Electron Engine ™
Printed Circuit Boards by Emissionlabs ®

EE20 Audio In/Out, with or without gain. Version 2.8

  1. Introduction
  2. Moving Coil Applications
  3. Audio In/Out, with or without gain. (You are here)
  4. Tuning of the EE20 Board

About the tuning circuit on this board

This board can be used stand alone, or with the external switch. Both methods leave all options open.

How to use this table?

  1. Choose the intended gain/attenuation factor from Col.2
  2. Then choose the transformer from Col.1. Use LL1550 only for high transfer ratio applications. If possible also with LL1544 or LL1545, use these.
  3. Stand Alone: Use Piano Switch Options from Col.7
  4. With External Switch: Use Piano Switch Options from Col.7 + Attach Board EE22. Each row can switch now one row up or down with the switch. All rows can be selected for this.

UNBALANCED to BALANCED (not moving coil)

Note the many gain variations, the EE20 board allows. LL1544A/LL1545A and LL1550 differ only on windings number. Mainly the LL1550 has less primary windings, giving 2x the step up ratio. Yet, 2x higher step up ratio of 1550 must be payed with 4x lower Input impedance. So LL1544A is probably the most recommended, because input impedance stays above 3k, and LL1544 can even attenuate if needed. Note, that attenuation reduces also noise of the driving signal. It can (and should) simply be tried what works best, by testing all gain settings.

Col. 1
Col. 2
Col. 3
Col. 4
Col. 5
Col. 6
Col. 7
Col. 8
Trans-former
Board Gain
Name
Possible Use
Input impedance if amplifier load is 47k
Value of R1 to get 47k input impedance. Insert J1 and J2 for this.

Stand Alone.

Piano Switch Numbers
Set to "On"

With External Switch Option3

Low / High is the switch position

LL1544A
LL1545A

0.5x
New! Possible with EE20 board
 
188k.
15k
1, 3, 7, 9, 11 7, 9, 11, Low
(High = 2x more gain)
0.75x
New! Possible with EE20 board
 
84k
47k
1, 3, 5, 7, 8, 11 5, 7, 8, 11, Low
(High = 2x more gain)
1x
Lundahl Alt A

10k / 10k
*2)

47k
Remove R1, this. will give 47k.
2, 7, 9, 11 7, 9, 11, High
(Low = 2x less gain)
1x
Lundahl Alt B
600R / 600R
*3)
n.a.
Remove R1
1, 3, 5, 7, 8, 10, 12 5, 7, 8, 10, 12, Low
(High = 2x more gain)
1.5x
New! Possible with EE20 board
 
21k
*1)
2, 5, 7, 8, 11 5, 7, 8, 11, High
(Low = 2x less gain)
2x
Lundahl Alt C
Most recommended
High Signal
12k
*1)
2, 5, 7, 8, 10, 12 5, 7, 8, 10, 12, High
(Low = 2x less gain)
2x
Lundahl Alt D
Only for low impedance Source
Normal Signal
12k
*1)

1, 3, 4, 5, 6, 8, 10, 12

4, 5, 6, 8, 10, 12, Low
(High = 2x more gain)
4x
Lundahl Alt E
 
3k
*1)
2, 4, 5, 6, 8, 10, 12 4, 5, 6, 8, 10, 12, High
(Low = 2x less gain)
1x
New! Possible with EE20 board
 
47k
Remove R1, this. will give 47k.
1, 3, 7, 9, 11 7, 9, 11, Low
(High = 2x more gain)
1.5x
New! Possible with EE20 board
 
20k
*1)
1, 3, 5, 7, 8, 11 5, 7, 8, 11, Low
(High = 2x more gain)
2x
Lundahl Alt A
High Signal
12k
*1)
2, 7, 9, 11 7, 9, 11, High
(Low = 2x less gain)
2x
Lundahl Alt B
Normal Signal
12k
*1)
1, 3, 5, 7, 8, 10, 12 5, 7, 8, 10, 12, Low
(High = 2x more gain)
3x
New! Possible with EE20 board
 
5k2
*1)
2, 5, 7, 8, 11 5, 7, 8, 11, High
(Low = 2x less gain)
4x
Lundahl Alt C
High Signal
3k
*1)
2, 5, 7, 8, 10, 12 5, 7, 8, 10, 12, High
(Low = 2x less gain)
4x
Lundahl Alt D
Normal Signal
3k
*1)

1, 3, 4, 5, 6, 8, 10, 12

4, 5, 6, 8, 10, 12, Low
(High = 2x more gain)
8x
Lundahl Alt E
 
734 Ohms
*1)
2, 4, 5, 6, 8, 10, 12 4, 5, 6, 8, 10, 12, High
(Low = 2x less gain)

*1) not possible to get 47k. Remove R1.

