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EEE20 Gold Plated Multi Purpose Board. Version 2.9


Lundahl LL1544A

EE20

Center tap not possible if with all windings in parallel.


Audio Board Applications - CONTENTS:

Part 1. How to use EE20 as Audio Input board? (Not moving coil)

IMPORTANT: Lundahl uses two approaches, to explain the possible options. This comes down to the same, though data sheets for this look different. These two ways are:

Part 2. COMPLETE CONFIGURATIONS

This board can be used stand alone, or with the external switch. (See below)

The Switch Board EE22 is optional, and allows to switch between two gain factors.

To achieve attenuation, the board is used reversed, so exchange output an input. (Section 4.5 "attenuating inputs")

This is according to the data sheet: LL1545A-ALT

 

Line nr
Trans-former
EE20
Switch Setting and Gain
EE20 +EE22

Switch Setting and Gain
Lundahl
Alt
Possible Use

EE20 Board Input impedance

Tuning options
Line 1

 

 1, 3, 7, 9, 11
Gain 0.5x		 7, 9, 11
Low Gain= 0,5x
High Gain= 1x		  
Factor 4, Impedance lowering, or attenuator.
47k (*1)

X1=15k. Close J2. Close J1 to activate the tuning
Line 2

1, 3, 5, 7, 8, 11
Gain 0.75x

 5, 7, 8, 11
Low Gain = 0.75x
High Gain= 1.5x
Factor 1.8, Impedance lowering, or attenuator.
47k (*1)

X1=15k. Close J2. Close J1 to activate the tuning
Line 3

2, 7, 9, 11.
Gain 1x

RCA+=L+
Ground=L-.
Do not connect CL.

 

7, 9, 11
Low Gain = 1x
High Gain= 2x

10k <=> 10k
*2)
47k (*1)

6k8 at X3, and 470pF at X2. Close J1 to activate the tuning
Line 4

2, 7, 9, 11.

Gain 1x

XLR1=CL, XLR2=L+, XLR3=L1.

 7, 9, 11
Low Gain= 0,5x
High Gain= 1x

10k <=> 10k
*2)

47k (*1)
 6k8 at X3, and 470pF at X2. Close J1 to activate the tuning.

Line 5
 2, 7, 9, 11.

Gain 1x

XLR1=CL, XLR2=L+, XLR3=L1. Out1=H+, Out2=H1,

 

Switch Board EE22 can not be used.
Alt A. Center Tapped, for XLR or other balanced input.
With SPLITTER Output, to drive Push Pull tube stage.
10k <=> 10k
*2)
47k (*1)
None
Line 6
 1, 3, 5, 7, 8, 10, 12 Gain 1x 5, 7, 8, 10, 12
Low Gain= 1x
High Gain= 2x
600R <=> 600R
*3)
600R
None
Line 7
 2, 5, 7, 8, 11
Gain 1.5x		 5,7,8,11

Low Gain = 0,75x
High Gain= 1.5X 		 
21k (*1)
None
Line 8
 2,5,7,8,10,12
Gain 2x		 5, 7, 8, 10, 12

Low Gain = 1x
High Gain= 2x
Alt C
Most recommended
High Signal
12k (*1)
None
Line 9
 1, 3, 4, 5, 6, 8, 10, 12 Gain 2x 4, 5, 6, 8, 10, 12

Low Gain = 2x
High Gain= 4x
Alt D
Only for low impedance Source
Normal Signal
12k (*1)
None
Line 10
 2, 4, 5, 6, 8, 10, 12 Gain 4x 4, 5, 6, 8, 10, 12
Low Gain = 2x
High Gain= 4x
3k (*1)
None
Line 11

1, 3, 7, 9, 11
Gain 1x

 7, 9, 11
Low Gain= 1x
High Gain =2x
47k (*1)
None
Line 12
 1, 3, 5, 7, 8, 11
Gain 1.5x		 5, 7, 8, 11
Low Gain=1.5x
High Gain=1.5x
20k (*1)
None
Line 13
 2, 7, 9, 11
Gain 2x		 7, 9, 11
Low Gain =1x
High Gain=2x
High Signal
12k (*1)
None
Line 14
 1, 3, 5, 7, 8, 10, 12 Gain 2x 5, 7, 8, 10, 12
Low Gain= 2x
High Gain= 4x
Normal Signal
12k (*1)
None
Line 15
 2, 5, 7, 8, 11

Gain 3x

 5, 7, 8, 11

Low Gain=1.5x
High Gain= 3x

  
5k2 (*1)
None
Line 16
 2, 5, 7, 8, 10, 12
Gain 4x		 5, 7, 8, 10, 12
Low Gain = 2x
High Gain= 4x
High Signal
3k (*1)
None
Line 17
 1, 3, 4, 5, 6, 8, 10, 12
Gain 4x		 4, 5, 6, 8, 10, 12
Low Gain =4x
High Gain= 8x
Normal Signal
3k (*1)
None
Line 18
 2, 4, 5, 6, 8, 10, 12 Gain 8x 4, 5, 6, 8, 10, 12
Low Gain =4x
High Gain= 8x
734 Ohms (*1)
None

*1) Output of board loaded with 47k amplifier input.

