Electron Engine ™
Printed Circuit Boards by Emissionlabs ®

EE21, EE23 Board V6.5. Input Applications.

    1. Overview
    2. MC Applications
    3. Input Applications (you are here)
    4. Output Applications
    5. All Connection Schemes, Complete Overview
    6. Unsorted Application Information

Part1. Create Balanced Inputs, with or without gain.

Some input transformers are intended for gain, some for 1:1. Some have high impedance, some have medium impedance, and then there is the core material to choose from. There is a great overlap with the applications.

A transformer creates gain free of any noise and hum, and a distortion level better than any tube. Also if a driver stage has 'almost' the required gain, do not add another tube stage, and get stuck with too much gain and noise. Just add a step up transformer!

Input Board
Low Gain
High Gain
Core
Characteristic
LL1588 EE23
1x
2x
Mu Metal
Neutral sound. Board may also be used reversed, to get attenuation.
LL1592 EE23
1x
2x
Mu Metal
Neutral sound, High Signal. Board may also be used reversed, to get attenuation.
LL1690 EE23
1x
2x
Amorphous Cobalt
Best Sound of Amorphous.
LL1674 EE21
4x
8x
Amorphous Cobalt
Medium Impedance. Board may also be used reversed, to get attenuation.
LL1676 EE21
2x
4x
Amorphous Cobalt
High Impedance. Board may also be used reversed, to get attenuation.
LL1948 EE23
1x
2x
Amorphous Cobalt
Best Sound of Amorphous, 6N 'Cardas' wire.
LL1922 EE21
4x
8x
Mu Metal
Neutral sound.
LL1930 EE21
5.8x
11.6x
Mu Metal
Designed for parafeed pre-amplifier output.
LL5402 EE21
1x
2x
Very low impedance output

 

Reading all data sheets is only confusing. Better is, from the ABOVE, make the preliminary choice of the transformer, and then final choice becomes easy. For instance for a high impedance input, there is LL1676 or LL1588. Do you want amorphous core? If so, LL1676 is the answer. For mu-metall, the answer is LL1592.

  1. Application with LL1588
  2. Application with LL1592
  3. Application with LL1690
  4. Application with LL1674, LL1676
  5. Application with LL1922

Inverted or None-inverted signal?

Ideally, an amplifier should not invert the signal, but amplifier manufacturers pay little attention to this, because they regard the product by itself. However an inverting amplifier can cause instability problems. Perhaps it happened to you, when removing the input cable, with the amplifier on, it responded with an very loud, very short whistle noise. That is such a case. Yet because few designers know about this at all, 50% of the amplifiers invert the signal. In case of adding an input or output transformer, simply check if the amplifier perhaps inverts the signal. If so, phase reversal at the transformer is recommended. It's what this option is intended for. There is no obligation to use it, but it is better. More information about this.

Creating an BALANCED input

I recommend this as a standard for tube amplifiers, by using the RCA (Cinch) input for this. Like this it stays compatible with all existing equipment, using the RCA (Cinch) connector, but there it creates the advantage of a hum-free, balanced input. More information about this. For this, an isolated ground type RCA (Cinch) connector has to be used, such as the Yamamoto.

Hint: When connecting a balanced RCA (Cinch) connector, even an XLR connector can be connected in parallel to it.

Fake XLR inputs

I do not like to say this, but several amplifiers (some with great brand names) have fake XLR inputs. It is clear why they do this, because a real (balanced) XLR input costs them either a transformer, or additional electronic circuitry. There is no other way. And users know, XLR is professional, so it makes them happy to see those professional inputs. Well it's a shame actually. What happens? The manufacturer buys a 1$ XLR connector from China, and internally dumps the XLR-3 signal in a resistor. So the signal is only used from the XLR-2 line of the balanced pair. If you buy it, you think you get XLR? Well yes, but an XLR connector only. Electrically it is a fake XLR input. So people pay the extra price to have for instance a pre amplifier with XLR outputs, and very expensive Mogami XLR cables, and then... connect it to a (fake) XLR input, and frankly it was all for nothing. This a fraud to my opinion, but please regard it my opinion only. The situation is however, such an amplifier has the appearance of the XLR hardware at the outside. So specially here, using the EE21 board for instance with LL1588 or LL1676 in 1:1 configuration is the BEST you can do. It creates a real, balanced XLR input.

Even so you can save some money, and use the EE31 board too, which is very basic and it does what it needs to do. So as a cost saver, and just as well a good solution, use the EE31 board.

Hint: When the EE21 or EE23 board is used, and connected 'balanced', an RCA (Cinch) and XLR can be connected in parallel. For this, an isolated ground type RCA (Cinch) connector has to be used, such as the Yamamoto.

Termination Network

A termination network is not mentioned in most Lundahl datasheets, when the transformers have no electrical error in the audible range. Above 20kHz, at some point some roll of begins. This comes in earlier if unsymmetrical used.

A termination network will make most transformers linear up to a higher frequency. Some types perform best with an RC network as load. Some other typed need only a resistor, and some need no termination at all. For this reason, a variable resistor allows just try it out, and also switch the damping on and off with Solder Jumper J8, to hear the effect. More information here.

