I have not used rechargeable 9v batts before, but I assume they will fit the standard case that you're targeting?

what do you do about the DC in/charge jack? where would that go on the case?

Except the DC jack would have to go on right side with the current pcb layout

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[Quoting linux-works]

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[Quoting tangent]

Your computer's motherboard probably has a few unpopulated chip footprints. Does that bother you, too?

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if there were things that could have been in the real estate but got pushed out for a de-populated option then yes, I would mind a little bit.

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Real estate is ever finite. That's what makes it valuable, and thus worth arguing over.

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[Quote]

just wondering if a set of relays could fit in those cap areas

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I certainly can't add relays as standard options to a design that's supposed to be portable.

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[Quoting bdhornback]

Maybe you could sell .9999 silver wire in your shop by the inch?

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I am liking the jumper-alternate-for-C1 idea. Consider this discussion closed, until I get the next board image out.

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[Quote]

have found anywhere from 10 mV to 28 mV on *PRO* gear

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[Quoting Mister X]

the DC jack would have to go on right side with the current pcb layout

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[Quoting tangent]

There was...ASUS chose not to include a tube headphone amp in the last motherboard I ordered from them, in favor of an option for a second LAN chip.

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and realtek, no doubt. harumph. I agree, even tubes would be better than realtek ethernets. but we digress.

relays..

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[Quote]

You've got the scratchpad area for that.

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true.

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[Quote]

I certainly can't add relays as standard options to a design that's supposed to be portable.

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yes, I know. for me, I keep thinking of this as a universal small sized preamp module that I can use for various projects I keep forgetting that the 95% case is inside a particular project box and meant to be portable and battery operated.

[Edited by linux-works on 03-05-2009 at 10:57 AM.]

EDIT: Removed board image and schematic links. They were replaced with newer versions, which you can see later in the thread; they don't apply to this revision level.

This week's changes:

- The front 3 pads of the scratchpad area are now connected together, giving three 2-pad groups behind it, instead of three 3-pad groups. This is needed to allow mounting a DPDT PC-mount switch here, as switches that fit this pad arrangement usually have mounting lugs that, with the previous arrangement would have shorted the front gang of the switch.

The faint yellow outline here is an E-Switch 200 series M6 model, which as you can see lines up fairly closely with the ALPS RK27 mounting surface. There are other switches, such as the NKK G22AH which are smaller and thus have their mounting surfaces at or behind the board edge, for more space constrained cases, such as the H-65. These two parts are just examples...this pin arrangement is popular for PC-mount DPDTs. There are enough alternatives to satisfy most any reasonable requirement.

The thicker lines coming out the back end of the switch show the front gang's leads, and the thinner ones the rear gang's. The hookup wires for the rear set are easy to add, but the front ones will have to either go on the bottom, or you will have to install them on the top side before you add the switch, and be satisfied with the switch not being strongly mechanically coupled to the PCB.

I don't intend to slide down the slippery slope of board-mounting all panel components. This just gives those who want more parts board-mounted a way to go further down that path. It's also important to realize that this switch has no fixed purpose, so it's no problem to leave it out and use that space for something else. Thanks go to Mister X for the backchannel discussion that led to this.

- Rear shoulders moved outward a bit, as there's only one boss it has to get around in the rear of the H-65; there are two in the front.

- Back edges of the board moved back 0.1" to use space available in H-65 case. Previous board length was a holdover from the META42 / PacTec HML compatibility days. It could go back maybe another 50 mils, but I'd like to leave a little slack here.

- Moved mounting holes, and rearranged input diodes, and enlarged B+ plane to make use of the new space.

- Swapped BATT and WALL Molices, as it gives better PCB layout, and makes more sense to put BATT nearer the contact end of the H-65 battery box.

- Rotated RCCS 90 degrees and moved it as close to board's rear edge as possible, to reduce interaction with right channel post-pot trace.

- B+ plane thickened in several places

- Let there be much rejoicing/wailing: the C1 jumper is gone. Will put a jumper in the part list as an alternate for C1, to reduce the chances of screwups.

