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francismorrin wrote:Thanks Brian,
but wait a bit - I'll seach a bit more, I really thought I had some 75R in the workshop. I'll look more tomorrow.
Fran Fran, I have some 75R Vishay Metal Film 1%, send me your address and I send you a couple, repay you for the board ;-) I can post tomorrow - you will have them next day I guess. Sorry I've not been back to you about the other stuff, just very busy with other work, I will! Russ Baldwin Edited by user Tuesday, April 14, 2009 12:24:23 AM(UTC)
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krgaunt wrote: So I have a bad IC that's causing these problems.
RossG I might also try to replace the IC then. Would OPA4227PAG4 be a suitable replacement for OPA4227PA. Any major concern using a socket? Nic
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Sidenius112 wrote:krgaunt wrote: So I have a bad IC that's causing these problems.
RossG I might also try to replace the IC then. Would OPA4227PAG4 be a suitable replacement for OPA4227PA. Any major concern using a socket? Nic Its basically the same part, just lead free. It is just fine. :) The socket should not cause any issues in this cct. but its also fine to leave it out. :)
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Also that 75 R resistor just set the current source for the relay. It absolutely does not need to be anything fancy. :)
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OK, well I found some 75R after all and finished up the 2 boards.   I hope I have that right! And Russ/Brian - everyone seems to be talking about 15V supply - is that OK? (My older couterpoint is lower just is all). Fran
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12-15V should work great.
They look fine to me. :)
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OK, So I hooked it all up tonight - and phew! no smoke anyway!! I do have a few questions though, but first some observations: The resistors on the LCBPS do get warm, but not really hot. My LM317 gets hot but thats because the Tx feeding it has 24V secondaries. With a 15V sec tx this would be a lot cooler. In short I'm guessing current draw is AOK. LEDs all light up, relays click on both boards but the transistors are fairly cool - on my earlier version of coutnerpoint they are pretty warm. (this is with 12V supply). So on one counterpoint I get very low offset - about 1mV from GND to each of out+/out-, but on the other counterpoint I get higher offset, GND to out+ I get -12mV and GND to out- I get -56mV. So I'm a bit suspicious of that one. I took some readings from the opamp, each is reading to GND from each pin: Low offset CP: 1: -3.28 2: ~0 3: ~1mV 4: 11.3V 5: 1.66V 6: 1.66V 7: 2.21V 8: 2.13V 9: 1.66V 10: 1.66V 11: -11.32V 12: ~1mV 13: ~1mV 14: 1.83V high offset CP: 1: -3.32 2: ~0 3: ~10mV4: 11.3V 5: 1.66V 6: 1.66V 7: 2.21V 8: 2.13V 9: 1.66V 10: 1.66V 11: -11.32V 12: ~-24mV13: ~-13mV14: ~2.93VSo do you guys think there is something I need to check out on this second CP or is that level ok? I can add a cap on the output so I'm not worried as such - just want to check that its correct is all. Let me know if there's other measurements you would like..... Fran (PS I haven't actually listened to this yet, this is with the DAC connected up, AVCC connected up (3.32V) but nothing on the outputs) EDIT: just thought I'd add here that measuring out+ to out- gives 50mV on the "bad" one and <1mV on the other. The other observation is that the offset is not steady, but floats up and down by 5-10mV or so. If I put my hand over the CP it reliably (+repeatably) drops by about 1/3 or so (say 50mV to 35mv) take away the hand and it rises again. Fran Edited by user Wednesday, April 15, 2009 5:07:40 PM(UTC)
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What strikes me is the voltage at pin 14.
That is the output pin for the integrator which is responsible for overall offset.
My guess is either an R or a Q is badly mismatched or possibly dead.
Its hard to say.
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OK,
so heres what I'll do:
First reflow all the solder connections just in case (the whole thing went together pretty smoothly though). But you never know!
Measure some voltages on each of the Qs.
Then listen! I'm happy enough to use a cap if its just mismatch - just don't want to do harm is all.
I'll report back later on with more details.
Fran
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Well I reflowed all the solder joints, but that made no difference.
I didn't get time to take all the measurements but I did hook it up to the amp. Sounds fine - no hint that theres anything wrong right now. I added in a cap on the output and that took care of the offset. I would like to figure whats wrong though. No turn on thump on the cheap disposable speakers though.
More testing and listening to follow.
Fran
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I'm still testing this out, but I can confirm that there is no turn on thump at all (or off either) in SE mode. And thats through some sensitive horns. I do have a little hiss on one channel, but its not loud enough to be a problem. Other channel (interestingly enough, the one with the higher offset) is quiet no hiss)
Fran
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OK, major advances made here.
The story:
I have my own buffalo here, its an early buffalo, and the very first incarnation of the counterpoints.
