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Old 30th August 2011, 07:06 PM   #261
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It seems Mouser has sold out of pots

I've revised the board (not published yet) to also use 15 mm shaft length pots if you cut off the tiny 0.8mm "nub" on the front (which is easy as it's a brittle casting). I avoided the 15mm pot initially because it does require cutting off the "nub" to work with the 2mm panel and push-on knobs. But now the PCB has both footprints (15mm and 20mm). So this allows use of:

Alps RK09712200MY (15mm long "D" shaft 3B taper)
Alps RK09712200MC (15mm long shaft 15A taper)
Bourns PTD902-2015F-A103 (15mm long "D" shaft)
Bourns PTD902-2015K-A103 (15mm long "star" shaft)

And the 20mm shaft pots:

Alps RK097122008T (20mm "D" shaft 3B taper)
Alps RK09712200HA (20mm "D" shaft 15A taper)
Bourns PTD902-2020F-A103 (20mm long "D" shaft)
Bourns PTD902-2020K-A103 (20mm long "star" shaft)

And, if all else fails, you can use a 20K version of the above but the noise performance will suffer a bit:

Alps RK09712200MT (20mm "D" shaft 15A taper 20K)
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Old 30th August 2011, 08:14 PM   #262
qusp is offline qusp  Australia
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do it while off the board, pretty sure i just killed some relays dremelling 5mm off a pot shaft while mounted, so the knob mounted flush. used a diamond cutoff wheel so took no time, but just the relays dont work properly, well one, they are wired in parallel so it stopped the other one working too. pita i even thought twice about it and did it anyway.
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Old 30th August 2011, 09:21 PM   #263
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IMPORTANT! This has unexpectedly killed most of my day, but I have revised the PC board to accommodate a wider variety of volume controls and that necessitated other changes. All the design files are now dated August 30th and available in O2 Resources.

I would very much appreciate another set of eyes or two to look things over, especially the Gerbers, and see if everything looks OK?

Here are the changes:

- I've added a section on "pot tapers". The Alps volume controls are available with two different tapers and you might want to decide which you would prefer. See the Obtaining The Components section.

- I've added a section with all the volume control part numbers explained.

- I've revised the BOM to reflect some of the latest changes at Mouser, new pots, and some other changes suggested by others.

- The optional R26 & R27 output resistors have been eliminated. You can accomplish the same thing by increasing R10, R11, R15 and R18. I needed the board space for the pot change.

- The off board output jack header, P2, has been moved to the other side of the output jack. This was to make room for R12 which was displaced with the new volume control option.

- The channels have been swapped at the volume control and output jack. This enables much cleaner high-current wiring of the output jack and doesn't change the function of the amp (tip in is still tip out) but might confuse someone familiar with the old schematic as U3 and U4 now serve the opposite channels.

- Minor improvements were made to the ground routing and ground fills made possible by the other changes.

- The gain stage components were tightened up and the inputs to U3 and U4 re-routed to further reduce EMI susceptibility.

- I've added a tools section.

OLDER CHANGES: Just to put everything in one place, the previous major changes were:

- C16 and C21 reduced to 0.022 uF

- C22 (now C1) increased to 1.0 uF

- C1 (AC input filter) eliminated

- Footprint revised for Eagle battery clips

- Larger hole size on U5, U6, Q1 and Q2 to accommodate more parts

- Gain change to 2.5X and 6.5X
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Old 30th August 2011, 10:05 PM   #264
Jokener is offline Jokener  Germany
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Thanks a lot for this lightning-fast reaction.
Its good to know you're not shying away from your project as it nears completion.
And don't worry, we are ready to have our minds blown... so no pressure ^^
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Old 1st September 2011, 05:10 AM   #265
Electrons are yellow and more is better!
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Originally Posted by RocketScientist View Post
When I use the Google Docs viewer it takes a second or two after you zoom in to download the hi-res version. Perhaps Australia is connected to the USA via dialup?
Google Docs works perfectly for me and I'm using a Mac.
/Per-Anders (my first name) or P-A as my friends call me
PA03 LM4780 amplifier group buy, SIGN UP HERE for the group buy 0 boards left. 118 paid.
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Old 1st September 2011, 10:14 PM   #266
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Based on all that's changed (see post 263 above), the group buy being well past 500 boards, PayPal delays on Oliver's side, and nobody else volunteering to get a small run of boards made, I went ahead and ordered a 4th round of proto boards. I paid more for quick-turn boards from a US supplier so I can get them them next week and hopefully not delay things too much past the existing PayPal delay.

At least it should help me sleep better not having to worry if there's a significant problem with the PCB files when the stakes are relatively high. I've removed the old PCB files from Google Docs for now pending approval of the new prototypes.

As I've said many times, this hasn't played out as I was expecting. I never imagined the very first group PC board order would be for more than 50 boards let alone more than 500. I also didn't imagine Mouser would sell out of substantial inventories of key parts due to the high demand necessitating a board re-design. I just wanted to design an amp that raised the bar and demonstrate what's possible on a modest budget with modest parts.
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Old 2nd September 2011, 01:33 AM   #267
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Hmm, doesn't really look like there are going to be pots available anyway once I get around to ordering my parts. I don't suppose the identical Alps with the switch can be used? Those are what I have on hand. That is why I always preferred wired pots and jacks. It simplifies the enclosure also. Drilling precise holes in a front panel is not one of my strong suits... My payment for the GB has been sent the old fashioned way. So I apologize in advance if I'm holding anything up.
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Old 2nd September 2011, 01:47 AM   #268
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@Rembrant, I'm not sure where the problem is? The 15mm shaft pots are in stock by the hundreds at Mouser and elsewhere and RS Compnents has the 20mm version in stock as well.

If the front panel is challenging, just order one from Front Panel Express or Schaeffer AG. Problem solved.
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Old 2nd September 2011, 04:52 AM   #269
orpheus is offline orpheus  United States
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Originally Posted by qusp View Post
no, what we have is a mass of different half assed solutions, i have been campaigning quite vocally for a standard connector that was a practical size for years. full size 4 pin xlr is becoming more popular for home, but its still pretty rare, as far as portables there is like 5 different proprietary connectors in use by different companies with everyone refusing to enter into dialogue on a standard, hirose HR10 being the best of them imo (but lemo is better) and at least more than one company is using it, though its mostly in asia its used.

******* stupid, i gave up and made my own lemo 'standard'

my RCA comment was in reply to a post on the previous page

What part numbers do you recommend for lemos for headphone amps? Do you use the Lemo for interconnects, and if you do, do you do two cables for stereo, or do you use just one for both channels? I've been thinking about getting some Lemos to try, I think they have the best design, and since we're building things ourselves, we might as well have the best connector.

I think that there are cable mount mini xlr's, I'll have to search around. Neutrik makes some, but I'm not certain they have male and female.
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Old 2nd September 2011, 05:04 AM   #270
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Originally Posted by qusp View Post
yeah Steve the redels...
Ah, ok.

Yeah, the Redels are a nice connector, though the one drawback I see for a small portable amp is the 11/16" diameter taken up by the "nuts."

Personally I think a 4 pin mini-XLR would be a good choice.

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