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K&K Audio / Lundahl Transformers Welcome! Need support, you got it. Or share youe ideas and experiences. |
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K&K Audio / Lundahl Transformers Welcome! Need support, you got it. Or share youe ideas and experiences. |
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In Reply to: Re: Selecting Output Transformers for WOT Line Preamp posted by Snoopyma on June 29, 2005 at 23:34:00:
"As the LL1689 does not have the frequency specification, can you give me some hints on the predicted freq. response in the case of WE437a running at 22ma using LL1689/18ma 18:2 connection that you recommend? "Not having tried your tube, but having used this transformer, I would expect response close to 1KHz levels at 20Hz and 20KHz, but I wouldn't be able to predict -3dB points/
"To me, LL1689 has the advantage of having 18:4, 18:2 and 18:1 connection alternatives so that I can play around to choose the most suitable one. Is there a difference in terms of freq. response for the 3 connection options?"
I expect that in the audio band there will be little difference, but if you are a bandwidth oriented designer there will be diffferences. Again, I couldn't presume to predict them with your circuit.
"For specifying the gap, I have the false common belief that running the tube at a current higher than the gapped one will saturate the core and deteriorate the performance at all levels, won't it?"
The Lundahl current spec is the current at which the transformer core is about 55% saturated. To reach saturation you will have to have current flowing at a proportionally higher level. It is easy enough to calculate what that would need to be for a given transformer and tube combination. From that you can calculate a maximum signal level and see if you are going to approach this under normal operating conditions. For line level signals of a few volts RMS, there really isn't a big need to worry if you are within 25% of the Lundahl current spec. In point of fact, until you get so high on the magnetic curve that you reach the saturation knee, you are in a region where the iron is more "linear" than it is at low current levels, due to the dominating presence of the air gap. Some believe that this is one reason why SE stages sound better than PP stages where current is flowing through the primary of the output transformer. With PP stages, the opposing currents cancel and there is little magnetic flux present under no signal conditions, whereas SE stages are biased in the region of 35-65% of saturation.
"What is the loss of gapping the cores at higher current assuming the same core and coil in terms of technical performance and sound quality? Could you elaborate."
More gap means less primary inductance and, therefore, for a given set of operating conditions, higher low frequency cutoff.
Kevin Carter
K&K Audio
www.kandkaudio.com
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Follow Ups
- Re: Selecting Output Transformers for WOT Line Preamp - KevinC 12:53:46 07/01/05 (1)
- Re: Selecting Output Transformers for WOT Line Preamp - Snoopyma 07:56:46 07/05/05 (0)
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