Part2. Termination Network (also called compensation)

When an RC termination network is mentioned the Lundahl datasheets, begin with just using this, and it will work very good to begin with. Some data sheets do not specify such a termination, but when we read the data sheet carefully, and it can be seen, a load of for instance 10k Ohms was used achieve the data sheet results. Now this is normal, because without any load at all, any tone transformer will self-resonate at some high frequency. In HiFi there is no requirement for very high impedance inputs. Only historically speaking, the old 47k requirement for RIAA amplifiers is still a good value, and it is a de facto standard. For other signal inputs it is definitely no need to use "47k" and you will hardly see this any more. To my opinion 10k is much better, this is not a difficult load for any normal signal source. This value is commonly used by Lundahl, and others.

Important is: Several tone transformers require a minimum load of 10k. If the pre-amp which it gets connected to, has 50k to 100k of it's own, that doesn't matter. If 10k is connected to the transformer, the total load will some 8k. So then we have achieved the minimum load of 10k, as intended.

Roll-off. A good tone transformer has no amplitude error, and no phase error in the audible range. Yet at some higher frequency, somewhere between 35kHz to 250kHz, roll of begins, or resonance will occur. Such that show earlier roll of, may not show resonance. If symmetrical used, generally the frequency range if (the same) transformer is a little better.

Termination network. This will make most transformers linear up to a higher frequency. Along with change of amplitude comes always a phase error as well. Personally I find the last more disturbing as a loss of amplitude outside the audible range. But since this comes always together anyway, best is to linearize the amplitude behavior, and like magic, the phase error is gone as well.

Some types perform best with an RC network as load. Some other typed need only a resistor, and some need no termination at all. For this reason, we use a variable network, which gives us many options to use it, and a variable load resistor. This allows just try many things out, and also switch the damping on and off quickly just with one Solder Jumper (J8), to check if there is an audible effect. More information here.

Moving Coil Schematic
The network is universal for all transformers.

Depending on the application, only some parts of the network are used.

Use procedure.
  1. Select J2 for low gain. Already now the board works, but a good grounding scheme and best gain has yet to be choosen. Not needed, but sometimes better, is to use some termination components, (Depending on transformer type).
  2. The Input side has has letters L+ and L-1. The output side has letters H+ and H-.
  3. The Output side has the termination network. (it works also without this)
  4. Initially input and output are floating. Normally, we need ground the board at the amplifier side. So no matter if used as sender or receiver, always the wires that go out of the cabinet are the floating wires.
  5. All four 'G' connections at input and output side are the same, and connected to the transformer metal, as well as both board ground planes (there is a ground plane on each side). So these are the best possible "hard" ground there is, free of induction. It doesn't matter which of the G connections used for this. There are a total of four, so to make shortest links, or to connect a load resistor to, or whatever you want to use a ground connection for.
  6. In addition, J6 centers the L-Side, (the input). This is only possible at low gain).
  7. J4 centers the H-Side (the output) . This is always possible.

Experiment with both gain factors. Basically it must work absolutely free of problems. The solder islands of the boards are very good quality and will not damage easily.

When it works all good, and the best sounding gain is chosen, the best termination network has to be found. A network is not always needed. Some applications like parafeed or other attenuating configurations work without it.

Optional: Some people do not like a variable resistor in the sound path, and it can be replaced by a fixed resistor. In that case, the variable resistor is shorted, and has no function any more. It can stay in, for later experiments. However to find out it's best value, the variable resistor has to be used. The way to do this, is as follows:

 

Solder Jumpers, at the back side of the board

 

APPLICATIONS BY TRANSFORMER TYPE

 

Application with LL1588

This is a neutral transformer, giving a gain of 1x or 2x. Yet by reversing the board, an attenuation of 2x can be achieved as well

LL1588 is universal. We see it often used in DAC applications. LL1588 has a mu metal core. This material will not be permanently magnetised if there is some small DC current. (Though this DC current is not specified).

Gain
Termination of LL1588
Jumpers
0,5x
This works without termination. To obtain attenuation, the board has to be used reversed. For this, "H-side " becomes the input, and "L-side" the output. Connection Scheme
J2
1x
C1=4n7, insert 1k resistor instead of P1, vertical mounted, in Pins 1-2 of the potentiometer. Pin numbers are indicated at back side of the board.
J1, J3, J7, J8
1x
With Variable network:
C1=4n7, P1=5k
Adjust for best response
J1, J3, J8
2x
C1=4n7, insert 1k resistor instead of P1, at Pins 1-2 of the potentiometer (indicated at back side of the board)
J2, J7, J8
2x
With Variable network:
C1=4n7, P1=5k
Adjust for best response
J2, J8
Adjustment procedure for best response of LL1588

Lundahl does not mention the use of an RC compensation network, and the transformer can of course be used without. I found frequency range is 100% linear in the audio range, and very far outside as well, without compensation. For commercial applications, or parts count reduction, just use the transformer alone, and this is really a very good way already. Using it with compensation is just for getting the ultimate result out of it.