*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.

*4) trying to get gain with a high impedance splitter is not recommended.

Part 3. Combine Input + Output configurations yourself

This is according to the data sheet: LL1545A.

Note this:

This data sheet has only REVERSED, so ATTENUATING Applications. It means H+ and H- is the INPUT. Lundahl did it this way, we just replicate this here.

 

Input Applications

This table is under construction!
Line Nr.
Scheme
Set Switches + Connections
Remarks
Line 19


XLR-IN
High Impedance

Set: Switch 2

Input H+, H-

 If XLR is used, connect XLR shield to chassis ground of the receiver.
Line 20


RCA-IN
High Impedance

Set: Switch 2

Input H+, H-

 Though the source is unbalanced indeed, Lundahl uses a 'ground lifted' input.

For a normal, grounded RCA input, connect H+ to ground with a wire link.

Line 21
 Correction network is connected from H+ to H-, and can be used to generate a defined input impedance.
  • For fixed input impedance, close J1 and J2, apply the input impedance to X1. High impedance is like 10k. Low impedance is like 600Ohms.
  • For adjustable high input impedance, close J1, open J2. attach 560Ohms to X1 (minimum impedance) and attach P1, with of value 10k. This allows change from appr. 560 Ohms to 10.5k.
  • To switch it off, open J1.
  • Note, the load impedance om L+ and L- is additional!

Output Applications
Line
Scheme
Set Switches
Connections
Line 22


Low Impedance Out
Universal

 4, 5, 6, 8, 10, 12
L1 = All Windings in parallel

For floating XLR, connect XLR1=G, XLR2=L+, XLR3=L1

For RCA connect L- with wire bridge to G. L+ becomes RCA out.

All "G" connections are the same, at least one of them should be grounded.
Line 23


XLR-Out
(or balanced out)
Medium impedance

 4, 6, 9, 11
L2B = 2Windings in series

For XLR connect: XLR1=G, XLR2=L+, XLR3=L1

All "G" connections are the same, at least one of them should be grounded.
Line 24


XLR-Out
(or balanced out)
High impedance

 7, 9, 11
L4B = 4Windings in series

For XLR connect: XLR1=G, XLR2=L+, XLR3=L1

All "G" connections are the same, at least one of them should be grounded.
 
      

Part 4. Phase Splitter Applications

A phase splitter transformer is an ideal application when using tubes. For driving a Push Pull stage, we need perfect symmetry. Otherwise this will add distortion if the signal is higher. (Which is just the moment where we do NOT want to add distortion...)

However with two drive tubes that is hard, because it needs two identical tubes, some call that a balanced tube. Read more about it here.

Even when do do get balanced tubes, they do not age the same way. So 1000 hours later, the balanced tubes are unbalanced again. This often ends up with a symmetry potentiometer, which needs to be adjusted by oscilloscope, as the tubes age, and sure at tube exchange. This is quite an unfavorable adjustment point. Yet for cost saving it is done. A half way good solution is to use a totem pole circuit, which can work without adjustment indeed, but such a circuit has different output impedance of both outputs, is also not free of aging, and it adds some to distortion at high signal. Moreover, if done with double triodes, the different heater-cathode potential of the channels stresses the tubes very much, and you may run into hum problems, blaming the tubes for this, but in fact maximum heater-cathode voltage is exceeded, or it comes just too close. From selling tubes, we can say, a totem pole is the #1 a trouble maker for crack and pop noise, specially with E88CC, for reasons explained here.

The typical Lundahl phase splitting capable transformers have what is called symmetrical windings, so there is no inductive or capacitive difference. These are from this series: LL1544 and LL1545. LL1550 is also possible. No microphonics, no aging, no adjustment, no hum, and no noise, and more cost effective too. A pair of NOS E88CC costs more.

Note, a 1:1 phase splitter gives 2x the load on the driver tube, and a 1: 2 splitter gives even 8x the load. So gain should be used with care, and needs a low impedance drive tube. So design with 1:1 and when you driver tube can take some gain, you can set the gain of the board higher.

If used as a splitter, in forward application, there are some more considerations:

Part 5. RCA Unbalanced Input

This is how to create a simple gain stage inside an amplifier. Select any ratio 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.

