Lundahl Transformers

Tibeliusgatan 7, 761 50 Norrtälje

Phone: +46 176 139 30

Fax: +46 176 139 35

I guess you are right. It _IS_ confusing.

If we assume a certain DC current, there are two ways to reach a desired core operating point:
1. With a given coil, adjust the core air-gap or
2. With a given core air-gap, adjust the number of turns on the coil

The type number LL1660S/18mA is designed such that at 18mA DC current and ALL PRIMARY WINDINGS CONNECTED IN SERIES, the core operating point is 0.9T But if you connect the windings in a different way (such as suggested in “Alt B”), the number of magnetizing turns will be different, and the core will have a different operating point unless you change the DC current.

So for LL1660S/10mA, used in connection “Alt B”, the necessary DC current required to reach the operating point 0.9T is 18mA

I hope this is an answer to your question.

SR504A is a microphone transformer 200 ohm : 2k

 

in+		2  
in-		3  
out+		6  
out-		7  
core		1  
Housing 	4  
Faraday shield 5

 

SR504a is similar to the more modern transformer LL1538

SR503 is a line output transformer with turns ratio 1.4 : 1.

 

in+	8  
in-	6  
out+	10  
out-	4

SR502 is a high impedance bridging input transformer.

 

in+	1  
in-	5  
out+	7  
out-	9  
Faraday shields 6+10

SR501 is a high level 600 ohm : 600 ohm isolation transformer.

 

in+	1  
in-	5  
out+	7  
out-	9  
Faraday shields 6+10

LL9305 is a line output transformer with Faraday shields.
Turns ratio 1+1 : 1.6 + 1.6

 

6  5  4  3  2  1





12 11    9  8  7

Usage (for 1:1.6 line output)

in+    pin 6
in-    pin 3
connect    pin 4 + pin 1

out+    pin 12
out-    pin 8
connect pin 7 + pin 11
Faraday shield pin 9

 

LL5801 is a 1+1 : 2 audio isolation transformer originally designed for Kungliga Dramatiska Teatern (Royal Theater) in Stockholm. Sorry, no data sheet. A modern replacemen is LL1527 or LL1588. LL5801 pinout and usage:

Pin configuration (transformer seen from component side with label readable)

    
4,  	3,  	2, 	1      	

    LL5801    

8,	 7,  	6,	 5    

(I am sorry, but I am unsure about orientation, as we have no samples left in stock.
There is connection between pins 1 and 2, but not between pins 5 and 6)    

LL5801 Usage (1:1)  
in+	pin 1  
in-	pin 4  
connect 	pin 2 + 3  
out+	pin 6  
out-	pin 7  
ground  pin 5+8	(Faraday shield)
LL5606 is a line output transformer designed for Calrec Audio, probably used as a 1:1 transformer. LL5606 has an internal Faraday shield.


LL5606 is a line output transformer designed for Calrec Audio, probably used as a 1:1 transformer. LL5606 has an internal Faraday shield.


Pin configuration (as seen from PIN side)    
6,  5,  4,  3,  2,  1              




12, 11,     9, 8,  7      

Usage (2 : 1):    
in+	pin 1  
in- 	pin 4  
connect pin 6 + 3    
out+	pin 7 + 12  
out-	pin 11 + 8  
Faraday shield + housing pin 9          

Usage (1 : 1):    
in+	pin 1  
in- 	pin 4  
connect  pin 6 + 3    
out+	pin 7  
out-	pin 11  
connect pin 12+8  
Faraday shield + housing pin 9
LL5602 is a line output transformer designed for Calrec Audio, probably used as a stepup output transformer, turns ratio 1 : 1.6 or 1 : 3.2.


Pin configuration (as seen from PIN side)    
6,  5,  4,  3,  2,  1              




12, 11,     9, 8,  7      


Usage (1: 1.6):    
in+	pin 1  
in- 	pin 4  
connect pin 6 + 3    
out+	pin 7 + 12  
out-	pin 11 + 8  
Faraday shield + housing pin 9          

Usage (1: 3.2):    
in+	pin 1  
in- 	pin 4  
connect  pin 6 + 3    
out+	pin 7  
out-	pin 11  
connect pin 12+8  
Faraday shield + housing pin 9
LL5011 is a pin version of LL5008, normally used 1 : 1 Very low leakage inductance.