Then I made a second set up for a friend only using the second round of buffalo and the newer counterpoints.
Sound on his one was not as good as mine. While the detail was there, the soundstage was not great and the bass a bit indistinct - now this was not a subtle difference - its exactly the nuance that we are all after.. So I had it over tonight to have a look at it again to see what the differences might be. I was concerned because there was offset on his new counterpoint (see posts above) but I just ignored that and used a cap on the output (exactly the same as in mine).
So I decide that the BC550/560 on his are considerably cooler than on mine maybe thats the reason so I try upping the feed voltage a bit. But the LCBPS runs out of steam at 15.5V even though its been fed with 24VAC. Thats when I remembered that some lads had problems with current draw on the LCBPS/counterpoints. So I replaced the 3W 10R with 1R5 3W and fired it back up.
Well wow, what a difference! The 2 sound very very similar now. I really happy with this development. It had been puzzling me for the past week or more what the hell was going on.
So its probably worth a try for anyone out there with the same setup.
One problem does still exist, I have a good level of hiss from one counterpoint. I have to investigate that yet. Sound is good though.
All this is single ended - and it was soooo useful to have the second buffalo to compare against. It would be great if someone tried this out.
I don't want to crosspost but I might put in a single line on the diyaudio thread to direct people here.
Fran
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Yes, for anything more than about 150ma at 15V you will typically need to reduce or jumper those resistors on the LCBPS. Either is fine. :)
I am glad your enjoying it!
Cheers!
Russ
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Any ideas on the hiss from one counterpoint Russ? Even ideas for where to look first? I've dealt with hum and even RF pickup before, but not hiss! None of the transistors are hot or anything. The only thing I can point to right now is that the LM317/337 are bloody hot as the Tx is 24V secondaries so they have to drop a lot of voltage - but they're not cutting out. Could that be it? Maybe reducing the voltage further (they're at +/-15V now)? And I know that 24VAC sec is too high - I'm waiting on a smaller one to get here..... Fran Edited by user Friday, April 24, 2009 5:13:20 PM(UTC)
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I have not sen any hiss myself on this PCB, so I am not sure what to say, but if I had to guess I would say there may be a GND loop or some EMI maybe.
Try using just one GND wire to VA GND on the DAC from the LCBPS GND. Do not connect the gnd on input of the CP to Buffalo. This way there will be a single path between the two supplies.
Cheers!
Russ
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OK did that but there was no change.
I've also found out that if I disconnect one of the inputs to that CP the hiss is gone ie its like its coming from the buffalo.
Second CP is fine. No difference if I run the CPs anywhere from 12V to 15V.
Fran
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Are you sure the caps from the inputs to GND are in place and working correctly on the CP with the hiss? It almost sounds like there is something amiss there.
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Thanks Russ, yes, checked that. Also increased the value of those caps to 10nF (no difference). then went up to 14.7nF and got a tiny bit of distortion on peaks but still had hiss. But I think I may have hit on something. I went right back and swapped the buffalo outputs to counterpoint L to R and the hiss changed sides - ie it seems its not the counterpoints, but the buffalo itself. Now i need to investigate that some more, but having looked at it for a while, I can't see anything obviously wrong. Heres another thing - it doesn't change volume with the volumite - so maybe its just something in one channel of buffalo ain't getting on with counterpoint?  Fran EDIT: I've been thinking abuot this all day. Seems to me like it could well be some oddball groundng thing (maybe?). Anyway am I imagining it or did you have some similar thing Russ with the first iteration of counterpoint? I seem to remember something about a cap on the inlet of the PS or something. Must search. Edited by user Sunday, April 26, 2009 1:28:37 PM(UTC)
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I had a hiss until I added the caps the inputs. That cured it.
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OK. Well that didn't do the job here. I can't see anything wrong with the ground wiring. In fact I have 2 of these DACs in front of me and both are wired exactly the same with the same components. I think I need to narrow this down more. So I think I'll swap my (perfect no hiss) buffalo DAC into the box with the new counterpoints and see what happens. Put the buffalo pcb from the hissy one into the one with the old counterpoints. At least then we can look more closely and see if its either the DAC or counterpoints. Russ - other than excess heat on the transistors/opamp, how exactly do I diagnose oscillation with a scope? Is there a decent online guide that you know of? On a side note, I had a really close look at the DAC chip this evening with some 3X glasses and I can see some sort of material in between the pins of the ESS chip. Maybe its just dust or something (shouldn't really be) but I think I'll bring it into work tomorrow and have a much closer look under one of the observation microscopes. If there was some short or something going on that might cause this. Here are a couple of pics of the counterpoint if you can see anything?   (input canps are red cos that was when I had the 10nF ones in) Fran 
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