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Old 8th December 2011, 12:36 AM   #1301
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@counter culture, thanks. I didn't know TI had a better part--although it would be interesting to see which wins in real world testing rather than the "datasheet wars" (I have no idea which would). I know some really high-end uber-priced gear has used the Cirrus part. But both, and their related overhead, are off the menu for now. I've looked at some of Wakibaki's posts, etc. He seems like an interesting guy, but last I checked, he was banned here so I haven't been able to contact him.
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Old 8th December 2011, 01:00 AM   #1302
qusp is offline qusp  Australia
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hehe yeah he's banned here but posts a lot over at hf and your banned over there but post a lot here.

agreed hes an interesting chap

BTW i do hope you know i was joking about my jealous comment on the magic bullet

Last edited by qusp; 8th December 2011 at 01:06 AM.
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Old 8th December 2011, 02:59 AM   #1303
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yep, theres a standard way to figure it out; you look at the datasheet =) as no there really isnt a hardline standard, some will have extra ground pins, some will have L or R duplicated etc. failing access to a datasheet, just put a mini without the barrel into the jack and use your DMM to ohm it out
Thanks for the tips, I'm just getting my feet wet in diy audio. I'm one of those that were enticed by the O2 and RS's detailed docs.

So the datasheet explains the components, but some things on the PCB I don't get.

The VR1 has 3 rows of 4 pads. I'm thinking a row for each channel. I also see that one column is not connected to anything, which I think is because you don't need that third pin for a pot. But I don't understand why are the 2 channels duplicated (if my assumption about one row per channel is correct).

Also looking at skkhai post #1254, I see that he's running a wire from the pot to the tab that is not connected to anything for both channels, am I missing something?

Also There are three pairs going to the 1/4" jack when there are only 3 tabs to connect to. So why run two wires to one tab?

May be I'm just going OCD on this, so apologies for that
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Old 8th December 2011, 03:18 AM   #1304
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The volume pot is explained in Circuit Board Construction. The 6 holes closest to the edge of the board are for the 15mm long pots. The 6 holes farthest from the edge are for the 20mm long pots. All 6 pins for each are connected and required, it's just that two have little "fingers" that connect the pads to the ground plane (it's called a thermal relief and is for soldering purposes). The two sets of 6 are electrically the same (duplicates).

If you're going to panel mount the pot, just wire each pin to either set of corresponding pins on the board. Each row of three (each channel) should be twisted together with the ground wire for that channel. or you could use 4 twisted pairs with 4 grounds. There are instructions for that in the article as well.
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Old 8th December 2011, 03:58 AM   #1305
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Thanks RS for the clarification. I went back to your blog and the pot part is pretty clear in my head.

I'm still fuzzy on the P2 connections though, does every twisted pair connect to one tab?
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Old 8th December 2011, 04:53 AM   #1306
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P2 is fairly non-critical. There are two grounds so you can have one twisted pair for each channel if you want. Some like to use 4 pin headphone jacks when their headphones are wired for use with "balanced" amps.
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Old 8th December 2011, 05:43 AM   #1307
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As I am building this O2 (actually in the ordering Mouser stage) I can't get the dismisal of DC offset as unimportant. Take my grado for example. Typical listening is about .3V across the voice coil. Now put 5 mV of offset across the voicecoil. That is I/R=0.15mA. Now with big push-pull amp coils people get a bit anxious about a milliamp or so of current. With a mic input transformer this would be dead in the water. I think of a grado headphone voicecoil as being very susiptable to flux modulation. I mean where is it a given that hysteresis distotion is negligible with 5 mV's of offset? To put it into tangle terms that Poffset= 0.15mA * 5mV = .75mW. With a speaker of 98db/mW how can we say this is insignificant?

So with a typical Grado listening listening level of 0.3V, the DC component from the amp is only -18 dB down. I am not saying it harms the headphones, but I would be surprised if it doesn't significanly impact the driver response?

Do you think more emphasis should be placed on trying to eliminate the this DS offset? And I am not picking on the O2, as have wondered about ths with any DC coupled amp I have built, coincidentally I've yet to find a dc couped amp that I like with grados, hoping this O2 will do the trick.

Are you able to measure waterfall or basic frequency response of O2 driven headphones with the dscope ?

Maybe I am being anal, but -18dB down doesn't seem insignificant, then again maybe I am just pissed that Mouser zapped my O2 project off my account and I have to start over again

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Old 8th December 2011, 05:47 AM   #1308
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Quote:
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To put it into tangle terms that Poffset= 0.15mA * 5mV = .75mW. With a speaker of 98db/mW how can we say this is insignificant?
Your calculator sucks I make that microwatts, not milliwatts.
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Old 8th December 2011, 06:10 AM   #1309
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Your calculator sucks I make that microwatts, not milliwatts.
yep microwatts, sorry for the typo (they really should have mu on keyboards

But the -18dB down figure is correct. The voltage ratio is .005/.3V = 0.0167= -18dB we have a DC "signal". Now I am not too hung up on it but it just seems significant, having read RS's awesome blog it is one thing that was a bit taken as as a given without an explaination or reference. I mean this is Objectists amp.

I also ejoyed his paragraph that I swear was directed at me regard powering my old discontinued AKG's I laughed my a$$ off( at myself), RS says to buy another amp in that paragraph!, I wish he would measure an amp that gives 11Vrms of clean power like the O2 does at 7Vrms (hint they don't exist)

Can't wait to get this little SS marvel in action though, I have a sneaking suspicion that 7Vrms on my old AKGs from the O2 will sound better than most other amps I have had my hand on.

Last edited by regal; 8th December 2011 at 06:15 AM.
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Old 8th December 2011, 06:18 AM   #1310
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But the -18dB down figure is correct. The voltage ratio is .005/.3V = 0.0167= -18dB we have a DC "signal". Now I am not too hung up on it but it just seems significant, having read RS's awesome blog it is one thing that was a bit taken as as a given without an explaination or reference. I mean this is Objectists amp.
Since you raise the issue of offset, perhaps you might find one or two of my observations illuminating

Caveat here - its been a while since I read through RS's awesome blog, so he might have updated things in the meantime. But as I recall the stated firgure for maximum output offset was wrong, by a factor of 2 if I recall correctly. The typical of course is considerably less. There's also a way to reduce the typical offset which is by balancing the impedances seen by the + and - input terminals of those output buffers. If you or anyone else is interested in output offset I'll be happy to share a few more details. The proviso is I haven't built an O2 myself so can't say that any mods I've thought up have been field tested. They'd need verification by at least one of the monster army of O2 devotees out there
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