  1. Fixed RC network: Like this there will of course be no adjustment and it can be used as is. Yet verification of the results, as described below, can be done four your own interest in the same way. The recommended fixed network, is working already very nice.
  2. Adjustable RC network: Required instruments: Sine wave generator, oscilloscope or AC voltmeter which works up to 250kHz.
  3. Best is to use the intended drive impedance and intended load.
  4. Open J8 to disable the compensation circuit
  5. Set for 10kHz sine wave, and adjust the input signal such that exactly 1 Volt output signal appears.
  6. Increase the frequency, until somewhere above 100kHz, the first resonance frequency appears. This can be seen as a sudden increase of output signal, almost a factor two. Adjust the frequency for the maximum output voltage. This is the worst case situation. There is also a significant phase error now.
  7. Adjustment: Close J8, and adjust P1 such that original output signal is 1 Volt again.
  8. To verify the result, sweep with a sine wave from 20kHz until the frequency which uses to give a resonance. The resonance and phase error will be gone now.
  9. By opening and closing J8 it can also be seen that sharp, needle-like overshoot of a square wave signal will be gone.
Reversed connection (For attenuation)

  • 2x Attenuation, using LL1588.
  • This attenuation can also be switched off by setting the gain to 1x. Either by solder bridges, or by connect the EE22 switch board.
  • Grounding scheme not included in this drawing.
  • This needs no termination network

Normal (forward) connection)


 

 

Application with LL1922

This is transformer for creating gain of 4x or 8x.

LL1922 data sheet

Gain
Termination of LL1922
Jumpers
8x
With Variable network:
R1=10k, P1=250k
Adjust for best response
J1, J3, J8
8x
With Fixed network
R1=47k
J1, J3, J5, J8
4x
With Variable network:
R1=10k, P1=250k
Adjust for best response
J2, J8
4x
With Fixed network
R1=47k
J2, J5, J8
Adjustment procedure for best response of LL1922
  1. Information follows

 

Application with LL1674 and LL1676

These are two very classical Lundahl transformers for impedance matching, or a 1:1 47k input with the LL1976. Used by many. Both have a core of amorphous iron.

Basically LL1974 is medium impedance, and LL1976 is high impedance, but here again the EE21 board offers some additional variations.

Gain
Termination Jumpers
         
Single Output, impedance matching
No Parts mounted.
4x
600 Ohms in, 10k Out. (Can be reversed)

J1, J3,

Phase Splitter Output
No Parts mounted.
4x
Source must be 150 Ohms
J1, J3, J4
High Impedance (47k) input
No Variable Resistor mounted.
1x
R1=33k
J2, J4, J5, J8
High Impedance (47k) input
1x
R1=4k7, R2=100k, adjust R2 for best square wave response
J2, J8
Medium Impedance (10k) input
No Variable Resistor mounted.
2x
R1=68k
J1, J3, J5, J8
Medium Impedance (10k) input
2x
R1=10k, R2=220k, adjust R2 for best square wave response
J1, J3, J8
  • J1, J2, J2 Set Gain. (J2 = low, J1+ J3, = high)
  • J8 connects Termination.
  • J7 shorts R2 and C1 (to use only the potentiometer)
  • J5 shorts the potentiometer (to use only R1-C1)
  • Open J5 and J7, to use both Potentiometer and R1-C1
  • J6 centers the input (only possible at low gain)
  • J4 centers the output (always possible)

 

Application with LL1592

LL1592 data sheet

This transformer will work very good in the audio range without tuning network. It can work however up to 100kHz, if an RC tuning network is used. The EE21, EE23 Board V6.5 has the option for this.

Gain
Termination Jumpers
         

From the above datasheet (screen shot)

Serial 1:1 connection (Above Picture 1)
  • Solder Jumpers J2, J4, J5, J8.
  • The variable resistor is not needed, but if it was already mounted, it can be left in, it is disabled by the J5.
  • R1 and C1 are the termination network, by the datasheet. 7k and 400pF.
  • Connect G to Ground
  • Inputs: L+, L-
  • Outputs: H+, H-
Phase Splitting for 2: 1+1 input (Above Picture 2)
  • Solder Jumpers J1, J3, J4.
  • The variable resistor is not needed, but if mounted, it can be left in.
  • R1 and C1 are the termination network, by the datasheet. 7k and 400pF.
    Connect G to Ground
  • Inputs: L+, L-
  • Outputs: H+, H-
Phase Splitting for 1: 1+1 input:

Solder Jumpers J2, J4.
The variable resistor is not needed, but if mounted, it can be left in.
R1 and C1 are the termination network, by the datasheet. 7k and 400pF.
Connect G to Ground
Inputs: L+, L-
Outputs: H+, H-

Fine tuning:

For fine-tune the termination network with an oscilloscope, a variable resistor can be used of appr 15k. Open Jumper J2. R1 becomes 1k, but it's value is uncritical. The functioning of such a termination network depends greatly on the RC-Time. This is why the capacitor can be a fixed value, and the resistor can be variable.

 

 

 

 

 

 

Some connection examples


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