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Old 2nd September 2010, 07:06 PM   #761
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Originally Posted by qusp View Post
yeah but you can omit the one on the IVY I would think, well I did too with the one I tried for the portable. I assume its to protect the opamps from the capacitive load and also perhaps output short protection yes? probably says in the manual.....
Not really to "protect" the opamp, but to prevent it from oscillations. It provides some isolation for the capacitance that the output cable may have have.
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Old 3rd September 2010, 10:48 AM   #762
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obviously the capacitive load isnt going to KILL the IV opamps, protect was just a choice of words. 'protect' like 'buffer from' the capacitive load.

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Originally Posted by stephen1212
t seems to me that the only hope of improving the power supplies is to eliminate as much wire as possible. I am thinking of a board that would stack above or between the dac and the I/V board. Is there a 1 to 1 drawing with the mounting and power hole positions and sizes available?
yeah i'm doing the same thing too. but for my IV stage/headamp too depending on the quote I get i'd like to go silver immersion PTFE on 4oz Cu, also relegating all shutdown signals to remote MCU and relay based switches, so I can keep the length of wire from the battery to the dac/amp as short as possible. all cells have had the tabs removed and hardwired together with 2 x 18AWG duelund silver foil (low Z and low profile), a braided 3x24AWG UPOCC silver wire connection for +/- and a 16AWG silver foil center tap.

the whole thing including the IV, amp, volumite, dac and buffered transformer coupled spdif line driver all exists in an area of ~ 4" x 3". at the moment the regulator board and molex interface is on a board 1.5x2", but I plan to make a PCB only slightly smaller than the area that contains the relay, regs and battery/shutdown manager and LED driver with nice thick traces for the direct battery connections and a heavy duty ground plane for as much of the underside as possible. then try to arrange everything so that DIY 18AWG silver pinheaders connect and hold everything together. the case is 7 x 4 x 1.1" and mostly the battery pack.

craziest wiring job i've ever done on a power supply, but as you say, keeping the length and impedance of the connection as low as possible, is about all there is left to do to these things to improve performance, since the output Z is better than most lowZ caps already. I have however tripled up on the input/reservoir caps for the IV which are low Z SMD oscons anyway. this is all wire I had lying around anyway and the lengths are short, all the same its the most uber looking battery pack i've ever seen

so yeah I was going to map out the scale drawing as well, for making the 'harness' so a layout drawing would be very handy
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Old 3rd September 2010, 07:50 PM   #763
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Who manufactures silver immersion PTFE on 4oz Cu boards ? Any pictures yet? For audio out I am considering two ( LME49990 - LME49600 ) balanced to single ended to replace the balse on the IVY and feed the balanced outputs then into another to provide single ended output. Obviously dual mono with two B2 DACs.
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Old 4th September 2010, 05:10 AM   #764
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will put up some pics later in the week. its in pieces again at the moment on the bench. most high quality PCB manufacturers will do Rogers PTFE/glass substrate with silver immersion over Cu; not sure that everyone does 4oz but some will.

I would love to get it done at Tresimine here in Sydney to keep it in the country, but depends on the quote they come back with when i'm finished this round of testing and get the final design done. so yeah just google Rogers PTFE substrate PCB manufacture in your location

some devices I cant try yet until I get the PCBs done, as they arent solderable by hand. like the new DFN package linear tech MCU/battery charge monitor and start/shutdown manager. the amp is DC coupled, so gotta make sure that low charge is handled properly to protect my JH13's. at the moment i'm just using a perf mockup with LT1763 on one of Peranders soic8->Dip PCBs without the dip part just wired down onto some perf and working on LT1964 (negative compliment of 1763) today for the latest tests and I havent been using it portable for a bit until I finish with the mounting hardware, then finally i'll get some front and rear panels milled for the hammond case, for now i'm using the stock panel, but the hole for the DSUB on the rear is a bit rough because I lost my patience with the file and got the dremel out .

