leo
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Post by leo on May 3, 2008 22:24:46 GMT
You done it yet ;D
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Post by PinkFloyd on May 3, 2008 22:31:29 GMT
You done it yet ;D No.... head still a bit "airy" at the moment but will get round to it soon.... just want to do EVERYTHING at the moment now I've returned to planet normal and pretty much racing around like a headless chicken at the moment...... I'll find a slot and zone in on the 744/811 one of these days tho! I've got quite a few of these chips Leo you fancy trying it yourself? Mike.
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Post by PinkFloyd on May 3, 2008 22:40:15 GMT
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leo
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Post by leo on May 4, 2008 2:13:39 GMT
You done it yet ;D No.... head still a bit "airy" at the moment but will get round to it soon.... just want to do EVERYTHING at the moment now I've returned to planet normal and pretty much racing around like a headless chicken at the moment...... I'll find a slot and zone in on the 744/811 one of these days tho! I've got quite a few of these chips Leo you fancy trying it yourself? Mike. Was only pulling your leg regarding if you tried it yet Great to hear your back into the diy again though Mike, thats good news! If you have any of these chips spare for flogging then sure, I'll give it a go, could piggy back em together and fit on my single to dual browndogs I'd have replied earlier but couldn't get on the site, it just timed out
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leo
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Post by leo on May 4, 2008 2:14:51 GMT
' Some good articles by Walt
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Post by dc on May 4, 2008 6:49:59 GMT
any benefit of doing that if you've got a discrete buffer after the AD744's comp pin out?
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Deleted
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Post by Deleted on May 4, 2008 7:40:07 GMT
dc That's a good question ! Adding the extra stage may not be beneficial. You could always try both methods, but the added I.C. may be much harder to implement. Alex
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pagan
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Post by pagan on May 4, 2008 10:13:49 GMT
Or is it helping the current capability of the opamp? ?? allan
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Post by Deleted on May 4, 2008 10:52:57 GMT
Allan Wouldn't taking the output from pin 5 (compensation) result in a DC offset ? Pin 5 is at the bottom of the 2 biasing diodes. i.e. the base of the PNP half of the O/P stage, or 1 VBE drop below the output pin. The simplified schematic may not be telling the complete story , though. Alex
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Post by PinkFloyd on May 4, 2008 12:08:51 GMT
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leo
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Post by leo on May 4, 2008 12:11:37 GMT
I was actually thinking about it causing an offset, I think Mikes already tried the simple AD744 with pin5 output on its own in this amp though and not reported any problem, have a look on page 8. I'm sure he measures for any offset problems before trying it out
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leo
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Post by leo on May 4, 2008 12:16:33 GMT
Is it my eyes going funny but do you have the +v caps on the right pin?
Pin8 is +v for duals , remember its wired for duals on the amp pcb, looks like its going across the output pin
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pagan
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Post by pagan on May 4, 2008 12:30:51 GMT
Alex I havn't looked at the circuit for a fair while... I'll need to go over it again.
allan
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Post by Deleted on May 4, 2008 12:35:15 GMT
Allan Scroll up for the simplified schematic Alex
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Post by PinkFloyd on May 4, 2008 12:36:49 GMT
Is it my eyes going funny but do you have the +v caps on the right pin? Pin8 is +v for duals , remember its wired for duals on the amp pcb, looks like its going across the output pin Argh!!!! BOLLOCKS! Looks like another trip to the soldering iron is imminent
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leo
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Post by leo on May 4, 2008 12:39:17 GMT
Is it my eyes going funny but do you have the +v caps on the right pin? Pin8 is +v for duals , remember its wired for duals on the amp pcb, looks like its going across the output pin Argh!!!! BOLLOCKS! Looks like another trip to the soldering iron is imminent Easily done mate, I only noticed because I was admiring the neat soldering
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Post by PinkFloyd on May 4, 2008 15:08:21 GMT
Easily done mate, I only noticed because I was admiring the neat soldering You gotta be kidding mate My head has been WELL AND TRULY up my arse this past week..... hell, I didn't even "think" about checking the DC offset but just have.... the figures I give are the highest on one channel I won't bother quoting the figure for each channel: LM4562 = 25mV AD8620 = 20.5mV AD843 = 179mV (back to the drawing board with that one!) LM6172 = 15.1mV AD8066 = 28mV DY2000 = 0.09mV AD797 = 270mV OPA2107 = 7mV NE5532 = 20mV AD823 = 7.9 VOLTS !!! TL082 = 4mV OPA2227P = 1mV OPA2228 = 10mV OPA2132P = 0.00mV OPA2134P = 0.07mV OPA2111 = 0.00mV So folks...... just goes to show you can't just "drop" anything into this circuit. The TI chips generally give the lowest offset.... trying the TLO82 at the moment and it's surprisingly good! (even though it's not "trendy" it sounds good) will report back.
