EE21, EE23 Board V6.5, All Connection Schemes, Complete Overview
EE21 or EE23 Board
There are two internal wire schemes Lundahl uses for this footprint transformer family. This the reason for two boards, EE21 and EE23. Apart from this, the optics and functioning is the same, but each transformer can only be used either with EE21 or EE23. Since those boards can only be ordered in combination with the transformers, it is not possible to order the wrong transformer-board combination anyway. (Basically EE23 is only for LL1588,1592 and 1690. All other transformers use EE21).
A Centered signal
This means we use a winding with a center tap, which becomes grounded. This enforces a ground reference to a balanced signal, and hum rejection becomes so good, that for aux connections, just a twisted wire pair may be used, so an unshielded cable.
- J4 centers the H-Side, and works always
- J6 centers the L-Side (works only at Low Gain setting)
Use of the Ground (G) Connections
These are all connected to the board ground plane. They are used if a cable connection needs to be shielded, or used to create an unbalanced input or output.
- A balanced connection which is floating at the receiver side, as well as on the sending side, may work, but is not a good idea still. Better is to center tap the sending side. Or, if this is not possible, use a cable shield and connect this to G.
- If L- (or H-) is is connected to G, the other end becomes an unbalanced connection. In the configuration pictures, there are many examples for this.
- If connecting L+ (or H+) to G, the other end (so L- or H-) becomes inverting. This is done to change an inverting amplifier into a non-inverting amplfier, which is how it should be. So when adding a transformer with the EE21 board, we can elegantly correct this, if needed.
- If two input or output windings are connected in series, we can also attach their center connection to ground. This normally done at the transmitting side. So the receiving side should be kept floating. This is done with the solder Jumpers J4 or J6.