- Changed the C1 pad arrangement, putting 2 pads on one side instead of just 1, to allow a shorting switch here. Defeat your input cap from the front panel!

- You can't see it, but the V+ and IG copper layers were removed from the upper left corner, under the scratchpad area. You can now safely drill through this to restore the mounting hole from previous versions; the bolt won't short layers.

- Also not visible are more bottom-side silk labels for all the recent SMD additions. This wasn't strictly necessary, as you could figure out which part was which by poking things through the holes and referring to the top-side silk, but that's weak.

- Added a serial number rectangle on bottom side silk, near logo and version number stuff. (Happy, B.D.? )

- Added 3 holes corresponding to rear pot gang. We discussed this above as a way to mount the pot off-board, connecting it to the board with standard 1x3 Molices. It was rejected with the argument that similar 2x3 connectors are also available, which would simply use the RK097 footprint. I came up with another reason to have these, so they're in now: the DACT CT2 stepped attenuator. There's only one trick: it extends just a bit into the S1/C4-/INPUTS area. If you want to solder it to the board, you probably aren't the sort to use Molices for S1 or INPUTS, so the only thing you have to work out is how to mount C4 to avoid bumping into the CT2, if you want that cap, too. If you're the sort to use connectors for everything, you can get riser connectors for the CT2 that lift it up above S1/C4-/INPUTS.

- Various tweaks to the other two pots while working on CT2 feature.

- Flipped headphone guy to make grin look right to people looking at the eventual board, as opposed to those of us looking at the bottom copper through the board.

- Added a second set of output pads just off the ends of the R7s closest to the op-amp, to make it easy to jumper the buffer position if you don't want it. This makes it easy to achieve CMoy or Mini3/PINT like topologies.

- Added a pad for a single 18mm diameter C2 in place of the two 12.5mm ones. Pad was positioned by Mr. Pythagoras and his friend Joey Trig, so you can use the V- hole for either C2A or C2B, depending on how you want the big cap to sit on the board. The faint yellow outlines show these cap positions.

- Moved OPALR amp section to the right a fair bit, getting R4L pads out from under the RK27 footprint, allowing...

- ...a form of bass boost I call "unity boost". The idea is, if your source doesn't need any voltage gain to drive your phones, you can use it to put the amp in G=1 except at bass frequencies. The difference between this and the PPA bass boost is lack of an "R7" in series between the output pad and R4; there's room to add it, but the traces to connect it...ah, the horror, the horror. Not that it's beautiful now anyway...this feature removes the ability to use a DIP-8 socket in place of R3-6 to allow socketing all of the the feedback loop resistors. You can still do it with individual pin sockets, but I'm not sure the gain outweighs the loss. I could move one of the R4 holes to the other side of the part to restore this, but it makes adding the shorting switch harder, and the trace between R6L and R7L becomes really hard to re-route. Another problem is that the left channel doesn't have much room for the cap, important if you use the thru-holes for the C and the SMT pads for the R, rather than vice versa. The values on the schematic only give an fc of 338 Hz, rather high. You can raise the value of R4 to lower the fc, of course, but raising the parallel C is better from a noise standpoint. Comments solicited.

- Right channel trace is now out from under C4+. Woo.

- Board image shows MLXFEED board outline. Notice that there is a second possible position, if your standoffs are long enough to lift the board over C2.

The length of this change list might make some of you despair that I'll never finish the design, but I'm really running out of room now. There's not much more possible short of minor tweaks, I think.

I looked into making it compatible with the Hammond 1593 series, which is similar to the Serpac H-65, but it would require major board surgery to make it fit in any but the largest case in this line. For most of the variants in this line that are close to the H-65's size, the current board is about 0.1" too wide and 0.3" too long. For a few, you'd have to add additional cutouts to get around some of the bosses, or mod the case so it doesn't use those bosses. For those who want to study this themselves, the current board dimensions are 2.4" wide x 3.1" long. The front shoulders are 0.6" back from the front, and the rear ones 0.45" back.

[Edited by tangent on 03-16-2009 at 05:12 AM.]