Part 6. RCA Balanced 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.

Part 7. XLR input

We don't want to mention names here, but some amplifiers have fake XLR inputs. This is really FAKE as can be. These 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.

If you have a FLOATING sender, this a bit unusual, but it may be. On that case, it may be a good idea, to ground the CL connected with a wire link to G. This is only possible for switch combinations from the table, which have switch #7 is closed. (In any other combination this will not work, and cause a short, yet you will see, these are still many possibilities)


Part 8. XLR input + balanced RCA input simultaneously

This is a really interesting option, since the only investment is the extra connector! Simply wire an RCA and XLR connector simultaneously, like in the above diagrams. When done, just use either the XLR, or the RCA, as you like. What we achieve here: The RCA input will still be truly balanced! Using fully the shielded properties of these transformers. Yet it stays fully compatible to any other RCA connected amplifier, no matter if it is a balanced or unbalanced type.

Part 9. Attenuating stage

This is advised, when the pre-amplifier has much more signal as required. Such a situation will give unwanted microphonics and other noise. Before considering an attenuating output, users often had a frustrating search for selected tubes with low noise. Better is, to step over the fixed idea, that if tubes appear microphonic, the ONLY explanation is "the tube". Of course, the problem is less with highly selected tubes, but this only indicates the pre amplifier is not well suited for unselected tubes. What can be the explanation for this?

In some cases, the power amplifier or the pre amplifier have more gain as needed. Or, even both amplifiers have too much gain. This may seem not important, because you have a volume control anyway. But, it will increase the effect of tube microphonics a lot.

The #1 misunderstanding of pre amplifier builders is always, these devices "must amplify" the signal. Which is wrong, when this ends up with too much total gain. Instead, these should lower the impedance, and if possible allow balanced inputs or outputs, and cutting the ground loop. If inputs or outputs are unbalanced, if output impedance is too high, if there is too much gain in the chain, or even these issues combined, you may have created a noise generator.

What to do against tube microphonics?

The solution:

If f the volume control is at the output of the pre amplifier, using the volume control will also reduce the noise. Even so, when the power amplifier has too much gain, which is often the case, this will amplify the noise even further. But not so, if the volume control is at the output of the pre amplifier. Since this (too high) gain will make you reduce the volume further, you will also reduce the noise accordingly. This is a second positive effect. Curiously, the extra gain of the power amplifier, is now used to reduce the noise of the pre amplifier. The effect of this is an amazing loss of microphonics. And then for a change, you do not need to select tubes any more.

 

This schematic is R2U and R4U from the data sheet at the Input side. At the output side the "L" Variations can be chosen by the Piano switch. The choice between R2U and R4U is either done by the external switch board, to achieve (external) switchable attenuation, or can be done without external switch board, and set it via the Piano Switch to R2U or R4U.

Output is RCA unbalanced. This configuration has common ground. (Because both ground links are inserted).

This schematic is R2U and R4U from the data sheet at the Input side. At the output side the "L" Variations can be chosen by the Piano switch. The choice between R2U and R4U is either done by the external switch board, to achieve (external) switchable attenuation, or can be done without external switch board, and set it via the Piano Switch to R2U or R4U.

Output is XLR.

Part 10. Balanced input with center tap.

For all those applications from the table, where switch #7 is closed ("On"), a balanced input with grounded center tap can be configured. For this, the CL connection is connected to G with a wire link. L+ and L- become the inputs. This would be useful for instance for a balanced amplifier, and LL1544/1545 is the driver transformer for the output stage. Note, this doubles the gain, because what was 0....+2Volt before, becomes now -1...0....+1Volt.

 

NOTES
The notes are put here, to make the above text shorter, but these things ARE important.

Balanced tubes. With two drive tubes it is hard to drive a balanced circuit. It needs two FULLY identical tubes, or you introduce distortion. If those tubes are in one bulb, some call that a balanced tube. This is of course not possible to achieve with tubes, which were not produced "unbalanced" to begin with. Just the problem is, we can not get the tubes out of the bulb, to balance them for you. This is a little bit the same story, and every time we tell it, everybody is very surprized, but no, of course not, we can not select balanced tubes from a lot of tubes which is made unbalanced. Tubes which are MADE balanced is the only type suited for this. And these are not many types, and they are always expensive, for good reasons of course. For instance E88CC (6922) is the BALANCED version of ECC88 (6DJ8). But to be balanced, they must be real NOS. New production is fake. (yes!) Meaning they write E88CC on it, and present you the data sheet of an UNBALANCED version, and sell of course unbalanced tubes as well. To make it crazier as it already is, they charge you to select "so called "balances tubes out of such a lot, which doesn't contain such.