and maybe having 2 of them inside some kind of plastic box. some kind of opening in the box and tabs mounted on a pcb (?) that might contact the batts.

charging could be done entirely outside of this 'system', since they are regular camera batteries and they take regular wallwart style chargers. if the batts can be hotswapped (or swapped easily) in the case, then there is really no need to ever charge in-circuit.

the ebay batts are in the $5 range (for the pany cams that I used to shoot) and they seemed easy enough to interface to (their battery terminal scheme). 2 of them next to each other would give enough voltage to run 'almost anything' we'd want and those batts and chargers are quite cheap and easy to source (and will be around for a long time, too).

[Edited by linux-works on 02-13-2009 at 10:46 AM.]

(Schematic)

What's changed? Lots:

- Added PINT v1-like power input scheme, including NiMH trickle charger

- All the power inlet stuff is at the back edge of the board now, where it belongs

- No more crowbar diode. The OR bridge needed to keep wall power and the batteries from interfering with each other gives us reverse supply protection as a side effect.

- Added second power LED, between Q1 and Q2. Allows both bipolar CCS schemes above, plus "option 3", depending on how you populate the board.

- Increased B+ bus to 0.175" wide

- Moved INPUT and S1 Molices to behind pot, to make room for connectors to right of pot.

- Added R11s, for LMH6321's current-limiting feature

- Better C1 part, which includes 1210/1206 SMT cap pads. (Good for PPS film.)

- Flipped layer stack-up: V- on top for buffer heat-sinking, then vground, V+ and main signal layer. Signals are better on the bottom side anyway, since components don't block them, and it lets the other layers provide more RFI protection. (Assuming you use a metal case, which protects from RFI coming from below.)

- Knocked more holes in the supply layers around the op-amps. (You can't see what happened to the inner layers in the picture above. Trust me. )

- Added perfboard section. I put a fair bit of thought into the pattern:

-- The first requirement is that you should be able to put a DIP-8 part here...another op-amp, a microcontroller, whatever. You don't have to do that, but I figure it's the most likely eventuality.

-- The pads under where a DIP-8 would go are tied to audio ground, with one additional ground pad sticking out past where the DIP-8 would go, for a hookup wire. Each of these pin pads has another pad connected to it, for easy hookup wiring.

-- The two pads straddling C2A connect to the supply layers. The V- one is nicely positioned to jumper it to DIP-8 pin 4, for an op-amp. Unfortunately, pin 7 or 8 is a little farther away from the V+ pad, but there's nothing to be done about that.

-- That leaves 6 pads off on their own, good for running O wires to, for use with an 0.1" board connector.

- Approximately four bazillion part positioning and trace tweaks

What didn't change:

- Bass boost. Just no room for it. Sorry.

- Crossfeed, ditto, only more so. (Well, not without going fully SMT.)

[Edited by tangent on 02-16-2009 at 04:03 AM.]

You realize this forces a complete flip in layer stack-up. That's a fair bit of work, but more critically it means you can't follow traces on the board as easily when all the parts are soldered down. It also reduces the RFI shielding effectiveness. Think of a PIMETA in a metal case -- shielded, yes, -- with a DAC board in there, too -- oops, not shielded against that.

EDIT: Another thing to think about: it's not like with op-amps, where you'll be rolling buffers. We're kind of stuck with this one chip in this design. Unless you fry them -- which shouldn't be happening if you populate R11 -- you shouldn't have to replace them, ever. If you ever do, you'll probably have to remove the output wire near each chip to replace it, to give enough room for the chip to slide off its pads, but that's no biggie.

EDIT2: The SO-8 op-amps being on the bottom isn't a feature, by the way. It's just a necessity of the way you have to do the routing. This layout of Morsel's is far superior to the BrownDog way, which requires that traces take some pretty horrible paths to get to their associated pins. It's a bad trade-off to get the SO-8 onto the top side, so we don't do it.

[Edited by tangent on 02-16-2009 at 05:40 AM.]

that actually makes sense as those 2 features really are 'options' and so a single option board would be the place to populate that.

as long as the board can plugin via some location (a well defined interface, like the feedback loop insert point as well as the audio in/out/passthru block - then the mezz board could be designed to mate with the bottom main board.

in fact, if you go with a 2nd board on top, THEN you could have room for relay switching of those features. no one wants SIGNAL wires running all over the case; but relay controlled - mmmm, that's nice

You may not have the space in that layout, though.

[Edited by tomb on 02-16-2009 at 02:07 PM.]

one of the features of the v1 was the hability to stack buffers and get the extra current output.

Will this be an option with this new design or does the buffer have enough current output for current hungry cans?

if you vertically piggyback/stack them, I can't see how the 2 can be effectively sinked.

one of them, per channel, runs hot enough as it is!