Lundahl Guidelines

 

Guideline for use of Lundahl output transformers

This is also to answer the most FAQ , and to help understand how to obtain the best possible
Results from the outputtransformer

Impedance ratio apply for SE & PP

You can use double the rating of primary current at the cost of primary inductance ,
2 primary windings in series and then parallel , this reduces inductance by 1/4 and doubles
primary current .

Also note when you get very low ratios that the internal wire resistance is going to be a big loss factor
And this should be checked for

For SE try to use the lowest number possible for your application , to get the best bass response
Offcourse this will reduce slightly the high frequency response

Basic Frequency response : 7Hz to 25kHz within 0,5 dB and 2Hz-75kHz within 6dB
Fase shift : 20kHz 13,5 ° and 2,2µs group delay

3 basic models :

---------------------LL1620 ------------LL1623-------------- LL1627
Each primary winding
Has a turn ratio = ---19,2 -----------------13,4------------------- 8,5

Primary winding DC resistance

---------------------77ohm ----------------41 ohm ---------------14 ohm

Each secondary winding
Has a turn ratio = ----1 ----------------------1--------------------- 1
Secondary winding DC resistance 0,4 ohm ---0,4------------------- 0,4

All transformers have 4 primary coils and 8 secondary coils
The max voltage across
Primary windings (all in series)

-------------PP=860v SE=380v ----PP=610vSE=270v----- PP=380v SE=170v

Formulas :

X = impedance ratio
N1 = primary turn ratio
N2 = secondary turn ratio

X= N1 * N1 / N2 * N2

Primary impedance or plate load=secondary impedance or speakerload * impedance ratio( X )

Also keep in mind that I am only studying 8 ohm connection but if you hook up 4ohms
As secondary load then the primary plate load is halved as well , but if you have 16 ohm load
Then plate load will double (compared to 8 ohm )

Lets study some possibilities :

Case 1 :

All primaries in series N1 = for each model ( primary turn ratio )

LL1620 = 19,2 * 4 = 76,8
LL1623= 13,4 * 4 = 53,6
LL1627= 8,5 * 4 = 34


Option 1 = all secondaries parallel so N2 = 1

For 8 ohm speaker the anode load will be :
LL1620 = 5898 * 8 = 47 k ( k = kilo ohm)
LL1623 = 2873 * 8 = 23 k
LL1627 = 1156 * 8 = 9,2 k

Option 2 = 2 secondaries in series and then the 4 groups parallel to each other N2=2

For 8 ohm speaker the anode load will be :
LL1620 = 1474 * 8 = 11,8 k ( k = kilo ohm)
LL1623 = 718 * 8 = 5,6 k
LL1627 = 289 * 8 = 2,3 k

Option 3= see alt C ( 2 secondaries in series and then in series with 2 secondaries parallel and this parallel to
The other secondary with identical scenario ) N2=3

For 8 ohm speaker the anode load will be :
LL1620 = 655* 8 = 5,24 k ( k = kilo ohm)
LL1623 = 319 * 8 = 2,55 k
LL1627 = 128 * 8 = 1 k

Option 4 = 4 secondaries in series and then parallel to each other N2=4

For 8 ohm speaker the anode load will be :
LL1620 = 368 * 8 = 2,95 k
LL1623 = 179 * 8 = 1,45 k
LL1627 = 72 * 8 = 576 ohm

Option 5 = 8 secondaries in series N2=8

For 8 ohm speaker the anode load will be :
LL1620 = 92 * 8 = 736 ohm
LL1623 = 45 * 8 = 360 ohm
LL1627 = 18 * 8 = 144 ohm

______________________________________________________________________________
Case 2 :

2 primaries in series and then parallel to each other N1 = for each model
(this will double the primary current rating and divide by 4 primary inductance = worse LF response )

LL1620 = 19,2 * 2 = 38,4
LL1623= 13,4 * 2 = 26,8
LL1627= 8,5 * 2 = 17


Option 1 = all secondaries parallel so N2 = 1

For 8 ohm speaker the anode load will be :
LL1620 = 1474 * 8 = 11,8 k ( k = kilo ohm)
LL1623 = 718 * 8 = 5,6 k
LL1627 = 289 * 8 = 2,3 k

Option 2 = 2 secondaries in series and then parallel to each other N2=2

For 8 ohm speaker the anode load will be :
LL1620 = 368 * 8 = 2,95 k
LL1623 = 179 * 8 = 1,4 k
LL1627 = 72 * 8 = 576 ohm

Option 3 = 4 secondaries in series and then parallel to each other N2=4

For 8 ohm speaker the anode load will be :
LL1620 = 92 * 8 = 736 ohm
LL1623 = 45 * 8 = 360 ohm
LL1627 = 18 * 8 = 144 ohm

