Imagine an IC having the pins numbered backwards but the pin definitions are correct in the datasheet.
There used to be some MiniCircuits devices in DIP-outline-compatible packages with very "creative" pin numbering. I forget which anymore, but it caused a few board re-layouts that I know of.
Looking good! Always a good feeling when the boards arrive and the first one is finished and ready for testing.
Why not treat us with a high resolution image and schematic!
Why not treat us with a high resolution image and schematic!
Thanks. It's nothing to special though. A bootstrapped amplifier but with CCS, LTP, and CM (current mirror) on the front end. Buffered VAS. Cdom and Cbypass are 47pf. Cbypass is supposed to be 10p but I can't find the bag of 10p capacitors.
So far so good. It plays. I had a ~20mv+ offset issue that turned out to be my mistake of putting a 100r resistor where a 180r should be. The \ through the 0 in the PCB software makes it look like an 8. Couldn't have been 188 so it must have been 100, right? Nope. Was 180. 🙂 Offset now 0.5mv but I'm sure it'll drift around. The adjustment range is good though. I need a good way to measure idle current. Maybe 1r in series with one of the rails?
I don't have a THD analyzer but I can get some scope pics soon.
So far so good. It plays. I had a ~20mv+ offset issue that turned out to be my mistake of putting a 100r resistor where a 180r should be. The \ through the 0 in the PCB software makes it look like an 8. Couldn't have been 188 so it must have been 100, right? Nope. Was 180. 🙂 Offset now 0.5mv but I'm sure it'll drift around. The adjustment range is good though. I need a good way to measure idle current. Maybe 1r in series with one of the rails?
I don't have a THD analyzer but I can get some scope pics soon.
You've got an emitter resistor for each output device - just measure the voltage drop over them (with no signal) and divide by the resistor value - that will be a quiescent current through a single output pair - just what you need.
You can measure each resistor one by one, however, you will get more precision if you measure across the pairs - R1 + R2 and / or R3 + R4 (see attached example).
Then, divide the voltage by the total resistance (0.44R for the example here).
It will give you the quiescent current through a single pair.
We assume that you've got zero offset at the output.
It's better to measure with no load connected.
Attachments
Ok I see what you mean now. So just probe a pair of output emitters? Offset can be adjusted to 0v. I'm really happy with how well that adjustment is working.
Yes, exactly - just measure the voltage between the emitters.
Some mV offset will not affect your voltage measurement (so, "close to zero" is ok), especially with no load connected.
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"just probe a pair of output emitters".... oh how many times have I blown something up when the probes slip... 😀
Been there,done that! It happened to me while adjusting the bias and one of my kids jumped off his bunk bed to the floor above my head!
Cheers
I even started making special holes on PCB for that purpose - in case we don't have a plug in place for current sensing, which is also very good for preventing the probes slipping 😉
No,
Bad alligator 🙂 too easy to short something out, with exposed metal.
I meant
http://ca.mouser.com/ProductDetail/...=sGAEpiMZZMs4AFwHyzhTm5l9RkZanDRIREAvVYO4CLc=
OR
http://ca.mouser.com/ProductDetail/...=sGAEpiMZZMs4AFwHyzhTm97H2KT2mt3USbjP34urCvU=
I just make my own, using the parts, as the Pomona pre-assembled stuff is expensive.
Bad alligator 🙂 too easy to short something out, with exposed metal.
I meant
http://ca.mouser.com/ProductDetail/...=sGAEpiMZZMs4AFwHyzhTm5l9RkZanDRIREAvVYO4CLc=
OR
http://ca.mouser.com/ProductDetail/...=sGAEpiMZZMs4AFwHyzhTm97H2KT2mt3USbjP34urCvU=
I just make my own, using the parts, as the Pomona pre-assembled stuff is expensive.
That's the right clip to use. Or solder a lead to the device pad or even the device lead itself if necessary.
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Joined 2009
Paid Member
I have found myself being to lazy - I have resorted to using these little cheapo wires with little crocodile clips on each end, I think I got a few off ePay sometime ago. I put crocodiles onto the circuit and the other ends onto the DMM probes. Seems to work ok.
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