*2) This 1:1 configuration transfers high impedance 1:1. So 10k in = 10k out, or 47k in = 47k out. Etc.

*3) This 1:1 configuration transfers low impedance 1:1. So 600R in = 600R out, or 1k in = 1k out. Etc.

1. GAIN Applications

LL1544a is an amorphous core transformer, and can do anything from 0.5x gain until 4x gain in fine steps, with the EE20 board.

LL1545a is a mu-metal version of LL1544a.

LL1550 is an amorphous core transformer. It gives always gives gain, from 1x to 8x. So when the gain range of 1544a (0.5 ....4x) is not enough, LL1550 can be used. There is no mu-metal version of LL1550.

2. ATTENUATING Applications

This is a curious way to use the EE20 Board, but it is sure possible and a very good way. When the compensation section is switched off, by opening the Jumper J10, the board can be reversed. For the logic, the "High Signal" side has the H+ and H- inputs, and the "Low Signal " side is called L- and L+. For attenuating, the input is H+ and H- and the attenuation factor becomes what was originally the gain (just use the above table for Switch settings. So set the board for instance of 4x gain, and reverse it, to get 4x attenuation. So attenuation of the reversed EE20 Board can be varied from 0.5x (which is gain) to 4x attenuation using LL1544A, or get an attenuation from 0 to 8x with LL1550. Moreover, when attenuating, the frequency compensation will not be needed anyway, because we can assume a low impedance signal source.

Advantages of attenuating: Basically this situation is as follows: The power amplifier has more gain as needed. So the amplifier begins to distort much for before the volume is at 100% loudness. Now with an attenuating board, the input signal has to be higher, which signal level is of course available. With 99% of the signal sources, this will improve the signal to noise ratio in the same ratio as the attenuation itself! So an drastic noise reduction will take place! The

Using LL1544A / LL1545A reversed, give attenuation of 4x, 2x, 1.5x, 1x, 0.75x or 0.5x (The last two options are in fact "gain"). All if this by just set the paino switch by the table.

Using LL1550A reversed, gives attenuation of 8x. 4x, 3x, 2x, 1x.

3.1 Create a balanced RCA input.

Most RCA connectors are grounded to the chassis by default. To convert this to a balanced RCA input, it should be replaced by an isolated ground type. Sometimes such an isolated ground RCA connector was already used, and it's ground was connected to the chassis with a wire piece. In that case, just cut this wire piece off. The center of the RCA cable is connected to X+. The shield is connected to X. Already now the input is balanced, even though it has RCA connectors.

 

3.2 Create a real XLR input

We don't want to mention names here, but some amplifiers have fake XLR inputs. Which are simply wired internally to an unbalanced input. So the amplifier already has all of the hardware, just the transformer was not installed. In this case, using the EE20 board is a VERY GOOD idea..

Note: You can even attach an RCA and XLR input TOGETHER, when connected like in the above pictures.

 

3.3 Create a Gain stage (unbalanced)

This is how to create a simple gain stage inside an amplifier. Select any ration from 0.5x (Attenuating) to 4x (Gain), by simply set the Piano switch by the table. This is using LL1544, LL1545, which are probably the most convenient to use, because these will also ATTENUATE if needed (So gain = 0.5x) if needed.

With LL1550, Gain can be selected from 1x to 8x. Whereas input impedance becomes quite low at 8x gain, impedance will be the same as with LL1544 or LL1545, if the same gain is chosen.

Moreover, by adding the Optional EE22 Switch Board in addition, the amplifier becomes a High-Low Sensitivity input.

 

3.4 Create an Attenuating stage (unbalanced)

By reversing the direction of the board, all gain factors from the table will become attenuating factors. This is much recommended if you have too much signal. In such a case, the pre-amplifier noise may become too high, the volume control is working on too small rotation angle, and the pre-amplifier will sound sterile too. This attenuating mode, will reduce the noise by the same ratio as the setting of the table. So at 4x (from the table) noise attenuation will be 4x as well. Since this is hard to predict what is needed, this EE20 board is ideal, because it provides so many possibilities.


3.5 A balanced input with center tap.

When a balanced signal source is floating, there is some risk on common mode signals being picked up, when the balanced input is also floating. In this case, the center tap of the EE20 input can be grounded, by setting Switch A5 to 'on'.

3.6 Create an unbalanced input.

For this, either X can be grounded, or X+ can be grounded, depending if phase reversal is wanted or not. Ground Terminal X by setting Switch A6 to 'on'. Or, Ground Terminal X+ with Switch A4 to 'on', which results in phase reversal. From switches A4, A5, A6, use only one at a time!