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Post by dc on May 4, 2008 15:16:12 GMT
how the hell did you get 7.9V from the AD823 without cooking the phones?
surely that is a faulty opamp or something happened during measurement...
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Post by PinkFloyd on May 4, 2008 15:18:44 GMT
how the hell did you get 7.9V from the AD823 without cooking the phones? surely that is a faulty opamp or something happened during measurement... erm............ I checked the offset with a multimeter...... NOT with my headphones!! Tried 3 diffferent AD-823 and the highest reading was the the 7 volt one..... the other two measured 1.5volt and 4 volt respectively. I've got about 15 AD-823 so will go and check a few more later on this evening just to make absolutely sure.
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Post by holland on May 4, 2008 15:59:15 GMT
SandyK and I had a small discussion about offset a page back. Your measurements don't jive with his for the LM4562 (less than 1mV). Do you have R3 and R6 populated (probably not)? Give it a go, see if you can correlate his measurements.
What happened with your AD8067? I figured that would have been your choice over the AD843, from what you posted.
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leo
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Post by leo on May 4, 2008 15:59:37 GMT
No not joking, these type of pcbs without the solder mask/screen is harder to make look neat, the solder tends to flow down the unmasked tracks so I thought yours looked neat, trust me I've seen much much worse at least it does not have blobs of brown shitty flux everywhere The fet input based op-amps should give the lowest DC offset, seems your getting almost half the pos rail voltage on some of those AD823's outputs. Wonder if its anything to do with removing those input coupling caps. Will have to check the Jaycars circuit and have a think
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Post by holland on May 4, 2008 17:01:39 GMT
Oh, the input coupling caps were removed? What about the low pass filter? Is that gone too? What's the gain at?
BTW, leo, what was edited out of my post? I don't think I put in anything offensive.
I'd tend to think the AD823 7.9V is a dead opamp
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leo
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Post by leo on May 4, 2008 17:38:54 GMT
BTW, leo, what was edited out of my post? I don't think I put in anything offensive. My mistake I hit edit instead of quote, I was going to quote but by the time I got around to it my session had timed out, nothing should be missing from your post
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Post by PinkFloyd on May 4, 2008 18:10:53 GMT
Scrub all those offset readings it was the omission of the 10uF input caps that was causing it <remembers to engage brain before weilding a soldering iron> Jesus what a week that's been!
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Post by canjunkie on May 4, 2008 20:20:02 GMT
Who me? ;D Looks like I'll have a bit of time before the rest of the kit turns up so I might as well. It would be most appreciated CJ.... you want me to put one of these transformers to one side for you? or you prefer notes in a brown bag? Whoops, missed that post - thought you were talking to Leo I've almost got what I need to etch a few boards, should be ready to pop one in the post to you by the end of the week - promise. Do you want it pre-drilled or just a is? Sort of got distracted by heating boilers dying, washing machine packing up & a roof leak but I've now got my priorities straight and am concentrating on the important things in life. If you could put a traffo aside I'd be grateful.
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