There are some quite nice surface-mount PPS film capacitors available these days, up to 1.0uF. Panasonic make some, here's a couple links: http://industri...PU1C105MA5+7+WW
http://industri...ecpu/index.html

These are 1210 size SMD devices ... it looks like there are surface mount pads for C1, I want to check if these little 1210 film caps fit?

I've heard good reports about these in Tripath Class D amplifiers.

edit: I also want to applaud the switchable input caps ... this will go a long way in educating the DIY public about the true effect of capacitors on sound quality. A nice big stick to bash superstition with!

[Edited by kristleifur on 03-09-2009 at 08:42 AM.]

[Edited by tangent on 03-09-2009 at 09:14 AM.]

Can you add similar pads to C4+ & C4-?
(I realize there is a small penalty with adding them there but since you have to order those caps in lots of 10@ Digi-key it would be nice if we could use them in more then one spot)

Edit:

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[Quote]

Oh and do you think it's possible to add pads for 1210 SMD C1 caps?
(digi-key # PCF1132CT-ND)

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Guess they were 1210s after all.

[Edited by Mister X on 03-10-2009 at 07:57 AM.]

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[Quoting Mister X]

Shows how much I pay attention to my own suggestions, I could have swore those PPS caps were 1206s.

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I think there's a few sizes floating around - the 1.0uF 16V are 1210, the 0.47uF 16V are 1206, and so on

They didn't use to go up to 1uF, I recall max of 68nF (and expensive to boot) but that was years ago, I guess they expanded the range now. Good to know .

[Edited by aos on 03-09-2009 at 07:07 PM.]

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[Quoting aos]

I have been using those PPS capacitors for analog duty in my builds for years, with good results. Expensive but cool, and very precise (2%). Being 1206, easy to solder too.

They didn't use to go up to 1uF, I recall max of 68nF (and expensive to boot) but that was years ago, I guess they expanded the range now. Good to know .

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There seem to be a few different versions around, the ones I was looking at were 20%, $0.5 at digi-key.

I'm very reluctant to swerve this thread off-topic ... but I'll ask: do you take any special precautions against film meltage when soldering these? Or is standard finish-joint-ASAP practice good enough?

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[Quote]

is standard finish-joint-ASAP practice good enough?

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Yes and then some.

From the datasheet you linked above:

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[Quote]

Reflow soldering : 240 ˚C max. and 30 sec max. at more than 220 ˚C (Temp. at cap. surface)

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http://search.di...me=PCF1132CT-ND

[Edited by Mister X on 03-09-2009 at 07:40 PM.]

The layout looks great (you've really been busy)! I'm not going to quote all the things I'm glad to see... so let's get some boards printed!

Thanks again!

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[Quoting tangent]

- Added a serial number rectangle on bottom side silk, near logo and version number stuff. (Happy, B.D.?

- Right channel trace is now out from under C4+. Woo.

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[Quoting Mister X]

SI could have swore those PPS caps were 1206s.

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[Quote]

Can you add similar pads to C4+ & C4-?

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[Quoting bdhornback]

let's get some boards printed!

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- No lamentation for the loss of DIP-8 compatibility for R3-R6? We can keep "unity boost"?

- Adding C4 SMT pads

- Recheck physical compatibility with H-65 with printouts and physical mockups

- Manually redline the copper. All those dual thru-hole/SMT parts are murder on EAGLE's DRC logic. It throws up so many silly warnings that there a risk that I've ignored something that matters. So, I'm going to have to do the checks the old fashioned way, with a bunch of printouts on a big working surface and a red pen. Fun.

Now if I could just get conductive toner for my printer!

Just my opinion, but I don't see the loss of DIP-8 compatibility for R3-R6 as a big deal. If someone wants to experiment with values... pin sockets are pretty easy to use.

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[Quoting tangent]

All those dual thru-hole/SMT parts are murder on EAGLE's DRC logic. It throws up so many silly warnings that there a risk that I've ignored something that matters. So, I'm going to have to do the checks the old fashioned way, with a bunch of printouts on a big working surface and a red pen. Fun.

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