Pin configuration (as seen from PIN side)    

5,   4,   3,   2,   1
        


10,  9,        7,   6,    

Usage (1:1):  
in+	pin 1  
in-	pin 4  
connect pin 2 + pin 5    
out+	pin 10  
out-	pin 7  
connect pin 9 + 6    
Pin 3 	not connected
LL5008 is a low profile, low leakage inductance line output transformer. Connections are made through short flying leads and not through pins. 
This was a solution to save board height. I am afraid we have no data sheet for this type. For similar function, please study the LL1524 or 
LL7401.


Pin configuration (transformer seen from side of flying leads)    
1		        5  
2		        6    

3	        	7  
4	     	        8      

LL5008 usage (1:1)  
in+	pin 2  
in-	pin 4  
connect pins 1+3  
out+	pin 6  
out-	pin 8  
connect pins 5+7
LL4902 is a high turns ratio (1+1 : 22) microphone input transformer with double Faraday shields. LL4902 was designed for a customer in 
Australia, and is probably suitable for a 75 ohm : 10k application. The LL4902 is discontinued and no data sheet is available, but we do 
actually have approx. 100 x (non-ROHS-compliant) LL4902 in stock.

Pin configuration (transformer seen from component side with label readable)    

4,    3,    2,    1

       LL4902      

8,    7,    6,    5        

LL4902 Usage (1:11)  
in+		pin 1  
in-		pin 4  
connect 	pins 2 + 3  
out+		pin 6  
out-		pin 7  
ground 1	pin 5  
ground 2 + case and core 	pin 8
LL4901 is a 200 ohm : 5 k microphone input transformer, winding turns ratio 1+1:10. The LL4901 is discontinued and no data sheet is available. 
For replacements, please study LL1538.


Pin configuration (transformer seen from component side with label readable)    

4,    3,    2,    1

      LL4901      

8,    7,   6,    5        

LL4901 Usage (1:5)  
in+		pin 1  
in-		pin 4  
connect pis 2 + 3  
out+	pin 6  
out-	pin 7  
ground  pin 5
LL4604 is a general purpose isolation transformer with a mu metal lamination core. Turns ratio 1+1 : 1ct.


Usage:  
in+	pin 1  
in-	pin 2  
in+	pin 4  
in-	pin 5  (Pins 1, 2, 4, 5 can be used in series or in parallel)    
out+	pin 7  
out centertap	pin 3  
out-	pin 9    
Shields	pins 6 and 10
LL4603 is an improved LL4601, normally used 1 : 1


Pin configuration (as seen from PIN side)    

4,     3,          1,                

8,    7,    6,    5,    

Usage (1:1):  
in+	pin 8  
in-	pin 5  
connect pin 6 + pin 7  
out+	pin 4  
out-	pin 3  
Faraday shield	pin 1
The LL4602 is a C-core line output transformer for unbalanced (single-end) drive. Internal structure is similar to the LL5402.


LL4602 usage (turn ration 1 : 1)

Pin 1 + Pin 5	primary ground  
pin 2 + pin 4	primary signal in (+)  
pin 3 not used      
pin 7		out +  
pin 10		out -  
pin 6 + pin 9	connect
 LL4601 is a high impedance line input transformer, 2:1+1.


Pin configuration (as seen from PIN side)
4,     3,            1,    

            
8,     7,    6,     5,   

Usage (1:1):  
in+	pin 8  
in-	pin 5  
connect pin 6 + pin 7  
out+	pin 4  
out-	pin 3  
Faraday shield	pin 1
The LL4501 is a C-core line output transformer. Standard version is gapped for DC current. LL4501G is gapped for a smaller current and has been 
used in telephone hybrid circuits.


Pin configuration (as seen from PIN side)    
4,      3,      2,      1 

          
8,               6,      5,      

LL4501 usage (turn ration 1 : 1)    
pin 1 		primary signal in (+)  
pin 3 		primary side ground  
pin 2 + pin 4	connect    
pin 8		out +  
pin 6		out -  
pin 5		Faraday shield. Ground.
LL4202 is a high level mu metal core output transformer, turns ratio 1:1.


Usage:  
in+	pin 1  
in-	pin 2  
out+	pin 6  
out-	pin 5  
Shields	pin 4
The LL3817 is identical to LL3814, a C-core line output transformer, turns ratio 3 + 3 : 1+1 except that height is 1 mm less.


