Where can you buy 1-1.5mA CRD's?

[TheSloth]

I've searched on the internet and can't find an online retailer that sells them here in the US. Does anyone know of a place?

 

[Sinbios]

Mouser.

 

[cetoole]

That one is 1.1mA, it should be pretty easy to find other values if you need.
http://www.mouser.com/index.cfm?hand...oductid=339524

 

[TheSloth]

CSD = CRD ?

 

[amb]

DO-35 package:
1N5297 (1.0mA)
1N5298 (1.1mA)
1N5299 (1.2mA)
1N5300 (1.3mA)
1N5301 (1.4mA)
1N5302 (1.5mA)

TO-92 package:
J505 (1.0mA)
J506 (1.4mA)

All available from Mouser.

 

[TheSloth]

What is the difference between the 2 packages? I'm going to use them to bias my 627's (DIP) into class A.

 

[Jazper]

Quote:

Originally Posted by TheSloth What is the difference between the 2 packages? I'm going to use them to bias my 627's (DIP) into class A.

TO92 is the normal package for transistors, 3 leg, D shaped package if you look down from the top, Radial leaded

DO35 looks a bit like a standard resistor with 2 legs axial leaded

 

[amb]

Quote:

Originally Posted by Jazper TO92 is the normal package for transistors, 3 leg, D shaped package if you look down from the top) Radial leaded

Except in this case, for the CRDs, they are two-leaded.

Look up the part numbers at mouser.com, follow the link to their datasheets and you'll see a drawing.

 

[Jazper]

Quote:

Originally Posted by amb Except in this case, for the CRDs, they are two-leaded. Look up the part numbers at mouser.com, follow the link to their datasheets and you'll see a drawing.

interesting, because the LM329 I have is 3 leaded (and only two are connected)

 

[skyskraper]

iirc thats (strictly speaking) a zener not CRD.

 

[tangent]

Quote:

Originally Posted by skyskraper iirc thats (strictly speaking) a zener not CRD.

Well, strictly speaking, it's not a zener, either. It just happens to look like a very good zener from the outside. But look at the equivalent schematic.

 

[TheSloth]

Would the 'class A sockets' on the following page work instead of the CRD's soldered to the opamp? I can't quite see if they are little plugs, or sockets soldered onto the board. http://www.fixup.net/products/macro/

 

[guzzler]

The Fixup sockets just have a resistor soldered from the output of the opamp to V- to bias it to Class-A. You could do the same yourself using CRDs if you wanted, or resistors if you have them lying about

 

[amb]

TheSloth, you didn't say what amp this is going into, but if the opamp will be driving headphones directly (a la cmoy, as opposed to another buffer stage), then doing this will not make the opamp "class A". In fact in a cmoy-style amp, you don't want to make it class A, because in order to do that you have to make the output stage constantly source (or sink) the maximum peak current into the lowest impedance load you desire.

For example, if you plan to drive 32Ω phones with the opamp, and it could swing 10V peak, then you will need to make it source or sink 312mA. Not only will most opamps have trouble doing this, you won't find a CRD that could do this either. Now in real life you don't need that much current because 10V in your 32Ω Grados would probably fry them, but even 1/10 that current is too much for most opamps in a continuous manner.

By contrast, if the opamp is merely driving another buffer stage with high input impedance, then it doesn't need to deliver much current at all. In such an amp the opamp will operate deeply in class A with just a 1mA CRD at its output.

 

[Dougigs]

Which leads me to wonder why there is still any desire to use op amps as driver stages in any design -- as near-impossible as it is to give them a decent operating point into a low-impedance load. Yet they do seem to be back in fashion...

The folks who are designing with the new high-current op amps don't seem interested in class A bias -- does this mean a) that these chips have a nice operating point already, with plenty of class A into our loads; or b) as I've suspected for a while, that the precision trimming etc in better chips makes AB so effective and asymmetry-free that it sounds indistinguishable from A?