I need to change the termination resistors and transformer (murata) on the spdif input too, as I just changed from 75R BNC to lemo 50 ohms mini BNC and may change to the DFN 1763, because its got all the functionality, where the soic8 package adjustable variant you have to choose either having the bypass pin or shutdown pin, I chose the bypass pin version, which allows you to bypass the internal reference, lowering noise and improving transient response. I would like the shutdown pin as well though, to allow the whole thing to be switched off by the charge monitor as is, without the need for an external relay/latch. i'm probably over thinking/over designing all of this, but its a fun exercise. I just cant face the thought of my JH13 dying a painful death from DC while deep in my ear canal if I fall asleep with them in or whatever.

perhaps Russ or someone could shed some light on what happens with the OPA1632 when power is low, or cut? I really want to keep this thing DC coupled, of course the easy option would be to put some caps on the output. or a servo, but finding a fast enough and accurate enough servo is another thing, I dont have the facility to zero VCOM on this IV/amp board, but I think it will be fine anyway, I do wonder about what happens at the limits of operation though, so I want avoid going there, I dont have a scope.

i've derailed the thread enough for one day though, sorry about the verbal dribble guys, perhaps I should start a thread

Last edited by qusp; 4th September 2010 at 05:26 AM.
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Old 4th September 2010, 04:40 PM   #765
qusp is offline qusp  Australia
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not murata transformers, newava
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Old 5th September 2010, 04:51 PM   #766
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Default SPDIF input experts???s

I am expecting my B-II module to arrive quite soon, and have everything ready to drop it with the Legato, power supplies, etc. I am now wondering about getting the SPDIF input right: I have a 75 ohm bnc jack on the chassis, and only about 2 cm of wiring to get from the jack (yes solder cup...) to the board. I assume on the board there is 75R termination. Considering the short distance, am I going to be inviting any problems by just running 2 cm. 24 gauge wire to the board, and not bothering with trying to strip and terminate such a short run of 75 coax?
Additionally, would I expect to gain anything by adding an pulse transforrmer (I have a Lundahl 1572 I could use)? Any sources I expect to use will have transformer coupled SPDIF outputs.
Thanks in advance for help...
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Old 6th September 2010, 01:55 AM   #767
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Quote:
Originally Posted by barrows View Post
I am expecting my B-II module to arrive quite soon, and have everything ready to drop it with the Legato, power supplies, etc. I am now wondering about getting the SPDIF input right: I have a 75 ohm bnc jack on the chassis, and only about 2 cm of wiring to get from the jack (yes solder cup...) to the board. I assume on the board there is 75R termination. Considering the short distance, am I going to be inviting any problems by just running 2 cm. 24 gauge wire to the board, and not bothering with trying to strip and terminate such a short run of 75 coax?
Additionally, would I expect to gain anything by adding an pulse transforrmer (I have a Lundahl 1572 I could use)? Any sources I expect to use will have transformer coupled SPDIF outputs.
Thanks in advance for help...
With this level of technology and herculean efforts, I am surprised you are not going directly to I2S...

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Old 6th September 2010, 02:48 AM   #768
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Yes, ultimately I do plan to go I2S-but only when I find a suitable I2S source. Hopefully TPA's XMOS USB solution will be "all that" when it is available, but I know that developing something like this might take awhile to get bug free and performing optimally.
In the meantime I plan on evaluating the B-II via SPDIF, and comparing with other SPDIF DACs as well as my bel canto CD-1.
For I2S I want to be able to install a board with uncompromised performance, which allows short I2S lines, and handles sample rates up 24/192-right now this does not exist, at least not that I am aware of. I would also prefer a USB-I2S solution that requires no additional drivers, but at this point such a solution seems unlikely...

Last edited by barrows; 6th September 2010 at 02:52 AM. Reason: spelling!
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Old 6th September 2010, 06:16 PM   #769
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Quote:
Originally Posted by barrows View Post
I am expecting my B-II module to arrive quite soon, and have everything ready to drop it with the Legato, power supplies, etc. I am now wondering about getting the SPDIF input right: I have a 75 ohm bnc jack on the chassis, and only about 2 cm of wiring to get from the jack (yes solder cup...) to the board. I assume on the board there is 75R termination. Considering the short distance, am I going to be inviting any problems by just running 2 cm. 24 gauge wire to the board, and not bothering with trying to strip and terminate such a short run of 75 coax?
Additionally, would I expect to gain anything by adding an pulse transforrmer (I have a Lundahl 1572 I could use)? Any sources I expect to use will have transformer coupled SPDIF outputs.
Thanks in advance for help...
I did it short wired.
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Old 7th September 2010, 03:10 AM   #770
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Originally Posted by avr300 View Post
I did it short wired.
Nice
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