MOX builder’s thread

[JensRasmussen]

Hello chipco3434,

C001 and C002 are the to make sure no high frequency noise gets into the filter, and C200 & C500 are the to ensure stability.

C800 & C900 are the main supply caps. The filter will work without the components, but I suggest you C001, C002, C800 and C900 eventually.

Sorry I can be of no help regarding the opamp.

Hope this helps you.

\Jens

[BDP]

chipco3434

3. I am unable to identify the components associated with C001 and C002, C200 & C500, and C800 & C900. I could use the values and even better, some part numbers.

C001-C002, I used what I had available, 39pF. A note to discrete op-amp users. The C800-C900 supply filter caps will have to be very narrow or go on the underside of the board in order to fit properly because the discrete input buffer gets in the way. Lucky for me I didn't install them until I had assembled the discrete op-amps.

A good part number from Mouser for the 8 pin DIP socket would be 575-113308. Those right angle headers are expensive so if you are not going to be exchanging op-amps it sure would save you a few dollars not having to buy sockets and/or headers.

AS far as C200- C500 I had a similar question and I believe MOAMPS thoughts were compensation would only be needed for input and output discrete op-amps and not for the filter op-amps. If you take a look at MOAMPS work this is how it is setup.

BDP

[chipco3434]

Thank you for the information on the caps...

Another newb question...

How do I power this thing. I would like to use a transformer and rectifier bridge or a wall wort? I, however, cannot discern the voltage requirement.

[tiroth]

A wall wart is actually a great idea as it keeps the transformer far away from your sensitive circuit. You need an AC wart though.

Here is a perfect supply. You can improve it in a number of ways, but for a novice, KISS is a good approach IMHO.

http://sound.westhost.com/project05.htm

[chipco3434]

Will that be 12VDC or 15VDC on the final output for the MOX?

[JensRasmussen]

The supply voltage needed for the module is greatly depending on what opamps you use.

Generally I suggest that you use +- 15V, but the filter will work on +-12V also.

Each filter will consume maximum 100mA so a LM78/7915 should be ok for a 10 board scenario.

I hope this answers any questions about power supply for the board.

I will try to get time to update the manual, with a power supply schematic for the filters and other information that might come in handy during the build process.

\Jens

[Ed LaFontaine]

As an extension of the discussion regarding power supplies, has anyone considered using voltages above 15V for the discrete op amp?
Mr. Pass says in his DIY Op-Amp paper that the sk389 works well with 32V. I felt from my reading that his preference was for higher voltage.
The article is available for download from his Legacy Projects here: http://www.passdiy.com/legacy.htm

[JensRasmussen]

I know it's off topic, but I can't help myself, I have to post it

An engineer died and ended up in Hell. He was not pleased with the level of comfort in Hell, and began to redesign and build improvements. After a while, they had toilets that flush, air conditioning, and escalators. Everyone grew very fond of him. One day God called to Satan to mock him, "So, how's it going down there in Hell?" Satan replied, "Hey, things are great. We've got air conditioning and flush toilets and escalators, and there's no telling what this engineer is going to come up with next."

God was surprised, "What? You've got an engineer? That's a mistake. He should never have gotten down there in the first place. Send him back up here."

"No way," replied Satan. "I like having an engineer, and I'm keeping him." God threatened, "Send him back up here now or I'll sue!" Satan laughed and answered, "Yeah, right. And just where are YOU going to get a lawyer?"

\Jens

[MBK]

Excellent joke Jens...

To Ed: maybe I give the short answer re: supply voltages far above 15V.

In short it's not that simple. The circuit values and components were chosen with a certain supply range in mind. 12V or 15V or maybe 18V won't change the circuit's behavior much. Large deviations from this figure (such as 32V) means, you would at least have to recalculate the bias currents to check if they're still in the optimal range with the original resistor values. A 32V supply may also exceed breakdown voltages for some of the other transistors (though the 2SK389 may take it).


Markus

[Ed LaFontaine]

I visited several sources with boards in hand, looking for screws to connect discrete op amp boards together. This is what I found necessary:
#2-56 x 5/8"long.

Sincere apologies to our metric friends.

McMaster-Carr has them available. Oval head, Stainless Steel
screw pn: 91802A083
nut pn: 91841A003

MBK: Thanks for your "caution" about other devices on the boards not withstanding increased voltages. Changing resistors for bias adjustment would be (for me) an acceptable part of finding the "sweet spot" in the performance of a circuit. At this time I will provide +/- 15V. My interest is in future tweaking of the op-amp.