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Brain, thanks for the Counterpoint, it arrived earlier today, I hope to get the boards built sometime this weekend and will let you know how it goes - lots of components - but it all looks pretty simple ;-) It will have to be single ended testing for the moment but I will watch out for the turn on thump.
Not sure if there is one yet, but is there a Counterpoint Manual?
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I was actually thinking about this this morning. There is not a Counterpoint manual yet. The only non-standard step to the build is the 4.7nF caps across the inputs. They go from +IN to GND and -IN to GND. It is probably best to mount these under the board, soldered to the terminal block pins. Everything else it just matching the part label to the silk. Be sure to get the relay orientation right, as their small pins tend to not like being desoldered. I also plan on building up a fresh set and taking a bunch of pictures that I can post as a review aid (the one I have now has had lots of work done on it from ironing out final part values). [EDIT]: Also, Russ was doing some playing around last week and found that if he powered the Buffalo with the positive rail of the LCBPS that he was using for the CP, the SE turn-off thump was just about eliminated. It is apparently cause by the DAC PS rail collapsing before the I/V rails. The +15VDC rail was fed into the LCDPS to drop it to about 6V for the Buffalo. Edited by user Friday, March 27, 2009 10:21:42 AM(UTC)
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Thanks Brian, I've just and a quick look at the board...
1. What is AVCC for?
2. Presume DAC Outputs go into IN-, one of the GND's and IN+?
3. Presume outputs to XLR from OUT-, one of the GND's and OUT+ ?
Not sure I quite understand the power arrangements for losing the thump.
4a. Are you talking about powering one side of the LCDPS as normal from a transformer and the other from the + rail of the of the LCBPS?
4b. Will there be nothing connected to the GND for this side of the LCDPS?
4c. I presume this is for the half of the LCDPS that would be powering the analogue side of the DAC and leave the digital side of the LCDPS powered from the transformer? Which would leave me a spare feed from the LCDBS transformer?
4d. Can the LCDBS power both Counterpoints boards and the Analogue side of an LCDPS for the Buffalo? Is it desirable?
Sorry if this is not very clear, I can a do picture if required? It is the end of a long week, so I may just be being dense ;-)
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1) It is for setting the input bias of the counterpoint to AVCC/2. You connect it to 3.3V. A couple good places to do that are either C11/12 or the tab of REG on the Buffalo. The AVCC voltage is heavily filtered on the CP so it is fine to use the REG1 tab(output). If you want the input bias to be at GND simply connect AVCC to GND. 2) Correct. But you can leave GND off if the PS is shared per #4. 3) Correct. 4) Connect V+ (from the LCBPS) to the input of one or both sides of the LCDPS. Connect GNDs only at the VIN terminals Buffalo. One other thing that seems to help the thump was increasing the size of R1 and R6 to 75R(just what I have tested so far) feel free to experiment here anything from 31 to 100R should work ok. Cheers! Russ Edited by user Friday, March 27, 2009 1:14:21 PM(UTC)
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Also I have been using 15V rails for the counterpoint. Seems to work well.
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1) Russ, sorry to be a pain, ref the AVCC/2 note, could you explain a little more about the differences of changing the input bias. Can it be left unconnected to ground for example or does it have to be ground or 3.3v. I'm not quite sure I understand how this works. What are the likely impacts sonically.. 4) Russ said "Connect V+ (from the LCBPS) to the input of one or both sides of the LCDPS. Connect GNDs only at the VIN terminals Buffalo." I presume that is the GND from the LCBPS to the VIN terminals of the Buffalo? 4e. So thinking aloud, you could effectively use one transformer to power the LCBPS and also power the LCDPS from the LCBPS in this scenario. Is it going to be enough power for both - are there likely any sonic impacts? I think what I may do is try it as is first - with the proviso I understand the AVCC thingy and the power from the LCBS, from your reply, and then try the other experiments after that e.g. a. Power DAC from LCBPS b. Changing R1 and R6 to 75R or some other value between 31 to 100R Many thanks, Russ Edited by user Saturday, March 28, 2009 12:57:35 AM(UTC)
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1) It sounds and measures better with AVCC connected to AVCC on the Buffalo. You can leave AVCC open and it will be pulled to GND by the lower half of the voltage divider. The effect will be that the DAC has to always source current instead of both sinking and sourcing. 4) Yes one 15VA transformer into the LCBPS should be plenty. I will try to diagram this if I can. Basically think of it like this: You have three nets coming off the LCBPS: 15V GND -15V. Of course the counterpoint boards are powered directly from those. Enough said about that. Now for LCDPS you wire 15V to one of the what would normally be AC inputs on each side, note only one wire is used. Now at the output side one goes to VA, and one to VD along with GND. See we do not connect GND at the input of the LCDPS just at the output to the Buffalo. Now run one wire from LCBPS GND to one of the GND terminals of the power input side of the Buffalo. Now counterpoint and the Buffalo will shutdown in a more synchronized way. The stock value for R1/R6 is 32.4R thats a good starting point but it runs a lot of current through the board. I would try 75R there at some point and see what you think. Cheers! Russ Edited by user Saturday, March 28, 2009 6:01:09 AM(UTC)
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Many thanks Russ, I think I have it now... a photo and a diagram would confirm this especially the AVCC link and power arrangements.
Got to go and watch some rugby, back later....
Russ
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Russ White wrote:1) It is for setting the input bias of the counterpoint to AVCC/2. You connect it to 3.3V. A couple good places to do that are either C11/12 or the tab of REG on the Buffalo.
Russ Russ, could you possibly show a picture of where to conveniently connect AVVC of CP on the Buffalo. Would an alternative be to use a LM1086-3.3 connected directly to one of the rails of the of the LCDPS feeding Buffalo? Cheers, Nic
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Russ White wrote:1) It is for setting the input bias of the counterpoint to AVCC/2. You connect it to 3.3V. A couple good places to do that are either C11/12 or the tab of REG on the Buffalo. The AVCC voltage is heavily filtered on the CP so it is fine to use the REG1 tab(output). If you want the input bias to be at GND simply connect AVCC to GND.
So I simply solder two wires to the tab of REG1 on Buffalo and connect them to AVCC on both CP's? Thanks, Nic
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yes, that should work just fine.
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Any chance that y'all could add a diagram to the Counterpoint page clearly showing the "preferred" connections? That would be way easier to follow than sifting through the individual posts. Its still not clear whether the LCDPS for the DAC is fully powered from the Bipolar supply for the Counterpoint or if the power transformer is still needed. I imagine this means that both Counterpoints need to use a common (shared) Bipolar supply. Thanks. Edited by user Wednesday, June 10, 2009 6:55:47 AM(UTC)
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I am not sure there is a preferred setup. :)
It is very much an experimenters board.
Typically you just use the LCBPS for the counterpoint and the LCDPS for the DAC as usual.
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