Usage, 3 : 2    
In+		pin 1 + pin 6  
in-		pin 3 + pin 4  
leave		pin 2 + pin 5      
Out+		pin 7  
Out-		pin 11  
Connect	pin 12 + pin 8  
Ground		pin 10  no pin at 9
LL3815 is a small mu metal core microphone / line input transformer, turns ratio 1+1 : 5.


Usage, 1 : 5    
In+		pin 1 + pin 4  
In-		pin 2 + pin 3    
out+		pin 8  
out-		pin 6  
Shields		pin 5    no pin at 7
The LL3814 is a C-core line output transformer, turns ratio 3 + 3 : 1+1.


Usage, 3 : 2    
In+		pin 1 + pin 6  
in-		pin 3 + pin 4  
leave		pin 2 + pin 5      
Out+		pin 7  
Out-		pin 11  
Connect	pin 12 + pin 8  
Ground		pin 10  no pin at 9
LL3803 is a very low impedance, high current output transformer.


2, 	                 	1        

       LL3803   
 
5,        4,        	3   

LL3803 Usage (1 : 1.1)  
in+	pin 1  
in-	pin 2  
out+	pin 3  
out_ct	pin 4  
out-	pin 5
LL3802 is a ”600 : 600 ohm” general purpose isolation transformer, turns ration 2:1+1 Core: Mu metal, ED style.


Usage 1:1   
in+	7  
in-	9  
out+	1  
out-	5  
connect 2 + 4  
Faraday shield 10 + 6  

Usage 2:1   
in+	7  
in-	9  
out+	1+4  
out-	2+5  
Faraday shield 10 + 6
LL2804 is yet a microphone input transformer with turns ratio 1+1:7 (200 ohm : 10k) The LL2804 is discontinued and no data sheet is available. 
For replacements, please look at LL1530 or LL1576.


Pin configuration:  
(Transformer seen from pin side. I am afraid I can not tell orientation, 
as our notes are  incomplete and we have no samples left.)    
4,    3,    2,    1       

   LL2804      

8,    7,    6,    5       
 
LL2804 Usage (1:7)  
in+	pin 2  
in-	pin 3  
out+	pin 6  
out-	pin 7  
Housing 		pin 1  
Core 			pin 4  
Faraday shield 	pin 5+8
Sorry, but there is no data sheet for the LL2801.


LL2801 is a 600 ohm output transformer, turns ration 1:1  
Core:	Radiometal lamination, ED style.    
Usage:    
in+	7  
in-	6    
out+	9  
out-	10
The LL2613 is a small size microphone input transformer Turns ratio 1+1 : 10


Usage:    
In+		pin 1 (coil 1) and pin 4 (coil 2)  
In-		pin 2 (coil 1) and pin 3 (coil 2)  
Centertap	pin 2    
Out+		pin 8	  
Out-		pin 6  
Faraday shields	pin 5
The LL2603 is a small size line isolation transformer, similar to the LL1532 Turns ratio 1ct : 1


Usage:    
In+		pin 1	  
In-		pin 4  
Centertap	pin 2    
Out+		pin 6	  
Out-		pin 7  
Faraday shields	pin 5 + 8

The LL1526 is a high impedance line input transformer, slightly bigger than the LL1531, but with the same pin configuration and usage.

 

For pinout description please see the data sheet for <a href=”/wp-content/uploads/datasheets/1531_32.pdf” target=”_blank”>LL1531</a>

The LL1521B is a high impedance line input transformer, very similar to the LL1540 but with a slight stepup. Turns ratio 1 + 1 : 2.28


Usage:    
In+		pin 1	(left row, bottom pin when viewed from component side)  
In-		pin 3  
connect		pin 2 + pin 4    
Out+		pin 5	(right row, bottom pin when viewed from component side)  
Out-		pin 8  
Shields		pin 6

No, I am afraid we have no data sheet for the LL1518. The LL1518 is a (solid state) line output transformer, similar to the LL1517.

 

 

Usage:

Turns ratio 1:1    
In+		pin 1 (left bottom, if you read transformer label correctly)
In-		pin 5    
Out+		pin 7   
Out - 	pin 10 (right top)  
Connect	pin 6 + 9  
Ground 		pin 8    
Turns ratio 2:1    
In+		pin 1 (left bottom, if you read transformer label correctly)  
In-		pin 5    
Out+		pin 7 + pin 9  
Out - 		pin 10 + pin 6  
Ground		pin 8
LL1515 is a microphone input transformer with turns ratio 1+1:7 (200 ohm : 10k) The LL1515 is discontinued and no data sheet is available. 
For replacements, please study LL1530 or LL1576.