Option 4 = 8 secondaries in series N2=8

For 8 ohm speaker the anode load will be :
LL1620 = 23 * 8 = 184 ohm
LL1623 = 11,2 * 8 = 90 ohm
LL1627 = 4,5 * 8 = 36 ohm

Case 3 :

all primaries parallel to each other N1 = for each model

gives you 4 times primary current rating and divides by 16 inductance , can be used with very low impedance tubes
or mosfets or transistors.(beeeuuuurk )

LL1620 = 19,2 * 1 = 19,2
LL1623= 13,4 * 1 = 13,4
LL1627= 8,5 * 1 = 8,5

Option 1 = all secondaries parallel so N2 = 1

For 8 ohm speaker the anode load will be :
LL1620 = 368 * 8 = 2,95 k
LL1623 = 179 * 8 = 1,4 k
LL1627 = 72 * 8 = 576 ohm

Option 2 = 2 secondaries in series and then parallel to each other N2=2

For 8 ohm speaker the anode load will be :
LL1620 = 92 * 8 = 736 ohm
LL1623 = 45 * 8 = 360 ohm
LL1627 = 18 * 8 = 144 ohm

Option 3 = 4 secondaries in series and then parallel to each other N2=4

For 8 ohm speaker the anode load will be :
LL1620 = 23 * 8 = 184 ohm
LL1623 = 11,2 * 8 = 90 ohm
LL1627 = 4,5 * 8 = 36 ohm

Option 4 = 8 secondaries in series N2=8

For 8 ohm speaker the anode load will be :
LL1620 = 5,75 * 8 =46 ohm
LL1623 = 2,79 * 8 = 22 ohm
LL1627 = 1,12 * 8 = 9 ohm

Study of 3 connection alternatives as suggested by the datasheet

Model LL1623 connection alternative B = 5600ohm to 8 ohm load

All primaries in series = 53,6 turn ratio = 2873

Secondaries :
here we have 2 groups of 4 windings parallel , each supplying one speaker terminal
1 group supplying the negative terminal has all its positives together
2 nd group has its negatives together and connected to the positive of group 1
this gives a turn ratio of 2 = 4

or for 8 ohm load : 2873/4*8=5746 ohm + dc resistance of coils (164 ohms )
_______________________________________
same model alternative C = 3000 ohm to 8 ohm

All primaries in series = 53,6 turn ratio = 2873

Secondaries :

here we have 2 groups in parallel ,
both identical = 2 windings in series and then in series ( 2 windings parallel )

this gives a turn ratio of 3 = 9

or for 8 ohm load : 2873/9*8=2553 ohm + dc resistance of coils (164 ohms )
________________________________________

same model alternative D = 1600 ohm to 8 ohm

All primaries in series = 53,6 turn ratio = 2873

Secondaries :
here we have 2 groups in parallel ,
each group = 4 windings in series

this gives a turn ratio of 4 = 16

or for 8 ohm load : 2873/16*8=1436 ohm + dc resistance of coils (164 ohms )


Small note on LL1663 & LL1664 :

The former has a ratio of 4+8 + 4+8 to 1

So the following connections are possible :
4 to 1 = not recommended
12 to 1 , ( double I dc inductance /4 ) = 144 * 8 = 1200 ohm primary
( can be obtained also with only one coil instead of 2 coils in parallel )
12+4 to 1 = 256 * 8 = 2 K
12+8 to 1 = 400 * 8 = 3,2K
12+12 to1 = 576 * 8 = 4,6K

the LL1664 :
9,6 + 9,6 to 1 = 368 * 8 = 3 K

what is missing here are a few inductance measurements
but excellent transformer for low power applications , because the high frequency response is astounding
and if not using lots of current then inductance is more then high enough for good low frequency response

If in doubt of the primary impedance of a transformer ,

You have 2 simple (almost identical ) methods of measurement ,
Step 1 : disconnect speaker & shut amp off ( discharge capacitors )
Step 2 : hook a 6 volt ac transformer (50 or 60Hz)on secondary side = instead of speaker
Step 3 : measure ac voltage secondary =U2
Step 4 : measure primary voltage (be carefull high voltage ) = U1
Step 5 : divide voltages step4/step3 = ratio n = U1/U2

Zprimary = Z secondary * square ratio n

The other method consist in using a frequency generator and a scope , and doing exactly the same

Final Conclusion :

There are still lots of possibilities on how to connect these trannies , like only using 3 primaries in series and not connecting the 4 winding , and on the secondary side , you could just use one winding and not connect the 7 others .

So this is truly a very high quality universal transformer , that requires a good understanding of how to play with it , I think it is best if you use all the windings and especially all primaries in series.


If you have any comments ( positive ones will be treated first) ,
please share by email,as I am always eager to learn more

sales@diyparadiso.com
Benny Glass

 

for info email me at sales@diyparadiso.com