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A muting delay & DC offset protection circuit from amb - Page 7

post #91 of 126
9/15/05 at 1:15pm
Quote:
Originally Posted by guzzler
Looks alright to me Chris. Which way up is your standard pinout? The pinout I have here from the Rapid Electronics catalogue is with the D facing down the way (like a bowl), with E-B-C left to right along the top. With the layout, the D is facing up so pins should be the other way round. I've attached the relevant portion of the board; check the other transistors as well
According to your .gif, they are backwards. See the chop of an ST datasheet attached, but with the flat of the "D" down, the pins are E-B-C across left to right.
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post #92 of 126
9/15/05 at 4:31pm
Thread Starter 
(guzzler's layout) Yup, Q1 through Q4 are reversed. The darlington is correct for a MPSA14 or ZTX604/605 though.
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post #93 of 126
9/15/05 at 5:08pm
Quote:
Originally Posted by amb
(guzzler's layout) Yup, Q1 through Q4 are reversed. The darlington is correct for a MPSA14 or ZTX604/605 though.
<slightly OT> Are there any other options for that darlington beside these mentioned?


/U.
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post #94 of 126
9/15/05 at 5:23pm
Nisbeth: A pair of 2N3904 (NPN) or 2N3906 (PNP) (or countless equivalents) as in the original schematic... but you probably already knew that
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post #95 of 126
9/15/05 at 5:34pm
Quote:
Originally Posted by Pars
Nisbeth: A pair of 2N3904 (NPN) or 2N3906 (PNP) (or countless equivalents) as in the original schematic... but you probably already knew that
Yup, I did I have a PCB for the circuit so I need a darlington that fits and I can't seem to find the MPSA14 or any of the ZTX-variants anywhere near me


/U.
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post #96 of 126
9/15/05 at 7:43pm
Thread Starter 
Any TO-92 NPN darlington with EBC pin assignments and Ic > 100mA, Vce > 25V, Hfe > 5000 should be fine. Such as:
KSP13, KSP14, KSP25, KSP26, KSP27, MPSA13, MPSA27, MPSA28, MPSA29, 2N6426, 2N6427, 2N7052, 2N7053, BC372, BC373

These are also good, but the pin-out is reversed (CBE):
BC517, BC618
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post #97 of 126
9/16/05 at 2:22pm
Sorry about that folks. The catalogue listed it as TO92B, which is (from your point of view, Chris) C-B-E. The only thing I can think of is that the one Rapid lists is made by Continental Devices, but I should have thought the 2N3904 pin out was standard.... Thanks for pointing that out
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post #98 of 126
9/16/05 at 2:25pm
Quote:
Originally Posted by guzzler
Sorry about that folks. The catalogue listed it as TO92B, which is (from your point of view, Chris) C-B-E. The only thing I can think of is that the one Rapid lists is made by Continental Devices, but I should have thought the 2N3904 pin out was standard.... Thanks for pointing that out
Does that mean that the pinout on the board is correct when using BCxxx devices?


/U.
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post #99 of 126
9/16/05 at 2:34pm
Yes, they should be fine. Just check the GIF above to make sure, it's the same for the NPN and PNP
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post #100 of 126
9/16/05 at 2:41pm
Quote:
Originally Posted by guzzler
The only thing I can think of is that the one Rapid lists is made by Continental Devices, but I should have thought the 2N3904 pin out was standard.
Yeah, you would think you wouldn't even have to think twice about tossing in some bog standard device like this! Really nice tight layout guzzler (which was why I was using it as a reference to begin with )... should be an extremely easy change, and if these things actually are available in a TO-92B package with C-B-E pinout, then any boards you had made up could still be used, or std. TO-92 pkgs could just flip the transistor and bend the base leg to fit OK.
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post #101 of 126
9/20/05 at 4:53pm
Per my previous posts on additions to Amb's e12, see the attached schematic and board images. Any comments/suggestions are welcome (be kind as I'm kinda new to Eagle and board layout/design). Thanks to guzzler for starting me in on this And of course to Amb for the design.

Chris
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post #102 of 126
9/24/05 at 1:15am
Thread Starter 
HI folks, I finally found the time to assemble and test this circuit on one of guzzler's boards (shown in post #99 above). Aside from the reversed Q1 through Q4, I found another minor error in the layout. The negative power rail is wrongly connected to pin 5 of U1 (the OPA551) instead of pin 4. Fortunately pin 5 is unused on the OPA551. So, to fix this, you can just solder a short jumper wire and bridge pin 5 to pin 4.

I also found that the Omron relay seems to have a lower pull-in voltage than the Tyco unit I previously tested with, so this results in a rather short delay time after power-up. Thus, I suggest changing R11 from 221KΩ to 475KΩ.

So in summary, if you are building on guzzler's board, you need to note the following deviations from the "officlal" v1.1 version found on my web site:
  • Instead of the Tyco RTE44012F relay (which doesn't fit), I recommend either the Omron G6A-234P-ST-US-DC12 or G5V-2-H1-DC12. Both are available from Mouser and Digikey.
  • Q5 and Q6 have been replaced with a single darlington transistor. I recommend MPSA14, but you can also use any of the alternatives listed in post #113 above.
  • If you use 2N3904 for Q1, Q3 and Q4, and 2N3906 for Q2, you must install them in exactly the opposite orientation than as marked on the board. If you use other transistors, check the pin-out against the layout.
  • Install a jumper wire between pins 4 and 5 of U1 (OPA551).
  • I suggest changing R11 from 221KΩ to 475KΩ.
  • Parts on the board are packed very tight, so be sure to choose parts that will fit their outlines and hole spacings.

Here is a picture of the assembled board:



Here is the bottom of the board showing the added jumper:

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post #103 of 126
9/24/05 at 2:57pm
What a silly mistake about power pins, wonder what kind of person would do that

Thanks for picking that up amb, much appreciated (and the design too )
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post #104 of 126
10/4/05 at 2:22pm

Request for layout comments

Per some previous posts, I have still been working on a layout for an enhanced version of Amb's board and would request any comments on this. The board is appoximately 3" x 2.2", and features the following additions:

1) Provision for a manual mute switch bypassing the delay

2) Addition of fault/mute and on LEDs

3) Use of a 555 timer instead of the resistor/capacitor time constant for driving the relay and setting the delay. A 1M Rt and a 4.7uf Ct gives a dalay of about 5.1 seconds, etc.

4) Will accomodate either the newer Omron relay package (smaller) or the original Tyco form factor relays, making it easier to source

5) Does not emply the pre-packaged Darlingtons, but rather 2N3904s and (1) 2N 3906 to make parts sourcing easier (E-B-C TO-92 package). Packaged Darlingtons could certainly be used if you have them laying around.

6) Configurable relay: Per some concerns (not mine) about running the audio signal thru a relay, there are jumpers which allow the relay to be configured to short the output, with the audio not going thru the relay (unless shorted). Provisions for paralleled back-back BAT43 Schottkys are there if you don't want a dead short. As Amb noted, this will limit the offset seen on the output to 0.3V (300mV), so low impedence cans will not be completely protected in this configuration.

Schematic:


Board:


Eagle files here:
board
schematic
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post #105 of 126
10/4/05 at 5:52pm
Thread Starter 
Pars, your changes look ok to me. Did you try breadboarding it to see if it works as intended?
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