Pin configuration (transformer seen from component side with label readable)

4, 	3, 	2, 	1

    LL1515    

8,	7,  	6,	5        

LL1515 Usage (1:7)
in+	   pin 1 + 3  
in-	   pin 2+4  
out+	   pin 6  
out-	   pin 7  
ground  pin 5

I’ve built an amp with 2A3 and LL1660. I like the sound of it,
but was a little frustrated when I measured the frequency response
today. Around 9.5KHz I get a climbing response
that doesn’t go away until I’ve reached the end of the bandwidth of the
amp. With a few measurements, I located the problem to be the 1660. It’s
wired in the ALT-T hookup, to allow 20mA current through the 6H30.

Is this expected? If not (and also if so, I suppose :-), what can I do
about this deviation?

Hi Per,

Seems I already got this explained to me by an audioasylum inmate, it’s
an impedance problem. So I’ve got something to work with now, sorry for
wasting your time.In case you want to know, 24K resistance from the grid of the 2A3 to ground made the frequency response curve perfectly flat. I can’t wait to listen to it and see how this changed the sonics of the amp. BTW, thanks a lot for making quality products for tube amps. I already absolutely love the sound of my new amp.

Jens Axboe

The interesting parameter for a mains transformer is the no-load current. For our mains transformers LL1648 — 51 the no load current is less than 100mA, indicating a no load impedance above 2kohms at 50 Hz. (corresponding to 6H) The no-load current should be compared to the full-load current, which for a 250VA transformer is around 1A. A 1:10 factor between no-load current and full load current is in my opinion quite acceptable.

Gain matching and CMR would not be so good.
Difference in copper resistance is due to difference in wire gauge. It is possible that we used wire from different runs or from different vendors. However, the number of turns should be correct. (I say ”should be” as shit do happens, even at Lundahls. But if the number of turns was not correct, the difference in copper resistance should have been around 100 ohms for the LL1674 (representing two full layers).)

Which problem will arise? The difference in DC resistance of the transformer should be compared to the impedance of the load. If the load impedance is 20k + 20k, (reasonable or even low load for the LL1674), the 40 ohms difference of the transformer is in the magnitude of 1/1000 of the load impedance. In my opinion, this is ignorable. Besides, is the core degaussed after measuring DC resistance with a DC current? This is probably a bigger problem.

The internal structures of the LL1581XL and LL1570XL are quite different. The LL1581XL is a splitting transformer with very high immunity to external noise and noise crosstalk. When used as a splitting transformer, the LL1570XL may pick up electromagnetic hum (from e.g. motrs or power supplies).

For such a low input impednace would suggesth the LL1570 used 1:2. The LL1538 are ideally used with amplifiers with around 5k optimum source impedance.

It appears that one should obtain a 50% tap in this manner.
Yes, you can use the LL1620 in UL mode if you connect the screens as you describe.

Please check the pinout descriptions.

In a step-up transformer the internal capacitance in high impedance windings are always high, due to the many turns of thin wire. In addition, the signal level across a high impedance winding is high (relatively) due to the step-up. When putting high impedance windings in parallel, the result is a high capacitive load on the primary, and dropping HF response. This is the reason why we generally recommend NOT to parallel high impedance windings.

In order to lift signal level from -10 to +4 you need a stepup transformer with turns ratio 1:5, such as LL1935 used 1:5 The consumer equipment output impedance should be reasonable low, and pro audio input impedance must be high, as the transformed output impedance will be 25 times higher than the original source impedance. The transformer should be placed close to the balanced input. If the source impedance is much higher than 600 ohms, the band width will be limited.

Yes, you can use our SE transformers in PP applications. The drawback is that due to the DC-accepting core airgap in the SE transformer, transformer inductance is less than for corresponding PP version.

The primary impedance of a transfomer in an application, as seen by the source, is the primary no load impedance in parallel with the transformed load. The ”primary no load impedance” for a gapped tube amp transformer is the primary inductance. The ”transformed load” is the secondary load as seen from the primary winding (Load * (turns ratio)*(turns ratio)). Thus, the transformer by itself does not have an impedance that can be used without a context.