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K&K Audio / Lundahl Transformers

Re: HF rolloff with LL1660S

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KevinC

(M)

In Reply to: HF rolloff with LL1660S posted by Danny T on September 12, 2003 at 02:33:03:

My speculation is that the essentially 1:2 connection you are using with the LL1660S/10mA means that the paralleled 5670 simply hasn't a low enough driving impedance to prevent high frequency roll-off. My experience has shown me that step-up IT connections only "work sonically" if the driving tube has a very low plate impedance (<1000 ohms). The increased bass response perception may be just that. With the absence of some high frequency level you perceive more bass.
If you can sacrifice the gain, try the LL1660S/10mA connected as 2.25+2.25:2+2 to see what happens. Use only half of the 5670.

Kevin Carter
K&K Audio
www.kandkaudio.com

Follow Ups:

Re: HF rolloff with LL1660S - Danny T 06:15:01 09/12/03 (2)
Thanks.
I think I'll revert back to the LL1660/18ma in the 4:2.25+2.25 configuration, this gives me just enough gain.
Putting the primaries all in serie with the LL1660S 4.5:2+2 will give me not enough gain and in this configuration the LL1660S is rated 10ma so I can use only one half of the 5670 and this will double the plate impedance.
- Re: HF rolloff with LL1660S - KevinC 06:24:54 09/12/03 (1)
  It does double the plate resistance compared to the LL1660/18mA implementation, but is still effectively 2 times lower than your current LL1660S/10mA implementation, so it is a "compromise" between the two that you may want to listen to just to see.
  
  Kevin Carter
  K&K Audio
  www.kandkaudio.com
  - Re: HF rolloff with LL1660S, solution found - Danny T 13:36:31 11/26/03 (0)
    I've found the reason for the high frequency rolloff:
    see other message:
    - http://www.AudioAsylum.com/forums/KandK/messages/1453.html (Open in New Window)

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